FI124419B - A method for recovering metals from oxide ores - Google Patents

Description

A method for recovering metals from oxidic ores

The invention relates to a process for the recovery of metals from oxide ores as disclosed in the preamble of claim 1.

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Many processes generate liquids in which metals are in dissolved form. Such processes include a variety of processes involving the treatment of solid state metals or metallic solids. The result is often liquid substances classified as waste in which the metals 10 are dissolved, for example in the form of a salt. In addition to purposeful treatment processes, such wastes may be generated when metals or metallic substances are otherwise in contact with liquids.

Purification of such liquids from metals, many of which (for example, heavy metals) are harmful to health or the environment, is hindered by their low concentration or other substances present in the solution. For example, ion exchange has been used in which the harmful metal cation is replaced by a harmless cation. However, such ion exchange applications are expensive.

In addition, methods are known for precipitating a dissolved metal from a solution with a suitable chemical containing an anion which forms an insoluble salt with the metal cation. Many precipitation chemicals are known in water purification, for example based on hydroxides, which precipitate metals as insoluble hydroxides. However, their functionality is dependent on other conditions, such as other substances in the water and, for example, pH.

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9 For example, a process is known from U.S. Patent No. 5,434,619 which uses calcium hydroxide or calcium oxide as a coagulant to sequentially precipitate metals at various pH values and to form valuable metals.

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recovery. A corresponding sequential precipitation process is disclosed in U.S. Patent Application Publication No. US-2011/233139, which discloses acid mine drainage. The problem with precipitation processes is that they in a way generate new waste in the form of precipitates or dissolved salts which are difficult to separate or have no further use.

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Oxidic ores have traditionally been processed by pyrometallurgical or hydro-metallurgical processes. Pyrometallurgical methods have the disadvantage of high energy consumption and are generally more profitable when the metal content of the ore is high.

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In hydrometallurgical processes, the metal is extracted from the ore with an acidic solution, usually a sulfuric acid solution, after which the dissolved metals are recovered by precipitation. For example, for the treatment of nickel and cobalt-containing laterite ores, a "high-pressure acid 10 leaching" (HPAL) process has been developed in which metals are extracted at high pressure (about 35-55 bar) and at a temperature (about 245-270 ° C) with sulfuric acid. The method has high energy and hardware costs. In addition, alternative methods have been developed, such as '' Atmospheric Leach 'process described in EP-1228257 (corresponding to U.S. Patents 6680035 and 6261527); "Resin-in-pulp" -15 method described in U.S. Patent No. 6,350,420. Both methods use sulfuric acid for the extraction of nickel and cobalt from ore.

Sulfuric acid treatment causes problems that are typical of acidic waters: environmental risks, the need to neutralize residual solutions, and the risk of corrosion for pipelines and tanks, which increases the cost of equipment.

It is an object of the invention to provide a hydrometallurgical process for the recovery of metals from oxide ores which avoids the treatment of acidic solutions. To accomplish this purpose, the method of the invention is essentially characterized by what is set forth in the characterizing part of the appended claim 1.

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o In the process, the oxide ore is contacted with water under conditions "in which the metal is released from the ore into the water, and from the solution thus obtained g is recovered by precipitation with the boron compound. The boron compound can be anything

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a suitable boron hydroxy compound or a compound containing boron as the oxo anion. In particular, the boron compound may be boric acid or borax, o

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° The method is suitable for recovering divalent metals from basic 35 oxide ores which are such that when the ore is slurried in water, the pH of the slurry is already basic and no addition of a base (e.g. sodium hydroxide) is required to precipitate the metal with 3 boron compounds. The method is particularly important in the recovery of nickel and possibly cobalt from laterite ores. About three-quarters of the earth's nickel deposits are in oxide ores (laterites) and the remainder in sulphide mal-5. Particularly suitable laterite ore is limonite.

