WO1999043408A1

WO1999043408A1 - Solvent extraction of ferric chloride

Info

Publication number: WO1999043408A1
Application number: PCT/US1999/004141
Authority: WO
Inventors: Satish C. Wadhawan
Original assignee: Wadhawan Satish C
Priority date: 1998-02-25
Filing date: 1999-02-25
Publication date: 1999-09-02
Also published as: CA2318823A1

Abstract

A method of purifying ferric chloride solutions with impurities having the following steps: first, the ferric chloride solution (10) containing impurities is treated with an organic solvent (24) selected from an alcohol having from about 4 to about 20 carbon atoms to selectively dissolve the ferric chloride. The resulting organic solvent (26) is then stripped from the selectively dissolved ferric chloride (30).

Description

SOLVENT EXTRACTION OF FERRIC CHLORIDE

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to the separation of chemicals and more particularly to processes for purifying ferrous or ferric chloride solutions.

(2) Brief Description of Prior Developments

The industrial use of pure the ultrapure iron chloride increases each year. The following processes are the major consumers: production of ferrites; production of pure iron powders; production of iron oxide elements; production of ultrapure alloys for the electronics industry; etching of copper plate or other copper materials; and synthesis of various compounds .

There are three principal methods to produce pure iron oxide. The first of these methods is the traditional means of obtaining salt by recrystallization to remove impurities, precipitation of iron hydroxide, followed by washing and calcination. Another method is the electrolytic production of metallic iron followed by conversion to the oxide. Still another method is the purification of iron in the melt followed by burning of the iron powder.

All of these methods involve multiple and laborious intensive steps. Research into novel methods has been on going for many years. The production of iron and its purification via liquid-liquid extraction is relatively new and was recently introduced to the industry to obtain pure solutions of FeCl and FeS0₄. The traditional, industrial method used to obtain iron oxide was recrystallization, which has been replaced with extraction.

A more effective method to achieve high-purity Iron oxide is the combination of the extraction of iron from a chloride solution, followed by pyrohydrolysis of the pure FeCl₃ solution, which simultaneously produces iron oxide (Fe₂0₃) and concentrated hydrochloric acid (HC1) .

The extraction of iron from acidic salt solution has been known for more than fifty years. The method is used in analytical chemistry as a means to purify various solutions from iron. With the introduction of new technology that utilizes pure Iron oxide as a basic material, the liquid extraction of iron has received increased attention from industry. Tributylphosphate, (C₄Hg)₃P0 (TBP) , easily extracts FeCl₃ from solutions containing HC1. The higher the concentration of HC1, the steeper the equilibrium curve that describes the partitioning of FeCl₃ between the organic and aqueous phases. The FeCl is completely extracted from the aqueous phase if the concentration of HCl exceeds 50-60 g/1. Laboratory tests conducted in KSC, on continuously operating equipment, have demonstrated the feasibility of extracting pure solutions of FeCl₃. However, in further testing at the pilot plant, using industrial FeCl₃ solutions, a problem arose with the use to tributylphosphate. The concentrations of Si and K exceeded the minimum allowable levels. In addition, P was also a major impurity, due to the use of TBP, which partially hydrolyzes when the concentration of HCl in the feedstock exceeds 90-100 g/1, which leads to large losses of TBP. In addition, salts of organic compounds, arising from the hydrolysis byproducts, completely contaminated the first attempts at extraction.

The rate of layering of the emulsion was slow, due to the high viscosity of the organic phase and the small difference in specific gravity between the organic and aqueous phases, especially at the stages of raffinate removal and water in flow for re-extraction.

Further experiments conducted completely corroborated the previous results. In addition, TBP did not yield solutions as concentrated as those yielded by sending the feed directly to the hydroprolysis equipment in the final analysis; TBP cannot be used for industrial production.

Trioctylamine, (C₈Hι₇)3N (TOA), after work-up with HCl, also easily extracts FeCl₃ at low Cl^" concentrations in the equilibrated aqueous phase (70 or more g/1) . TOA is usually used with a dilutent (kerosene) , and problems are usually not encountered with separating the aqueous and organic phases.

However, TOA also has certain disadvantages: low concentrations of FeCl₃. For example, low concentration re-extracts can lead to the co-extraction of other elements, i.e. Zn. For this reason,

TOA is also not used in the industrial production of ultrapure iron oxide.

