Utilization and detoxification of gypsum sludge by replacing limestone in reduction smelting of high lead slag

Gypsum sludge refers to a hazardous solid waste produced by the non-ferrous smelting industry, and its disposal and utilization are environmentally challenging. To investigate the feasibility of replacing limestone with gypsum sludge for smelting slagging, the effect of gypsum sludge and smelting conditions on high lead slag reduction smelting was studied through thermodynamic calculation and experiments. It was found that calcium sulfate in the gypsum sludge consumed the reducing agent and vulcanized the metal oxide, thus, controlling its dosage was necessary. The optimal conditions for comprehensive recovery of valuable metals were as follows: calcium silicon mass ratio, dosage of carbon powder, mole ratio of calcium sulfate to calcium oxide, smelting temperature, and holding time were 0.8, 3.5 wt%, 1: 5, 1200 °C, and 1.5 h, respectively. The direct recovery of lead and zinc under these conditions was 94.43% and 58.43% respectively. Meanwhile, toxicity leaching experiment of sulfuric acid and nitric acid method indicated that the collaborative melting process stabilized the reduced slag.