Abstract
A new synergistic treatment of stainless steel slag and low zinc content electric arc furnace (EAF) dusts is proposed to immobilize harmful chromium in stainless steel slag. The effects of ZnFe2O4 addition on the mineralogic phase and chromium leachability of CaO-SiO2-MgO-Al2O3-Cr2O3 synthetic slag were investigated to explore the feasibility of this method. The mineralogic phases in stainless steel slag were investigated by scanning microscopy equipped with energy-dispersive spectroscopy and X-ray diffraction. The leaching concentration values of chromium and zinc were evaluated according to an alkaline digestion for the hexavalent chromium (US-EPA-3060A) and toxicity characteristic leaching procedure (TCLP, US-EPA-1311) method, respectively. It was found that all synthetic slags mainly contain α-Ca2SiO4, merwinite and spinel phase, in line with the calculation results by FactSage. The crystallization of spinel and merwinite phases was enhanced by the addition of ZnFe2O4 but suppressed the precipitation of α-Ca2SiO4. It was revealed that the leaching concentration of chromium was depressed by adding ZnFe2O4 and was far below the chemical limits defined in the French proposal for a criterion and evaluation methods for waste ecotoxicity (0.1 mg L−1). In addition, the zinc leaching concentration meets the sanitary landfill standard. The proposed synergistic treatment method was further validated on industrial stainless steel slags and EAF dusts. Experimental results indicated that the synergistic treatment method can immobilize chromium effectively and the final slags can be disposed of by sanitary landfilling or recycling as constructional materials. A schematic technologic route diagram of the synergistic treatment was also proposed.
Highlights
SIGNIFICANT amounts of stainless steel slag that contain harmful chromium are generated during stainless steel production.[1]
We proposed a synergistic treatment method using stainless steel slag and low-zinc-content electric arc furnace (EAF) dusts
To immobilize chromium in stainless steel slag effectively, a synergistic treatment of stainless steel slag and EAF dusts was proposed in this work
Summary
SIGNIFICANT amounts of stainless steel slag that contain harmful chromium are generated during stainless steel production.[1] For a long time, the massive amounts of stainless steel slag were land-filled or stored in slag yards as hazardous solid waste (waste category in China: HW21), which occupied a large amount of land and polluted the natural environment. Previous studies[2] have shown that trivalent chromium in unstable phases among the stainless steel slag could be converted into highly toxic hexavalent chromium in Manuscript submitted September 30, 2019. Continuous leaching of hexavalent chromium can contaminate the surrounding environment, such as soil and underground water.[2] stainless steel slag must be treated harmlessly before being reused or released to the environment
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