Method for producing metallic silver by electro-deposition

Abstract

A method for producing metallic silver by electro-deposition, including electrolyzing an electrolyte solution containing Ce(NO.sub.3).sub.3 in an anode zone and an electrolyte solution containing AgNO.sub.3 in a cathode zone by using an electrolytic cell with a specific diaphragm, wherein the electrolyte solution in the anode zone is not allowed to enter the cathode zone. After the electrolyzing is complete, the metallic silver with a high purity is obtained at the cathode, and a Ce.sup.4+-containing solution is obtained in the anode zone.

Claims

1. A method for producing metallic silver by electro-deposition, comprising electrolyzing an electrolyte solution containing Ce(NO.sub.3).sub.3 in an anode zone and an electrolyte solution containing AgNO.sub.3 in a cathode zone by using an electrolytic cell with an anion exchange membrane, wherein the electrolyte solution in the cathode zone and the electrolyte solution in the anode zone are not in fluid communication with each other, and after the electrolyzing is complete, the metallic silver is obtained at a cathode of the electrolytic cell, and a solution containing Ce.sup.4+ is obtained in the anode zone, wherein the electrolyte solution in the cathode zone has H.sup.+ at a concentration of no more than 0.1 mol/L.

2. The method according to claim 1, wherein the electrolyte solution in the anode zone has H.sup.+ at a concentration of at least 0.01 mol/L.

3. The method according to claim 1, wherein the electrolyte solution in the anode zone has H.sup.+ at a concentration of at least 0.1 mol/L.

4. The method according to claim 1, wherein the electrolyte solution in the cathode zone has Ag.sup.+ at a concentration of at least 0.5 mol/L.

5. The method according to claim 1, wherein the electrolyte solution in the cathode zone has Ag.sup.+ at a concentration of at least 0.9 mol/L.

6. The method according to claim 1, wherein the electrolyte solution in the cathode zone has Ce at a concentration of no more than 0.2 mol/L.

7. The method according to claim 1, wherein the cathode during the electrolyzing has a current density ranging from 100 to 650 A/m.sup.2.

8. A method for producing metallic silver by electro-deposition, comprising electrolyzing an electrolyte solution containing Ce(NO.sub.3).sub.3 in an anode zone and an electrolyte solution containing AgNO.sub.3 in a cathode zone by using an electrolytic cell with a diaphragm, wherein the diaphragm is one selected from the group consisting of an anion exchange membrane, a membrane with micropores and a membrane with nanopores, wherein only a unidirectional flow of the electrolyte solution in the cathode zone to the anode zone is enabled, and after the electrolyzing is complete, the metallic silver is obtained at a cathode of the electrolytic cell, and a solution containing Ce.sup.4+ is obtained in the anode zone, wherein the unidirectional flow is carried out by means comprising providing at least one of pressure and overflow.

9. The method according to claim 8, wherein the electrolyte solution in the anode zone contains silver ions.

10. The method according to claim 8, wherein the electrolyte solution in the anode zone has H.sup.+ at a concentration of at least 0.01 mol/L.

11. The method according to claim 8, wherein the electrolyte solution in the cathode zone has Ag.sup.+ at a concentration of at least 0.5 mol/L.

12. The method according to claim 8, wherein the cathode during the electrolyzing has a current density ranging from 100 to 650 A/m.sup.2.

13. A method for producing metallic silver by electro-deposition, comprising electrolyzing an electrolyte solution containing Ce(NO.sub.3).sub.3 in an anode zone and an electrolyte solution containing AgNO.sub.3 in a cathode zone by using an electrolytic cell with an anion exchange membrane, wherein the electrolyte solution in the cathode zone and the electrolyte solution in the anode zone are not in fluid communication with each other, and after the electrolyzing is complete, the metallic silver is obtained at a cathode of the electrolytic cell, and a solution containing Ce.sup.4+ is obtained in the anode zone, wherein the electrolyte solution in the anode zone contains silver ions.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) In order to facilitate understanding of the present application, the present application lists embodiments as follows. Those skilled in the art should understand that the embodiments are intended merely to help understand the present application and should not be considered as a specific limitation to the present application.

