Research On Preparation And Activation Of Lead-zinc Tailing Based Alkali-activated Cementitious Material

Lead-zinc tailings are solid waste generated during the flotation process of lead-zinc mines.Concentrated storage can be harmful to the ecological environment.Therefore,the resource utilization of lead-zinc tailings has become a hot research direction for metal tailings treatment in recent years.Lead-zinc tailings are rich in elements such as Si,Ca,and Al.They can generate cementitious materials under the action of alkaline activators.This article studied a method of preparing alkaline-activated cementitious materials with lead-zinc tailings as the main raw material.The experimental lead-zinc tailings were taken from the Shenxiandong tailings dam in Jianshui,Yunnan.They are rich in Si,C,Ca elements,and low in Al content.Dolomite is the main mineral component of lead-zinc tailings,and they also contain quartz,calcite,and a small amount of silicoaluminate minerals.The average particle size（D50）of lead-zinc tailings is 59.71μm,and the particle size distribution is uneven with a dispersion of 3.26.The microscopic morphology of lead-zinc tailings particles is relatively regular,mostly in long block structures,with smooth and flat surfaces and clear crystal characteristics.The leaching concentrations of Pb and Zn heavy metals in the original lead-zinc tailings reached 66.593 mg/L and 519.724 mg/L,respectively.The main work and conclusions of this article are as follows:（1）Lead-zinc tailings were used as the main raw material,supplemented with slag,steel slag,and fluorogypsum,and activated by sodium silicate to prepare a lead-zinc tailings-based alkali-activated binder.An L₉（3⁴）orthogonal experiment with three factors and four levels was designed to determine the optimal preparation conditions:sodium silicate modulus of 1.8,sodium silicate dosage of 15.0%,and tailings dosage of 70%.After curing for 3d,7d,and 28d,the compressive strength of the alkali-activated binder was 4.10 MPa,9.32 MPa,and 18.94 MPa,respectively,and the leaching concentrations of Pb and Zn were only 0.007 mg/L and 0.098 mg/L,respectively,indicating good mechanical performance and environmental safety.After treatment with sodium silicate,the tailings produced a three-dimensional network of hydration products,including C-S-H and silica-aluminate polymers,which formed a dense overall structure covering the mineral surfaces and providing the strength of the solidified material.In the initial reaction stage,minerals such as quartz rapidly dissolved in the alkali to form C-S-H and silica-aluminate polymers.Carbonate minerals,such as calcite,dissolved at a slower rate and participated to a lesser extent in the hydration reaction,leading to lower early strength of the lead-zinc tailings-based alkali-activated binder.In the later stages of the reaction,the dense network structure encapsulated minerals with lower contents,such as quartz,preventing them from reacting with the alkali activator.The newly formed hydration products were mainly hydrated silicate gels generated by the reaction between calcite and the alkali activator.Pb and Zn in the original tailings were fixed in the lattice of the hydration products,mainly in the form of residues,with low environmental risk.（2）Thermal and mechanical activation treatments can significantly enhance the activity of lead-zinc tailings.Characterization test results show that the surface electron binding energies of elements in the tailings are affected by activation treatment.The electron binding energies of Si,Ca,and Al in thermally activated tailings are significantly lower than those in the original tailings.Mechanical activation can reduce the electron binding energies of Si and Al in the tailings,with no significant effect on Ca binding energy.The chemical bonds of minerals such as quartz in the activated tailings are lowered or broken,and their crystal structures are destroyed.Thermal activation treatment can decompose carbonate minerals such as calcite in the tailings,generating oxides such as Ca O,and improving the solubility of Ca and Mg in the alkali activator.Mechanical activation can significantly reduce the particle size of the tailings and increase the contact area for hydration reactions.（3）The compressive strength of the lead-zinc tailings-based alkali-activated cementitious materials prepared using activated tailings was significantly improved.Under the condition of thermal activation at 1000℃,the compressive strength of the alkali-activated cementitious materials cured for 3 d,7 d,and 28 d can reach 22.68 MPa,26.68 MPa,and 28.05 MPa,respectively.The early compressive strength of the material was significantly improved.A large amount of amorphous gel was generated inside the thermally activated alkali-activated cementitious materials during the initial curing stage,and the gel substances were tightly bound to each other,forming a large area network structure that covers and encapsulates the tailings to form a dense whole.After ball milling the tailings for 60 min,the compressive strength of the alkali-activated cementitious materials prepared was 7.09 MPa,16.83 MPa,and 24.02 MPa after curing for 3 d,7 d,and 28 d,respectively.The early compressive strength of the mechanically activated alkali-activated cementitious materials was not significantly improved.The optimal activation conditions for the lead-zinc tailings-based alkali-activated cementitious materials were obtained through a response surface experiment design,which were as follows:thermal activation temperature=1060℃,ball milling time=66 min,and curing temperature=40℃.The compressive strength of the alkali-activated cementitious materials prepared under this activation condition was 23.58MPa,32.71 MPa,and 37.84 MPa after curing for 3 d,7 d,and 28 d,respectively.After28 days of curing,the leaching concentrations of Pb and Zn were only 0.103 mg/L and0.211 mg/L,respectively.