Recovery of metals from industrial wastewater of low metal concentration

Abstract

The invention relates to a multi-step method for the selective, environmentally friendly and economical recovery of non-ferrous metals from industrial wastewater. The method is based on the principle of the complexing of the non-ferrous metals, separating out of the complexes and subsequent decomplexing of the non-ferrous metals. Siderophores are used as complexing agents. The siderophores are recovered within the process. The method can be used in particular even in the case of low non-ferrous metal concentrations. The method is efficient, environmentally friendly and economical.

Claims

1. A method for recovering non-ferrous metals from industrial wastewater, comprising: A: complexing the metal to be recovered by adding siderophores to the industrial wastewater; B: separating the metal-siderophore complex; C: releasing the metal from the metal-siderophore complex; D: separating the metal; E: recovering the siderophore; and F: separating the siderophore, wherein either: C: releasing the metal from the metal-siderophore complex is executed via adding Fe(III) ions and forming an Fe(III)-siderophore complex; and E: recovering the siderophore is executed via adding a reductant and/or a chelator or C: releasing the metal from the metal-siderophore complex is executed via adding a chelator, as a result of which a metal-chelator complex is formed; and D: the metal is separated as this metal-chelator complex.

2. The method according to claim 1, wherein: C: releasing the metal from the metal-siderophore complex is executed via adding Fe(III) ions and forming an Fe(III)-siderophore complex; and E: recovering the siderophore is executed via adding a reductant and/or a chelator.

3. The method according to claim 2, wherein the reductant is selected from H.sub.2SO.sub.3, ascorbic acid and salts thereof.

4. The method according to claim 1, wherein: C: releasing the metal from the metal-siderophore complex is executed via adding a chelator, as a result of which a metal-chelator complex is formed; and D: the metal is separated as this metal-chelator complex.

5. The method according to claim 4, wherein the metal is selected from Ga, In, Sc, Pu, Co, Ge, V, Al, Mn, Th, Ti, Zr, Hf, Nb, Ta, Mo, Bk, Eu, Dy, Pa, Gd, Yb, Ce, La, Rh, Tl, Bi and Pd.

6. The method according to claim 1, wherein the metal is selected from Ga, In, Sc, Pu, Co, Ge, V, Al, Mn, Th, Ti, Zr, Hf, Nb, Ta, Mo, Bk, Eu, Dy, Pa, Gd, Yb, Ce, La, Rh, Tl, Bi and Pd.

7. The method according to claim 1, wherein the siderophores are selected from desferrioxamines and fatty acid-containing siderophores and salts thereof.

8. The method according to claim 7, wherein the siderophores are selected from desferrioxamine B (DFO-B), desferrioxamine E (DFO-E), marinobactins, aquachelins, amphibactins, ochrobactins and synechobactins and salts thereof.

9. A method for recovering non-ferrous metals from industrial wastewater, comprising: A: complexing the metal to be recovered by adding siderophores to the industrial wastewater; B: separating the metal-siderophore complex; C: releasing the metal from the metal-siderophore complex; D: separating the metal; E: recovering the siderophore; and F: separating the siderophore, wherein, in at least one of the separation steps B, D and F, the method for separation is selected from: chromatographic methods; solid phase extraction; precipitation; filtration and/or nanofiltration; immobilisation of the siderophores on a carrier material; and concentration of the metal-siderophore complexes by foaming and collecting the foam; and combinations of the above-mentioned methods.

10. The method according to claim 1, wherein the temperature is consistently between 10 and 50° C.

11. The method according to claim 1, wherein the metal is selected from Ga, In, Sc, Pu, Co, Ge, V, Al, Mn, Th, Ti, Zr, Hf, Nb, Ta, Mo, Bk, Eu, Dy, Pa, Gd, Yb, Ce, La, Rh, Tl, Bi and Pd, and wherein the siderophores are selected from desferrioxamines and fatty acid-containing siderophores and salts thereof.

12. The method according to claim 11, wherein the siderophores are selected from desferrioxamine B (DFO-B), desferrioxamine E (DFO-E), marinobactins, aquachelins, amphibactins, ochrobactins and synechobactins and salts thereof.

13. The method according to claim 11, wherein: C: releasing the metal from the metal-siderophore complex is executed via adding Fe(III) ions and forming an Fe(III)-siderophore complex; and E: recovering the siderophore is executed via adding a reductant and/or a chelator.

14. The method according to claim 13, wherein the reductant is selected from H.sub.2SO.sub.3, ascorbic acid and salts thereof.

15. The method according to claim 11, wherein: C: releasing the metal from the metal-siderophore complex is executed via adding a chelator, as a result of which a metal-chelator complex is formed; and D: the metal is separated as this metal-chelator complex.