(2) Embodiment 1

(3) An electrolytic cell was divided into a cathode zone and an anode zone by an anion exchange membrane, a platinum-plated titanium mesh was used as the anode, and a silver plate was used as the cathode. The current density of the cathode was controlled to 400 A/m.sup.2 for electrolysis. The initial solution in the cathode zone was 0.5 mol/L AgNO.sub.3 neutral solution, and the initial solution in the anode zone contained 0.5 mol/L Ce(NO.sub.3).sub.3, 0.01 mol/L H.sup.+ and 0.01 mol/L AgNO.sub.3.

(4) 0.8 mol/L AgNO.sub.3 neutral solution was continuously added into the cathode zone as the electrolyte solution in the cathode zone. By controlling the liquid level, the solution in the cathode zone was enabled to overflow the membrane and slowly flow into the anode zone. A solution containing 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L HNO.sub.3 was added to the anode zone as the electrolyte solution in the anode zone as required. During the electrolysis, the solution in the cathode zone was maintained at [Ag.sup.+]≥0.5 mol/L and [H.sup.+]≤0.1 mol/L, and the solution in the anode zone was maintained at [H.sup.+]≥0.01 mol/L by timely supplementing the corresponding raw materials.

(5) Ag.sup.+ was reduced to metallic silver on the silver plate cathode, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode, and the produced Ce(NO.sub.3).sub.4 was timely removed. A part of nitrate required for the anode was supplemented by NO.sub.3.sup.− in the cathode zone passing through the anion exchange membrane, and the other part was supplemented by the solution at the cathode that overflowed.

(6) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, the current efficiency of the cathode was 80%, and the current efficiency of the anode was 87%.

(7) Embodiment 2

(8) An electrolytic cell was divided into a cathode zone and an anode zone by a porous membrane with a pore diameter of 100 micronss or less, a platinum sheet was used as the anode, and a titanium mesh was used as the cathode. The current density of the cathode was controlled to 100 A/m.sup.2 for electrolysis. The initial solution in the cathode zone was 1.5 mol/L AgNO.sub.3 solution having [H.sup.+] of 0.01 mol/L. The initial solution in the anode zone contained 0.2 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L H.sup.+.

(9) 1.5 mol/L AgNO.sub.3 neutral solution was continuously added into the cathode zone as the electrolyte solution in the cathode zone. By controlling the liquid level, the solution in the cathode zone was enabled to slowly flow into the anode zone through the pores in the membrane. A solution containing 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L HNO.sub.3 was added to the anode zone as the electrolyte solution in the anode zone as required. During the electrolysis, the solution in the cathode zone was maintained at [Ag.sup.+]≥0.5 mol/L and [H.sup.+]≤0.1 mol/L, and the solution in the anode zone was maintained at [H.sup.+]≥0.1 mol/L by timely supplementing the corresponding raw materials.

(10) Ag.sup.+ was reduced to metallic silver on the cathode, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode, and the produced Ce(NO.sub.3).sub.4 was timely removed. A part of nitrate required for the anode was supplemented by NO.sub.3.sup.− in the cathode zone passing through the anion exchange membrane, and the other part was supplemented by the solution at the cathode that passed through the membrane.

(11) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, the current efficiency of the cathode was 95%, and the current efficiency of the anode was 80%.

(12) Embodiment 3

(13) An electrolytic cell was divided into a cathode zone and an anode zone by a nanofiltration membrane, a platinum mesh was used as the anode, and a silver plate was used as the cathode. The current density of the cathode was controlled to 650 A/m.sup.2 for electrolysis. The initial solution in the cathode zone was 1.5 mol/L AgNO.sub.3 solution having [H.sup.+] of 0.05 mol/L and further containing 0.1 mol/L Ce(NO.sub.3).sub.3. The initial solution in the anode zone contained 2 mol/L Ce(NO.sub.3).sub.3, 1 mol/L H.sup.+ and 1 mol/L AgNO.sub.3.

(14) A solution containing Ce(NO.sub.3).sub.3 was added into the closed anode zone through a pipeline for electrolysis, and a solution containing Ce.sup.4+ was output through a pipeline. A certain negative pressure was applied to the closed anode zone. Due to the pressure difference, only ions and water molecules in the cathode zone were allowed to enter the anode zone through the membrane. A solution containing AgNO.sub.3 was continuously added to the cathode zone as the electrolyte solution in the cathode zone. During the electrolysis, the solution in the cathode zone was maintained at [Ag.sup.+]≥0.5 mol/L and [H.sup.+]≤0.1 mol/L, and the solution in the anode zone was maintained at [H.sup.+]≥0.1 mol/L by timely supplementing or removing the corresponding components.