Methylisobutylketone, C₄H₉COCH₃, (MBK) is also a good extractor of iron. However, it has a high vapor pressure and is extremely flammable. Its use in hot climates (such as India's) is not possible. In addition, much liquid is lost during operations to evaporation and given the low concentration of

FeCl in re-extracts, extractions using MBK do not yield the desired economic returns. The above analysis shows that a new extractant is needed.

SUMMARY OF THE INVENTION The present invention comprises a process to purify ferrous or ferric chloride solutions with high amounts of impurities, especially impurities such as Ca, Na, Ma, V, Cr, Ni, and the like, that cannot be removed by conventional technologies using selective precipitation. The process developed is based on using a selective organic solvent that will selectively extract ferric chloride and leave the impurities in the raffinate. The process can be used for either ferrous or ferric chloride, since the ferrous chloride, if the solution contains any ferrous chloride, must be converted to the ferric chloride form by oxidizing with chloride.

Also, in order to have a high degree of iron recovery, the iron in the raffinate is recovered by a subsequent extraction stage. Final recovery of ferric chloride from the organic solvent is achieved by stripping the solution with pure water.

Since the ultimate aim is to produce high-purity iron oxide in a spray roaster plant, it is also essential to produce a relatively high concentration of ferric chloride in the purified solution. To achieve about 30-35% ferric chloride in the final solution, the impure liquor is concentrated to about 50% ferric chloride by evaporation. Depending upon the final requirement, two to three stages of solvent extraction and two to three stages of evaporation may be used. Each solvent extraction stage may contain as much as fifteen or more cells, consisting of as much as nine cells for extraction and six cells for stripping.

Also, due to very high amounts of impurities, it may be advantageous to introduce an intermediate washing with the water stage. In such a case, each solvent stage will have extraction, washing, and stripping

In order to economize the steam consumption, the multiple effect evaporators may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawing, wherein corresponding .reference characters indicate corresponding parts in the drawing and wherein:

FIG. 1 is a schematic illustration of a preferred embodiment of the process of the present invention;

FIG. 2 is a schematic illustration of an alternate preferred embodiment of the processes of the present invention; and

FIG. 3 is a schematic illustration of the leach liquor processing unit employed in the process of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is an initial feed solution of FeCl₃ provided in line 10 to an evaporation apparatus 12. Condensate from this evaporation apparatus is transported in line 14; the stripping apparatus 16; pure water is added to the condensate in line 18. Ferric chloride solution is transported from the evaporation apparatus 12 in line 20 to an extraction apparatus 22. Organic solvent that is preferably N-octanol is introduced to the extraction apparatus 22 in line 24. The solution is removed from the extraction apparatus 20 in line 26 to the stripping apparatus 16. Solvent is removed from stripping apparatus 16 in line 28 and a pure solution of ferric chloride is removed in liquor line 30. Raffinate is removed from extraction apparatus 22 in line 32 to line 34 and then introduced to evaporation apparatus 36. Condensate is removed from evaporation apparatus 36 in condensate line 38, which connects to strip solution line 40 and strip solution line 42. A feed line 44 connects the evaporation apparatus 36 to an extraction apparatus 46, and organic solvent is introduced to the extraction apparatus 46 through an organic solvent line 48. Line 50 removes solution from the extraction apparatus to a stripping apparatus 52, and there is an off-line 54 from this stripping apparatus as well as a liquor line 56 that connects to the initial feed line 10. A raffinate line 58 connects the extraction apparatus 46 to another extraction apparatus 60, which also is provided with solvent through organic solvent line 62. Line 64 connects extraction apparatus 60 with stripping apparatus 66 that has an off-line 68 and liquor line 34. Raffinate is removed from the extraction apparatus 60 as waste solution in raffinate line 70.

