PROCESS SOLUTIONS OF ZINC-CONTAINING WASTE DISPOSAL IN STEEL INDUSTRY

Steel industry can be characterized by a significant amount of by-products including fine dust (up to 1.5% of heat size). Dust of gas cleaners, containing above 0.5% Zn and 50% Fe, cannot be directly returned to basic melting facilities due to high contents of zinc that destroys its lining. High consumption of reducing agent, furnace lining corrosion, final product of high impurities content made difficult use of hydrometallurgical processing. Use of hydrometallurgy technologies is held back by zinc in dust, primarily, as ferrites that cannot be opened using alkali, while acids make iron transfer into solution. As a result, major part of smelters stockpiles the dust. Secondary deposits of zinc-containing steelmaking dust can be involved into processing thus expand the feedstock of zinc industry, increase efficiency of steel making and reduce negative impact on environment. The paper contains chemical and mineralogical analysis of steel dust sample from PAO Severstal and study results on hydrometallurgical extraction of zinc from dust using salt solution. It has been established that ammonium chloride leaching of zinc from electric arc furnace dust takes place within external diffusion region; optimum parameters of ammonium chloride leaching can result in almost complete and selective extraction of zinc into solution and producing ferrous cake that is applicable for blastfurnace processing. It was revealed that higher level of zinc ferritization in leach has minor negative impact on zinc extraction into solution and keeps minimum iron transfer into solution. Zinc can be extracted from leach solution by zinc hydroxide deposition using ammonia stripping, followed by drying and deposit calcination to produce saleable zinc oxide.