(15) Ag.sup.+ was reduced to metallic silver on the silver plate cathode, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode, and the produced Ce(NO.sub.3).sub.4 was removed timely.

(16) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, the current efficiency of the cathode was 95%, and the current efficiency of the anode was 80%.

(17) Embodiment 4

(18) An electrolytic cell was divided into a cathode zone and an anode zone by an anion exchange membrane, and a platinum mesh was used as the anode, and a silver plate was used as the cathode. The electrolyte solution in the cathode zone and the electrolyte solution in the anode zone were prevented from fluid communication with each other. The current density of the cathode was controlled to 350 A/m.sup.2 for electrolysis. The initial solution in the cathode zone was 1.5 mol/L AgNO.sub.3 solution at pH 2, and the initial solution in the anode zone contained 1 mol/L Ce(NO.sub.3).sub.3 and 0.01 mol/L H.sup.+.

(19) The electrolysis was performed by applying direct current, and the electrolysis was stopped when [Ag.sup.+] in the electrolyte solution in the cathode zone decreased to 0.9 mol/L. Ag.sup.+ was reduced on the silver plate cathode to obtain metallic silver, and Ce(NO.sub.3).sub.3 was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode. Nitrate required for the anode was supplemented by NO.sub.3.sup.− in the cathode zone passing through the anion exchange membrane.

(20) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, the reduction current efficiency of the cathode was 98%, and the oxidation current efficiency of the anode was 97%.

(21) Embodiment 5

(22) An electrolytic cell was divided into a cathode zone and an anode zone by an anion exchange membrane. The electrolyte solution in the cathode zone and the electrolyte solution in the anode zone were prevented from fluid communication with each other. The electrolyte solution in the cathode zone contained 0.1 mol/L acetic acid and 2 mol/L AgNO.sub.3, and the electrolyte solution in the anode zone contained 1 mol/L Ce(NO.sub.3).sub.3, 0.01 mol/L AgNO.sub.3 and 1 mol/L HNO.sub.3. A platinum sheet was used as the anode, and a titanium mesh was used as the cathode. The current density of the cathode was controlled to 650 A/m.sup.2 for electrolysis. During the electrolysis, the cathode zone and the anode zone were continuously supplemented with the solutions with the above-mentioned compositions individually as needed, and the excess solutions were individually discharged from the electrolytic cell through overflow ports. Ag.sup.+ was reduced on the titanium mesh to obtain metallic silver, and Ce(NO.sub.3).sub.4 solution was obtained at the anode.

(23) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, the current efficiency of the cathode was greater than 90%, and the current efficiency of the anode was greater than 90%.

(24) Embodiment 6

(25) An electrolytic cell was divided into a cathode zone and an anode zone by an anion exchange membrane. The electrolyte solution in the cathode zone and the electrolyte solution in the anode zone were prevented from fluid communication with each other. A neutral solution containing 0.5 mol/L AgNO.sub.3 was added into the cathode zone as the electrolyte solution in the cathode zone. The electrolyte solution in the anode zone contained 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L HNO.sub.3. A graphite plate was used as the anode, and a titanium mesh was used as the cathode. The current density of the cathode was controlled to 100 A/m.sup.2 for electrolysis. During the electrolysis, the cathode zone was continuously supplemented with 0.55 mol/L AgNO.sub.3 solution, and the excess electrolyte solution in the cathode zone was discharged into a storage tank through an overflow port. The solution in the storage tank was taken into a new storage tank, followed by adding concentrated nitric acid and solid Ce(NO.sub.3).sub.3 to prepare a solution containing 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L HNO.sub.3, and then the anode zone was supplemented with the solution as the electrolyte solution in the anode zone. Ce(NO.sub.3).sub.4 produced in the anode zone was pumped out intermittently by a pump.

(26) It was detected that the purity of the metallic silver obtained at the cathode reached 4N grade.

(27) Embodiment 7

(28) An electrolytic cell was divided into a cathode zone and an anode zone by an anion exchange membrane. A solution containing 0.5 mol/L AgNO.sub.3 and 0.1 mol/L HNO.sub.3 was added into the cathode zone as the electrolyte solution in the cathode zone. The electrolyte solution in the anode zone contained 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L HNO.sub.3. A platinum mesh was used as the anode and a silver mesh was used as the cathode. The current density of the cathode was controlled to 100 A/m.sup.2 for electrolysis. During the electrolysis, AgNO.sub.3 solution at a high concentration was continuously added to the cathode zone. Due to the difference in the liquid level between the cathode and anode, the electrolyte solution in the cathode zone was enabled to enter the anode zone through small holes in the cathode frame or the anode frame. The small holes had a size that did not allow the anolyte to counterflow into the cathode zone. The anode zone was continuously supplemented with Ce(NO.sub.3).sub.3 solution at a high concentration, and Ce(NO.sub.3).sub.4 produced was pumped out by a pump.