16. The method according to claim 15, wherein the temperature is consistently between 10 and 50° C.

17. The method according to claim 11, wherein, in at least one of the separation steps B, D and F, the method for separation is selected from: chromatographic methods; solid phase extraction; precipitation; filtration and/or nanofiltration; immobilisation of the siderophores on a carrier material; and concentration of the metal-siderophore complexes by foaming and collecting the foam; and combinations of the above-mentioned methods.

18. The method according to claim 11, wherein the temperature is consistently between 10 and 50° C.

19. The method according to claim 12, wherein the temperature is consistently between 10 and 50° C.

20. The method according to claim 12, wherein, in at least one of the separation steps B, D and F, the method for separation is selected from: chromatographic methods; solid phase extraction; precipitation; filtration and/or nanofiltration; immobilisation of the siderophores on a carrier material; and concentration of the metal-siderophore complexes by foaming and collecting the foam; and combinations of the above-mentioned methods.

Description

(1) The invention is explained in the following figures and embodiments, without limiting the invention thereto.

(2) FIG. 1 shows an embodiment of the first variant of the multi-step method according to the invention for recovering non-ferrous metals from industrial wastewater on the basis of the exemplary use of the complex-forming properties of the siderophore desferrioxamine E and a purification method by means of C18 reverse-phase chromatography.

EMBODIMENTS

1. First Variant of the Method According to the Invention

(3) Method Description for Industrial Wastewater Having Low Ga Concentration (4 mg/L) Using DFO-E:

(4) 0.05 mL of a 2 mM solution of desferrioxamine-E is added to 1.95 mL of industrial wastewater having a low Ga concentration and the resulting solution is stirred for 15 minutes at room temperature. 100 μL of this solution is pumped into a ZORBAX Eclipse XDB-C18 4.6×150 mm, 5 μm, a commercially available chromatography column, at a solvent flow rate of 0.8 mL/min. The working temperature is 25° C. 10 mM KH.sub.2PO.sub.4 (solvent A) and acetonitrile (HPLC grade, solvent B) are used as solvents in the gradient mode. To reduce process costs, it is also possible to use solvent A in a lower concentration in the gradient mode, specifically 1 mM H.sub.3PO.sub.4. The proportion of solvent B increases from 10% to 15% within 10 minutes. After the elution follows an equilibration phase of 20 minutes with a solvent mixture of 90% 10 mM KH.sub.2PO.sub.4 and 10% acetonitrile.

(5) Contaminants in the industrial wastewater were collected in a fraction between 2.5 and 4.5 minutes (1.6 mL). The gallium-desferrioxamine-E complex was collected as a fraction at an elution time of between 8 and 10 minutes (1.6 mL). The yield of the gallium desferrioxamine E complex was 92.0%±2.5% based on the gallium originally contained. 4.75 μL of an aqueous 2 mM Fe.sup.3+ solution is added and the pH is brought to a value of 2.5±0.3 using 0.1 M HCl. The total volume is now 1.6475 mL. After ultrasound treatment for 12 hours and at a temperature <50° C., 100 μL of this solution is pumped onto a “ZORBAX Eclipse XDB-C18 4.6×150 mm, 5 μm” chromatography column (commercially available) at a solvent flow rate of 0.8 mL/min. The fraction at an elution time of 2.5-4.5 minutes contains the gallium to be recovered. The gallium yield is >90%. The fraction at 8-10 minutes contains the Fe-desferrioxamine-E complex in a yield of 91%. The total volume of this latter fraction is 1.6 mL. 28 μL of an aqueous 10 mM Na.sub.2SO.sub.3 solution is added to the solution and the pH value is adjusted to 3.5±0.3 using 0.5 M HCl. Another 28 μL of a 2 mM aqueous ethylenediaminetetraacetic acid solution (EDTA) is added. After the solution has stood for 24 hours at room temperature, the solution is placed on a “ZORBAX Eclipse XDB-C18 4.6×150 mm, 5 μm” chromatography column and chromatographed at a solvent flow rate of 0.8 mL/min. The fraction between the elution time of 2.5 and 4.5 minutes contains the waste. The regenerated desferrioxamine-E is collected in the fraction between 16.5 and 18.5 minutes.

(6) Method Description for Industrial Wastewater Having Low In Concentration (10 mg/L) Using DFO-E:

(7) 0.09 mL of a 2 mM solution of desferrioxamine-E is added to 1.91 mL of industrial wastewater containing 0.087 mM indium and the resulting solution is stirred for 15 minutes at room temperature. 100 μL of this solution is placed on a chromatography column. The remaining steps are carried out as in the experiment for low Ga concentrations using DFO-E described above. In the case of the industrial wastewater containing indium, the following other contaminating elements were contained in ion form: Na, K, Ca, Mg, P, S, Si, Zn and Pb.

