METHOD AND APPARATUS FOR GA-RECOVERY

Abstract

The present invention encompasses a method of selectively separating Ga from wastewaters with the aid of a dialysis method. This exploits the particular complexation behaviour of Ga, which forms an unstable tetrahalo complex. This forms only in the case of a sufficiently high halide concentration. Since the halide concentration becomes lower across the membrane, the Ga-tetrahalo complex breaks down in the membrane, as a result of which the Ga is retained. Other metals such as In and Fe do not show this behaviour, and therefore the tetrahalo complexes of these metals can pass through the membrane and hence can be selectively separated off.

Claims

1-15. (canceled)

16. A process for separating gallium from impurities in an aqueous solution, the process comprising: performing a dialysis procedure between a feed solution and a dialysate separated by an anion exchange dialysis membrane, wherein: the feed solution is acidic and comprises anionic halide ions and cationic gallium ions in respective concentrations suitable for formation of anionic gallium-halide complexes; the impurities comprise one or a combination of two or more of: an arsenic species, an iron species, and an indium species; and wherein the anionic gallium-halide complexes are selectively retained in the feed solution by the membrane and the impurities pass through the membrane into the dialysate.

17. The process according to claim 16, further comprising: maintaining a sufficient halide concentration gradient at the membrane between the dialysate and the feed solution so that the anionic gallium-halide complexes formed in the feed solution disintegrate into constituent cationic gallium ions and anionic halide ions when sorbed into the membrane.

18. The process according to claim 17, wherein the impurities comprise the iron species and/or indium species.

19. The process according to claim 18, wherein the iron species and/or indium species comprise anionic halide complexes comprising cationic iron ions and/or cationic indium ions, wherein the anionic halide complexes remain stable when sorbed into the membrane and pass through the membrane into the dialysate.

20. The Process according to claim 19, wherein the anionic halide complexes comprise tetrahalogeno-complexes MX.sub.4.sub. wherein XCl or Br and M=In or Fe.

21. The process according claim 16, wherein the impurities comprise the arsenic species.

22. The process according claim 21, wherein the arsenic species comprises an arsenic acid in an anionic form as H.sub.2AsO.sub.4.sub..

23. The process according to claim 16, wherein the concentration of the anionic halide ions in the feed solution is at least 2 moles per liter.

24. The process according to claim 16, wherein the concentration of the gallium ions in the feed solution is 0.3 moles per liter or less.

25. The process according to claim 16, wherein the anionic gallium-halide complexes comprise gallium-tetrahalogeno complexes.

26. The process according to claim 16, wherein the halide ions comprise bromide ions.

27. The process according to claim 16, wherein the halide ions comprise chloride ions.

28. The process according to claim 27, wherein the gallium-halide complexes comprise gallium-chloro-complexes.

29. The process according to claim 28, wherein the gallium-chloro-complexes comprise gallium-tetrachloro complexes.

30. The process according claim 16, wherein the feed solution comprises a hydrogen halide acid.

31. The process according to claim 30, wherein the feed solution further comprises a nitric acid.

32. The process according to claim 16, wherein the feed solution has a pH value of 3.

33. The process according to claim 16, wherein the feed solution has a pH value of 2.

34. The process according to claim 16, wherein the anion exchange dialysis membrane comprises: a backbone comprising a copolymer having a degree of crosslinking; and a modification of a membrane layer at least on the feed side of the membrane, the modification being one or a combination of two or more of: having a higher degree of crosslinking than the backbone of the membrane; impregnating a surface of the membrane with weakly basic anion exchange groups; and a targeted control of membrane synthesis.

35. The process according to claim 16, further comprising applying an external electric field to the feed solution and the dialysate to superimpose an additional electric potential gradient between the feed solution and the dialysate.

