Extraction and separation of zinc and chromium from electroplating effluent

Toxicity of industrial effluent is mainly due to the presence of heavy metals like Zn, Cd, Cr, Pb, As, etc. The treatment of these effluents will not only reduce environmental pollution but also conserve the natural resources. Present paper reports selective extraction and separation of zinc and chromium from the electroplating effluent (~15 g/L Zn and ~30 g/L Cr) using solvent extraction technique. Initial studies were carried out from synthetic solution containing Zn (1.78 g/L) and Cr (3.6 g/L) using 10% DE2PHA diluted with kerosene. Various process parameters viz. effect of pH, time, O/A ratio, loading capacity, etc. were studied and optimized. 98.17% Zn gets extracted in 5 min at equilibrium pH 2.5 maintaining O/A ratio 1. 10% H₂SO₄ was used for stripping the loaded organic. The optimum condition for extraction was validated with the original electroplating effluent supplied by M/s Sinha Electrochemical Plant, Jamshedpur, India. Complete extraction of Zn from the original effluent takes place in 5 min at an equilibrium pH 2.5 and phase ratio (O/A) 1, leaving 99% Cr in the raffinate. From the pure solution obtained, metal or salt could be produced by evaporation, precipitation, electrowinning, crystallization, etc.