Microwave Drying Kinetics of Chromium-Rich Electroplating Sludge

Abstract

Chromium-rich electroplating sludge (CRES) is a hazardous solid waste with a high content of moisture requiring efficient drying before subsequent treatment. In this study, the microwave drying kinetics of CRES were examined. The results showed that CRES had good microwave absorptivity, contributing to a much shorter drying time and better drying performance compared with conventional drying. In comparison with conventional drying at 105 °C, the time of microwave drying at 600 W for total moisture removal was reduced by 98.5%. Compared to load mass and particle size, microwave power played a more important role in microwave drying. Based on the kinetics analysis, the microwave drying process of CRES could be divided into three successive stages, in which the drying rates were limited by external diffusion (before 110 s), both external diffusion and chemical reaction (between 110 s and 160 s), and chemical reaction (after 160 s), respectively. The Danish model was found to have the best fit with the microwave drying process of CRES.