A new strategy for the comprehensive utilization of zinc leaching residue and spent carbon cathode to efficiently solidify zinc, fluorine and recover valuable elements

Abstract

Zinc (Zn) leaching residue, a globally prevalent hazardous waste containing Zn, is conventionally treated through redox smelting at 1523–1723 K. However, high residual Zn in slag causes environmental risks and valuable metal loss. Similarly, spent carbon cathode with soluble fluoride (F) and carbon (C), produced globally at over 1.7 million tons annually, threaten soil, groundwater, and biological safety. This study proposes a novel co-treatment strategy for hazardous waste comprehensive utilization. The effects of spent carbon cathode addition, temperature, and holding time on Zn, F, and Fe transformation pathways were examined. At 1373 K, ZnFe₂O₄ and Zn₂SiO₄ in the desulfurized Zn leaching residue transformed to Ca₂ZnSi₂O₇, (Zn,Fe)O, and ((Zn,Fe)O)_slag, and then reduced to Zn(g) and Fe through spent carbon cathode. F-containing phase from spent carbon cathode were immobilized in molten slag, enhancing Fe particle growth and Zn reduction. Subsequent cooling transformed to Ca₄F₂Si₂O₇, achieving a F solidification ratio of 99.92 % and a leaching content of 7.84 mg/L, thereby minimizing environmental risks. Compared with conventional methods, the proposed strategy improved Zn and Fe recovery ratios by 4 % and 78 %, respectively, and reduced Zn leaching content to 0.11 mg/L. This approach utilizes waste to treat waste, contributing to the sustainable development of the global Zn and Al industries.