Valuable metals recovery and vitrification of chromium-containing electroplating sludge

In this work, a two-stage process was developed to recover the valuable elements from chromium-containing electroplating sludge (CES). The low sulfur/carbon Fe-Si-Cr alloy containing 31.61%Fe, 31.78%Cr, 36.59%Si, 0.01%C and 0.01%S was produced, and the recovery extent of Cr reached 98.62%. The CES was pre-desulfurized at 1000–1200 ℃, and reaction between components CaSO4 and Fe2O3 in the CES to produce CaFe4O7 was the main desulfurization mechanism. The desulfurized CES was then reduced by silicon at 1600 ℃ to prepare the Fe-Si-Cr alloy, and the SiO2 generated from the silicothermic reduction helps the vitrification of the slag. The presence of silicon in alloys and the CaO in the slag are the key factors for the low content of sulfur in alloy. Adding CaO also helped to decrease the viscosity of slag, and thus reduced the metal loss by enhancing the slag-metal separation efficiency.