CN112585096A - Treatment of tailings - Google Patents

Abstract

Methods of consolidating tailings, such as from the processing of metallic and non-metallic species ores, are disclosed. The process includes mixing the tailings with a high concentration of a highly water soluble salt or aqueous solution thereof to destabilize and consolidate solids in the tailings, and separating the consolidated solids from the process water.

Description

Treatment of tailings

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional application No.62/699,335 filed on 7/17/2018, the entire disclosure of which is incorporated herein by reference.

Technical Field

The present disclosure relates to dewatering and consolidation of aqueous compositions comprising solids such as tailings. Such tailings are derived from processing ores such as metal-based ores, phosphate-based ores, and coal-based ores.

Background

Various mining and mining processes produce tailings streams characterized by slurries of particulate matter in water. These tailings often contain harmful components that cannot be discharged directly into rivers and streams. It is conventional practice to store tailings in tailings ponds that are very large or have multiple sites. For example, it is currently estimated that oil sands tailings ponds in canada cover an area of about 200 square kilometers. In the united states, the environmental protection agency has identified over 500 coal ash slurry reservoirs, mostly located in the abacavirus (appaachian) coal mine area. In florida, phosphorite mining produces about 100,000 tons of phosphate clay per day in the form of a slurry, which is also stored in tailings ponds. Dewatering is extremely difficult and about 40% of the mine area in the phosphate industry remains in unstable clay settlement areas. Mining and mining of aluminum, copper, zinc, lead, gold, silver, etc. ores also produces tailings streams. Furthermore, it is of particular interest to process the ore to recycle water, but such recycling is hampered by the particulate matter suspended in the wastewater.

The problems in the management and sustainability of tailings ponds are prominent and increasing. Damming or fencing used to form tailings ponds is typically constructed of local materials, which present serious potential hazards. Coal slurry dam accidents in West Virginia (West Virginia) have resulted in Buffalo stream (Buffalo Creek) floods that have caused more than 125 people to be distressed. In recent years, various other breaches of tailings containment ponds have resulted in serious, even catastrophic, environmental damage. For example, in 2016, a tailings dam incident in Henan province, China released about 2,000,000 cubic meters of red mud, thereby flooding a nearby village. In 2015, accidents occurred in the waste rock heap produced by the mining of Burma's jade, resulting in at least 113 distress.

In the oil sands industry, particles having a diameter equal to or less than 44 μm are defined as fines. Fines are the portion of the waste stream that settles at a much lower rate than the grit, leaving an aqueous layer near the surface of the tailings pond that carries some fines. This water is reused in the bitumen extraction process. Initially, the majority of the fines (mainly silica and clay particles) form an intermediate layer known as Fluid Fine Tailings (FFT). The solids content of the stream is low, between 15% and 30%, which is also known as Thin Fine Tailings (TFT). Over time, settling continues, but the negative surface charge of the mineral particles limits aggregation and a distinct layer called Mature Fine Tailings (MFT) is formed. MFT has an average solids content of about 30%, but its solids content varies with depth. MFT has gel-like properties and is therefore difficult to handle and dewater. It is estimated that these tailings constituents will take decades to hundreds of years to consolidate and settle to achieve land reclamation by relying solely on the action of gravity. In florida, tailings from phosphate mining form a similar gel-like structure. Below the surface crust, these tailings have a solids content of about 25% and a fluid-like consistency.

So-called lagoons (impound mends) are used to store two types of waste from coal processing and combustion. Coal ash, which is the residue of combustion, is a material that includes several components (fly ash, bottom ash, etc.). The EPA estimated that in 2012, the united states produced one hundred million tons of coal ash. There is a dry treatment method and the coal ash can be reused as a building material, but for economic reasons, a wet treatment of discharging the coal ash to a slag trap is common practice. The EPA estimates that there are over 500 sinks at over 200 power plants. There are increasing environmental concerns regarding the percolate from these basins.

A second type of lagoons used for coal processing waste stores material as a product of coal preparation plants where dust and rocks are removed from raw ore coal to reduce its ash content and increase its value. This is done by washing. However, such coal cleanup processes produce a discharge stream in the form of sludge or mud. This slurry contains very fine coal particles as well as other materials (e.g., clay) and, like the tailings streams described above, is very difficult to dewater economically using standard methods. The united states now has about 600 so-called mud lagoons, which store these wastes, mostly located in the abalachese sub-coal production area. These mud lagoons are up to 50 acres in size and contain billions of gallons of toxic sludge. These materials represent economic costs both in terms of loss of valuable resources (in the form of coal fines) and in terms of major environmental hazards. Washington post (24 months 4 in 2013) reports: the American open Mining Reclamation execution Office (Office of Surface Mining Reclamation and implementation) study found that many mud lagoon walls were weak and known to have leaked. Historically, catastrophic accidents of ash and slurry ponds (ash and slurry ponds) have occurred several times, resulting in severe casualties and environmental degradation. As the coal industry declines and mining companies apply for bankruptcy, lagoons that are still in service and lagoons that have been abandoned become a serious and increasing problem.

The mining of alumina from bauxite also produces large tailings streams. Approximately 77,000,000 tons of strongly alkaline waste are produced each year, which is mainly composed of iron oxide and is called red mud or red mud. As mentioned above, this can create serious disposal problems and tailings dam accidents that can have catastrophic consequences.

There has been a need for: aqueous compositions comprising suspended solids (e.g., tailings) are managed and remediated to reduce the volume of such tailings and/or to dewater and consolidate the solids in the tailings in a manner that facilitates land reclamation, remediation, and/or reclamation of water for use in mining operations.

Disclosure of Invention

Advantages of the present disclosure include methods of dewatering aqueous compositions (e.g., tailings) comprising suspended solids to produce high solids content materials.

These and other advantages are at least partially satisfied by a method of consolidating solids in tailings. The process involves treating the tailings with a highly water soluble salt. Advantageously, the process may comprise treating the tailings with at least one highly water soluble salt or solution thereof, and the process may optionally comprise one or both of: (i) at least one polymeric flocculant or a solution thereof and/or (ii) optionally coarse, e.g. sand, to form treated tailings. The treated tailings may comprise consolidated material in the process water, which may then advantageously be separated from the consolidated material.

Methods of practicing the present disclosure include, for example, (i) treating tailings with at least one highly water soluble salt to form treated tailings comprising consolidated material in process water; (ii) treating the tailings with at least one highly water soluble salt and at least one polymeric flocculant to form treated tailings comprising consolidated material in the process water; (iii) treating the tailings with at least one highly water soluble salt and coarse particles to form treated tailings comprising consolidated material in the process water; and (iv) treating the tailings with at least one highly water soluble salt, at least one polymeric flocculant, and coarse particles to form treated tailings comprising consolidated material in the process water. These embodiments may each include an aqueous solution of salt and/or polymer flocculant to treat the tailings. These embodiments may each include separating the process water from the consolidated material. Advantageously, the consolidated material may have a density greater than the density of the process water.

Embodiments of these methods include one or more of the following features, either alone or in combination. For example, the tailings subjected to treatment may be from processing metal-based ores, phosphate-based ores, or coal-based ores. In some embodiments, the solubility of the at least one highly water soluble salt in water (salt/water solubility) may be at least about 5g/100g at 20 ℃, for example, the solubility is at least about 10g/100g at 20 ℃. In other embodiments, the at least one highly water soluble salt is a non-hydrolyzable salt. In still other embodiments, the at least one highly water soluble salt may have a monovalent cation and may include an ammonium salt, a phosphate salt, or a sulfate salt, or a combination thereof.

In certain embodiments, the tailings salt concentration of the at least one highly water soluble salt in the treated tailings can be at least 0.5 wt%, and preferably is not less than about 0.70 wt%, such as at least about 1 wt%, 1.25 wt%, 1.5 wt%, 1.75 wt%, 2 wt%, or even at least about 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, and the like. In some embodiments, the at least one polymeric flocculant is polyacrylamide or a copolymer thereof. The concentration of the tailings polymer of the at least one polymer flocculant in the treated tailings can be no less than 0 and up to about 0.001 wt%, for example, up to about 0.003 wt%, 0.005 wt%, 0.01 wt%, or 0.04 wt%. In other embodiments, the tailings are treated with coarse (e.g., sand) particles having a sand to fine ratio of less than 4:1, including for example from about 2.5:1.0 to about 0.5:1 or from about 2.25:1 to about 0.75: 1. Advantageously, the polymeric flocculant, when added, can form a high density floc, for example, a floc having a density greater than the process water, which aids in the separation and dewatering of the consolidated material.

