Recovery of Chromium from Waste Taning Liquors by Magnesium Oxide

This is a case study of AL-Za’afaraniya tanning factory, 15 km to the south of Baghdad, to spot light on simple chemical treatment of the discharged water to solve the environmental problems associated with its chromium content management. The treatment was extended to the recovery and reuse of chromium. Chromium was precipitated by the addition of magnesium oxide which also aid as a neutralizer for the acidic effluent. The laboratory treatment was carried out to find the optimum conditions. The wastewater samples were taken from the outline area of the tannery. Box-Wilson method was adopted to find useful relationships between the operating variables (temperature, mixing period and magnesium oxide dose) and the pH and chromium content of effluent. The experimental data were successfully fitted to second order polynomial mathematical models for the treatment. The most favorable operating conditions for the treatment were: temperature, 30 ?C; mixing period, 50 min and magnesium oxide concentration, 3000 mg/L. On using the optimum conditions a mathematical model simulating the operation for the treatment was obtained as follows: Cr = 6.0848 – 0.001839 X11 – 0.105334 X12 – 0.041038 X13 pH = 10.29086 – 0.001223 X11 – 0.140043 X12 – 0.00953 X13 Experimentally Cr concentration was decreased to about (0.5 mg/L) in wastewater after raising the pH value to (7.35) by adding magnesium oxide.