Leaching Behavior and Immobilization of Heavy Metals in Zinc Leach Residue Before and After Thermal Treatment

Abstract

The aim of the present study was to investigate the metal leaching behavior of the hazardous waste of zinc industry before and after thermal treatment. Samples were subjected to the TCLP (Toxicity Characteristic Leaching Procedure) and ASTM (American Society of Testing and Materials) methods. The results of TCLP and ASTM leaching methods demonstrate that addition of clinoptilolite, blast furnace slag, and red mud to the zinc leach residue reduces the heavy metal content in the effluent and the red mud performs better than clinoptilolite and blast furnace slag. The leaching tests showed that the content of some elements in the waste before thermal treatment exceeded the regulatory limits and cannot be disposed of in the present form. Metal releases decreased at higher temperatures from 600°C and 800°C and reached to minimum levels at 1200°C because of heat-induced formation of a glassy matrix. The levels of Zn2+ released for 1200°C was 0.025 mmol/L. Therefore, a stabilization or inertization treatment is necessary prior to disposal. Thermal treatment can be an acceptable method for disposal of zinc leach residue. © 2008 American Institute of Chemical Engineers.