GB1044961A - A method of treating and eliminating copper from sulphuric acid-containing and nitric acid-containing effluents derived from pickling processes - Google Patents

Abstract

Copper is removed from a sulphuric acid-containing or nitric acid-containing effluent from a pickling plant by precipitating the copper as a hydroxide and/or oxide by addition of sufficient caustic alkali, separating the precipitate from the effluent and the precipitate is then dissolved in sulphuric or nitric acid and the resultant solution electrolyzed to recover metallic copper. Typically water used in rinsing copper sheets from a rolling mill pickled in sulphuric acid is brought to pH 7.8 to 8.1 with caustic soda to precipitate the copper content and the resultant clear water is either run into a drain or used for cooling. The precipitate is dissolved in sulphuric acid mixed with part of the pickling bath, and electrolyzed between a copper cathode and a lead anode with an applied potential of 2.3v at a current density of 12 to 14 amps/dm2 to cathodically deposit copper. The freed sulphuric acid is returned to the pickling bath which is kept at an acid content above 159 e.g. 25% and a copper content below 30 g/l. For rinsing water from brass wire pickled in a nitric acid-chromic acid the pH is raised with caustic soda to 7.9-8.5 to produce a copper-zinc sludge, and the clear water is treated to remove the chromate content either by ion exchange or by deposition as barium chromate before discharge to a drain. The copper-zinc sludge is thickened, dissolved in nitric acid and electrolyzed between a graphite anode and a copper cathode to deposit a mixture of metallic copper and zinc on the cathode.