Typically, the process is particularly well suited to the treatment of metal-poor ores for hydrometallurgical processes and can utilize, for example, low-ore nickel ores, as well as high-content laterite ores.

In the following, the invention will be described in more detail by describing also the invention according to the previous patent application.

From the applicant's prior patent application FI-20120381, which is still filed at the time of filing this application, a method is known in which hydroxide together with a boron compound is used for the precipitation of metals. The boron compound may be any suitable boron hydroxy compound or boron oxoanone compound. An example of the above is boric acids (oxygen-20 acids), especially boric acid H3BO3. An example of the latter is borate salts, especially borax. Boric acid H3BO3 is the most common boron acid and low cost precipitating chemical capable of forming sparingly soluble precipitates with metal hydroxides. Borax, on the other hand, is a common form of boron that functions in the same way. Subsequent changes in conditions, such as changes in pH, also have no effect on the precipitation because the metal hydroxides form the boron compound.

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^ very fine fines held jointly with the OH groups.

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9 Certain boron compounds in which boron is attached to oxygen have a tendency to "chain or cross-link precisely because of the hydrogen bond g 30 formed by the hydroxy groups. The precipitate is borate to which the metal to be separated is bound.

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o The process can be used to recover metals for the purpose of permanently binding o £ 2 soluble form (ions) metals for final disposal, or for their further utilization. This precipitation method can replace the sulphide precipitation used in the mining industry for the precipitation of metal sulphate from ore extraction for further processing.

The precipitation of the metal converted from the ore to the solution form (sulfate) with hydroxide and boric acid can be described by the following reaction equation: 1) MeSO4 + 2NaOH + 4H3B03 -> [Me (OH) 2 + Na2 (B407) * 5H2O] + H2SO4

Substances that form a permanent precipitate are enclosed in square brackets. The solution remaining from the precipitate 10 contains sulfuric acid, which has many uses. For example, it can be recycled to dissolve metals under acidic conditions. The sulfuric acid can be separated from the solution by heat, whereupon it evaporates. Heat can be obtained from an exothermic reaction, or if the reaction heat alone is insufficient, the solution may be heated. The recovery process utilizes 15 vacuum.

A permanent precipitate is formed as follows:

2) Me (OH) 2 + Na 2 (B407) * 5H 2 O -> Me (B407) * 5H 2 O + 2NaOH

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If sulfuric acid is not recovered, the resulting hydroxide neutralizes the sulfuric acid. The number of borate crystal water molecules may vary depending on the conditions.

The formulas should not be understood as the only possible since borates are a very diverse group of salts and can be present eg in different boron and oxygen? ratios and amounts of bound water,

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^ habits vary. It is essential that the metal to be removed is bound to borate co tn.

00 g 30 "Me" may be any divalent metal (divalent metal ion

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forming metal) such as Cu, Fe, Ni, Co, Mn, Mg or Zn.

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In particular when Me is Cu, Ni or Co, the process can be used to recover dissolved valuable metals from process and waste water from the mining industry with the aim of subsequently separating the metal from the precipitate. Such process water may be, for example, water derived from ore lime pellet extraction in which the metal is dissolved in sulphate.

Instead of boric acid, borax may be used for the precipitation, however, about 4 times more is needed. Similarly, the hydroxide can be more than sodium hydroxide, since it is only important to introduce the hydroxide ions into the solution. If different metals are to be separated, their precipitation at different pH values is utilized. Since the metal hydroxide binds to the boron compound present, there is no re-dissolution of the metal as a result of an increase or decrease of pH 10. If desired, the metals can be separated by always recovering the metal borate precipitated at a certain pH before precipitating the next metal at the following pH.

Now, the boron compound is also utilized in the recovery of metals from oxide ores according to the present invention.

The method is particularly suitable for the separation of metals from laterites. The metal of particular interest to the process is nickel because three-quarters of the earth's nickel deposits consist of ultra-basic oxide laterite. There are three such ore deposits: limonite, silicate or transition ore. Transition ores are intermediate forms of the previous two. Of particular interest is limonite.

