Selective extraction of chromium from chromium-bearing electroplating sludge by pressure oxidation alkaline leaching

Abstract

The selective extraction of chromium (Cr) from Chromium-bearing electroplating sludge (CES) has positive significance for harmless disposal and reducing dependence on native resources. Herein, the process of pressure oxidation alkaline leaching of CES is reported. The leaching ratio of Cr was reached 89.9 % under the optimal conditions, i.e., temperature of 125℃, NaOH concentration of 1.5 mol/L, liquid-solid ratio of 10, oxygen partial pressure of 2Mpa and reaction time of 2 h, while other elements such as Cu, Ni, Fe and Zn were virtually not leached out. In addition, the concentration of NaOH required for the maximum of the leaching ratio of Cr decreased with the increase of temperature, which attributed to the synergistic effect of temperature and NaOH concentration on the solubility and diffusion coefficient of the oxidant. As the oxygen partial pressure was increased to 2 MPa, the liquid-solid ratio was raised to 10, and the reaction time was extended to 2 h, respectively, the leaching ratio of Cr reached maximum and then remained as a constant. Kinetic studies showed the leaching process of chromium was controlled by chemical reaction, and the apparent activation energy was 112.1 kJ/mol. The efficient selective recovery of Cr is of great significance to reduce the difficulty of comprehensive recovery of valuable metal elements in the CES.