Low-cost Simple Processing Method for Wastewater Containing High Concentration of Hexavalent Chromium

Abstract

The processing of the wastewater containing high concentrations of hexavalent chromium, which has been commonly used as a powerful oxidant in many industrial production processes, is not able to be implemented easily in developing countries. To develop a simple processing method for wastewater containing high-concentration of hexavalent chromium that can be easily implemented at low cost in developing countries, we examined the processing of artificial wastewater containing high-concentration hexavalent chromium (dichromate ion) using an inexpensive treatment agents. In 100 mL of artificial wastewater containing potassium chromate (hexavalent chromium ion: 1000 mg / L), hexavalent chromium was completely removed after processing in the order of calcium hydroxide (1000 mg) and ferrous chloride (500 or 1000 mg). The XRD spectra of the precipitates obtained after processing artificial wastewater containing potassium dichromate in the order of calcium hydroxide and ferrous chloride showed productions of Fe₆Cl_12-X(OH)_12＋X and CaCO₃. It was suggested that dichromate ions in artificial wastewater containing hexavalent chromium ion changed to chromate ions under strong basicity by adding calcium hydroxide, and then might react with Fe₆C_l2-X(OH)_12＋X to generate the precipitates containing iron-chromate complex (Fe₆Cl_6-X (OH) _6+X (CrO₄) ₃) and iron chromate (FeCrO₄).