Process for recovering silver from scrap materials and electrolyte composition for use therein

Claim 2

A process as set forth in claim 2 wherein the metals in elemental form in said scrap material dissolve electrolyitically during electrolysis, the metals in combined form in said scrap material dissolve chemically in said electrolyte, and all metals other than silver accumulate in the electrolyte during electrolysis.

Claim 3

A process as set forth in claim 1 wherein said electrolyte is prepared by adding silver oxide to water, heating the resulting mixture, adding an amount of sulfamic acid to the mixture to dissolve the silver oxide, in excess of the stoichiometric amount required to react with the silver present to form silver sulfamate, adding said glutamic acid compound to the resulting solution, and thereafter removing impurities which plate out preferentially to silver by subjecting the solution to electrolysis in the presence of inert electrodes.

Claim 4

A process as set forth in claim 2 wherein, upon termination of electrolysis, the resulting electrolyte is thereafter separately subjected to further electrolysis in which an inert electrode is employed as the anode and a corrosion-resistant material is employed as the cathode, substantially pure silver being deposited at the cathode and the silver ion concentration of the electrolyte being substantially depleted as electrolysis proceeds.

Claim 5

A process as set forth in claim 5 wherein, upon termination of said further electrolysis, the resulting electrolyte is further treated by adding thereto a water soluble compound whose anionic component reacts with silver ions remaining in the electrolyte to form an insoluble silver compound, and the resulting precipitate of the insoluble silver compound is recovered by filtration.

Claim 6

A process as set forth in claim 6 wherein the solution resulting from said filtration is subjected to further treatment by adding thereto a water soluble compound whose anionic component reacts with cadmium ions to form an insoluble cadmium compound and the resulting precipitate of the insoluble cadmium compound is recovered by filtration.

Claim 7

A process as set forth in claim 2 wherein, upon termination of the said electrolysis, the resulting electrolyte is further treated by adding thereto a water soluble compound whose anionic component reacts with silver ions to form an insoluble silver compound, the resulting precipitate of the insoluble silver compound is recovered by filtration, the solution resulting after recovery of the silver compound is subjected to further treatment by adding thereto a water soluble compound whose anionic component reacts with cadmium ions to form an insoluble cadmium compound, and the resulting precipitate of the insoluble cadmium compound is recovered by filtration.

Claim 8

A process as set forth in claim 1 wherein said glutamic acid compound is monosodium glutamate monohydrate.

Claim 9

A process as set forth in claim 4 wherein the resulting electrolyte contains between approximately 60 and 140 grams of silver ions per liter, between approximately 5 and 15 grams of monosodium glutamate monohydrate per liter and an amount of between approximately 7 and 15 grams of free sulfamic acid per liter.

Claim 10

A process as set forth in claim 1 wherein, during electrolysis, the temperature of the electrolyte is maintained between approximately 140* F. and 170* F., the current density is between approximately 30 and 300 amperes per square foot and the electrolyte contains between approximately 60 and 140 grams of silver ions per liter, between approximately 5 and 15 grams of monosodium glutamate monohydrate per liter, an amount of between approximately 7 and 15 grams of free sulfamic acid per liter and less than approximately 260 grams of cadmium ions per liter.

Claim 11

A process as set forth in claim 11 wherein electrolysis is terminated when the cadmium ion concentration is between aPproximately 200 and 260 grams per liter.

Claim 12

A process as set forth in claim 6 wherein said water soluble compound is sodium chloride.

Claim 13

A process as set forth in claim 7 wherein said water soluble compound is sodium hydroxide.

Claim 14

A process for recovering substantially pure silver from silver-bearing scrap material containing materials selected from the group consisting of silver, silver oxide, cadmium, cadmium oxide and other metals in elemental or combined form which comprises the steps of preparing an aqueous electrolyte solution containing between approximately 60 and 140 grams of silver ions per liter, between approximately 5 and 15 grams per liter of a glutamic acid compound selected from the group consisting of glutamic acid and the water-soluble salts thereof, and an amount of between approximately 7 and 15 grams of free sulfamic acid per liter, immersing an anode of said scrap material and a cathode of a corrosion-resistant material in said solution, electrolyzing said solution while maintaining the temperature thereof at a temperature between approximately 140* F. and 170* F. and the current density between approximately 30 and 300 amperes per square foot, silver and any other metals in elemental form in the scrap material being dissolved electrolytically and any metals in the combined form in the scrap material being dissolved chemically in the solution, depositing the silver at the cathode without substantial codeposition of any other metals in the scrap material, subjecting the resulting electrolyte to further electrolysis at a temperature between about 140* F. and 170* F. and a current density of not more than 300 amperes per square foot, in which an inert electrode is employed as the anode and a corrosion-resistant material is employed as the cathode to thereby deposit substantially pure silver at the cathode, and thereafter treating the resulting electrolyte with a water soluble compound whose anionic component reacts with silver ions remaining in the electrolyte to form an insoluble silver salt and recovering the resulting precipitate by filtration.

Claim 15

In an electrolytic process for recovering substantially pure silver from silver-bearing scrap material in which the scrap material is employed as the anode and a corrosion-resistant material is employed as the cathode, the improvement which comprises carrying out the electrolysis in an electrolyte comprising an aqueous solution of silver sulfamate, a glutamic acid compound selected from the group consisting of glutamic acid and the water soluble salts thereof, and an amount of free sulfamic acid.

Claim 16

An electrolytic process as set forth in claim 16 wherein, during said electrolysis, the temperature of the electrolyte is maintained between approximately 140* F. and 170* F., the current density is between 30 and 300 amperes per square foot and the electrolyte contains between approximately 60 and 140 grams of silver ions per liter, between approximately 5 and 15 grams of monosodium glutamate monohydrate per liter, an amount of free between approximately 7 and 15 grams of sulfamic acid per liter and less than approximately 260 grams of cadmium ions per liter.

Claim 17

An electrolytic process as set forth in claim 17 wherein electrolysis is terminated when the cadmium ion concentration is between approximately 180 and 260 grams per liter.

Claim 18

An electrolyte composition for use in the recovery of substantially pure silver from silver-bearing scrap materials which comprises an aqueous solution containing silver sulfamate, a glutamic acid compound selected from the group consisting of glutamic acid and the water soluble salts thereof, and an amount of free sulfamic acid.

Claim 19

An electrolyte composition as set forth in claim 19 wherein said glutamic acid compound is monosodium glutAmate monohydrate.

Claim 20

An electrolyte composition as set forth in claim 20 wherein said solution contains between approximately 60 and 140 grams of silver ions per liter, between approximately 5 and 15 grams of monosodium glutamate monohydrate per liter and an amount of between approximately 7 and 15 grams of free sulfamic acid per liter.

Claim 21

An electrolyte composition as set forth in claim 21 additionally containing an anionic surfactant.