Referring to FIG. 2, in an alternate embodiment ferric chloride is introduced in feed line 72 to evaporation apparatus 74. Condensate is then removed from this evaporation apparatus 74 in condensate line 76 to extractor apparatus 78. There is an organic input line 80 for this extractor apparatus 78 as well as an extractor output line 82, which connects to a washer apparatus 84. A washer output line 86 connects to a stripper apparatus 88 that is outputted to line 80. Condensate is introduced to stripper apparatus 88 in condensate lines 75 and 90, and solution is removed from the stripper apparatus in output line 92 that connects to an evaporator feed line 94 and a liquor output line 96. Line 94 connects to an evaporator 98, which is outputted in line 100 to line 89. Evaporator 98 is also connected to washer apparatus 84 by line 102. For solutions that have a medium range of multiple impurities, it is essential to use one or more washing steps. The number of washing steps would depend upon the nature of the solution and the extent of impurities. Raffinate line 104 comes off the extraction apparatus 78 to connect to line 106 for introduction of solution to another evaporator 108 from which condensate is removed in line 110. Organic solvent is introduced in lines 111 and 112 to extractor apparatus 114 from which solvent is removed in line 116 to washer apparatus 118. Solvent is removed from the washer apparatus 118 in line 120 to a stripper apparatus 122, which is connected to solvent line 112. A condensate line 124 also brings condensate from line 110 to stripper apparatus 122, and a stripper output line 126 to remove solution from the stripper 122. Line 128 removes solution from washer apparatus 118 and is connected with stripper output line 126 to flow into recirculation line 130 which is connected to feed line 72. Washer apparatus 84 is connected by line 132 to washer apparatus 118. Extraction apparatus 114 is connected by raffinate line 134 to recirculation line 136 and to waste solution line 138. Referring to FIG. 3, leach liquor feed line 140 is connected to a leach liquor filter 142. The leach liquor filter output line 144 is connected to leach liquor preheater 146 that is heated by steam provided in steam header 148. Condensate is removed from the preheater 146 in condensate return line 150 and line 152 connects evaporated liquor to chlorination column 154. Chlorine is provided to the chlorination column 154 in chlorine line 156. Chlorinated liquor is removed to a storage tank in line 158 and evaporated material is removed in line 160 to a chlorination scrubber 162. Line 164 recirculates material from the chlorination scrubber 162 to the leach liquor filter output line 144. Chlorination scrubber output line 166 removes liquor to an ilmenite liquor storage tank (not shown) . It was discovered that waste acid derived form the pickling of stainless steel contains a very high amount of nickel and chromium (1-3%) . It seems that solutions can be purified even without the washing step and a revised flow sheet was developed or indicated in FIG. 3. In such a scheme, two independent stages of Mixer-Settler, without the washing stage was selected. N-octanol does not extract iron from aqueous solutions below 270-300 g/1 FeCl₃. This means FeCl₃ cannot be completely extracted with N-octanol, but above this concentration, it can be used. N-octanol extracts FeCl₃ efficiently in the 280-850 g/1 concentration range, while impurities are weakly extracted. The equilibrium extraction curve (the dependence of the concentration of FeCl₃ in the organic solvent on the concentration in the aqueous phase) is practically a straight line. Here the Y-axis is expressed as the solution density, which can easily be converted to concentrations, knowing the corresponding concentration of HCl. However, the given information is sufficient to evaluate the extraction. The extraction proceeded well; taking into account the decrease in the volume flow of the water phase, the extraction of V into the

10 organic phase reaches 70-73%. Depending on the concentration of FeCl₃ in the feed and water phase, the concentration of FeCl₃ in the organic phase can reach 180 g/1. At high concentrations of HCl, the extraction proceeds easily; the final concentration of FeCl₃ is 250-260 g/1 (if the organic phase is not already saturated with iron) . If the HCl concentration is low, the raffinate reaches a density of 1,230-1,240 g/1, which corresponds to a FeCl₃ of 280-300 g/1. In working with certain solutions (high HCl concentrations, the necessary concentration of the raffinate was 1,165 g/1 (830 g/1 for the opposing organic phase), which was practically without FeCl₃. The re-extraction of the water results in a liquor with a concentration of 400 g/1 FeCl₃ and higher. During the re-extraction of the condensate containing HCl, the concentration of FeCl₃ and the presence of acid in the water phase, which was in equilibrium with the organic phase, limits the FeCl₃ in the organic phase, lowering the efficiency of the re-extraction process.

The work with N-octanol has demonstrated the following: l.A sufficiently high-purity of liquor (only traces of impurities) .

