SILVER RECOVERY AS Ag NANOPARTICLES FROM ION-EXCHANGE REGENERANT SOLUTION

Patent metadata

Field	Value
Publication number	US-2019151838-A1
Application number	US-201816193034-A
Country	US
Kind code	A1
Filing date	Nov 16, 2018
Priority date	Nov 17, 2017
Publication date	May 23, 2019
Grant date	—

Abstract

Silver is recovered as Ag0 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 Ag0 nanoparticles are monodisperse, spherical in shape, and have a mean diameter of about 6 nm.

First claim

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

• B01J49/60

  Cleaning or rinsing ion-exchange beds · CPC title

• C02F1/42

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

• B01J39/04

  Processes using organic exchangers · CPC title

• B01J49/06 Primary

  containing cationic exchangers · CPC title

• B01J49/53

  for cationic exchangers · CPC title