Method for preparing cadmium phosphide from copper-cadmium slag

The invention relates to a method for preparing cadmium phosphide by using copper-cadmium slag, which comprises the following steps: (1) oxidizing and acid leaching: mixing the copper-cadmium slag, ammonium dichromate and water, stirring to react, controlling the pH value at the end point to be 5-5.2, and performing solid-liquid separation to respectively obtain a mixed solution of zinc sulfate and chromium sulfate and a solid phase; (2) zinc and chromium separation: adding ammonia water into the mixed solution of zinc sulfate and chromium sulfate for chromium precipitation reaction to respectively obtain a [Zn (NH3) 4] (OH) 2 solution and a mixed precipitate of chromium hydroxide and chromium oxysulfate; (3) copper and cadmium separation: adding a sulfuric acid solution and water into the solid phase for acid leaching reaction to respectively obtain a cadmium sulfate solution and copper slag with the copper content of more than 90%; and (4) preparing cadmium phosphide: pumping the cadmium sulfate solution in