In various embodiments, treating the tailings can include combining the tailings with a solution containing at least one highly water soluble salt and at least one polymeric flocculant. In some embodiments, treating the tailings may comprise combining a tailings stream (e.g., tailings from processing a metal ore such as a copper ore) with a stream comprising a solution of at least one highly water soluble salt and another stream comprising a solution of at least one polymeric flocculant. Alternatively, or in combination, treating the tailings may comprise combining a tailings stream with a stream comprising a solution of both at least one highly water soluble salt and at least one polymeric flocculant. Coarse particles (e.g., sand) may also be added to the tailings or streams thereof and/or any or all of the solution streams. Advantageously, the mixing of the streams can be carried out in-line and/or by means of an in-line mixer. In certain embodiments, treating the tailings may be performed at ambient temperature, e.g., no more than about 2 ℃ to about 5 ℃ above ambient. In other embodiments, treating the tailings may be carried out at a temperature of no greater than about 50 ℃, for example no greater than about 40 ℃ or 30 ℃. In yet another embodiment, treating the tailings comprises treating the tailings with one or more highly water soluble salt solutions derived from natural or existing sources, such as seawater or high salinity waters, or from brine waste streams.

In yet another embodiment, the process water may be separated from the consolidated material by any one or more of decantation, filtration, vacuuming, gravity drainage, electro-filtration, and the like, or combinations thereof. In various embodiments, separating the process water from the consolidated material may include mechanically dewatering the consolidated material, for example, by a screw dehydrator, industrial filter, or the like. After separation, the consolidated material may be transferred for further dewatering or processing.

In practicing aspects of the disclosed methods and various embodiments thereof, the separated process water may comprise at least one highly water soluble salt, and the method may further comprise one or more of: (i) recovering at least a portion of the separated process water; (ii) recycling at least a portion of the recovered separated process water to treat other tailings; (iii) purifying at least a portion of the recovered process water; or (iv) concentrating at least one highly water soluble salt in the recovered process water to form a brine and using the brine to treat other tailings.

Another aspect of the present disclosure includes recovering useful materials from aqueous compositions of fines (e.g., tailings). Useful materials may include Rare Earth Elements (REEs) associated with solids (e.g., clays in tailings) from various types of aqueous fines (e.g., tailings streams). Thus, in practicing certain aspects of the methods of the present disclosure and various embodiments thereof, the aqueous composition may further comprise a rare earth element material, which may be recovered by treating the tailings with at least one highly water soluble salt (e.g., an ammonium salt, such as ammonium sulfate) to form treated tailings comprising the REEs in the process water and/or the consolidated material. In some embodiments, the method further comprises separating the process water from the consolidated material, and recovering the REE from the separated process water and/or consolidated material.

Advantageously, the methods of the present disclosure can consolidate solids in tailings to produce consolidated materials having a solids content of greater than about 45 wt%, for example, a solids content greater than about 50 wt%, and greater than about 60 wt%, 65 wt%, 70 wt%, and 75 wt%.

In practicing certain aspects of the disclosed methods and various embodiments thereof, the consolidated material formed in the treated tailings can achieve high solids content in a short time after mixing and/or dewatering of the treated tailings according to certain embodiments. In some embodiments, the solids content of the consolidated material after mixing and/or dewatering may be greater than about 50 wt%, and may be at least about 60 wt%, 65 wt%, 70 wt%, 75 wt%, and 80 wt%.

Another aspect of the present disclosure includes an aqueous solution for treating aqueous fines. The aqueous solution comprises a highly water soluble ammonium salt and a polymeric flocculant, for example, a water soluble polymer. Embodiments also or respectively include an aqueous solution of one or more highly water soluble salts at a concentration of not less than about 1% by weight, for example, at a concentration of at least about 2%, 5%, 10%, 20%, 30%, and even up to 40% by weight, or an aqueous salt slurry. The aqueous solution may also include one or more polymeric flocculants at a concentration of not less than 0 and up to about 0.005 wt%, such as up to about 0.01 wt%, 0.04 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%.

Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

Drawings

Referring to the drawings wherein elements having the same reference number designation represent like elements throughout, and wherein:

figure 1A schematically illustrates a method of consolidating a tailings stream, according to aspects of the present disclosure.

Fig. 1B schematically illustrates other methods of consolidating a tailings stream according to aspects of the present disclosure.

Fig. 2 is a photograph of a vial containing a waste coal slurry treated according to an embodiment of the disclosure. The photograph shows the coal slurry after addition of ionic solution (left panel), after subsequent centrifugation (middle panel) and removal of supernatant (right panel).

Fig. 3 is a photograph of the dewatered coal slurry from fig. 2 after removal from the jar (left image), and subsequent manual squeezing between paper towels.

Fig. 4 shows a photograph of a vial containing mature fine tailings from oil sands processing that were treated with an ammonium salt solution containing a polyacrylamide flocculant, where the concentration of the polyacrylamide flocculant is shown in the figure.

Figure 5 shows a photograph of a vial containing mature fine tailings treated with an ammonium salt and a polyacrylamide flocculant and showing the effect of increasing the salt concentration and decreasing the polymer concentration under the test conditions.

Fig. 6 shows photographs of vials containing mature fine tailings from oil sands processing that were subjected to treatment with seawater containing varying amounts of polyacrylamide flocculant.

Fig. 7A, 7B and 7C show photographs of treating tailings produced by processing copper ores.

Detailed Description

The present disclosure relates to treating tailings and other aqueous compositions comprising solids to consolidate and dewater the tailings. Tailings are typically produced when mining and processing ores, such as metal-based ores, e.g., aluminum, copper, zinc, lead, iron, gold, silver, molybdenum, lithium, etc., and ores, e.g., non-metal-based ores, e.g., phosphate ores, nitrate ores, iodine ores, oil sands, etc. Fine-grained aqueous compositions are also produced when processing coal. For example, some processes finely grind coal prior to combustion to more readily release pyrite (a sulfur-based compound), thereby reducing sulfur release from the ground coal upon combustion. This process can produce fine coal particles and other fine minerals or minerals in the aqueous composition that are difficult to recycle.

The particulate solids in the tailings or aqueous compositions of the present disclosure may be mineral and mineral-like materials, i.e., minerals, clays, silt (slit), and their size ranges between fine to coarse solids. The term fines as used herein is consistent with the canadian oil sands classification system and refers to solid particles having a size equal to or less than 44 micrometers (μm). Sand refers to solid particles greater than 44 μm in size. The composition of the fines depends on the source of the material, but typically the fines comprise mainly silt and clay material, sometimes minerals or minerals depending on the ore. The tailings may have different solids contents and have different fines contents as their solids contents. Tailings treated according to embodiments of the present disclosure may include an effective amount (by weight) of fines (> 5 wt%) as their solid content. Such tailings may comprise at least about 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or more fines as a solid content thereof.

Advantageously, the process of the present disclosure is capable of consolidating solids of tailings to produce a consolidated material having a solids content of greater than about 45 wt%, for example, a solids content of greater than about 50 wt% and greater than about 60 wt%, 65 wt%, 70 wt% and 75 wt%.

The terms coagulation and flocculation are often used interchangeably in the literature. However, coagulation as used herein refers to particle aggregation occurring by the addition of a hydrolysis salt, whereas flocculation refers to particle aggregation initiated by a flocculating polymer. The hydrolysis salts hydrolyze upon addition to water to form metal hydroxides which precipitate out of solution, thereby capturing fines and other minerals in the aggregate. The hydrolyzed salts are generally less soluble in water and are used as flocculants. Rather, it is believed that aggregation initiated by flocculation results from the polymer binding to the particles, thereby binding the particles together to form a so-called floc, thereby causing aggregation of the particles.

