Innovative methodology for the utilization of low-grade pyrite cinder containing heavy metals via hydrothermal alkali melting followed by chlorination roasting

Abstract

Low-grade pyrite cinder (LPyC) is a typical industrial solid waste from sulfuric acid production and is considered an important potential iron resource. This study investigated the utilization of LPyC containing heavy metals through hydrothermal alkali melting followed by chlorination roasting. Results indicated that the hydrothermal alkali melting showed a significant selectivity for the dissolution of silica, alumina and sulfur under optimum conditions (melting at 200 °C for 90 min, 30 wt% NaOH, and a liquid-to-solid ratio of 2:1). Chlorination roasting results indicated that the separation of heavy metals from iron can be realized under optimum conditions (roasting at 1100 °C for 90 min and 4% MgCl2). Moreover, the efficiency of volatilization (EV) of the heavy metals was found in following sequence: EVPb>EVZn>EVCu. After undergoing the entire process, the LPyC containing only 49.34% Fe was purified to about 60.12% with an acceptably low level of heavy metal impurities (0.05% copper, 0.07% lead and 0.11% zinc), and the Fe recovery of concentrate reached 89.65%. To reveal the mechanism of present process, the phase transformation, microstructure and basic thermodynamic evaluation of the process were researched by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy and HSC, respectively.