Alberta Inventors and Inventions

Thomas Etsell and Wasyl Kunda’s process for recovering waste silver from photographic solutions improved the efficiency of the process while making it essentially self-contained.

Photographic film uses a silver halide coating to help register the image. Film processing uses a fixer chemical that converts some of the sliver halide to metallic silver. Large uses like photo processing labs and hospitals used thousands of gallons of the fixer chemicals annually to processing film and x-rays.

The amount of waste silver from this process was significant, Etsell and Kunda said in their 1992 patent claim: "during processing about 33 1/3 percent to 40 percent of the silver remains on the film and the remaining 60 percent to 66 2/3 percent is washed into the photographic fixer solution." Recovering that silver made economic and environmental sense as firms could recover some of their processing cost, and silver, a metallic pollutant, would kept out of the waste stream.

Nonetheless, technologies for recovering silver, especially electroplating from the solution, tended to be costly to build and maintain, were inefficient and could not recycle the fixer solution. "A chemical process, which could selectively remove silver from spent fixer solution without destruction of the thiosulfate in the solution and which would allow the fixer to be reused, would have the advantages of lower costs, ease of operation, and a reduced environmental hazard", Etsell and Kunda’s patent application claimed.

Kunda and Etsell’s new process injected various sulfate solutions into the photographic fixer solution. This reacted with the solution and precipitated silver sulfide while maintaining the PH and reagent levels in the fixer solution, making it available for reuse. The silver sulfide left over from the process could be easily extracted and processed for their metal content.

Kunda and Etsell’s process required no special equipment and could be set up in smaller locations like rural hospitals. The pair of researchers sold the North American rights for the process to Vancouver-based Photochemical Recycling Systems. The company invested $7 million in developing and designing a process that could be a closed-loop system.

Silver Recovery from Spent Photographic Solutions