Flowsheet development for the recovery of cadmium and indium from copper flash furnace electrostatic precipitator dust via hydrometallurgical processing

Abstract

Copper flash furnace electrostatic precipitator (FF ESP) dusts contain significant amounts of copper, as well as bismuth, lead, arsenic, cadmium and the critical element indium. Disposal of dusts results in losing the copper values, but recycling the dusts directly back to the smelting furnace creates recirculation loads of elements problematic to downstream operations. Avoiding the reintroduction of such deleterious elements, particularly bismuth, requires processing the dust. FF ESP dust treatment also presents further advantage, as it provides an opportunity for the recovery of cadmium and indium used in thin film solar energy generation essential to the green energy transition. FF ESP dust is a complex material, with numerous elements in a range of different phases. The primary economic motivation for dust treatment is the selective leaching of copper away from bismuth, lead and arsenic. Most previous methods make use of water or sulfuric acid, achieving varying degrees of success. A novel ammoniacal flowsheet was developed to selectively leach copper and cadmium away from bismuth, lead, arsenic, iron, and indium. Treatment of the leachate for copper precipitation and ammonia regeneration necessitates the use of a bleed stream, from which cadmium is recovered. Combining this cadmium with tellurium to form CdTe was performed, turning a hazardous metal into a source material for renewable energy technologies. The residue of ammoniacal leaching contains bismuth, lead, arsenic, iron, indium, and the remaining copper, which undergoes further treatment with NaCl and H2SO4. Previous methods using H2SO4 alone recovered bismuth, but the addition of NaCl enabled to simultaneous removal of lead into the solution. This leachate is the most enriched indium stream, however further investigation is necessary for indium recovery. Economic analysis of the process based upon ammoniacal leaching was compared to an alternative, with cost estimates calculated based upon METSIM process modeling of both the proposed and previous flowsheets. The ammoniacal flowsheet developed was economically competitive with the alternative for the conditions evaluated, with the added benefit of providing an outlet for cadmium recovery and indium enrichment.