(29) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, and the current efficiency was greater than or equal to 90%.

(30) Embodiment 8

(31) An electrolytic cell was divided into a cathode zone and an anode zone by an anion diaphragm. The cathode zone and the anode zone were prevented from direct fluid communication with each other. A saturated AgNO.sub.3 solution at room temperature was added into the cathode zone as the catholyte, and a saturated Ce(NO.sub.3).sub.3 solution containing 2 mol/L HNO.sub.3 was added into the anode zone as the anolyte. A platinum mesh was used as the anode, a titanium mesh was used as the cathode, and the current density of the cathode was controlled to 100 A/m.sup.2 for electrolysis. During the electrolysis, the concentration of Ag.sup.+ was controlled to ≥0.9 mol/L, the concentration of H.sup.+ was controlled to ≤0.1 mol/L, and the concentration of Ce was controlled to ≤0.2 mol/L in the solution in the cathode zone, and the concentration of in the solution in the anode zone was controlled to ≥0.1 mol/L. Ag.sup.+ was reduced on the titanium mesh to obtain metallic silver. The solution in the cathode zone and the solution in the anode zone each flowed independently. The catholyte in the cathode zone maintained the composition and concentration requirements by continuously supplementing with the saturated AgNO.sub.3 solution. At the same time, fresh anolyte was timely added to the anolyte, and Ce(NO.sub.3).sub.4 solution produced at the anode eventually flowed out from an overflow port.

(32) It was detected that the purity of the metallic silver obtained at the cathode exceeded 99.99%, which met 1 # silver standard in GB standards, and the current efficiency was 98%.

(33) Embodiment 9

(34) An electrolytic cell was divided into a cathode zone and an anode zone by an anion diaphragm. The cathode zone and the anode zone were prevented from direct fluid communication with each other. A solution containing 0.1 mol/L HNO.sub.3 and 0.9 mol/L AgNO.sub.3 was added into the cathode zone as the catholyte, and a solution containing 0.2 mol/L Ce(NO.sub.3).sub.3, 0.5 mol/L H.sup.+ and 0.01 mol/L AgNO.sub.3 was added into the anode zone as the anolyte. A platinum mesh was used as the anode, a silver plate was used as the cathode, and the current density of the cathode was controlled to 500 A/m.sup.2 for electrolysis. During the electrolysis, the solution in the cathode zone was controlled to maintain the following conditions: the concentration of Ag.sup.+≥0.9 mol/L, the concentration of H.sup.+≤0.1 mol/L, and the concentration of Ce≤0.2 mol/L, and the concentration of H.sup.+ in the solution in the anode zone was controlled to ≥0.1 mol/L. Ag.sup.+ was reduced on the silver plate to obtain metallic silver, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode. Nitrate required for the anode was supplemented by NO.sub.3.sup.− in the cathode zone passing through the anion diaphragm. The solution in the cathode zone and the solution in the anode zone were supplemented and removed separately. The catholyte in the cathode zone was maintained to meet the composition and concentration requirements by continuously supplementing with the concentrated AgNO.sub.3 solution. At the same time, the anolyte was supplemented with Ce(NO.sub.3).sub.3, and the produced Ce(NO.sub.3).sub.4 was removed timely.

(35) It was detected that the purity of the metallic silver obtained at the cathode reached 5N grade, and the current efficiency was 80%.