36. The process according to claim 16, wherein the dialysis is performed in continuous countercurrent mode.

Description

EXAMPLE 1

Diffusion Dialysis for the Separation of Ga and As in a Batch Plant

[0071] FIG. 6 compares the concentration curves of gallium and arsenic in dialysate using uncoated and coated diffusion dialysis anion exchange membranes in a batch plant (150 ml feed with 10 g/l Ga (0.143 mol/l) and 11 g/l As (0.147 mol/l) and an initial chloride concentration of 2.2 mol/l; 230 ml dialysate; 8 cm.sup.2 membrane area). The coated membrane is of the Selemion APS4 type. It is based on a polysulfone skeleton with quaternary amines and is coated on the feed side. The uncoated membrane is of the Neosepta AFN type and is based on a PS-DVB resin with quaternary amines of type 2.

[0072] The gallium-chloro complexes contained in the feed (see FIG. 6 A) permeate much more slowly through the coated membrane than the arsenic-containing species (see FIG. 6B), whereby the gallium concentration in the dialysate remains below 5 mg/l (0.072 mmol/l) over the entire dialysis period. The coating only slightly reduces the permeability of arsenic acid in contrast to the permeability of gallium.

EXAMPLE 2

GaAs Separation in a Continuous Countercurrent System

[0073] FIG. 7 shows the design of a continuous countercurrent dialysis system. The gallium concentration in the dialysate remains below 5 mg/l (20.072 mmol/l). For a feed flow of 280 l per day and 10 g/l (0.143 mol/l) Ga and 10 g/l As (20.133 mol/l) and at an initial chloride concentration of 2 mol/l, the target concentration of 0.5 g/l (0.0067 mol/l) As can be undershot if the membrane area is 100 m.sup.2 and the dialysate wastewater flow is twice as high as the feed volume flow.

EXAMPLE 3

Separation of Ga and In in Chloride-Containing Solution

[0074] FIG. 8 shows the dependence of the mole fraction of the indium(III)-chloro-complexes on the Cl concentration in an equilibrium. The initial concentration of In was 0.25 mol/l at 25 C. and a pH value <2. The values are taken from: P Kondziela, J. Biernat (1975): Determination of stability constants of Indium Halogenide complexes by Polarography, Electroanalytical Chemistry and Interfacial Electrochemistry 61, pp. 281-288, and I. Puigdomenech (2013): Hydra-Medusa, software with database for the calculation of chemical equilibria, software version August 2009, database version January 2013.

[0075] Here it becomes clear that an indium-tetrachloro-complex is already formed at a chloride concentration of 0.5 mol/l and above.

[0076] FIG. 9 shows experimental results of a separation of Ga and In. Here the concentration curves of indium and gallium in the dialysate are compared.

[0077] In both experiments an HCl solution with a concentration of 5 mol/l HCl was used as feed, with indium and gallium present as chloro-complexes. In the experiment with Ga an initial concentration of 0.15 mol/l Ga was used, in the experiment with indium an initial concentration of 0.06 mol/l In was used. InCl.sup.4 is already stable in 0.5 mol/l HCl (cf. stability diagram of indium chloro complexes in FIG. 8) and thus has a greater stability than GaCl.sub.4.sub.. Thus, InCl.sub.4.sub. can pass through the membrane much more easily than the corresponding gallium complex. The Ga transport from hydrochloric acid solution is therefore much slower than the In transport.

EXAMPLE 4

Separation of Ga and Fe in Chloride-Containing Solution

[0078] FIG. 10 shows experimental results of a separation of Ga and Fe. Here the concentration curves of iron and gallium in the dialysate are compared. The experiment was carried out in a two-chamber cell equipped with a Selemion DSV membrane with an area of 25 cm.sup.2. The feed volume was 200 ml and the dialysate volume 300 ml. The following initial concentrations were present in the feed: c.sub.Fe=4 g/l (0.072 mol/l), c.sub.Ga=0.5 g/l (0.0072 mol/l), c.sub.Cl=1.8 g/l (0.005 mol/l). However, the number of chloride ions already present in the feed solution as complexes of Ga and Fe cannot be quantified here.

[0079] In this example, lower Ga concentrations are used than in the above example. Hence, also the minimal concentration of Cl.sup. is respectively lower.