Silver recovery process

• US 3,899,323 A
• Filed: 10/29/1973
• Issued: 08/12/1975
• Est. Priority Date: 11/01/1971
• Status: Expired due to Term

• Current Assignee: William Jan Van Slyke
• Original Assignee: William Jan Van Slyke
• Inventors: Van Slyke, William Jan
• Primary Examiner(s): Rutledge, L. Dewayne
• Assistant Examiner(s): Andrews, M. J.
• Application Number:
  US05/410,920
• Time in Patent Office: 652 Days
• Field of Search: 75/63,83 264/262 194/453 137/219
• US Class Current: 75/635
• CPC Class Codes: C22B 11/025 from manufactured products, e.g. from printed circuit boards, from photographic films, paper, or baths
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

Silver-bearing manufactured organic products such as photographic film, photographic paper, printed circuit boards, etc., are loaded into a reduction zone of a retort and pyrolyzed by hot non-oxidizing gases produced by the burning of the carbon residue of previously pyrolyzed organic products in an adjacent oxidation zone in the same retort. The carbon residue is oxidized by subjecting the residue to a heated air and water vapor mixture. The rate of pyrolyzation is controlled so that the film entering the retort is contacted by non-oxidizing gases and vapors having a temperature less than 200* C. The off-gases of the pyrolysis are burned to heat the air and water vapor mixture.

Claims

1. A PROCESS FOR RECOVERING SILVER FROM SILVER-BEARING PHOTOGRAPHIC FILM CONTAINING SILVER SALTS COMPRISING THE STEPS OF:

A. SUBJECTING THE PHOTOGRAPHIC FILM TO HOT NONOXIDIZING GASES TO PROLYZE THE PHOTOGRAPHIC FILM TO FORM A SILVERBEARING CARBON RESIDUE AND A PYROLYTIC OFF-GAS MIXTURE SAID HOT NONOXIDIZING GASES BEING A GASEOUS MIXTURE CONTAINING SUFFICIENT HYDROGEN TO REDUCE SILVER SALTS TO METALLIC SILVER, B. BURNING THE SILVER-BEARING CARBON RESIDUE IN AN OXIDIZING ATMOSPHERE OF A HEATED AIR AND WATER VAPOR MIXTURE OF A SUFFICIENT TEMPERATURE AND RATIO TO BURN THE RESIDUE TO FORM A SILVER-BEARING ASH AND PRODUCE SAID HOT NONOXIDIZING GASES, C. DIRECTING SAID NONOXIDIZING GASES TO THE PHOTOGRAPHIC FILM TO PERFORM STEP (A), AND D. SEPARATING THE SILVER FROM THE ASH TO RECOVER THE SILVER.

2. The silver recovery process as defined in claim 1 further comprising the step of utilizing the off-gas mixture to heat the air and water vapor mixture.

3. The silver recovery process as defined in claim 1 wherein the off-gas mixture is burned to produce a hot gaseous product for heating the air and water vapor mixture.

4. The silver recovery process as defined in claim 1 wherein the water vapor to air ratio and temperature of the air and water vapor mixture is sufficient to maintain the bed temperature of the burning silver-bearing carbon residue at approximately 700* C.

5. A pyrometallurgical process for recovering silver from silver-bearing photographic film containing silver salts comprising the steps of:

a. feeding said photographic film into a reduction zone of an enclosed retort;

b. subjecting said photographic film to hot nonoxidizing gases of sufficient termperature to pyrolyze the photographic film to form a silver-bearing carbon residue and an off-gas mixture, said hot nonoxidizing gases being a gaseous mixture containing sufficient hydrogen to reduce silver salts to metallic silver;

c. directing the silver-bearing carbon residue to an oxidizing zone of the retort;

d. burning the silver-bearing carbon residue in an oxidizing atmosphere of a heated air and water vapor mixture of a sufficient temperature to reduce the residue to form a silver-bearing ash and said hot nonoxidizing gases of the sufficient temperature;

e. directing the hot nonoxidizing gases from the oxidizing zone to the reduction zone to perform step (b);

f. removing the silver-bearing ash from the retort; and

g. separating the silver from the ash to recover the silver.

6. In a process for recovering silver from silver-bearing photographic film containing silver salts;

preheating an oxygen and water vapor mixture to a temperature sufficient to burn a carbonaceous material to produce hot substantially oxygen free gases;

contacting the carbonaceous material with the preheated oxygen and water vapor mixture to burn the carbonaceous material to form an ash and the hot substantially oxygen-free gases; and

contacting the silver-bearing photographic film with the hot substantially oxygen free gases to pyrolyze the silver-bearing photographic film to form a silver-bearing carbon residue and pyrolytic off-gases, said hot substantially oxygen free gases being a gaseous mixture containing sufficient hydrogen to reduce silver salts to metallic silver.

7. In a process for recovering silver from silver-bearing photographic film material, comprising the steps of:

moving photographic film material fed from an entrance through an enclosed retort;

passing a hot non-oxidizing gaseous fluid through the photographic film material countercurrent to the movement of the photographic film material to progressively heat, and pyrolyze the photographic film material as the organic refuse moves through the retort to reduce the photographic film material to a silver-bearing carbon residue; and

controlling the initial temperature and flow rate of the non-oxidizing gaseous fluid so that the temperature of the non-oxidizing gaseous fluid will progressively decrease from an initial temperature of between 500* and 800* C. as the non-oxidizing gaseous medium passes through the phoTographic film material to a temperature contacting the entering photographic film material of less than 200* C.

8. In the silver recovery process according to claim 7 wherein the flow rate of the non-oxidizing gaseous fluid through the photographic film material is equivalent to a superficial velocity of less than 0.45 ft. per second.

9. In the silver recovery process according to claim 7 further comprising the step of:

feeding an oxidizing gaseous fluid into the retort downstream of the entrance to contact the silver-bearing carbon residue and reduce the silver-bearing carbon residue to a silver-bearing ash residue and produce said non-oxidizing gaseous fluid which is passed countercurrent through the photographic film material.

10. In the silver recovery process according to claim 9 wherein the oxidizing gaseous fluid contains free oxygen and water and wherein the initial temperature and flow rate of the non-oxidizing gaseous fluid is controlled by controlling the flow rate and free oxygen and water vapor content of the oxidizing gaseous fluid and thereby control the rate and temperature of silver-bearing carbon residue oxidation.

11. In the silver recovery process according to claim 10, further comprising the step of preheating the oxidizing gaseous fluid to a temperature between 300* and 800* C. before contacting the silver-bearing carbon residue.