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US3649250A Expired / Lapsed US ⏱️ 0.0 years remaining

Silver recovery process

Assignee: Minerals Technology Corp
•
Filing: 1969-05-12
•
Granted: 1972-03-14
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Expires: 1989-05-12
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Abstract

Abstract Silver is recovered from silver-containing scrap paper (e.g., scrap thermographic office copy paper) by a process which involves conditioning the silver-containing paper (e.g., with hot dilute aqueous sodium hydroxide) to thereby convert the silver in the paper from its usual organic acid salt form (e.g., silver behenate) into a different form of silver (e.g., converted into silver metal or some silver oxide) which is more readily converted into silver cyanide than is the organic acid salt of silver, and simultaneously or subsequently treating the new silver form with a silver-cyanide forming reagent (e.g., a dilute aqueous sodium cyanide solution) to thereby form silver cyanide. Metallic silver can then be recovered from the resulting silver cyanide solution by standard processing (e.g., zinc dust precipitation in the Merrill-Crowe process) as known in the art.

Inventors

  • 👤 Adrian C Dorenfeld
  • 👤 Gust Bitsianes

Bibliographic Details

Application Number —
Jurisdiction US
Data Source google_patents
Last Synchronized 2026-11-08 00:21
CPC Classifications
C; C22; C22B; C22B11/00; C22B11/08

Claims Analysis

Total Claims: 12
Claim 1
Independent Claim 39 words
The process of claim 1 wherein said conditioning agent comprises sodium hydroxide, wherein the conditioning of step (b) is performed prior to the treating of step (c), said conditioning being performed at a temperature of about 70* -85* C.
Claim 2
Dependent Claim 13 words
The process of claim 2 wherein the alkali metal cyanide comprises sodium cyanide.
Claim 3
Dependent Claim 22 words
The process of claim 3 wherein the silver present in the untreated paper is present as a fatty acid salt of silver.
Claim 4
Dependent Claim 30 words
The process of claim 3 wherein the silver in the paper is present as silver behenate and wherein the conditioning of step (b) is continued until the paper is blackened.
Claim 5
Dependent Claim 18 words
The process of claim 3 wherein the silver present in the untreated paper is present as silver behenate.
Claim 6
Dependent Claim 34 words
The process of claim 6 wherein at least part of the water needed for forming the slurry of step (a) is provided by using aqueous sodium hydroxide as the conditioning agent of step (b).
Claim 7
Dependent Claim 23 words
The process of claim 6 wherein the silver is recovered by zinc dust precipitation of a pregnant cyanide solution formed during step (c).
Claim 8
Dependent Claim 20 words
The process of claim 1 wherein the conditioning of step (b) is performed simultaneously with the treating of step (c).
Claim 9
Dependent Claim 35 words
The process of claim 9 wherein the conditioning and treating are performed simultaneously by heating the aqueous slurry of paper to a temperature of 70*-85* C. in the presence of sodium cyanide and sodium hydroxide.
Claim 10
Dependent Claim 98 words
The process of recovering silver from paper which is coated with a silver-containing coating, said process comprising: a. forming an aqueous slurry of a heat sensitive copy paper having a coating thereon which includes silver behenate; b. heating the slurry above 60* C. in the presence of sodium hydroxide for a time sufficient to blacken the paper; c. separating an aqueous phase from the blackened paper; d. contacting the blackened paper with aqueous sodium cyanide to extract silver from the blackened paper; thereby forming a solution pregnant with silver; and e. thereafter recovering silver from said pregnant solution.
Claim 11
Dependent Claim 19 words
The process of claim 11 wherein the extraction of silver with sodium cyanide is performed at about room temperature.
Claim 12
Dependent Claim 21 words
The process of claim 11 wherein silver is recovered by zinc dust precipitation of the pregnant cyanide solution of step (d).

References Cited (Backward Citations)

US2219781A Cited
US1281249A Cited
US1397684A Cited
US2273569A Cited
US3094417A Cited

USPTO Annuity & Maintenance Windows

Annuity Stage Window Opens Payment Deadline Surcharge Period Until Estimated Fee Status
3.5 Years (Year 4) 1975-03-14 1975-09-13 1976-03-14 $2000.00 Window Closed / Lapsed
7.5 Years (Year 8) 1979-03-14 1979-09-13 1980-03-14 $3760.00 Window Closed / Lapsed
11.5 Years (Year 12) 1983-03-14 1983-09-13 1984-03-14 $7700.00 Window Closed / Lapsed

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