In the practice of the present disclosure, the tailings, as well as other aqueous compositions of solids and process water, may be consolidated by treating the tailings with one or more highly water soluble salts or aqueous solutions thereof to destabilize and consolidate the solids in the tailings, for example, to destabilize and consolidate coarse solids and fines in the tailings. Aggregation due to the addition of salt is thought to be due to the following reasons: the particles suspended in the fluid are destabilized by altering or masking the surface charge of the particles to reduce the repulsion forces between the particles (which prevents agglomeration from occurring). In certain embodiments, tailings (e.g., a suspension of particulate solids that may include fines in process water) are treated. Such tailings that may be treated comprise tailings streams or coal slurries from the processing of metallic-type ores, non-metallic-type ores. The method includes treating the tailings with one or more highly water soluble salts or aqueous solutions thereof to form treated tailings comprising consolidated materials, such as consolidated solids and/or fines, in the process water. The process water may then be separated from the consolidated material. Advantageously, the consolidated material has a solids content of at least 45% by weight, such as a solids content greater than about 50% by weight, and greater than about 60%, 65%, 70% and 75% by weight.

Salts useful in practicing the present disclosure include salts having high solubility in water. A highly water soluble salt as used herein is a salt having a solubility in water per 100g of water at 20 ℃ of greater than 2g of the salt (i.e., a salt/water solubility of 2g/100 g). Preferably, the highly water soluble salt has a water solubility of at least about 5g/100g at 20 deg.C, for example, a water solubility of at least about 10g/100g (salt/water) at 20 deg.C.

Further, the highly water soluble salts used in the methods of the present disclosure are preferably non-hydrolyzable salts. The hydrolysis salt hydrolyses on addition to water to form a metal hydroxide which precipitates from the solution. It is believed that such hydrolyzed salts form open flocs (open flocs) that are low in solids content and are not easily recovered for use with other tailings in a continuous or semi-continuous process. Furthermore, the solubility of the hydrolyzed salts in water is low and use at high temperatures to ensure sufficient solubility to achieve aggregation is a process that requires large amounts of energy. Patent document US 4,225,433 discloses the use of lime as a coagulant at a temperature of 75 ℃.

In addition, highly water soluble salts are preferably not carboxylates, since such organic acid salts tend to be more expensive than inorganic salts and may be harmful to plant and/or animal life.

Highly water soluble salts that are not hydrolyzable and that can be used to practice the methods of the present disclosure include salts with monovalent cations, for example, alkali halide salts such as sodium chloride, potassium chloride; in addition, salts having monovalent cations such as sodium nitrate, potassium nitrate, sodium and potassium phosphates, sodium and potassium sulfates, and the like, can also be used to practice the methods of the present disclosure. Other monovalent cation salts useful for practicing the methods of the present disclosure include ammonium salts, such as ammonium acetate (NH)₄C₂H₃O₂) Ammonium chloride (NH)₄Cl), ammonium bromide (NH)₄Br), ammonium carbonate ((NH)₄)₂CO₃) Ammonium hydrogen carbonate (NH)₄HCO₃) Ammonium Nitrate (NH)₄NO₃) Ammonium sulfate ((NH)₄)₂SO₄) Ammonium hydrogen sulfate (NH)₄HSO₄) Ammonium dihydrogen phosphate (NH)₄H₂PO₄) Diammonium hydrogen phosphate ((NH)₄)₂HPO₄) Ammonium phosphate ((NH)₄)₃PO₄) And the like. Mixtures of these salts may also be used.

Ammonium-based salts can be used in the practice of the present disclosure because residual ammonium-based salts located on the consolidated material after the ammonium-based salts are combined with aqueous fines (e.g., tailings) are beneficial to plant life. In fact, many ammonium salts are useful as fertilizers, such as ammonium chloride, ammonium nitrate, ammonium sulfate, and the like. Many monovalent sulfates and phosphates are also useful as fertilizers. In certain embodiments of the present disclosure, highly water soluble salts or salts used in the methods of the present disclosure are preferably non-toxic and beneficial to plant life, thereby facilitating environmental remediation and recovery of the mine site.

Highly water soluble salts useful in practicing the methods of the invention can also include salts with multivalent cations. Such salts include, for example, divalent cation salts, such as calcium and magnesium, such as calcium chloride (CaCl)₂) Calcium bromide (CaBr)₂) Calcium nitrate (Ca (NO)₃)₂) Magnesium chloride (MgCl)₂) Magnesium bromide (MgBr)₂) Magnesium nitrate (Mg (NO)₃)₂) Magnesium sulfate (MgSO)₄) (ii) a And trivalent cation salts, such as aluminum and iron (III) cation salts, such as aluminum chloride (AlCl)₃) Aluminum nitrate (Al (NO)₃)₃) Aluminum sulfate (Al)₂(SO₄)₃) Iron (III) chloride (FeCl)₃) Iron (III) nitrate (Fe (NO)₃)₃) Iron (III) sulfate (Fe)₂(SO₄)₃) And the like. As set forth above, the highly water soluble salt used in the methods of the present disclosure is preferably a non-hydrolyzed salt. Many multivalent cation salts are hydrolyzable and therefore are not preferred for the reasons set forth above. Furthermore, experiments with multivalent salts showed increased vessel fouling and formation of less cohesive consolidated materials compared to highly water soluble salts with monovalent cations. In addition, some multivalent salts such as FeCl₃And Fe₂(SO₄)₃Has high corrosivity and can oxidize pyrite to form Fe₂(SO₄)₃Resulting in acid mine run-off, which makes these salts less preferred for use in the process of the present disclosure.

When treated tailings contain sufficiently high concentrations of highly water soluble salts, the salts can destabilize and consolidate solids in the tailings. For relatively short process times and relatively low energy input, the tailing salt concentration of the at least one highly water soluble salt should preferably be at least 0.5 wt.%, and preferably not less than about 0.70 wt.%, such as at least about 1 wt.%, 1.25 wt.%, 1.5 wt.%, 1.75 wt.%, 2 wt.%, or even at least about 2.5 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, etc. The term "tailings salt concentration" as used herein refers to the concentration of highly water soluble salts in the treated tailings, as determined by dividing the mass of highly water soluble salts by the percentage obtained by the total mass of salt plus tailings and total water used to dilute the salt. For example, a 1 wt% tailing salt concentration is obtained by mixing 1 part by weight undiluted (e.g., pure) salt with 99 parts by weight tailing. Alternatively, by treating the tailings with an equal weight of 2 wt% salt solution, the resulting treated tailings also had a tailings salt concentration of 1 wt%.

The compositions of the present disclosure may be treated with one or more highly water soluble salts as solids, for example, by mixing the salt as a powder with the tailings. Alternatively, the treatment may be carried out using a salt as a solution, for example, by mixing an aqueous salt solution with the tailings. In some aspects of the present disclosure, aqueous solutions of highly water soluble salts can be prepared at concentrations of no less than about 1 wt%, e.g., at concentrations greater than about 2 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, and even up to 40 wt%, or as aqueous salt slurries. The tailings and salt solution or salt slurry should be mixed in a ratio sufficient to destabilize the tailings and thereby initiate consolidation of the solids therein. In one aspect of the disclosure, the mixing ratio of tailings and salt solution may range from about 80:1 to 1:1, for example, 70:1 to 1:1, 50:1 to 1:1, 30:1 to 1:1, 20:1 to 1:1, 15:1 to 1:1, 10:1 to 1:1, 5:1 to 1:1, and/or about 2:1 to 1: 1.

In some embodiments of the present methods, it is more advantageous to use a natural source of highly soluble salts, such as highly soluble salts in natural waters that contain sufficiently high concentrations (e.g., at least about 2 wt%, even at least about 3 wt% or more) of these salts. For example, sea or seawater may be used as a source of highly soluble salts, which may greatly improve the economics of the process under certain conditions. The salinity of most seawater is between 31g/kg and 38g/kg, namely 3.1% -3.8%. On average, the salinity of seawater in the ocean worldwide is about 3.5% (35g/L, 599 mM). The seawater contains a salt mixture containing not only sodium cations and chloride anions (amounting to about 85% of the dissolved salts present), but also sulfate anions and calcium, potassium and magnesium cations. Other ions (e.g. bicarbonate) are also present, but these are the main components. Other natural sources of highly soluble salts that may be used as a source of highly soluble salts include high salinity waters, such as high salinity lakes, ponds, or reservoirs. High salinity water areas are water areas with high concentrations of sodium chloride and other highly soluble salts, which exceed seawater, for example, greater than 3.8% by weight, and typically greater than about 10% by weight. Such high salinity waters are located at the surface as well as underground and can be brought to the surface by ore mining operations.

