Hydrometallurgical valorization of chromium, iron, and zinc from an electroplating effluent

Hydrometallurgical removal of heavy metals (like chromium, iron, and zinc) from an industrial effluent, and their valorization into less-toxic species has been studied. At first, the solvent extraction of Cr(VI) was investigated with tri-butyl phosphate (TBP) to separate this carcinogenic metal from an electroplating effluent containing 3.43 g.L-1 Cr, 1.3 g.L-1 Zn, 0.41 g.L-1 Fe, and 1.23 mol.L-1 free acid of chloride medium. The study based on parametric variation revealed the spontaneity in adduct formation (HCrO3Cl center dot 2TBP) into organic phase through the exothermic extraction process (Delta H degrees, -18.8 kJ.mol(-1)). The extracted species of Cr(VI) was efficiently stripped (similar to 99%) as less-toxin Cr(III) by 30 min of contact with 2.0 mol.L-1 ascorbic acid solution. Thereafter, the hydrolytic precipitation of Crain from stripped solution at pH similar to 9.0, and Fe(III) from raffinate at pH 3.5 under continuous air-flow could yield the precipitates of Cr(OH)(3) and FeOOH center dot 2H(2)O, respectively. From the Fe-removed solution, a 5% stoichiometric excess of oxalic acid could effectively precipitate > 99.8% zinc in 30 min at 50 degrees C.