(8) Method Description for Industrial Wastewater Having Higher Ga Concentration (40 mg/L) Using DFO-E:

(9) A similar experiment of the whole process is carried out using 1.6 mL of an industrial water sample having a Ga concentration of 40 mg/L. 0.4 mL of a 2 mM aqueous desferrioxamine-E solution is added to the solution. All steps of the above-mentioned method are employed in a similar manner. The only difference lies in the amounts of reagents used: 41.6 μL of a 1 mM Fe.sup.3+ solution and later 28 μL of a 10 mM solution of Na.sub.2SO.sub.3 are employed.

(10) Method Description for Industrial Wastewater Having Low Ga Concentration (4 mg/L) Using DFO-B

(11) and

(12) Method Description for Industrial Wastewater Having Higher Ga Concentration (40 mg/L) Using DFO-B:

(13) Gallium is recovered from both industrial wastewater having a higher Ga concentration and from industrial wastewater having a lower Ga concentration in a similar manner to the above methods, using desferrioxamine-B instead of desferrioxamine-E. All method steps are employed in a similar manner except for the fractions that are collected. The Ga-desferrioxamine-B complex and also the Fe-desferrioxamine-B complex are collected at an elution time of 4.5-6.5 minutes instead of 8-10 minutes.

(14) M=mol/L.

2. Second Variant of the Method According to the Invention

(15) Method Description for Industrial Wastewater Having Low Ga Concentration (4 mg/L) Using DFO-E:

(16) 0.05 mL of a 2 mM solution of desferrioxamine-E is added to 1.95 mL of industrial wastewater having a low Ga concentration (4 mg/L) and the resulting solution is stirred for 15 minutes at room temperature. 100 μL of this solution is pumped into a ZORBAX Eclipse XDB-C18 4.6×150 mm, 5 μm, a commercially available chromatography column, at a solvent flow rate of 0.8 mL/min. The working temperature is 25° C. 10 mM KH.sub.2PO.sub.4 (solvent A) and acetonitrile (HPLC grade, solvent B) are used as solvents in the gradient mode. The proportion of solvent B increases from 10% to 15% within 10 minutes. After the elution follows an equilibration phase of 20 minutes with a solvent mixture of 90% 10 mM KH.sub.2PO.sub.4 and 10% acetonitrile.

(17) Contaminants in the industrial wastewater were collected in a fraction between 2.5 and 4.5 minutes (1.6 mL). The gallium-desferrioxamine-E complex was collected as a fraction at an elution time of between 8 and 10 minutes (1.6 mL). The yield of the gallium desferrioxamine E complex was 92.0%±2.5% based on the gallium originally contained.

(18) 2.1 μL of a 10 mM ethylenediaminetetraacetic acid solution (EDTA) is added to the 1.6 mL of the gallium-desferrioxamine-E fraction and stirred at room temperature for 24 hours. Then 100 μL of this solution is pumped onto a “ZORBAX Eclipse XDB-C18 4.6×150 mm, 5 μm” chromatography column (commercially available) at a solvent flow rate of 0.8 mL/min. The working temperature during the chromatography is 25° C. 10 mM KH.sub.2PO.sub.4 (solvent A) and acetonitrile (HPLC grade, solvent B) are used as solvents in the gradient mode. The proportion of solvent B increases from 10% to 15% within 10 minutes. After the elution follows an equilibration phase of 20 minutes with a solvent mixture of 90% 10 mM KH.sub.2PO.sub.4 and 10% acetonitrile. The fraction at an elution time of 3.5-5.5 minutes contains the gallium-EDTA complex. The regenerated desferrioxamine-E is collected in the fraction between 16.5 and 18.5 minutes. 93% (±1.5%) of the gallium-EDTA complex and 92% (±2.5%) of the desferrioxamine-E were recovered compared to the amounts used.

(19) The isolated gallium-EDTA complex can be used directly for the production of GaN wafers or GaAs wafers.

(20) To decomplex the gallium-EDTA complex, 2.56 μL of a 1 mM Fe(III) solution is added and is stirred at room temperature for 24 hours. This results in the gallium being released and the Fe(III)-EDTA complex being formed.

3. Method Step B: Chromatography to Separate the Metal-Siderophore Complex

(21) Optimised Chromatography Resin to Maximise Loading and Minimise Solvent Loss—Using a Reverse-Phase Chromatography Resin

(22) When searching for optimised chromatography resins for separating or purifying Ga-siderophore complexes, the following optimisation was carried out.

