China Nonferrous Metallurgy

Red mud (RM), fly ash (FA) and phosphogypsum (PG) have the characteristics of large production and low utilization rate, and long-term storage will have a serious impact on water resources, soil and air. In this paper, phosphogypsum is proposed to replace alkali lime CaO, and three kinds of solid wastes are co-treated with high temperature sintering, alkali leaching of aluminum and magnetic separation of iron. The effects of sintering process conditions on the recovery of aluminum and iron are investigated. Under the conditions of sintering temperature 1100℃, holding time 30min and calcium ratio 2.0, the iron recovery rate reaches 79.2%, iron grade reaches 74.5% and aluminum dissolution rate reaches 75.9%. Increasing the sintering temperature is conducive to the recovery of iron and aluminum, but the clinker will appear sticky and hinder the dissolution of aluminum when the temperature is higher than 1100℃. The holding time has little effect on the recovery of aluminum and iron. CaO and Na₂CO₃ help to activate the activity of mullite in fly ash and improve the recovery rate of aluminum. At high temperature, Fe₃Ti₃O₁₀ and Ca₃Fe₁₅O₂₅ will be formed when phosphogypsum is added in excess, which leads to the decrease of iron grade and iron recovery. Using this test process, every 1t of red mud, 0.5t of fly ash and 1.5t of phosphogypsum can recover 75.9% of aluminum and 0.3t of iron concentrate, and the alkali cycle can be realized in the production. At the same time, the generated 2CaO·SiO₂, 2CaO·SiO₂ and other by-products can be used to prepare sulfoaluminate cement. The whole process realizes the coordinated consumption of three kinds of solid waste, and effectively realizes the comprehensive utilization of resources.