I New Process for Electrolytic Silver Stripping
The electrolytic silver stripping equipment is designed independently by Material Recycling and Utilization Institute which uses graphite as cathode and stainless steel drum as anode. There are many pores on the drum. .Sodium citrate and sodium sulfite are the electrolyte, and the silver-plated pieces enter the drum from the head end of the drum and then sent out by the tail end. The silver on the surface of the plated piece dissolves into the electrolyte while the matrix remains intact and can be withdrawn and electroplated again for use.Recovery rate of silver is 97-98%, silver purity is 99.9%.
II Recycle and Utilization of Waste Silver - Zinc Battery
The silver content in the waste silver-zinc battery is 52.55% and zinc content is 42.7. Zinc is the cathode, and silver oxide is the anode.And they are coated on the skeleton in the copper network. Material Recycling and Utilization Institute uses dilute sulfuric acid to leach zinc and copper separately, silver powder is melted and crystallized directly.. Add oxidant when leach copper with dilute sulfuric acid., the zinc-containing liquid after being enriched and crystallized produces zinc sulfate, and the copper-containing liquid after being enriched and crystallized produces copper sulfate. Zn recovery rate > 98%, silver recovery rate is 98% and purity of silver ingot > 99%.
III Recovery of Silver from Waste Film
Kunming Institute of Precious Metals uses dilute sulfuric acid solution to elute the silver-containing emulsion layer on the color film, heat chloride and precipitate to get silver halide, adopt chlorinate burning or organic solvent cleanse to remove organic substance, and use carbohydrate to suspend and restore alkaline medium to get pure silver. The silver purity is 99.9% pure silver, direct recovery rate is 98%. This technique has been applied for patent. Material Recycling and Utilization Institute (former Material Recycling and Utilization Institute of Ministry of Internal Trade) adopts sodium thiosulfate solution to dissolve the silver halide on the waste film, and during the course of dissolution add inhibitor to prevent gelatin on the film from being dissolved, solution for dissolving undergone electrolysis to recover silver and the film base is recycled and utilized again. Silver leaching rate> 99%, recovery rate is 98% , silver purity is 99.9%. This method has been applied to industrial production.
IV Recovery of silver from spent fixing bath
After the photosensitive material undergone exposure, developing and fixing, about 70-80% of silver on the black and white film enters into the fixing bath and almost all silver on color film enters into the fixing bath.Recovery of silver from spent fixing bath has been highlighted both in domestic and abroad and a lot of researches have been done, the recovery methods adopted are ion precipitation, electrolysis, metal replacement, drug reduction, and ion exchange etc. The advantage of electrolysis lies in that the fixing bath after undergoing silver elution can be returned to use for fixing. All large film studios in the mainland use this method to recover silver.