Kinetics and thermodynamic treatments of the reduction of hexavalent to trivalent chromium in presence of organic sulphide compounds

Whereas trivalent chromium is essential in human nutrition, most of hexavalent chromium compounds are toxic. Reduction of Cr (VI) to Cr (III) is crucial to protect our health and environment. The effect of 4(4-carboxy-2-nitrobenzyl thio) derivatives on the rate of reduction of Cr (VI) ion to Cr (III) was measured using a rotating iron cylinder at different concentrations of sulphide compounds. It was found that the mass transfer coefficient decreased by an amount which ranged from 22.7–83.1% depending on the types and concentrations of organic compounds. The rate of reduction was also measured at 125, 250, 375, 500, 625, 750 and 1000 rpm and was found to increase by increasing the rate of rotation. Also the rate of reduction was found to increase by increasing the temperatures. It was found that mass transfer coefficients or the rates of reduction increase by increasing rotation and temperature, and decreased in the presence of organic compounds. Thermodynamic parameters ΔG#, ΔH# and ΔS# are given and the adsorption isotherm was studied.