Enhanced bioleaching of Cr and Ni from a chromium-rich electroplating sludge using the filtrated culture of Aspergillus niger

Abstract

Electroplating sludge is classified by environmental agencies as a hazardous waste, the disposal of which can be a serious environmental concern. In the present study, the recovery of Ni and Cr from chromium-rich electroplating sludge was conducted using the filtrated culture of Aspergillus niger for the first time. Pulp density, leaching temperature, and leaching duration were identified as variables affecting the recovery optimization. Leaching temperature of 66 °C, leaching duration of 1 day, and pulp density of 10 g/L were found as the optimal conditions. Under optimum conditions, Cr and Ni recoveries were 53% and 95.7%, respectively. Toxicity Characteristic Leaching Procedure and Synthetic Precipitation Leaching Procedure tests showed that electroplating sludge was effectively detoxified by bioleaching. The kinetic studies demonstrated that the leaching proceeded with one stage kinetics for Cr and two stages kinetics for Ni. Cr recovery was controlled by interface transfer and diffusion across the product layer. Also, the first stage of Ni leaching was controlled by interface transfer and diffusion across the product layer, and the second stage of Ni leaching was a mixed-control mechanism and both diffusion through the product layer and chemical reaction were involved. Eventually, the results of this study represent the filtrated culture of Aspergillus niger has the ability to recover metals from electroplating sludge and detoxify it.