Treatment of solutions containing trivalent chromium by electrodialysis

Trivalent chromium is present at high concentration in effluents from the tanning process in the leather industry. The chromium recycling process must be able to separate chromium from other cations (mainly Na+ but also Ca2+, Mg2+) because their presence has a negative effect on the quality of the tanned leather. Moreover, in order to recycle chromium, a concentration step is necessary to increase the concentration of Cr(III) in the concentrate stream. In this paper, a two-step Cr(III) separation–concentration process is proposed. In the first step, a cation-exchange membrane, Nafion®117, modified by electrodeposition of polyethylenimine (PEI) was used to separate successfully Cr(III) from NaCl solutions. In the second step, conventional electrodialysis with Nafion® 117, Nafion® 324 or CMX membranes permits to increase the concentration of Cr(III) in the solutions produced in the separation stage.