Energy-efficient reduction of hexavalent chromium on a rotating packed bed of woven steel screens

Abstract

This study investigates the rate of hexavalent chromium (Cr6+) reduction by scrap iron using a rotating packed bed of horizontally stacked woven iron screens. The primary focus is on enhancing the diffusion-limited reduction of Cr6+ by taking advantage of the centrifugal force induced by bed rotation and the high turbulence-promoting ability of the screen wires. The results show that the rate of diffusion-controlled reduction of Cr6+ increases with the increase in bed rotational speed, initial concentration of Cr6+, and mesh number. A correlation has been developed to predict the mass transfer coefficient under the studied conditions and serve in designing and scaling up industrial reactors. Additionally, the energy utilization efficiency of the reactor has been assessed as a performance indicator to be used for comparing the performance of the present reactor with other reactors which use different methods of mass transfer enhancement such as pulsation. Under optimum conditions, 99 % of Cr6+ was reduced to Cr3+ within 20 min and the energy consumption was 0.04–0.72 W/kg. The rotating bed with woven steel screens provides a low-cost and effective means of enhancing the rate of Cr6+ reduction, contributing to the development of more sustainable wastewater treatment solutions.