Electroplating sludge metal recovering with vitrification using mineral powder additive

Abstract

Electroplating sludge is a potential secondary metal resource. In this study, vitrification process was employed to recover the metal from plating sludge, and the mineral powder additive was used to improve the recovery efficiency of vitrification process. Plating sludge was collected from an industrial Ni electroplating workshop in Taiwan. Mineral powder composed of dolomite, limestone, and cullet was employed as the reductant additive to improve the efficiency of producing metallic ingot in the vitrification process. The metals Al, Ca, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were analyzed with an atomic adsorption spectrometer (AAS). Ni, Fe, and Cr are potential candidates for recovery using the vitrification process due to their relatively high mass content. To determine the optimal efficiency, vitrification processes were performed with additive to sludge mass ratios of 5:5, 6:4, 7:3, 8:2, and 9:1. The results indicate that the optimal metal recovery efficiency of Ni, Fe, and Cr was achieved at an additive to sludge ratio of 8:2. In addition, the toxicity characteristic leaching procedure (TCLP) test results for the slag meet the Taiwan EPA's regulated level of Cr(VI), Cr, Pb, and Cu. To examine the changes in microstructure, the crystalline phases of slag were analyzed with XRD. The XRD patterns show that the appearance of pseudowollastonite improves the metal recovery efficiency, whereas the appearance of diopside and quartz decreased efficiency. The preliminary economic analysis indicated that the vitrification was not only a feasible but also a cost-effective technology for the electroplating sludge treatment in this study. However, the practical application should further depend on the building cost of the plant and financial support from the government.