SELF-RIPENING PRECIPITATION PROCESS - A LINEAR POLYMERIC PRECIPITANT AND CROSS-FLOW MICROFILTRATION SYSTEM TO REMOVE SILVER FROM PHOTOPROCESSING WASH WATER

A technology for reducing silver concentration in waste wash water fro m photoprocessing to a level below 0.01 mg/L was developed by combinin g a polymeric precipitating agent (SRP) and a cross-flow type microfil ter. The SRP is a hydrophilic linear polymer with a dithiocarbamate gr oup in the recurring unit. The polymer loses water solubility when the functional group reacts with silver ion and precipitates as a tangled mass. The precipitate is separated from water by a microfilter (pore size 0.45 mu m) in cross-flow mode, which prevents the pores from bein g clogged and passes water effectively. The separated precipitate laye r on the membrane surface further traps residual silver salts and lowe rs the silver concentration in permeating water to 0.01 mg/L. Successf ul field tests were conducted in processing laboratories in Japan and Germany.