Jarosite wastes reduction through blast furnace sludges for cast iron production

Abstract

Jarosite is a dangerous waste derived from the hydrometallurgical route of zinc production, and it cannot be safely disposed of due to its acidic pH and the risk of toxic metal leaching. A new process at laboratory scale for the utilization of jarosite sludges is proposed, with the aim to obtain cast iron and an inert slag, using blast furnace sludges as reducing agent. Jarosite-reducing agent mixes were reduced in a muffle furnace at 1500 °C for 15 min. Two reducing agents were used: pure graphite (as control) and blast furnace sludges. Two CaO concentrations (5, 15%wt. on jarosite mass) and four equivalent C concentrations (7.5, 15, 30, 60%wt. on jarosite mass) were analysed. Cast iron was obtained from all of the mixes, but the highest reduction yield was obtained at 15%wt. equivalent C. The slag obtained from the control batch had a fully crystalline structure, while the one related to the sample with BF sludges showed an incipient vitrified structure, that could prevent the leaching of hazardous elements. The best process parameters to profitably obtain cast iron and a glassy slag are 15% of equivalent C, 5% CaO and blast furnace sludges as reducing agent.