In other embodiments of the present process, it may be advantageous to use the brine produced in the desalination of salt water as a source of highly soluble salts. The brine may be used as a source of highly soluble salts alone or in combination with other sources of highly soluble salts such as seawater. Seawater has been used in grinding and flotation processes for mining copper ores. See "The use of sea water as process water at Las cement hopper-molybdenum benedication plant in tantalum (chip)" by Moreno et al, Minerals Engineering 2011:24: 852-. However, the use of seawater requires increased capital and maintenance costs to combat the corrosive effects of seawater. Seawater may also adversely affect the yield of certain copper minerals produced. See Jeldres et al, "efficiency of sea water on refractory flow: a Review", Mineral Processing and extraction metallic Review 2016:37(6): 369-. To counteract the adverse effects of seawater, some mining operations desalinate seawater to produce desalinated water for their mining operations. However, desalination of seawater produces a waste brine stream. See "Innovative Solutions for Seawater Use in minimizing Operations", Case Study of Innovative Projects Bernardo Llamas, IntechOpen ", DOI 10.5772/Intechopenn.68191, by G.lvez et al, published in 2017, 30/8. It is believed that neither seawater nor spent brine is used to treat the tailings. Thus, in some embodiments of the process of the present invention, tailings from ore processing (e.g., metal ore processing) may be treated using the waste brine from desalination as a source of at least one highly water soluble salt, with or without other sources of highly soluble salts such as seawater.

After treatment of the tailings with at least one highly water soluble salt, the solids in the tailings may be consolidated, for example, by mixing followed by gravity settling in a settling tank, or by mechanical consolidation, for example by pressing or centrifuging, to increase the rate of formation of consolidated material in the treated tailings. The consolidated material can be separated from the process water by decantation, filtration, electro-filtration, cross-flow filtration, evacuation, and/or mechanical dewatering (i.e., application of an external force to the consolidated material). After separation, the consolidated material may be transferred for further dewatering or disposal.

Although highly water soluble salts can destabilize and consolidate solids in tailings, it has been found that the process can be significantly improved by the addition of one or more polymeric coagulant agents. The addition of the polymeric flocculant to the treated tailings shortens the time to form consolidated material.

One or more polymeric flocculants may be added simultaneously with or after treating the tailings with at least one highly water soluble salt to form treated tailings. The one or more polymeric flocculants may also be added prior to treating the tailings with the at least one highly water soluble salt, but it appears more effective to add the flocculant simultaneously with or after the at least one highly water soluble salt to form the treated tailings, even for tailings that already contain a polymeric flocculant, such as thickener underflow tailings.

In addition, the methods of the present disclosure may also include treating the aqueous fines with coarse particles (e.g., particles greater than 44 μm in size), such as sand, to significantly increase the solids content. Mixing with sand is suitable for aqueous fines having solids that are mostly fine, as the fines can be located in the voids between the coarse particles, thereby enhancing packing and increasing the solids content. However, it has been found that for some compositions such as coal slurries and metal ore tailings, the addition of sand is not required to achieve high solids content, since there is already enough coarse in the tailings to obtain high solids content material in a short time.

Accordingly, embodiments of the disclosed methods include, for example, (i) treating tailings with at least one highly water soluble salt to form treated tailings, the treated tailings comprising a consolidated material in process water; (ii) treating the tailings with at least one highly water soluble salt and at least one polymeric flocculant to form treated tailings, the treated tailings comprising consolidated material in process water; (iii) treating the tailings with at least one highly water soluble salt and coarse particles to form treated tailings, the treated tailings comprising consolidated material in the process water; and (iv) treating the tailings with at least one highly water soluble salt, at least one polymeric flocculant, and coarse particles to form treated tailings, the treated tailings comprising consolidated material in the process water. These embodiments may each include treating the tailings with an aqueous solution of salt and/or a polymeric flocculant. These embodiments may each include separating the process water from the consolidated material. Advantageously, the consolidated material has a density greater than the density of the process water. The process water can then be readily separated from the consolidated material by one or more of decantation, filtration, gravity drainage, electro-filtration, cross-flow filtration, vacuum extraction, and other evaporation techniques, and/or by one or more of equipment used to dewater the consolidated material, such as a centrifuge, a decanting centrifuge, a screw extractor, a cyclone, a belt vacuum filter, a filter press, or a pressing device. Furthermore, the separated consolidated material may be treated or deposited in a containment structure (containment structure) that is capable of removing water released by the consolidated material. In addition, process water separated from the treated tailings may be recycled back to treat other tailings.

Polymers useful in the practice of the present disclosure include water-soluble flocculating polymers, such as polyacrylamides or copolymers thereof, for example: a non-ionic polyacrylamide; anionic Polyacrylamides (APAMs), such as polyacrylamide-co-acrylic acid; and Cationic Polyacrylamides (CPAM), which may contain comonomers such as acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride (DMDAAC). Other water-soluble flocculating polymers that may be used in the practice of the present disclosure include polyamines, such as polyamines or quaternized forms thereof, e.g., polyacrylamide-co-dimethylaminoethylacrylate, polyethyleneimine, polydiallyldimethylammonium chloride, polydicyandiamide or copolymers thereof, polyamide-co-amines, and polyelectrolytes such as sulfonated polystyrene may also be used. Other water soluble polymers such as polyoxyethylene and its copolymers may also be used. Polymeric flocculants can be synthesized in forms with different Molecular Weights (MW), charge types and charge densities to meet specific requirements. Advantageously, the flocculating polymer used in the practice of the disclosed method does not include the use of a sufficient amount of activated polysaccharide or activated starch (i.e., heat treated polysaccharide and starch) to reduce the density of the floes to below the density of the process water from which the floes are separated. When such activated polysaccharides and activated starches are used in sufficiently high amounts, low density flocculants tend to form that rise to the surface of the aqueous composition, which can interfere with the removal of solids in large scale operations involving high solids content, and can also interfere with the dewatering of the consolidated material.

Preferably, the amount of polymer used to treat the tailings should be sufficient to flocculate the solids in the tailings, as well as any added coarse particles (e.g. sand). The amount of polymer used to treat the tailings can be described as a concentration based on the total weight of the tailings, or as an amount based on the weight percentage of solids in the tailings.

In some embodiments of the present disclosure, the concentration of the one or more polymeric flocculants, i.e., the tailings polymer concentration, in the treated tailings is up to about 0.001 wt%, e.g., up to about 0.003 wt%, 0.005 wt%, or up to about 0.01 wt%. For relatively short treatment times, consolidation of solids can be achieved when the tailings polymer concentration is not less than about 0.04 wt.%. The term "tailings polymer concentration" as used herein refers to the concentration of flocculating polymer in the treated tailings, which is determined by dividing the mass of polymer by the percentage obtained by the total mass of polymer plus tailings and all water used to dissolve the polymer. For example, a 0.01 wt% concentration of tailings polymer is obtained by mixing 1 part by weight of undiluted (e.g., pure) polymer with 9999 parts by weight of tailings. Alternatively, by treating the tailings with an equal weight of 0.02 wt% polymer solution, the resulting concentration of tailings was also 0.01 wt%. In certain embodiments, the tailings are treated with at least one polymer flocculant to obtain a concentration of tailings polymer of up to about 0.02 wt%, such as up to about 0.03 wt%, 0.04 wt%, 0.05 wt%, or even up to about 0.07 wt%, 0.09 wt%, 0.1 wt%, 0.2 wt%, and the like. The amount of polymer flocculant can be used in greater concentrations. However, high concentrations have difficulty dissolving the flocculant, the solution becomes too viscous, and the economics of the process are reduced.

In some embodiments of the present disclosure, the one or more polymeric flocculants in the treated tailings have the following concentrations: the amount thereof (weight of flocculant to weight of solids in the tailings) is not less than 0 and up to about 0.005 wt%, for example up to about 0.01 wt%, and in some embodiments up to about 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.03 wt%, or 0.04 wt%.

If the tailings salt concentration is increased, the amount of polymer flocculant may be reduced. Although the reason for this effect is not clear, if the tailings salt concentration is increased, very low concentrations of tailings polymer, for example, of up to about 0.001 wt%, such as up to about 0.003 wt%, 0.005 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, can achieve very rapid consolidation of solids in the tailings.

