Reduction of hexavalent chromium using zerovalent iron spheres packed in a rotating basket reactor: kinetic and mass transfer study

摘要

Kinetics of hexavalent chromium reduction to trivalent chromium onto iron spheres, packed in a rotating basket reactor was investigated under different conditions, such as H_2SO_4 acid concentration, basket rotational speed, sphere diameter, and solution temperature. The rate of Cr(VI) reduction was found to increase with increasing basket rotational speed, H~+ ions concentration, and temperature. On the other hand the rate decreases with increasing the diameter of iron spheres. The activation energy was found to be 4.9kcal/mol which confirm the diffusion controlled nature of the reaction. The thermodynamic parameters for the present study were calculated at 25℃ and was found to be 17.99kJ mol~(-1), 278.98Jmol~(-1) K~(-1) and 103.6 kJ mol~(-1) for △H, -△S, and AG, respectively. Rate of Cr(Ⅵ) reduction expressed in terms of the rate of mass transfer was correlated to the controlling parameters by the dimensionless equation Sh = 0.3463 Re~(0.55) Sc~(0.33) The present mass transfer data was found to agree with the surface renewal theory.