Sodium borohydride can also be used to precipitate out silver as silver metal. Ion Exchange Silver in low concentration levels can be removed by pumping the solution through an anion-exchange resin column. The silver is trapped in the resin column, and then be recovered on or off-site. Unfortunately recovery of the silver can be difficult, but concentration levels as low as 0.1 ppm are achievable. A controlled direct electric current is passed between two electrodes suspended in the solution.
Silver then plates out n the cathode as an almost pure metal.
In some cases the silver bearing solution can actually be reused. Unfortunately very low levels of silver concentration can not be achieved with this method alone, and it is often used in conjunction with one of the other treatment systems. Silver Recovery From Photographic Film or Paper Silver in scrap film or paper can be removed by treating these materials with a sodium hypochlorite solution to oxidize any silver metal. This solution can then be added to the fixer solution and the silver can be recovered in the same manner as from conventional photo-processing waste solution. Some facilities may choose to use fixer solution that they are preparing for disposal anyway.