Removal of Chromium (VI) and Other Heavy Metals from Groundwaters in Neutral and Alkaline Media

A method has been developed for removing the dissolved chromium(VI) and nickel compounds from groundwaters polluted as a consequence of uncontrolled solid wastes disposal. The chromium(VI) compounds (4-25 mg/L)were reduced in both neutral and alkaline media (10.0-11.0 pH range) with the help of FeSO4.7H2O. The partly colloidal, poorly water-soluble chromium(III) hydroxides developed in the course of the oxidation-reduction processes and the nickel compounds precipitated in an alkaline medium are coagulated by the iron(III) hydroxides produced. The addition of an anionic flocculant promoted the flocculation processes, so that in the effluent from conventional solid-liquid phase separation (settling and sand filtration) the chromium (and nickel) concentration was lowered to below the 100 µg/L level. The effluent can thus be recharged safely into the soil, or discharged into a recipient.