WO2003070993A1 - Device and process for solvent extraction - Google Patents

Abstract

A device for use in a solvent extraction process for the selective extraction of a metal species from an aqueous solution containing said metal species, said device including a container for receiving said aqueous solution and containing absorbent particles having absorbed therein a reagent for extraction of said metal species.

Description

DEVICE AND PROCESS FOR SOLVENT EXTRACTION

FIELD OF THE INVENTION

The present invention relates to a device and a process for the extraction and/or purification of metal containing species, using a solvent extraction technique. The invention is particularly directed to a device and process which utilise absorbent particles in the solvent extraction process. BACKGROUND OF THE INVENTION

The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of any of the claims.

Traditional production technologies throughout the world for producing metals, especially base metals such as copper, zinc, lead, etc rely on pyrometallurgical processes, such as smelting and/or roasting to economically extract the contained metal content from the mineral ores or concentrates. These processes are traditionally capital-cost intensive and must therefore be of large capacity. In many cases they suffer from serious environmental problems, particularly relating to gaseous emissions. While emerging technology has, by necessity, addressed this issue to some degree, nevertheless, almost 50% of the world's copper producers still capture less than 84% of their SO₂ emissions, and 10% capture none at all.

Environmental and cost issues have, therefore, continued to fuel intensive interest in the development of hydrometallurgical processes (i.e. those utilising chemical solutions), and the use of these processes for commercial operations is growing.

The development of new competitive hydrometallurgical processes for the extraction of metals from their host minerals as a solution of their salts mπst similarly be accompanied by innovative and cost effective support processes for conversion of the metal salts into pure metal. One of these supporting processes is liquid/liquid ion exchange for the extraction, concentration, separation and purification of the non-ferrous metals referred to above, commonly known in the industry as solvent extraction.

Over the past twenty years, solvent extraction (SX) processes have become accepted technology, with almost total acceptance in the uranium industry world wide and now finding increased usage in the copper industry in North America, Chile, Zambia and Australia. In the copper industry, for example, continued improvement in the selectivity of SX reagents and in the technology of electrowinning have enabled on-site production of London Metal Exchange (LME) grade 'A' cathode copper (i.e., a purity of 99.999% copper) from low grade deposits, with consequent favourable impact on the economics of small to medium tonnage producers.

SX technology has also been applied commercially to the extraction and purification of nickel, cobalt and rare-earth metals, and will be extended to the production of many other metals as the technology becomes more competitive. Figure 1 illustrates a typical conventional solvent extraction circuit comprising two extraction stages and two strip stages, together with a scrub stage. Each stage consists of one or more mixers in series with a settler.

In each extraction stage, an aqueous leach liquor containing dissolved metal ions including the primary target metal from the leaching of a mineral ore or concentrate using a chemical lixiviant, is contacted in a mixer with an organic liquid comprising an organic extractant dissolved in a diluent such as kerosene. The extractant is designed to be selective in extracting the target metal from the aqueous leach liquor. This results in the extraction of the target metal from the aqueous leach liquor into the organic phase, leaving a raffinate solution.

The mixture of aqueous and organic phases are allowed to separate in a settler. The organic phase containing the target metal is then pumped to the next stage, and the raffinate which contains the chemical lixiviant (as well as any other potentially valuable metal ions), is recycled to the leaching process. In the stripping stage, the target metal, now contained in the organic phase is contacted in another mixer with a pure aqueous chemical lixiviant (such as dilute sulphuric acid in the case of copper processing) to extract the target metal back into this aqueous phase in a purified form. The metal containing aqueous phase is then transferred directly to an electrowinning stage for the electrolytic recovery of the pure metal. The organic phase is then recycled to the first stage for contacting with fresh leach liquor.

A number of solvent extraction plants are commercially available and incorporate various technologies for ensuring adequate mixing, phase disengagement and for the provision of low extractant entrainment. Selection of an appropriate mixer settler is dependant on a number of issues including the type of metal being extracted, influence of the suspended solids and the site topography and climate.

The need to use large volumes of diluent in conjunction with the organic extractant (typically 10-15% organic extractant concentration) contributes to high equipment inventories and a high fire risk.

Furthermore, many plants operate in high temperature climates and settlers must be installed with lids to prevent diluent loss due to evaporation. The- capital cost of lids can be quite high depending on the size and type of the settler.

