FIELD: chemical or physical processes.
SUBSTANCE: invention relates to regeneration of nitrate-ammonium solution for removal of cadmium coatings by reagent-electrolysis method. Solution of phosphoric acid with concentration of 0.1–85 wt.% or a solution of ammonium dihydrophosphate with concentration of 1–200 g/l is added to the regenerated solution at pH=4–8, or their mixture in ratio of 1:10 to 10:1 in amount of 90–100% of stoichiometrically required for deposition of cadmium ions by phosphate ions. Precipitate of cadmium phosphate is separated from the filtrate, which is a regenerated nitrate-ammonium solution for removing cadmium coatings. Cadmium phosphate precipitate is mixed with a solution of phosphoric acid with concentration of 0.1–85 wt.% or with a solution of ammonium dihydrophosphate with concentration of 1–200 g/l or with a mixture thereof in ratio of 1:10 to 10:1 until complete dissolution. Residual concentration of cadmium ions of 0.1–0.5 g/l is achieved by electrolysis in the obtained solution. Solution purified from cadmium ions is reused for deposition of cadmium ions from the nitrate-ammonium solution for removing cadmium coatings.
EFFECT: invention enables to quickly regenerate a nitrate-ammonium solution for removing cadmium coatings while maintaining the concentration of the main component—nitrate ions available at the time of regeneration, by controlling residual concentration of cadmium ions and obtaining metal cadmium with high current output.
3 cl, 1 ex
