The Utilization Of Alkali-activated Lead-zinc Smelting Slag For Chromite Ore Processing Residue Solidification

China is rich in lead and zinc reserves.The lead-zinc smelting industry is developing rapidly and produced a large amount of smelting slag,which occupied land resources,and the migration of heavy metals in the smelting slag was harmful to the environment.Therefore,attention should be paid to the treatment and resource utilization of lead-zinc smelting slag(LZSS).Because LZSS contains a large number of active ingredients such as SiO₂,CaO,Al₂O₃,it has the potential to prepare alkali-activated materials to solidify hazardous wastes.Chromite ore processing residue(COPR)is an industrial by-product containing highly toxic hexavalent chromium,which needs to be landfilled or reused after harmless treatment.In this paper,LZSS was used as raw material to prepare alkali-activated materials and solidified COPR.Based on the experimental analysis,the following conclusions were obtained:(1)The appearance of LZSS was black particles in different sizes,with a water content of 1.97%,a pH of 8.38,and the main components were SiO₂,Fe₂O₃,CaO,Al₂O₃;the average particle size of LZSS after ball milling was 66.17?m;LZSS mainly contained three kinds of crystals i.e.zinc aluminum iron oxide,zinc oxide,and wustite;the leaching concentration of heavy metals in LZSS did not exceed the critical limits(EPA standards and GB5085.3-2007).The moisture content of COPR was 20.21%,the pH was 11.64,and the main components are Fe₂O₃,Al₂O₃,MgO,and Cr₂O₃;COPR itself had a small particle size and a relatively concentrated particle size distribution,with an average particle size of 56.00?m;COPR had legible crystal peaks,mainly involved magnesiochromite,magnesium chromium oxide,and magnesium aluminum iron oxide;the leaching concentrations of total Cr and Cr(?)in COPR exceed the critical limits(EPA standard and GB5085.3-2007);The size of COPR particles varied,and there were a few lamellar structures and acicular structures.(2)LZSS and alkali activator(water glass and sodium hydroxide)were used to prepare alkali-activated materials.The best conditions were obtained through single factor and orthogonal experiments:alkali content was 2.5%,water glass modulus was1.5,the liquid-solid ratio was 0.19,and the initial curing temperature was 35?,the 28d compressive strength of alkali-activated LZSS(LZAC)reached up to 84.49 MPa.The solidification efficiency of Zn in LZAC reached 67.66%and 94.91%,respectively(TCLP method and sulfuric acid nitric acid method).And the form of Zn shifted from the form with strong migration ability(acid-soluble,reducible,oxidizable)to the more stable form(residual).LZSS reacted with the alkali activator to form C/N-A-S-H gels,forming a dense structure and providing strength to LZAC.Zn was effectively fixed by the formation of crystalline phases,physical fixation,and chemical bonding.(3)Alkali-activated LZSS was used to solidify 0?40%COPR.When the COPR content was 30%,the compressive strength dropped to 26.37 MPa;when the COPR content was 40%,the compressive strength dropped to 1.42 MPa.The leaching concentrations of heavy metals in solidified bodies with COPR(LZC)were lower than the critical limits(EPA standard and GB5085.3-2007).A small amount of COPR(10%)mixed with alkali-activated LZSS could improve the pore structure(total porosity decreased by 8.19%)and reduce the leaching concentration of heavy metals.Excessive content of COPR would destroy the dense structure of the alkali-activated LZSS,resulting in a decrease in strength and an increase in the leaching concentration of heavy metals.Combined with the analysis of pore structure,XRD,FTIR,ESEM-EDS,it was found that heavy metals in LZSS and COPR were effectively fixed through adsorption,reduction,precipitation,formation of crystalline phase,physical fixation,and ion exchange.