Kibble useful for practicing certain methods of the present disclosure is preferably sand, and when used in the treatment composition, the amount of such particles is preferably: the sand to fines ratio (SFR ratio) is less than 4:1, for example including from about 2.5:1.0 to about 0.5:1, or including from about 2.25:1 to about 0.75: 1. The SFR ratio is calculated by determining the amount of sand in the estimated weight of solids fines added to the aqueous fines by weight. The use of coarse particles is believed to contribute to the accumulation of consolidated fines, thereby advantageously increasing the solids content and even enabling the formation of consolidated solids compact structures, i.e. structures in which the individual consolidated solids particles are no longer free to move relative to each other.

Tailings (e.g., tailings from the processing of metal and non-metal ores) can be treated in a variety of ways with one or both of at least one highly water soluble salt, and optionally with at least one polymeric flocculant and/or optionally sand. In certain embodiments, treating the tailings comprises combining and/or mixing the various components. Furthermore, at least one salt may be added directly to the tailings as undiluted solid in powder form or as a solution; the at least one polymer flocculant may be added directly to the tailings as undiluted material or as a solution, and optionally, coarse particles (e.g., sand) may be added directly to the tailings or added to the tailings with the salt and/or polymer or a solution thereof. The salt and polymer may be combined in a single solution with or without sand and then combined with the tailings. The order of combination of salt, polymer and optionally sand with the tailings can give comparable results and the optimisation of the process depends on the nature of the tailings and the scale and equipment used in the process.

However, it is more convenient to do this: one or more solutions comprising one or more highly water soluble salts and one or more polymeric flocculants are used and then combined with the tailings. In certain embodiments, an aqueous solution of one or more highly water soluble salts at a concentration of not less than about 0.5% or 1% by weight, such as at least about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 15%, 20%, 30% by weight, or even up to 40% by weight, may be used, or an aqueous salt slurry used to treat the tailings. The aqueous salt solution may also include one or more polymeric flocculants, and the concentration of the one or more polymeric flocculants may be up to about 0.005 wt%, such as up to about 0.01 wt%, 0.04 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%. The tailings may be treated with an aqueous solution of highly water soluble salts and polymeric flocculants, and such aqueous solution may be combined with such tailings at a ratio of tailings to salt solution in the range of about 80:1 to 1:1, for example, 70:1 to 1:1, 50:1 to 1:1, 30:1 to 1:1, 20:1 to 1:1, 15:1 to 1:1, 10:1 to 1:1, 5:1 to 1:1, and/or about 2:1 to 1: 1. Optionally, sand may be combined with the tailings before, during, or after the tailings are combined with the aqueous solution of salt and/or polymer flocculant.

Because of the use of highly water soluble salts and polymer flocculants, preferably having water solubility, in the process of the present disclosure, there is no need to raise the temperature of the treated tailings above ambient temperature to practice the process. In certain embodiments, treating the tailings according to various embodiments herein may be carried out at about ambient temperature or no more than about 2 ℃ to about 5 ℃ above ambient temperature. In other embodiments, treating the aqueous coal waste composition may be performed at a temperature of no greater than about 50 ℃, such as no greater than about 40 ℃ or 30 ℃.

In a practical aspect of the present disclosure, tailings (e.g., from metal ore and non-metal ore processing) may be consolidated by treating such tailings with at least one highly water soluble salt or aqueous solution thereof to form treated tailings, and such tailings may optionally comprise one or both of: at least one polymeric flocculant (e.g., a water-soluble polymeric flocculant) or an aqueous solution thereof, and/or optionally grit (e.g., sand). Treating the tailings in this manner can destabilize and consolidate solids (e.g., fine and coarse solids) in the treated tailings to form a consolidated material that can aggregate relatively quickly in the process water.

The treated tailings and/or consolidated material can be further dewatered to further separate process water from the consolidated material, and in some cases, to further consolidate the solids. In some embodiments, the consolidated material formed in the treated tailings can be separated from the process water by one or more of decantation, filtration such as electro-filtration, cross-flow filtration, gravity drainage, vacuuming, and other evaporation techniques, and/or by one or more mechanical dehydrations, i.e., external forces applied to the consolidated material using a consolidated material dehydration apparatus (e.g., by the application of a centrifuge, a decanting centrifuge, a screw dehydrator, a cyclone, a filter press or pressing apparatus, or the like, or combinations thereof). In one aspect of the method of the present disclosure, the process water may be separated from the consolidated material by: the treated tailings stream is passed through a cross-flow filter (e.g., a perforated or slotted pipe) that filters and dewaters the treated tailings stream to separate the process water from the consolidated material. The process water is then easily separated from the consolidated material. In another aspect of the disclosed method, the process water may be separated from the consolidated material by gravity drainage to achieve a solids content of at least about 70% within about one month after treating the tailings, for example, at least about 70% within about two weeks or about one week of gravity drainage time after treating the tailings. In another aspect of the disclosed method, consolidated material may be separated from the treated tailings and deposited in a thin lift deposition (thin lift deposition) to further dewater the consolidated material.

Advantageously, the consolidated material formed in the treated tailings has a high solids content, for example, a solids content of greater than about 50 wt%, and at least about 60 wt%, 65 wt%, 70 wt%, and 75 wt%. Furthermore, after mixing and/or dewatering the treated tailings according to certain embodiments within a short period of time, the consolidated material formed in the treated tailings may have a high solids content. In embodiments of the present disclosure, the solids content of the consolidated material after mixing and/or dewatering may be greater than about 50 wt%, and at least about 60 wt%, 65 wt%, 70 wt%, 75 wt%, and 80 wt%. In certain embodiments, at least about 70% solids content is obtained within about one month of gravity drainage time after treating the tailings, for example, at least about 70% solids content is obtained within about two weeks or about one week of gravity drainage time after treating the tailings.

In embodiments of the present disclosure, the method includes mixing the tailings with a highly water soluble salt (e.g., an ammonium salt), a water soluble polymer (e.g., polyacrylamide), and optionally sand, e.g., a sand to fines ratio of between about 2.25:1 and about 0.75:1, to form treated tailings comprising consolidated material having a high solids content in less than 10 minutes, wherein the solids content is greater than about 50 wt%, e.g., at least about 60 wt%, 65 wt%, 70 wt%, or more, depending on the dewatering method used.

Another advantage of the disclosed method is the recovery of material from tailings containing rare earth elements. For example, certain tailings may contain valuable minerals containing rare earth elements. The Rare Earth Element (REE) defined by IUPAC is one of 17 chemical elements in the periodic table (specifically fifteen lanthanides and scandium and yttrium). Scandium and yttrium are considered rare earth elements because they tend to appear in the same deposit as the lanthanide elements and exhibit similar chemical properties. Many REEs are used in electronics, magnets, high performance coatings. Such REEs include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).

The REEs in the aqueous fines are typically in ionic or oxide form. For example, the zirconium can be zircon, ZrSiO₄May exist in the form of the minerals ilmenite, leucotite and rutile. Coal ash and coal cleaning waste contain rare earth elements. The chamotte ash (Fire clay coal) has very high concentrations of yttrium and zirconium. Oil sands tailings also contain REE.

The methods of the present disclosure may also be used to recover REE. It is believed that in some tailings, the REEs adsorb on the clay surface in the tailings. In other tailings, the REE is primarily contained in the solids of the tailings, but may also be located in the process water. Due to the exchange between ammonium ions and REE ions, the adsorbed REE can be exchanged with the highly water soluble salts (e.g., ammonium based salts) of the present disclosure. The REE can be obtained from solids in tailings by leaching the solids with acid followed by extraction and precipitation, or by caustic decomposition followed by acid leaching.

Another aspect of the disclosed method includes consolidating the tailings comprising the re material by treating the tailings comprising the re material with at least one highly water soluble salt (e.g., an ammonium salt, such as ammonium sulfate), thereby forming treated tailings comprising the consolidated material in the process water, the treated tailings comprising the re material in the process water and/or the consolidated material. In one aspect of the disclosure, the treated tailings consolidate the fines and also separate the REE material from the solids and pass it into the process water. The process water may then be separated from the consolidated material, and the REE material may be recovered from the separated process water. The REE material may be recovered from the process water by precipitation using oxalic acid or by extraction. Other methods of recovering the REE from process water include mineral processing and physical beneficiation, eutectic solvent extraction/ionic liquid extraction, acid dissolution, high temperature phase separation, use of a REE selective adsorbent, photophoresis, in-situ brine injection and extraction (in-situ brine injection and extraction), reactive grinding (reactive grinding), and the like. In other aspects of the disclosure, the treated tailings consolidate the fines and the REEs are located in the consolidated material. The process water may then be separated from the consolidated material. The consolidated material may then be leached with an acid (e.g., nitric acid, sulfuric acid, etc.), followed by extraction with a solvent and/or an ion exchange resin, and then precipitated. Alternatively, the consolidated material may be treated with a caustic agent (e.g., sodium hydroxide) to decompose certain materials and form the hydroxide of the REE, followed by leaching with an acid (e.g., HCl).