2. No problems with evaporation; the rate of striation of the emulsion is good.

3. N-octanol is not volatile at the process temperatures.

11 4. Phase mixing is not significant.

5. A "third phase" is observed only in the first three

(counting the number of extractions of the water phase) stages of the extraction.

6. At high FeCl₃ and HCl concentrations in the water phase and temperatures of 20 - 30°C, the solution partially crystallizes; this can be avoided in practice if the the feed is held at 40-45° C before pumping.

7. A washing of the organic phase with a non-volatile liquor is effective.

The waste solution from synthetic rutile production (after • chlorinaton) could be characterized as "impure" with aiig HCl concentration. Here, it was not possible to directly achieve a high-purity liquor, that is, without washing. The washing required a 580 g/1 FeCl₃ liquor. That concentration corresponds to the equilibrium concentration of FeCl₃ in the water phase in the first stage of extraction. The washing must not be done with a lower concentration of FeCl₃, since a significant portion of FeCl₃ will enter the water phase and the concentration in the organic phase will fall and the liquor will be lower in FeCl than permissible. In the experiments, the liquor was washed two times. Practically, the industrial process should include three washings. The washings should be returned to the extraction

12 process. The re-extraction with highly acidic condensates is not desirable. If in the process of evaporation it is possible to achieve a condensate lower in HCl concentration and use it in the re-extraction, this would be the better solution to use.

The raffinate, after the first stage of the extraction, is again evaporated. Raffinate-2 is added to the first raffinate to achieve the required extraction of FeCl₃. The organic phase, after the second phase after the second extraction, will contain many more impurities than after the first extraction, and must be washed more carefully. In fact, the possible extraction processes are defined by which extraction stage the solutions are sent back to after the first and second washings.

Raffinate-1 is mixed with the recycled and amalgamated solutions after washing and is sent to the evaporator a second time. The condensate is used for the re-extraction. The evaporated solution undergoes seven stages of extraction until the organic phase saturates at 162.5 g/1 FeCl₃. Then it undergoes two washings of three stages each. The first stage is the amalgamated solution after I and III washings; the second stage is the final washing with fresh solution. The re- extract-2 is likewise put through five stages with the condensate. The re-extract-2 should reach the same quality as the re-extract-1. Raffinate-2 is divided into two parts; the

13 majority goes into the recycled solution to undergo another extraction of FeCl₃, while some is discarded as waste.

The major difficulty in developing the technology is the large concentration of impurities in the solution entering the second extraction. The impurities are nearly half of the FeCl₃ concentration. It is difficult to achieve an ultrapure product from that, while simultaneously minimizing washing.

Similar purification of ferrous chloride solution, using the above solvent extraction process can be achieved by first chlorinating ferrous chloride to ferric chloride solution. The exhaust gases are scrubbed with the impure ferrous chloride solution. The exhaust gases are scrubbed with impure ferrous chloride solution to achieve acceptable chlorine emissions.

A system consisting of solvent extraction with/without chlorination and spray roaster acid regeneration is used to produce high-purity Iron oxide. The system is designed and coordinated so that excess condensate water is used as make-up water for the absorber to produce regenerated acid. This will eliminate any wastewater stream and produce 18% or 32% HCl, to produce high concentration acid (above 26% HCl) .

While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments

14 may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.

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Claims

What is claimed is:

1. A method of purifying ferric chloride solutions with impurities comprising the steps of:

(a) treating said ferric chloride solution with impurities with an organic solvent selected from an alcohol having from about 4 to about 20 carbon atoms to selectively dissolve the ferric chloride; and

(b) then stripping the organic solvent from the selectively dissolved ferric chloride.

2. The method of claim 1 wherein the organic solvent is a normal alcohol .

3. The method of claim 2 wherein the organic solvent has from about 6 to about 10 carbon atoms.

4. The method of claim 3 wherein the organic solvent is N- octanol.

5. The method of claim 4 wherein in step (a) the ferric chloride solution is partially evaporated before addition of the solvent.

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6. The method of claim 5 wherein in step (a) raffinate is removed after addition of the solvent.

7. The method of claim 6 wherein in step (a) after removal of raffinate, solution is added to the raffinate after which said solution and raffinate is further evaporated.

8. The method of claim 7 wherein steps (a) and (b) are successively repeated a plurality of times.

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