Study On Solidification Mechanism Of Antimony-containing Tailings By Using BFS-SS-FGDG Based Cementitious Materials

In the Nandan mining area,Guangxi Province,China,there are many disorderly stacked non-ferrous metal tailings and unstable tailings reservoir,which seriously damage the ecological environment of the surrounding area and is the primary source of heavy metal pollution in the Diaojiang River basin,especially antimony pollution.In order to reduce and recycle industrial solid wastes,this paper adopted ground granulated blast furnace slag(BFS),basic oxygen furnace steel slag(SS)and flue gas desulfurized gypsum(FGDG)industrial solid wastes as cementitious materials and antimony-containing tailings as aggregate to prepare backfill materials.The mechanical performances of the backfill material were investigated according to the Chinese national standard GB/T2419-2005 and GB/T17671-1999.The static and semi-dynamic leaching teats were employed to investagate the leaching characteristics of antimony.The hydration mechanisms of the industrial solid waste-based cementitious materials were investigated to reveal the potential influences of antimony incorporation on the hydration schemes of industrial solid waste-based cementitious materials.By synthesizing the doped AFt,AFm,C-S-H gel,the solidification mechanisms were deeply investigated.Meanwhile,the roles of the prepared hydration products on the adsorption mechnisms of Sb(Ⅴ).When the content of FGDG was fixed at 10%,the fluidity and compressive strength of slurry in each ratio met the backfill requirements.When the BFS to SS ratio was 2:1,the leaching concentration of Sb in samples of different curing ages was lower than that of the cement control group.Leaching test results indicated that the leaching mechanism of Sb in the backfill materials was mainly diffusion control.The results showed that the immobilization effect of AFt,C-S-H gel,and AFm on Sb(Ⅴ)is AFt<C-S-H gel<AFm.With the increase of Sb(Ⅴ)incorporation,AFt structure became loose and lost the rod-like structure,C-S-H gel polymerization degree decreased,and AFm gradually dissolved and transferred into AFt.In addition,the immobilization mechanism of BFS-SS-FGDG cementitious materials system was the result of multiple mechanism of adsorption,physical package and crystallization,and the reaction between Sb(OH)6-and Ca2+to generate calcium antimonate with low solubility.The immobilization mechanism of AFt treated Sb(Ⅴ)mainly involved the adsorption of Sb(Ⅴ)on the columnar surface of AFt calcium aluminate.The immobilization mechanism of C-S-H gel treated Sb(Ⅴ)involved adsorption.The immobilization mechanism of AFm treated Sb(Ⅴ)mainly involved the entrance of Sb(OH)6-into the interlayer of AFm to form AFm-Sb phase.The experimental results of single mineral adsorption performance indicated that the adsorption capacity of AFt and AFm increased with the increase of pH value of the solution,and the optimal adsorption pH value was 12.The adsorption capacity of C-S-H gel decreased with the increase of pH value of the solution,and the optimal pH value of adsorption was 10.Increasing the reaction temperature was beneficial to improving the adsorption performance of AFt and C-S-H for Sb(Ⅴ)but had a marginal effect on the adsorption capacity of Sb(Ⅴ).The experimental results of single mineral adsorption kinetics exhibited that the quasi-second-order kinetic model had a excellen fitting effect on AFt,C-S-H and AFm.The adsorption of AFt,C-S-H gel and AFm on Sb(Ⅴ)was a process of coexistence of chemisorption and physical adsorption,in which AFt and AFm were dominated by chemisorption The experimental results of single mineral isothermal adsorption model exhibited that Langmuir,Freundich and D-R isothermal adsorption models had good fitting effects on AFt,C-S-H gel and AFm adsorption of Sb(Ⅴ).The adsorption stability of the single mineral was AFt<C-S-H gel<AFm,and the adsorption reaction is spontaneous.