(36) Embodiment 10

(37) An electrolytic cell was divided into a cathode zone and an anode zone by an anion diaphragm. The cathode zone and the anode zone were prevented from direct fluid communication with each other. A solution containing 2 mol/L AgNO.sub.3, 0.2 mol/L Ce(NO.sub.3).sub.3 and 0.01 mol/L H.sup.+ was added into the cathode zone as the catholyte, and a solution containing 1 mol/L Ce(NO.sub.3).sub.3, 0.01 mol/L AgNO.sub.3 and 1 mol/L HNO.sub.3 was added into the anode zone as the anolyte. A platinum sheet was used as the anode, a titanium mesh was used as the cathode, and the current density of the cathode was controlled to 650 A/m.sup.2 for electrolysis. During the electrolysis, the concentration of Ag.sup.+ was controlled to ≥1.8 mol/L, the concentration of H.sup.+ was controlled to ≤0.1 mol/L, and the concentration of Ce was controlled to ≤0.2 mol/L in the solution in the cathode zone, and the concentration of in the solution in the anode zone was controlled to ≥0.1 mol/L. Ag.sup.+ was reduced on the titanium mesh to obtain metallic silver, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode. The solution in the cathode zone and the solution in the anode zone each flowed independently. The catholyte in the cathode zone was maintained to meet the composition and concentration requirements by continuously supplementing with the AgNO.sub.3 solution. At the same time, the anolyte was supplemented with Ce(NO.sub.3).sub.3, and Ce(NO.sub.3).sub.4 in the solution was removed timely.

(38) It was detected that the purity of the metallic silver obtained at the cathode met 1 # silver standard in GB standards, and the current efficiency was 95%.

(39) Embodiment 11

(40) An electrolytic cell was divided into a cathode zone and an anode zone by an anion diaphragm. The cathode zone and the anode zone were prevented from direct fluid communication with each other. A solution containing 1 mol/L AgNO.sub.3 and 0.1 mol/L Ce(NO.sub.3).sub.3 was added into the cathode zone as the catholyte, and a solution containing 0.5 mol/L Ce(NO.sub.3).sub.3 and 0.1 mol/L was added into the anode zone as the anolyte. A graphite plate was used as the anode, a titanium mesh was used as the cathode, and the current density of the cathode was controlled to 200 A/m.sup.2 for electrolysis. During the electrolysis, the concentration of Ag.sup.+ was controlled to ≥0.9 mol/L, the concentration of H.sup.+ was controlled to ≤0.1 mol/L, and the concentration of Ce was controlled to ≤0.2 mol/L in the solution in the cathode zone, and the concentration of in the solution in the anode zone was controlled to ≥0.1 mol/L. Ag.sup.+ was reduced on the titanium mesh to obtain metallic silver, and Ce(NO.sub.3).sub.4 was obtained by oxidation reaction at the anode. The solution in the cathode zone and the solution in the anode zone each flowed independently. The catholyte in the cathode zone was maintained to meet the composition and concentration requirements by adding AgNO.sub.3. At the same time, the anolyte was supplemented with Ce(NO.sub.3).sub.3 and HNO.sub.3, and Ce(NO.sub.3).sub.4 was removed timely.

(41) It was detected that the purity of the metallic silver obtained at the cathode met 1 # silver standard in GB standards, and the current efficiency was 93%. The Ce(NO.sub.3).sub.4 produced in the anolyte was directly used as an oxidant for etching circuit boards.

Comparative Example 1

(42) An electrolytic cell was divided into a cathode zone and an anode zone by a conventional filter cloth. The solutions and ions in the cathode and anode zones were allowed to diffuse and flow freely. Both the electrolyte solutions at the cathode and anode contained 1 mol/L AgNO.sub.3, 1.5 mol/L Ce(NO.sub.3).sub.3 and 0.5 mol/L HNO.sub.3. A platinum mesh was used as the anode and a titanium mesh was used as the cathode. The current density of the cathode was controlled to 400 A/m.sup.2 for electrolysis. Ag.sup.+ was reduced on the titanium mesh to obtain metallic silver, and Ce.sup.3+ was converted to Ce(NO.sub.3).sub.4 by oxidation reaction at the anode. With the progress of electrolysis, the upper part of the anode zone showed a clear red color (Ce.sup.4+), and the red color diffused through the filter cloth into the cathode zone, and the Ce.sup.4+ was reduced on the surface of the cathode (the red color disappeared).

(43) It was detected that the purity of the metallic silver obtained at the cathode was 99.95%, which did not meet 1 # silver standard in GB standards. Since Ce.sup.4+ produced at the anode diffused to the cathode and was reduced preferentially over Ag.sup.+, the current efficiency of the silver reduction at the cathode was 12%, which was significantly lower than the method of the present application.

(44) Applicant declares that in the present application, the above embodiments are used to describe the process flow of the present application, but the present application is not limited to the above-mentioned process flow. That is, it does not mean that the present application must rely on the above-mentioned specific process flow to be implemented.