Typically, the efficiency of metal transfer in each stage is about 90% for each extraction stage and about 95% for each strip stage. The stage efficiency can be improved, such as by use of multiple mixers instead of single mixers, or by increasing the retention time in each mixer. However, there is often the need to balance the costs of using additional equipment or ionger retention times with increased metal recovery due to improved stage efficiency.

In most cases, however, a compromise between costs and efficiencies must be made when using prior art solvent extraction technology.

There is accordingly a need for a solvent extraction device and process which overcome, or at least alleviate, one or more disadvantages of the prior art. SUMMARY OF THE INVENTION

In one form, the present invention provides a device for use in a solvent extraction process for the selective extraction of a metal species from an aqueous solution containing said metal species, said device including a container for receiving said aqueous solution and containing absorbent particles having absorbed therein a reagent for extraction of said metal species.

The present invention also contemplates a process for the selective extraction of a metal species from an aqueous solution containing said metal species, said process including the steps of: (i) impregnating absorbent particles with a reagent for the selective extraction of said metal species from said aqueous solution; (ii) contacting the impregnated absorbent particles with the aqueous solution containing said metal species, whereby said reagent selectively extracts said metal species from said aqueous solution into said impregnated particles; and (iii) contacting said particles containing said metal species with a stripping solution in order to recover the metal species therefrom and into said stripping solution.

DETAILED DESCRIPTION OF THE INVENTION

The inventive device is typically a highly permeable column containing particles of an absorbent material. The column can be of any shape, such as a vertical or horizontal tank of narrow or wide dimensions or, a straight or coiled piping or tubing. The absorbent particles are of an appropriate size, however, these are preferably 1mm in size or greater.

The absorbent particles are typically particles having a relatively high surface area and comprise a material which is not chemically reactive with other species in the process. Examples of suitable absorbents include ceramic powders (e.g. silica, titania, clays) or carbon. Preferably the absorbent particles include or consist of activated carbon.

The device of the invention typically includes an inlet through which the metal species containing aqueous solution is admitted and an outlet through which the raffinate solution exits after extraction of the metal species. One or both of the inlet and outlet may comprise an opening in the housing of the device having a screen thereacross with a mesh size small enough to prevent the escape of absorbent particles. In the case where the device comprises a vertical column, typically the inlet is located towards the top of the column and the outlet is located towards the bottom, so that the metal species containing aqueous solution flows downwardly from the inlet to the outlet under the influence of gravity. In such a set up, it may only be necessary for the outlet to be screened, especially if the inlet is located above the bed of absorbent particles. However, this configuration may be reversed to suit particular circumstances.

The absorbent particles are impregnated with a reagent which has the property of preferentially extracting the metal containing species from the aqueous solution when it is passed through the column. The reagent is typically an organic liquid. Organic liquids used in conventional solvent extraction techniques are suitable. Examples of organic extractant reagents which are suitable for extraction of copper containing species from leach liquors include those based upon hydroxy oximes which include the two classes ketoximes and aldoximes. Ketoximes were first generation extractants based upon formulations of 2-hydroxybenzophenone oxime or 2-hydroxy-5 nonyl acetophenone and include those extractants marketed under the trade name LIX84 (Cognis). Aldoximes are second generation extractants developed to overcome the short comings of the ketoximes. They are stronger extractants than ketoximes and typically must be combined with an equilibrium modifier or a ketoxime so that they can be efficiently stripped. Aldoximes may be based on 5-nonyl benzaldoxime, either alone or in combination with a modifier or a ketoxime. The modifier may be nonylphenol (as in the reagent available under the trade name Acorga P5100 and P5300 by Acorga Ltd.), an aliphatic alcohol such as tridecanol or an ester, such as in the reagent available under the trade name Acorga M-5640 by Acorga Ltd. An example of an aldoxime-ketoxime reagent is that marketed under the trade name LIX984 (Cognis). Examples of other extractants include a mixture of β hydroxybenzophenone oxime and α hydroxy oxime, available under the trade name LIX64N produced by General Mills Chemicals, Inc. Another suitable reagent is an alkyl β hydroxy quinoline based reagent, such as that sold under the trade name Kelex 100, by Ashland Chemical Co, or Kelex 120, the latter of which is a mixture of Kelex 100 and nonyl phenol. Another suitable extractant is one based on an aryl alkylbetadiketone, such as that sold by Henkel Corporation under the trade name LIX 54-100.

The absorbent particles are contacted with the extractive reagent which is absorbed into the particles. The particles may absorb up to their equivalent weight, or volume, of reagent. However, typically, the maximum absorption level is around 60%.

