Reduction of Cr(VI) in the wastewater by using pyrite

III SUMMARY Master Thesis Reduction of Cr(VI) in the Wostewater by Using Pyrite Mehmet ERDEM University of Fırat Graduate School of Natural and Applied Science Department of Chemical Engineering 1996, Page 72 Chromium, widely used as Its alloys and compounds, constitutes one of the important pollutants for environment. Compared to the other species, hexavalent chromium is more toxic and its concentration is restricted as 50 jig/1 in water. It must be primarily reduced to trivalent state before removing from aqueous systems. In the chromium removal practices, iron (II) sulphate, S02 and alkali sulphites are commonly used as reducing agents. In this study, effects of the parameters such as acid concentration, amount of pyrite, contact time, Initial CKVI) concentration, temperature, particle size on the CKVI) reduction in the aqueous solutions were investigated by using pyrite through batch experiments. Additionally, the reducing capacity of pyrite was determined. On the other hand, fixed bed columnar tests were carried out to determine the continuous reduction characteristics. The removal of chromium present and heavy metals released from pyrite were investigated by applying precipitation to the solutions obtained after reduction.IV It was found that the chromium reduction efficiency increased by increasing the amount of acid and pyrite, contact time and temperature for a solution containing the certain amount of Cr(VI). Increasing both the initial concentration of Cr(VI) and particle size of pyrite, affected adversely the reduction. At the end of shaking period of 75 min, it was found that chromium was completely reduced in the mixture Cat 25°C) containing 0.4 ml H2SO4 (97I)/1 and 100 rng Cr(VI)/l of 100 ml dichromate solutions and 1 g pyrite (-270 mesh). Chromium reducing capacity of pyrite used was found to be 42.5 rng Cr(VI)/g pyrite by applying succesive reducing for the same pyrite sample In the columnar study, it was found that reducing capacity of pyrite was very low even at very low flow rates. It was found that the precipitation applied at pH 7.5 to the solution obtained after reduction removed the Cr, Fe, Cu, fin and Zn. Key Words: Chromium (VI), heavy metal, reduction, removal, pyrite.