Silver recovery as Ag0nanoparticles from ion-exchange regenerant solution

Patent metadata

Field	Value
Publication number	US-10807085-B2
Application number	US-201816193034-A
Country	US
Kind code	B2
Filing date	Nov 16, 2018
Priority date	Nov 17, 2017
Publication date	Oct 20, 2020
Grant date	Oct 20, 2020

Abstract

Silver is recovered as Ag 0 nanoparticles from the spent solution obtained from the regeneration of an Ag-loaded ion exchange resin using electrolysis. The reclaimed regenerant solution is recycled and reused in a closed-loop scheme over multiple cycles. The recovered Ag 0 nanoparticles are monodisperse, spherical in shape, and have a mean diameter of about 6 nm.

First claim

The invention claimed is:

1. A method of recovering silver from silver-containing waste water solution, comprising:
(a) providing an ion exchange column comprising an ion exchange resin;
(b) introducing the silver-containing waste water solution to the ion exchange column to absorb silver in the ion exchange resin;
(c) eluting the loaded ion exchange resin with an acidified thiourea regenerant solution to remove silver from the resin and to obtain a spent regenerant solution containing a thiourea-silver complex, Ag(TU) x + , where x=1-4;
(d) electrolytically separating the silver from the Ag(TU) x + complex of the spent regenerant solution by electrodepositing silver onto a substrate, and removing the silver depleted thiourea regenerant solution;
(e) electrolytically recovering the silver as Ag 0 nanoparticles from the silver-deposited substrate by submerging the silver-deposited substrate and a graphite electrode in an electrolyte solution comprising a stabilizing agent comprising citric acid in an electrolytic cell, and applying current to the electrolytic cell; and
(f) reusing the silver depleted thiourea regenerant solution removed in step (d) in subsequent elution of loaded ion exchange resin.

2. The method of claim 1 , wherein the ion exchange resin comprises a thiol functionalized ion exchange resin.

3. The method of claim 1 , wherein the ion exchange resin comprises a macroporous polystyrenic acidic cation exchange resin containing thiol functional groups.

4. The method of claim 1 , wherein the recovered Ag 0 nanoparticles have about 100% purity.

5. The method of claim 1 , wherein the amount of recovered silver is at least 90% by weight of the silver in the silver-containing waste water.

6. The method of claim 1 , wherein the amount of recovered silver is at least 94% by weight of the silver in the silver-containing waste water.

7. The method of claim 1 , wherein the recovered Ag 0 nanoparticles are substantially spherical in shape and have an average diameter of 3.4 nm to 8.7 nm.

8. The method of claim 1 , wherein the pH of the acidified thiourea regenerant solution is in the range of 1.0 to 1.3.

9. The method of claim 1 , wherein the electrolytic separation step (d) does not include the addition of external chemicals to the electrolyte solution.

10. The method of claim 1 , wherein the stabilizing agent further comprises sodium docedyl benzene sulfonate.

11. The method of claim 1 , wherein the pH of the electrolyte solution in step (e) is about 6.

12. The method of claim 1 , wherein the thiourea content of the silver-depleted thiourea regenerant solution of step (f) is at least 95% of the thiourea content of the regenerant solution of step (c).

13. The method of claim 1 , wherein the substrate comprises a titanium plate.

14. A method of recovering silver from greywater, the method comprising:
(a) providing an ion exchange column comprising an ion exchange resin;
(b) introducing the silver-containing greywater to the ion exchange column to absorb silver in the ion exchange resin, wherein the greywater contains at least one detergent composition;
(c) eluting the loaded ion exchange resin with an acidified thiourea regenerant solution to remove silver from the resin and to obtain a spent regenerant solution containing a thiourea-silver complex, Ag(TU) x + , where x=1-4;
(d) precipitating silver from the thiourea composition by adjusting the pH of the spent regenerant solution to recover the silver, wherein the silver is recovered as Ag 2 S nanoparticles and/or high purity powder; and
(e) obtaining silver depleted thiourea regenerant solution.

15. The method of claim 14 , wherein the ion exchange resin comprises a thiol functionalized ion exchange resin.

16. The method of claim 14 , wherein the at least one detergent comprises one or more component selected from sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), alcohol ethocylate non-ionic surfactant, diethylenetriamine pentaacetate (DTPA), zeolite, sodium metasilicate pentahydrate, sodium carbonate, 4,4′-diamino-2,2′-stilbenedisulfonic acid, sodium perborate, tetraacetyleneethylenediamine (TAED), and combinations of two or more thereof.

17. The method of claim 14 , wherein adjusting the pH of the spent regenerant solution comprises increasing the pH to about 11-12 by adding NaOH solution.

18. The method of claim 14 , further comprising readjusting the pH of the silver depleted regenerant solution to about 1.5, and reusing the silver depleted regenerant solution in subsequent elution of loaded ion exchange resin.

Assignees

• Univ Massachusetts

Inventors

• Nawaz Tabish
• Sengupta Sukalyan
• Yang Chen-Lu

Classifications

• C02F2103/002

  Grey water, e.g. from clothes washers, showers or dishwashers · CPC title

• C02F1/42

  by ion-exchange (ion-exchange in general B01J) · CPC title

• B01J49/60

  Cleaning or rinsing ion-exchange beds · CPC title

• B01J49/06 Primary

  containing cationic exchangers · CPC title

• B01J39/04

  Processes using organic exchangers · CPC title