The device and process of the invention can be used to extract target metal containing species from aqueous solutions, such as from pregnant leach liquors resulting from mineral processing using hydrometallurgical processes. The process can be applied to the extraction of all metal ions capable of forming stable salt solutions, particularly the transition metal ions. It is particularly applicable to extraction of metals which are capable of being extracted using conventional solvent extraction techniques. Examples are the base metals, i.e. copper, lead and zinc, although the process may be extended to extraction of transition metals and/or precious metals. The process and device are especially applicable to extraction of copper.

The device and process of the invention can also be used for multiple stage extractions of one or more secondary target metal ions contained in the raffinate derived from the first stage extraction.

The metal containing aqueous solution is passed through the device of the invention, preferably under pressure such as pressure exerted by a feed pump, and the extractive reagent absorbed into the absorbent particles selectively extracts the metal species from the aqueous solution. Preferably, this proceeds until the extractive reagent is saturated with the metal species, at which stage the flow of aqueous solution into the device is terminated. The device is then typically washed with water, or a dilute aqueous process solution, and then removed from the voids of the column. This de-entrainment step is preferably effected by air blowing. The container or column of metal and extractive reagent impregnated absorbent is subsequently irrigated by passing a stripping solution therethrough, preferably under pressure. The stripping solution should be one capable of recovering the target metal from the extractive reagent. The stripping process is preferably continued until all of the target metal is released from the extractive reagent with the stripping solution.

The target metal is now present in the stripping solution in a purified form. It can subsequently be utilised as a feed solution to a conventional electrowinning process in order to produce pure metal, or to a chemical process to produce a high grade chemical product. The invention will become more readily apparent from the following exemplary description in connection with the Example and accompanying drawings. DESCRIPTION OF DRAWINGS

Figure 1 is a schematic flow diagram of a typical conventional solvent extractant circuit.

Figure 2 is a flow diagram showing the general features of the process of the invention.

Figure 3 is a more detailed flow diagram of the process of the invention. Figure 4(a) is a flow diagram showing details of the feed cycle of the process of the invention.

Figure 4(b) is a flow diagram showing details of the strip cycle of the process of the invention. Figure 4(c) is a flow diagram showing details of the crystallising cycle of the process of the invention.

Figure 4(d) is a flow diagram showing details of the make-up cycle of the process of the invention. EXAMPLE An absorption column constructed from PVC water pipe of 50L volume was supported on a frame and was connected to a piping arrangement as illustrated schematically in Figure 3. The detail of the individual feed, strip, crystallising and make-up cycles of the arrangement is illustrated schematically in Figures 4(a), (b), (c) and (d) respectively. 25kg of an activated carbon was contacted with copper-specific organic extractant and charged to the column. The activated carbon had a bulk density of 0.53 gem^"3 and a void factor of 30%. The column was then flushed with water until extractant was not visible in the elutriate. Approximately 15kg of extractant was retained in the carbon within the column. During the feed cycle, pregnant liquor prepared to similar levels of impurity as a leach liquor resulting from the leaching of copper ore, and containing 1.0 g/l Cu was fed from a Pregnant Liquor Copper source comprising an agitated storage tank into the absorption column as depicted in Figure 4(a). The feed was continued until the raffinate concentration exiting the circuit started to exceed a "steady-state" concentration of 0.05 g/l Cu. Approximately 565 litres of liquor had been pumped at this stage.

Approximately 1 column volume (50 litres) of wash water was then pumped to the column and passed forward with the raffinate. This was followed with an air blow also equivalent to 1 column volume (50 litres) to discharge raffinate from the column voids.

The strip cycle is illustrated in Figure 4(b). After altering the appropriate valves the column was fed with 15 litres of a strip solution containing 60 g/l Cu (as CuSO₄) and 1.0kg concentrated (98%) H₂SO₄ and heated to 45°C. A residence period of 2 minutes was observed after which the column was flushed forward with wash water with the first half going to the strip circuit and the second half going to the pregnant liquor storage tank. The liquor trapped in the column void was blown with air back to the pregnant liquor storage tank (see Figure 3).

The resultant liquor from the first half of the strip contained 104.4 g/l Cu and had a temperature of 40°C. This liquor was cooled to 26°C in an agitated tank with a cooling coil, and the resultant slurry was filtered and dried to recover the purified copper sulphate pentahydrate crystals. The crystallising cycle is illustrated in Figure 4(c).

