A new method for simultaneous separation and solidification of arsenic from arsenic-bearing gypsum sludge using waste carbon cathodes

Arsenic ( As ) -bearing gypsum sludge, one of the biggest As-bearing wastes, has seriously threatened ecological security due to the great mobility and leaching toxicity of As. Unfortunately, most of this sludge was discharged into tailing ponds without treatment. In this paper, a novel co-process of As-bearing gypsum sludge, waste carbon cathode (WCC) and Fe powder for simultaneous separation and solidification of As is proposed via reduction-magnetic separation. In the reduction process, Ca 3 (AsO 4 ) 2 was reduced and then enriched to α-Fe (Fe-As solid solution), and the As solidification ratio reached 90.5%. Meanwhile, NaF in waste carbon cathodes was transformed into CaF 2 and NaCa 2 FSiO 4 . The As and F leached content were only 0.053 mg/L and 3.10 mg/L, when evaluated using the toxicity characteristic leaching procedure. After magnetic separation, α-Fe (magnetic phase) was separated and recovered, and the weight and volume losses of As-bearing waste were 70% and 60%, respectively, compared with the raw material. The As residual content in the non-magnetic phase met the standard of solid waste (As < 0.1 wt%), which acted as a flux during the smelting process, minimizing the environmental risk and realizing resource recycling. Moreover, waste carbon cathodes can be reused as fuel and as a reducing agent, which significantly reduces production costs. This proposed technique reduces hazardous waste, is more effective, and is also more economical.