Study of the electrocoagulation of electroplating industry wastewaters charged by nickel (II) and chromium (VI)

The coagulation-flocculation is one of the techniques used for the treatment of industrial wastewaters. in this process,the principle of treatment consists on destabilizing negative colloidal particles,by addition of salts metal cations. the positive charge of cations compresses the electrical double layer which surrounds the colloidal particles characterized by a negative potential (ζ,zeta potential). the iron and aluminum salts are the most used. electrocoagulation is derived from the conventional coagulation technique. the cations are generated in solution by electrolytic dissolution of the metal electrodes. the main advantages of this process,highlighted by several authors,are low dose of coagulant,reduction of salinity,enhanced reactivity of metal cations,oxidation of certain pollutants,compactness of installations,lower volume of sludge,and elimination of the small size colloidal particles. this paper reports a research work on wastewaters eletrocoagulation of an electroplating industry located in casablanca (morocco). the goal is to carry out some tests of depollution applying two voltages 6 and 12 v on aluminum electrodes and to evaluate its performance. abatement rates determined for 6 v reached 57%,63% and 42%,and 12 v for 77%,88% and 66%,respectively for chemical oxygen demand (cod),nickel and chromium. the elimination of these pollutants was done by adsorption on aluminum hydroxide or its polymers which were formed in the ph range of this study,but also by the precipitation of nickel (ii) and chromium (iii) which forms afterward the cathodic reduction of chromium (vi).