(23) DFO-B or DFO-EA is added in an equimolar manner (with respect to the concentration of Ga) to a solution containing the various metals Ga, Zn, Ca, Cu, Mg and As (0.25 mM-1.0 mM each). The mixture is incubated for 24 hours at 30° C. while being stirred. Then 5 mL or 8 mL of this solution is injected into chromatography columns, each containing different packing materials (chromatography resins). The fractions containing the Ga-siderophore complex are collected during the chromatography. The purity and the consumption of acetonitrile per mmol of the isolated Ga-siderophore complex were calculated. The results are shown in Table 1.

(24) TABLE-US-00001 TABLE 1 Comparison of different chromatography columns for purifying/separating Ga-siderophore complexes MeCN Carbon consumption Purity of the Chromatography proportion Mobile phase/ [L per mmol Ga-siderophore column [%] Solvent Comment of complex] complex [%] Zorbax 150 mm 10 10% acetonitrile DFOB + Ga 0.25 mM 1.706 67.3 (MeCN) with DFOE + Ga 0.25 mM 2.126 95.5 gradient EDTA B 0.5 + 3 mM free dfo 0.598 99.0 EDTA E 0.5 + 3 mM free dfo 1.112 99.0 Zorbax 250 mM 10 2.5% MeCN DFOB + Ga m as 1 mM 5 ml 0.132 96.9 10% MeCN without DFOE + Ga m as 1 mM 5 ml 0.438 98.6 gradient 10% MeCN with EDTA B 0.5 + 3 mM 5 ml 0.448 99.0 gradient EDTA E 0.5 + 3 mM 5 ml 1.364 99.0 YMC C18 20 10% MeCN without DFOB + Ga m as 1 mM 8 ml 0.288 83.0 gradient DFOE + Ga m as 1 mM 8 ml 0.448 100.0 10% MeCN with EDTA B 0.5 + 3 mM 5 ml 0.938 99.0 gradient EDTA E 0.5 + 3 mM 5 ml 1.472 99.0 Reprosil-pur 200 12 10% MeCN with DFOB + Ga m as 1 mM 5 ml 1.228 74.3 ODS-3 gradient DFOE + Ga m as 1 mM 5 ml 0.994 92.5 EDTA B 0.5 + 3 mM 5 ml 0.966 99.0 EDTA E 0.5 + 3 mM 5 ml 2.032 99.0 Reprospher 100 16 2.5% MeCN DFOB + Ga m as 1 mM 8ml 0.112 95.8 C18-DE 10% MeCN without DFOE + Ga m as 1 mM 8 ml 0.358 99.6 gradient 10% MeCN with EDTA B 0.5 + 3 mM 5 ml 0.518 99.0 gradient EDTA E 0.5 + 3 mM 5 ml 1.32 99.0 Ecoprep 120 24 10% MeCN with DFOB + Ga m as 1 mM 5 ml 1.844 79.1 C18-NE gradient DFOE + Ga m as 1 mM 5 ml 1.112 89.0 EDTA B 0.5 + 3 mM 5 ml 2.32 99.0 EDTA E 0.5 + 3 mM 5 ml 1.362 99.0 ReproSil Saphir 02. Jan 1% MeCN DFOB Ga + As + Me 0.25 mM 5 ml 0.15 61.7 1000 C18 2.5% MeCN DFOE Ga + As + Me 1 mM 5 ml 0.154 97.3 10% MeCN with EDTA B 0.5 + 3 mM 5 ml 2.32 99.0 gradient EDTA E 0.5 + 3 mM 5 ml 1.362 99.0 ProSphere 300  4 2.5% MeCN DFOB Ga + As + Me 0.5 mM 5 ml 0.536 60.1 C18 5% MeCN DFOE Ga + As + Me 1 mM 5 ml 0.272 98.2 10% MeCN with EDTA B 0.5 + 3 mM 5 ml 0.904 99.0 gradient EDTA E 0.5 + 3 mM 5 ml 0.84 99.0

(25) All chromatography columns were 4.6 mm in diameter. Except for ZORBAX (150 mm and 250 mm) all columns had a length of 250 mm. The ZORBAX and YMC C18 TRIART columns were filled with a chromatography resin that had a particle size of 5 μm; the other resins had a particle size of 10 μm.

(26) The best chromatography columns for purifying/separating a Ga-DFO-B complex are ZORBAX and REPROSPHER 100 C18-DE, as can be seen in Table 1. For a Ga-DFO-E complex, the best chromatography columns are REPROSIL SAPHIR 1000, PROSPHERE 300 C18 and REPROSPHER 100 C18-DE. REPROSPHER 100 C18-DE is the best column for the Ga-siderophore complexes having the DFO-B and/or DFO-E siderophores. During chromatography, this column results in high purity and low solvent consumption.

LITERATURE

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