Customized slag system design for low-temperature smelting of electroplated chromium sludge to prepare ferrochromium alloy

Electroplated chromium sludge (ECS) is a hazardous waste containing high levels of Cr(VI). Its complex composition presents significant challenges for global disposal. Although reduction smelting is an effective way to treat ECS, the absence of a suitable smelting slag system has hindered efficient ferrochromium alloy production from ECS. Leveraging the natural high-Ca/low-Mg–Al characteristics of ECS, a customized regulation model for the CaO–SiO₂–Al₂O₃–MgO– Cr₂O₃ quinary slag system was constructed. The effects of various parameters such as Al2O3 and Cr2O3 contents, basicity, and other parameters on the properties of smelting slag were systematically investigated. Under the optimized slag regime (Al₂O₃ 10–15 wt.%, Cr₂O₃ <1 wt.%, binary basicity 0.95–1.20, MgO/Al₂O₃ 0.46–0.57), the smelting temperature was reduced to 1600 ℃, representing a 100 ℃ decrease compared to conventional chromite smelting processes. Notably, over 98 wt.% of the chromium in ECS was recovered into a ferrochromium alloy conforming to the FeCr55C6.0(II) standard. A key finding was that 10–15 wt.% Al₂O₃ significantly improved slag fluidity at high temperatures, thereby effectively promoting slag–metal separation.