Limonite contains 0.8-1.5% nickel and is highly iron-containing, typically above 25-40%. The mineralogical structure of limonite is very uniform and thus suitable for hydrometallurgical processing. Limonite's main mineral ™ is goethite, where nickel is dispersed in iron.

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o 'The separation method described above can thus be applied to the separation of laterite nickel g 30 by slurrying it in water to form a pre-basic solution.

Iron also precipitates as hydroxide, but does not interfere with the separation if the precipitate is initially mixed. A prerequisite for this is the strong agitation of the laterite slurry at $ 2 to remove the nickel from the solid to the solution, δ

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In one experiment, the behavior of the Ni ion was measured at an initial concentration of 500 ppm when iron precipitated, which was a rapid event.

6 The Ni content dropped to almost 0 levels. Later, when this precipitate was stirred with a magnetic stirrer, the N 1 concentration again rose to 500 mg / liter. Precipitating iron readily adsorbs other ions, such as heavy metals, on its surface.

In practice, the invention is carried out by initially making the laterite a water slurry. For example, in limonite [(Fe, Ni) O (OH)] the pH of the aqueous slurry is approximately neutral, whereby the nickel adsorbed on the iron hydroxide is soluble in water. The slurry is stirred vigorously. The nickel-containing excess (clear solution) 10 is passed to the precipitated nickel borate as described above. All other sludge precipitated material, as well as ore-derived mineral material (e.g. silicate minerals), can easily be kept separate, e.g. If necessary, any liquid / solid separation method, for example by weight, may be used. Thus, the invention is also suitable for use with laterite ores that have other stone besides limonite.

When boron compound is added to the separated liquid, nickel is bound as borate. It is important to keep the pH basic in the best nickel deposition range, preferably above 9.

If the laterite-containing aqueous slurry remains basic, as is usually the case with these ultra-basic laterites, the process can be described qualitatively by the reaction equation (boric acid expressed as divate borate): 25 NiO (OH) 2 + H 2 O 3 + H 2 O -> Ni (0B 2 O 3 H 2 O) the aqueous slurry containing laterite is acidified eg with ore

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o because of the sulfur present, the process can be described by the reaction equation: "NiO (SO4) + Na2 (B4O7) 10H2O -> Ni0 (B407) · 10H2O + Na2SO4 fr 30

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As above, the borate so formed is a stiff ligand which can be readily filtered from water,

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Sometimes, depending on the quality of the limonite, it may be necessary to adjust the pH of the basic slurry to a slightly acidic range to better remove NiO from goethite. Here, the first precipitated nickel hydroxides act as precipitation nuclei for further precipitation in a manner known in hydrometallurgy. Precipitation cores can be added as needed. When borax is added to the liquid, the pH is raised to a range favorable to the nickel hydroxide precipitation, while nickel is bound as shown in the last reaction equation.

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The invention is not limited to the above examples, but can be modified within the scope of the claimed invention. It is essential that the metal be bonded to the borate and not re-solubilized, for example due to pH changes, and any of the 10 suitable boron hydroxy compounds or boron oxo anion compounds can be used. The invention can also be used to co-precipitate cobalt with nickel or separately. The invention can also be used in objects not mentioned above.

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Claims (3)

A process for recovering nickel or cobalt from alkaline oxide laterite ores by hydrometallurgical treatment, characterized in that the laterite ore 5 is contacted with water to obtain a laterite slurry which is vigorously agitated to separate the metal from the ore into the slurry solids, by precipitation at a basic pH with a boron compound which is a hydroxy compound of boron or a compound containing boron as an oxo anion, in particular boric acid or borax. Method according to Claim 1, characterized in that the laterite ore contains limonite. 15 Process according to Claim 1 or 2, characterized in that boric acid or borax is used for the precipitation. 't δ c \ j CO o CO X cc CL O CO o o CO δ CVJ