Further, the tailings comprising the REE material may be treated with at least one polymeric flocculant and optionally sand to form treated tailings. The tailings salt concentration of the at least one highly water soluble salt in the treated tailings is at least 0.5 wt%, and preferably not less than about 0.70 wt%, such as at least about 1 wt%, 1.25 wt%, 1.5 wt%, 1.75 wt%, 2 wt%, and even at least about 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, etc., of the at least one highly water soluble salt.

The process of the present disclosure enables the treatment of tailings on a large scale by a continuous or semi-continuous process and further recovering, recycling and purifying at least a portion of the process water in the tailings, and optionally recovering the REE material. When non-hydrolyzable, highly water soluble salts are used in the process of the present disclosure, the process water separated from the initially treated tailings may advantageously contain a significant amount of one or more highly water soluble salts (which were initially used to treat the tailings).

In practical aspects of the disclosed methods and various embodiments thereof, the separated process water may comprise at least one highly water soluble salt, and the method may further comprise one or more of: (i) recovering at least a portion of the separated process water; (ii) recycling at least a portion of the recovered separated process water to treat other tailings; and/or (iii) purifying at least a portion of the recovered process water. In some embodiments, the recovered separated process water (which contains highly soluble salts) may be treated to concentrate the highly soluble salts in the water. For example, reverse osmosis systems that produce desalinated water and waste brines may be used to produce brines containing highly soluble salts from separated process water from the recovery of treated tailings.

In other embodiments, the separated process water comprises a REE material salt, and the method further comprises recovering at least a portion of the separated process water, and recovering the REE material and/or purifying at least a portion of the recovered process water.

FIG. 1A schematically illustrates an exemplary continuous or semi-continuous process. As shown, the tailings are treated with one or more highly water soluble salts and optionally one or more polymeric flocculants and optionally grit (sand) by combining a salt stream (101a), which may be an aqueous solution, with a tailings stream (103 a). Optionally, the tailings may also be treated with one or more polymeric flocculants by combining a flocculant stream (102a), which may be an aqueous solution, with the tailings stream (103 a). Alternatively, the salt and flocculant may be combined together into a solution to treat the tailings as a tailings stream. Grit may also be added to the tailings or tailings stream and/or may be added to any or all of the streams.

The solution streams of salt and polymer may come from storage tanks 101 and 102, respectively, and the tailings stream and sand stream may come from storage tanks 103 and 105, respectively. Alternatively, the tailings may be derived directly from an ore extraction process.

For this embodiment, the salt stream (101a) and the polymer stream (102a) and the tailings stream (103a) are brought to a mixing apparatus 107 and mixed. (sand stream (105a) may optionally be added). Mixing device 107 can be an in-line mixer, a mixing tank, a helical ribbon mixer, or other mixing device capable of mixing streams 101a, 102a, 103a, and optionally 105 a. For this embodiment, the tailings are combined with the salt as a solution, followed by combination with the polymer. However, the tailings may be treated with an aqueous solution comprising both salt and polymer. In some embodiments, combining the streams in-line may achieve sufficient mixing so that a separate mixing device (e.g., in-line mixing) is not required, and the combined streams may be taken directly to a tailings pond or mechanical dewatering device to separate the consolidated material from the process water.

As shown in the embodiment of fig. 1A, after passing through the mixer 107, the treated tailings (which comprise the consolidated material and the process water) are transferred to a solid/liquid separator 109 to separate the process water from the consolidated material. Such means include, for example, one or more of decantation, filtration, electro-filtration, cross-flow filtration, gravity drainage, or vacuuming means, or combinations thereof, and/or dewatering means utilizing one or more consolidated materials, such as centrifuges, decanting centrifuges, screw dehydrators, cyclones, belt vacuum filters, filter or press devices, or the like, or combinations thereof.

The separated process water may be recovered and collected in a tank or reservoir (111), and the separated consolidated material may be recovered and collected or transported (113). For this embodiment, the recovered process water stream (111) comprises process water from the tailings diluted with stream 101a, thus comprising residual salt from the one or more highly water soluble salts, and possibly comprising residual polymer from the one or more polymer flocculants and components from the tailings. If the tailings comprise a REE material, the recovered process water stream (111) and/or the consolidated material (113) may also comprise a REE material. Highly water soluble salts may also be present as components of the original treated tailings and these salts are part of the recovered process water (111). The recovered process water (111) may be transferred to a water purification system (115) to purify at least a portion of the recovered process water 117, which may be recycled in the mining process. Water purification systems that may be used in embodiments of the disclosed methods include reverse osmosis systems, vacuum distillation systems, electrodialysis, filtration systems, and the like. The remaining, unpurified recovered process water or brine (119) containing the highly water soluble salts from stream 101a and potentially highly water soluble salts as components of the raw tailings can be recycled back to the treatment process. For this embodiment, at least a portion of the raw recovered process water may be returned to the storage tank 101 and the salt or polymer under concentration may be corrected by adding additional highly water soluble salt or polymer flocculant from one or more of the makeup tanks (e.g., makeup vessels 121 and 122).

The methods of the present disclosure may also include recovering the REE material from recovered separated process water or from consolidated solids. The REE material can be recovered from the process water by precipitation (e.g., using oxalic acid) or extraction. Other methods of recovering the REE from process water include mineral processing and physical beneficiation, eutectic solvent extraction/ionic liquid extraction, acid dissolution, high temperature phase separation, use of a REE selective adsorbent, photophoresis, in situ brine injection and extraction, reactive milling, and the like. The methods of the present disclosure may also include recovering the REE material from the consolidated solids by acid leaching or caustic decomposition.

In addition, consolidated solids can be recovered. The recovered consolidated solids may contain residual highly water soluble salts from tailings treatment. When the salts used for tailings treatment are beneficial to plant life (e.g., ammonium or sulfate or phosphate salts), the residual salts and consolidated solids can act as fertilizers. The recovered consolidated solids may comprise the REE material, which may be separated from the consolidated solids as described elsewhere herein.

FIG. 1B schematically illustrates other exemplary continuous or semi-continuous processes. For this embodiment, tailings from metal ores, such as tailings from copper ore processing, are shown. As shown, a flotation tank or concentrator (201) produces tailings 203. Many processing of metallic or even non-metallic ores includes a concentration step in which the useful minerals are concentrated by flotation in an aqueous mixture containing various reagents. Separating the valuable minerals and producing a tailings stream. In this particular example, the tailings can be a thickener underflow tailings stream. Such thickener underflow streams may still benefit from treatment with highly water soluble salts and optionally other polymeric flocculants to further consolidate solids in accordance with the methods of the present disclosure. According to an aspect of the process of the invention, the tailings stream is treated with an aqueous stream comprising at least one highly water soluble salt. For this embodiment, the aqueous solution further comprises at least one polymeric flocculant. As shown in fig. 1B, the tailings stream 203 is combined with an aqueous stream (202a) comprising at least one highly water soluble salt and at least one polymeric flocculant to produce a treated tailings stream 207. For this embodiment, the aqueous solution stream 202a and the tailings 203 are mixed in-line to produce treated tailings 207. Combining the streams (202a and 203) produces a treated tailings comprising consolidated material in the process water.

Although not shown, the tailings may be treated with separate streams of salt and flocculant. An aqueous stream of salt and polymer flocculant may be sourced from reservoir 202. In certain embodiments, seawater is used as a supplemental source of salt in 220 for the source of highly water soluble salts. In other embodiments, brine from the reverse osmosis system is used as a supplemental source of salt in 220 for the source of highly water soluble salt, and in yet another embodiment, both seawater and brine are used as supplemental sources of salt in 220 for the source of highly water soluble salt.

