Smelting of various steel-plant dusts to evaluate recovery of zinc and iron via the Enviroplas^TM process

Abstract

Abstract Steelmaking plants are associated with the generation of large quantities of dust streams from unit processes such as the blast furnace, electric arc furnace, basic oxygen furnace, and argon-oxygen decarburisation furnace. The dust streams are commonly recycled to the smelting process step (in-process recycling). In-process recycling of dust results in the build-up of zinc and other volatile heavy metals such as lead, arsenic, and cadmium, which renders the dust unsuitable for further recycling. The unsuitable dust is either discarded in landfills or temporarily stockpiled pending further processing. If the dusts are stockpiled for extended periods, they tend to pose operational challenges. A cost-effective solution is needed to avoid long term stockpiling of these materials. Mintek developed the Enviroplas TM process to treat such technogenic materials to recover valuable metals and generate a non-hazardous slag by-product. A large pilot smelting campaign was completed in a 1 MW electric arc furnace to demonstrate the recovery of zinc-rich dust and pig iron, as well as an innocuous slag from the processing of various steel-plant dusts via the Enviroplas process. The test work was undertaken as a feasibility study for Australian steelmaker, BlueScope, to evaluate the Enviroplas process as a suitable technology for treating historical stockpiles and new arisings of dust from their steel plant in Port Kembla. The test work demonstrated that zinc-rich dust with 63–75 % ZnO, pig iron with 94–98% Fe, and a non-hazardous slag can be produced from the various steel-plant dusts. It was noted that minor operational improvements such as a better feed system design to limit the carryover of feed dust into the gas stream, and efficient control of the bag plant extraction to better define the suction pressure at the gas offtake, can further improve the grade of ZnO in the product dust stream.