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

Abstract

Kinetics of hexavalent chromium reduction to trivalent chromium onto iron spheres, packed in a rotating basket reactor was investigated under different conditions, such as H₂SO₄ 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 4.9 kcal/mol which confirm the diffusion controlled nature of the reaction. The thermodynamic parameters for the present study were calculated at 25°C and was found to be 17.99 kJ mol⁻¹, 278.98 J mol⁻¹ K⁻¹, and 103.6 kJ mol⁻¹ for ΔH, −ΔS, and ΔG, 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

The present mass transfer data was found to agree with the surface renewal theory.

Keywords:

• Hexavalent chromium
• Reduction
• Packed basket
• Iron spheres
• Kinetics
• Mass transfer
• Thermodynamic
• Rotating reactor