1.21kg of the crystals were recovered and the purity was confirmed by Atomic Absorption analysis. The separated mother liquor contained 60 g/l copper.

In the make-up cycle illustrated in Figure 4(d), sulphuric acid was then added to the mother liquor prior to return to the strip circuit.

Further, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of steps and parts previously described without departing from the spirit or ambit of the invention.

Claims

CLAIMS:

1. A device for use in a solvent extraction process for the selective extraction of a metal species from an aqueous solution containing said metal species, said device including a container for receiving said aqueous solution and containing absorbent particles having absorbed therein a reagent for extraction of said metal species.

2.- - The device of claim 1 , wherein said device is a highly permeable column.

3. The device of claim 1 or 2, wherein said absorbent particles are at least 1mm in size.

4. The device of any preceding claim, wherein said absorbent particles include or consist of carbon particles.

5. The device of claim 4, wherein said carbon particles comprise activated carbon.

6. The device of any preceding claim including an inlet through which said metal species containing aqueous solution is admitted into said container and an outlet through which raffinate solution exits after extraction of said metal species.

7. The device of claim 6, wherein said inlet is located higher in said device than said outlet, such that said aqueous solution flows downwardly from said inlet to said outlet under the influence of gravity.

8. The device of claim 6 or 7, wherein at least one of said inlet and outlet includes a screen thereacross having a mesh size sufficiently small to substantially prevent escape of said absorbent particles.

9. The device of any preceding claim, wherein said reagent is an organic liquid.

10. The device of claim 9, wherein said organic liquid is suitable for the extraction of precious metals or transition metals, such as base metals, preferably copper containing species.

11. The device of claim 10, wherein said organic liquid is based upon hydroxy oximes, such as a mixture of β hydroxybenzophenone oxime and α hydroxy oxime.

12. The device of claim 10, wherein said organic liquid is an alkyl β hydroxy quinoline-based reagent.

13. The device of claim 10, wherein said organic liquid is based on aryl alkylbetadiketone.

14. A process for the selective extraction of a metal species from an aqueous solution containing said metal species, said process including the steps of: (i) impregnating absorbent particles with a reagent for the selective extraction of said metal species from said aqueous solution; (ii) contacting the impregnated absorbent particles with the aqueous solution containing said metal species, whereby said reagent selectively extracts said metal species from said aqueous solution into said impregnated particles; and (iii) contacting said particles containing said metal species with a stripping solution in order to recover the metal species therefrom and into said stripping solution.

15. The process of claim 14, wherein said process is carried out in a highly permeable column.

16. The process of claim 14 or 15, wherein said absorbent particles include or consist of carbon particles, preferably activated carbon.

17. The process of any one of claims 14 to 16, wherein said absorbent particles are at least 1mm in size.

18. The process of any one of claims 14 to 17, wherein said reagent is an organic liquid.

19. The process of claim 18, wherein said organic liquid is suitable for the extraction of base metals, preferably copper containing species.

20. The process of claim 18 or 19. wherein said organic liquid is based upon hydroxy oximes, such as a mixture of ^β hydroxybenzophenone oxime and α hydroxy oxime, or said organic liquid is an alkyl β hydroxy quinoline-based reagent, or said organic liquid is based on aryl alkylbetadiketone.

21. The process of any one of claims 14 to 20, wherein said aqueous solution is passed through said impregnated absorbent particles under pressure, such as by using a feed pump.

22. The process of any one of claims 14 to 21 including a further step between steps (i) and (ii) of removing excess aqueous solution once the absorbent particles become saturated with said aqueous solution, said removal step comprising washing said saturated particles with water or a dilute aqueous solution.

23. The process of claim 22, wherein said removal step further includes substantial de-entrainment of said water or dilute aqueous solution from voids between said particles by air blowing.

24. The process of any one of claims 14 to 23, wherein said stripping solution is passed through said particles under pressure.

25. The process of any one of claims 14 to 24, including a further step (iv) after step (iii) of subjecting the stripping solution to:

(a) an electrowinning process to extract purified metal therefrom; or

(b) a chemical process to produce a compound containing said metal.

26. A device according to claim 1, substantially as herein described with reference to the accompanying drawings.

27. A device according to claim 1, substantially as herein described with reference to the Example.

28. A process according to claim 14, substantially as herein described with reference to the accompanying drawings.

29. A process according to claim 14, substantially as herein described with reference to the Example.