Treatment of a wastewater from a galvanizing industry containing chromium(VI) and zinc(II) by liquid surfactant membranes technique

Galvanizing industries generate large amounts of effluents rich in toxic and carcinogenic chromium(VI) species. Effective and sustainable treatments are required to comply with environmental regulations. This work focused on the development of innovative treatments for Cr(VI) by its removal from a galvanizing industry wastewater (pH(initial) = 5.9) containing Cr (78 mg.L-1) and Zn (2178 mg.L-1) using the liquid surfactant membranes technique. The membrane phase carrier was Alamine (R) 336 in Escaid (TM) 110. For a synthetic solution (Cr(VI) = 353mg.L-1, pH(internal phase) = 1.5), 99.9% of Cr(VI) was extracted in three stages ([KOH](internal phase) = 0.27 mol.L-1). For the galvanizing wastewater, two selective extractions treatments were proposed: (1) 87% of Cr(VI) and 2% of Zn(II) were extracted in a single stage ([HCl](feed phase) = 0.03 mol.L-1, [KOH](internal phase) = 0.6 mol.L-1); (2) 95.6% of Cr(VI) and practically no zinc were extracted in a single stage ([HCl] (feed phase) = 10(-6)mol.L-1, [HCl] (internal phase) = 5mol.L-1). In another treatment condition ([HCl] (feed phase) = 2mol.L-1 and [KOH] (internal phase) = 1.2 mol.L-1), the simultaneous Cr(VI) and Zn(II) extractions (95% and 70%, respectively) were obtained in a single stage and more than 99% of both metals in three stages. This resulted in a depleted feed phase with 0.01 mg.L-1 of Cr(VI), that allows its discharge, according to the Brazilian legislation (<= 0.1 mg/L).