For this embodiment, the treated tailings are transported to a solid/liquid separator (209). The S/L separator separates process water of the treated tailings from the consolidated material. Such S/L separators include, for example, one or more of a centrifuge, a decanting centrifuge, a dewatering screw, a hydrocyclone, a vacuum belt filter, a filter press, or a pressing device, or the like, or combinations thereof. The S/L separator 209 produces a stream 213 of consolidated material and a separated process water stream 211. The process water stream 211 comprises process water from the tailings stream 203 diluted with the aqueous solution stream 202a, and thus comprises residual salts from the one or more highly water soluble salts, and possibly residual polymers from the one or more polymer flocculants. At least a portion (if not all) of process water stream 211 may be recovered and purified by reverse osmosis system 215.

The reverse osmosis system 215 may concentrate at least one highly soluble salt in the recovered portion of the separated process water 211 to form a brine 219. At least a portion (if not all) of the brine 219 may be recycled back to the salt/polymer flocculant storage 202 to treat other tailings 203. The reverse osmosis system 215 may concentrate the at least one high solubility salt to a concentration greater than 2 wt%, such as greater than 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, and higher, such that the salt-composition concentration in the salt/polymer flocculant reservoir may be at equilibrium, from about 2 wt% to about 10 wt%, and values therebetween or higher. The aqueous solution stream (202a) comprising at least one highly water soluble salt and at least one polymer flocculant may be combined with the tailings stream 203 at a ratio range of tailings to salt solution including tailings to salt solution of about 30:1 to 1:1, 20:1 to 1:1, 15:1 to 1:1, 10:1 to 1:1, 5:1 to 1:1, and/or about 2:1 to 1: 1.

The reverse osmosis system 215 may also be used to produce desalinated water 240 from seawater 250, where the desalinated water 240 is used in other processes of mining operations. The spent brine from system 215 may be used as a source of highly soluble salts to treat tailings, thereby increasing the efficiency of the overall operation and reducing the adverse environmental impact of discharging the brine to the environment. In addition, seawater may be used as a source of highly water soluble salts to treat tailings, such as providing seawater in the supplemental source 250.

Examples

The following examples are intended to further illustrate certain preferred embodiments of the present invention without limiting the nature thereof. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific materials and procedures described herein.

Consolidation of coal ash slurry

An initial sample of the coal ash slurry was analyzed by infrared spectroscopy to determine the solids content. Further, it is estimated that the sample contains 30% or more of coal fines, i.e., a mixture of fine coal particles and fine mineral particles. Approximately 5g of the coal slurry was placed in a vial and an equal weight of aqueous ionic solution was added and the diluted slurry was shaken to mix the ingredients. The aqueous ionic liquid consisted of water, 10 wt% ammonium sulfate and 0.1 wt% Polyacrylamide (PAM). As can be seen from the left hand diagram in fig. 2, settling occurs immediately. The vials were then centrifuged at 3000rpm for 30 seconds, as shown in the middle panel of fig. 2, and the granules consolidated into a compact mass. The supernatant appeared clear, containing no visible suspended particles. As can be seen from the right hand image in fig. 2, when the supernatant is removed, the dense solid is found to have sufficient cohesive strength to retain its shape when the vial is inverted.

The material was removed from the vial (fig. 3, left panel) and a portion was dried. The initial solids content of the consolidated material was 54%. Some of the remaining consolidation material was squeezed (by hand) between the tissues (fig. 3, right panel). The extruded material had a solids content of 74%.

Treating different salts and salt concentrations in oil sand tailings

Other experiments were performed using various high water soluble salts of different concentrations with or without sand to treat oil sand tailings. A series of salt/polymer solutions were prepared. All salt/polymer solutions contained 0.1 wt% Polyacrylamide (PAM), but the salt species and concentrations varied. For example, a series of 10 wt%, 5 wt% and 2 wt% calcium chloride solutions, each containing 0.1 wt% PAM, were prepared for treatment of MFT. Additional 10 wt%, 5 wt%, and 2 wt% salt solutions of ammonium sulfate, potassium chloride, etc., each containing 0.1 wt% PAM, were prepared. Equal weights of the specific salt/polymer solution were then combined with MFT with or without sand in a vial, followed by vigorous mixing. The vials were then centrifuged on an LW Scientific laboratory centrifuge at 3000rpm to form a consolidated material in slurry form. After centrifugation, the supernatant was separated from the consolidated material by pipette. The consolidated material is then weighed, dried and weighed again to determine the solid content of the consolidated material. The various salts used to treat MFT and their concentrations, as well as the resulting solids content values, are summarized in tables 1 and 2 below.

Table 1: solids content of MFT treated with equal weight of salt/PAM solution (no sand added) after centrifugation.

Table 2: solids content of MFT treated with equal weight of salt/PAM solution (sand addition, SFR ratio 1:1) after centrifugation.

1. The tailing salt concentration was about 5 wt%.

2. The tailing salt concentration was about 2.5 wt%.

3. The tailing salt concentration was about 1 wt%.

Table 1 reports the solids content of the dried consolidated material after treatment of MFT with various salt/polymer solutions (no sand added). The high water soluble salt provides a solids content of the consolidated material ranging between about 31% and 37% after about 30 seconds of centrifugation. However, under the test conditions, the use of highly water soluble salts with multivalent cations (such as aluminum and ferric cations) resulted in fouling of the vial walls and a less cohesive consolidated material compared to highly water soluble salts with monovalent cations. In some tests using a 10% salt concentration, clear water above the consolidated material was removed using a pipette and the wet solid was squeezed between paper towels. By using salts with monovalent cations (e.g. NH)₄Cl and (NH)₄)₂SO₄Iso-ammonium salt) with polyvalent cations (aluminum chloride (AlCl)₃) Iron chloride (FeCl)₃) And calcium chloride (CaCl)₂) Which deposits a substantial amount of viscous material on the vial wall) has low cohesion of the resulting extruded solid.

Table 2 reports the solids content of the dried consolidated material after treatment of the MFT with various salt/polymer solutions and sand. Sand was added at a sand to fines ratio of 1:1 (i.e., 1.5g of sand was added to 5g of MFT with 30% solids, resulting in a sand weight/solids in MFT ratio of 1: 1). After 30 seconds of centrifugation, the high water soluble salt provides a solids content range for the consolidated material of between about 46% and 58%, which is significantly higher than the solids content range when sand is not used. The centrifuged slurry was approximately equal in volume, although the solids content of the vial containing the added sand was twice that of the vial without sand.

The data in tables 1 and 2 show that the addition of a 2 wt% salt solution to treat MFT has the same effect as the addition of a 10 wt% salt solution. That is, a tailing salt concentration of 1 wt% has the same effect as a tailing salt concentration of 5 wt%. Since an equal weight of salt/polymer solution was used to treat MFT, the salt concentration of the added salt in the treated tailings was half of the salt concentration in the salt/polymer solution, i.e., 2 wt% salt solution was added to give a 1 wt% concentration of tailings salt and 10 wt% salt solution was added to give a 5 wt% concentration of tailings salt. The concentration of tailings salts in the treated MFT can be achieved in a variety of ways. To facilitate handling in the foregoing vial test, it is convenient to combine an equal weight of salt/polymer solution with MFT. However, comparable results are obtained with consolidated materials when a smaller amount of high concentration salt/polymer solution is used to obtain the same concentration of salt in the tailings.

Centrifugation in flat bottom vials is not as efficient as using centrifuge tubes in producing high solids materials. It should be remembered that in all experimental groups of laboratory vials and tubes there was always a solution present in the interstices between the particles. As will be shown below, the solids content of the consolidated material can be readily increased to a solids content range of over 46% to 58% by simple draining or by using mechanical draining methods known in the art (e.g., filter presses, belt filters, cross-flow filtration, screw sand dryers, decanting centrifuges, cyclones, etc.).

Treating different salt concentrations and polymer concentrations in oil sand tailings

When salt, polymer and sand are used together, a concentration of salt in the tailings of greater than 0.5 wt% and preferably no less than about 0.70 wt%, for example at least about 1 wt%, should be used to achieve a suitably rapid consolidation of the solids in the tailings. Furthermore, although some consolidation of the fines/sand mixture is obtained in a relatively short process time when the tailings polymer concentration is as low as 0.01 wt%, excellent results are obtained when the tailings polymer concentration is above 0.05%. These preferred concentrations were determined by a series of vial experiments. The upper row of vials in FIG. 4 is shown by mixing 5g of 2 wt.% ammonium sulfate ((NH)₄)₂SO₄) The solution (which contained PAM) was added to 5g of MFT. Sand was also added so that the sand/fines ratio was 1:1 (i.e., 1.5g of sand was added). The amount of PAM in the solution varied between 0.1% (by weight) and 0.02% (by weight). The lower set of vials shows the phenomenon observed when 1 wt% ammonium sulfate was used. The vials were centrifuged at 3000rpm for 30 seconds to accelerate sedimentation.

