Conversion of impure silver halide to ultra-pure silver metal

摘要

A method for preparing ultra-pure silver from a crude silver halide matrix containing metallic and/or non-metallic impurities, said method comprising;roasting the crude silver halide matrix to substantially remove carbonaceous material;treating the roasted crude silver halide matrix with ammonium hydroxide to dissolve the silver halides and form an ammonium hydroxide reaction mixture;adding an initial reducing agent to the ammonium hydroxide reaction mixture to precipitate a crude silver powder mixture;separating the crude silver powder mixture from the ammonium hydroxide reaction mixturedissolving the crude silver powder mixture in nitric acid to form a crude silver nitrate solution;adding a first selective reducing agent to the crude silver nitrate solution to precipitate a silver/contaminant matrix and form a partially purified silver nitrate solution;separating the partially purified silver nitrate solution from the precipitated silver/contaminant matrix;adding a second selective reducing agent to the partially purified silver nitrate solution to precipitate pure silver powder; andisolating the pure silver powder.