It can be seen that (NH) is present at 1% by weight₄)₂SO₄In solution treated vials, there was some settling of fines and sand, but the supernatant contained a large amount of suspended particles. Furthermore, there was a degree of separation of sand and fines visually. In contrast, 2% by weight of (NH)₄)₂SO₄The solution (which contained 0.1 wt% PAM) treated MFT showed settled dense solids, which were contacted with the clarified supernatant. As the amount of polymer in the solution from vial a4 to E4 decreased, the clarity of the supernatant decreased because more suspended particles remained in the liquid phase. Longer centrifugation times will result in a cleaner supernatant, but for shorter treatment times it is preferred to treat the MFT so that the tailings salt concentration is not less than about 0.5 wt% and the tailings polymer concentration is not less than about 0.04 wt%.

The solids content of the consolidated material in each vial shown in fig. 4 was determined by drying by separating the centrifuged consolidated material from the supernatant, weighing the wet mass, drying, and weighing again to determine the solids content. The solids content of the consolidated material for these vial groups is summarized in table 3.

Table 3: solids content of ammonium sulfate/PAM treated MFT after centrifugation (solids content was measured by separating and drying the consolidated material).

It can be seen that for 2 wt.% (NH) containing 0.1 wt.% PAM₄)₂SO₄Solution, a solid content slightly higher than 60% is obtained. When MFT was treated with solutions having PAM concentrations of 0.08 wt% and 0.06 wt%, the solid content decreased only slightly, but when PAM concentrations were lower, the solid content decreased significantly. For each vial A4-E4, equal weights of (NH) were used₄)₂SO₄When MFT was treated with polymer solution, the resulting concentration of tailing salt was about 1 wt%, and the concentration of tailing polymer in vial a4 was about 0.05 wt% PAM, in vial B4 was about 0.04 wt% PAM, in vial C4 was about 0.03 wt% PAM, in vial D4 was about 0.02 wt% PAM, and in vial E4 was about 0.01 wt% PAM. For 1 wt.% (NH)₄)₂SO₄The solution, solids content varied indefinitely, indicating that there was a problem with the separation of coarse and fine particles in the consolidated material in these experiments.

Higher salt concentrations allow the polymer concentration to be reduced

When salt, polymer and sand are used together to treat tailings, it is observed that in certain cases, the tailings polymer concentration can be reduced if the tailings salt concentration is increased. Thus, if the tailings salt concentration is increased, very low tailings polymer concentrations can achieve very rapid consolidation of solids in the tailings. Figure 5 shows that as the salt concentration increases, less polymer flocculant is required to obtain a clear supernatant. For these experiments, the tailing polymer concentration increased from 0.01% to 0.05% in a 0.01% increase from right to left, while the tailing salt concentration increased from 1% to 2% from top to bottom.

Different polymer concentrations when treating oil sand tailings with seawater

For these experiments, solutions of non-ionic polyacrylamide (from SNF, FA920) in seawater (taken from the atlantic ocean on the east coast of the usa) at concentrations between 0.1% (by weight) and 0.02% (by weight) were prepared. The concentration of highly water-soluble salts in seawater is believed to be greater than 3% by weight. MFT from oil sands processing is treated with a seawater-polymer solution. In a vial, MFT was treated with an equal amount of seawater-polymer solution (about 5g of seawater-polymer solution was added to about 5g of MFT). The treated mixture was first stirred and then the vials were centrifuged at 3000rpm for 30 seconds to accelerate sedimentation. These results are shown in the photograph of fig. 6. From left to right, the seawater used to treat MFT contains about 0.1 wt%, 0.08 wt%, 0.06 wt%, 0.04 wt%, and 0.02 wt% of a polymeric flocculant, respectively. These experiments show that mixtures of highly water soluble salts derived from seawater can be used in the methods of the present disclosure.

Treatment of tailings from copper ore processing

A sample of tailings produced from processing copper ore is mixed with approximately equal amounts of aqueous ionic solution in a 500ml beaker. The aqueous ionic solution comprises water, a highly water soluble salt and a flocculating agent (polyacrylamide (PAM)). Upon combining and slightly mixing the tailings with the aqueous ionic solution, solids almost immediately begin to consolidate. After standing for a few minutes, the solids aggregate and settle to the bottom with a clear aqueous layer above the consolidated solids. See fig. 7A. The consolidated solids are also cohesive. The consolidated material removed from the beaker was easily compacted by hand to form a ball (see fig. 7B). A hand-compacted ball as shown in fig. 7B was placed between the paper towels and the test by the tester's stepping showed that the consolidated material did not soil the towels (see fig. 7C). This test is an indication of how easily the consolidated material can be filtered and mechanically dewatered, where a low degree of fouling (fouling) indicates good filterability and mechanical dewatering. The solids content of the pressed tailings was determined to be about 75%.

Only the preferred embodiments of the invention and but a wide variety of examples of its uses are shown and described in this disclosure. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Thus, for example, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific substances, steps and arrangements described herein. Such equivalents are considered to be within the scope of this invention and are covered by the following claims.

Claims (21)

1. A method of consolidating tailings, the method comprising:

treating the tailings with at least one highly water soluble salt to form treated tailings comprising consolidated material in the process water; and

separating the process water from the consolidated material,

wherein the tailings salt concentration of the at least one highly water soluble salt in the treated tailings is at least 0.5 wt%.

2. The method of claim 1, wherein the at least one highly water soluble salt is a non-hydrolyzed salt.

3. The method according to any one of claims 1 to 2, wherein the at least one highly water soluble salt is an ammonium salt.

4. The method of claim 1, wherein treating the tailings with at least one highly water soluble salt comprises treating the tailings with seawater.

5. The process of claim 1, wherein the tailings salt concentration of the at least one highly water soluble salt in the treated tailings is at least 1 wt%.

6. The process of claim 1, further comprising treating the tailings with at least one polymeric flocculant to form the treated tailings simultaneously with or after treating the tailings with the at least one highly water soluble salt.

7. The method of claim 6, wherein the at least one polymeric flocculant is polyacrylamide or a copolymer thereof.

8. The process of any one of claims 6 or 7, wherein the tailings polymer concentration of the at least one polymer flocculant in the treated tailings is at most about 0.05 wt%.

9. The process of claim 1, wherein treating the tailings comprises combining a tailings stream with a stream comprising the aqueous solution of the at least one highly water soluble salt to produce a treated tailings stream.

10. The process of claim 6, wherein treating the tailings comprises combining a tailings stream with a solution comprising the at least one highly water soluble salt and the at least one polymeric flocculant to produce a treated tailings stream.

11. The process of claim 6, wherein treating the tailings comprises combining a tailings stream with a stream comprising the aqueous solution of the at least one highly water soluble salt and a stream comprising the aqueous solution of the at least one polymeric flocculant to produce a treated tailings stream.

12. The method of any one of claims 9 to 11, wherein the stream comprising the at least one highly water soluble salt in aqueous solution comprises seawater.

13. The process of any one of claims 9 to 11, wherein the streams are mixed in-line, and optionally mixed using an in-line mixer, to produce a treated tailings stream.

14. The method of claim 1, wherein separating the process water from the consolidated material comprises mechanically dewatering the consolidated material.

15. The method of claim 1, wherein the consolidated material has a solids content of at least 45% by weight.

16. The process of claim 1, further comprising recovering at least a portion of the separated process water from the treated tailings stream and concentrating the at least one highly soluble salt in the separated recovered portion of the process water to form a brine.

17. The process of claim 16, further comprising recycling at least a portion of the brine to treat other tailings.

18. The method of claim 1, further comprising purifying at least a portion of the separated recovered process water.

19. The process of claim 1, wherein the tailings are tailings from processing a metal-based ore.

20. The process of claim 19, wherein the tailings from processing metal species ores are thickener underflow tailings.

21. The process of claim 1, wherein the tailings comprise Rare Earth Elements (REEs), and treating the tailings with the at least one highly water soluble salt forms treated tailings comprising the REEs in the process water and/or the consolidated material; and further comprising recovering the REE from the separated process water and/or consolidated material.

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