Study On The Mechanism Of Synergistic Activation Of Lead And Zinc Tailing/Metallurgical Slag And The Preparation Of Filling Material For Mine Goaf

Mineral resource is an important base of a country's economic development.However,the goaf formed after mining has become a main potential safety hazard of mining subsidence,which needs to be filled as soon as possible.Meanwhile,the tailings and the metallurgical slags around the mining area is not only a serious damage to the ecological environment but also a waste of land resources.Studies on the application of the tailings and metallurgical slags in the preparation of cementing material that could fill the goaf will be a developing demand of “dealing with harm by waste”.A novel type of goaf filling material was prepared by using lead-zinc tailings and lead-zinc metallurgical slags in this research.Performance optimization,mechanism of gel strength,dissolution behavior of Pb²⁺ and the fixation of Pb²⁺ by the filling material were studied.The main results of this paper are listed below.The phase characteristics of lead-zinc tailings and metallurgical slags from Guangdong Fankou were studied.The main phases of lead-zinc tailings are quartz and kaolinite,the dominant chemical compositions of which are Si O₂ and Al₂O₃,and the content of quartz is relatively high.The main elements and oxides contained in the metallurgical slags are FeO,CaO,Al₂O₃,MgO and Si O₂.They existed as alpha quartz,wustite,and calcium aluminum oxide hydrates,which show potential hydraulic cementing property.The effect of mechanical activation and chemical activation on the cementing performance of the filling material prepared by using lead-zinc tailings and metallurgical slags was studied.It was found that simply relying on mechanical activation could not meet the requirements of the strength properties.Chemical activation was necessary.Four alkali activators were studied,and Na2SiO3 was chosen.With the increasing amount of Na2SiO3,the bending strength and compressive strength of earlier stage increased as well;nevertheless,the bending strength and compressive strength of later stage decreased.In order to improve the gel strength,a combined activator was used,which was composed of gypsum and Na2 Si O3 with a mass ratio of 5:6.The results showed that the bending strength and compressive strength of earlier stage could reach up to 2.37 MPa and 11.04 MPa,and those of later stage could reach up to 5.52 MPa and 32.68 MPa,respectively.The gelatinization and hydration process of the filling material was discussed.It was believed that a hydration film would form on the surface of the raw materials once Ca?OH?₂ was produced during the hydration of cement clinker.Ca?OH?₂ would continue to crystallize to form a thin alkali film solution.Due to the activation of the alkali solution,the pozzolanic reaction started on the surface of the tailings and metallurgical slags,and resulted in partial C-S-H gel and ettringite.With the increasing of time,the thin alkali film continued to extend to the inner parts as an activator until the hydration of the active minerals was done.The dissolution behavior of Pb²⁺ contained in the lead-zinc tailings,slags and the gel material was studied as well.When the pH value was the same,in order of the fixation ability of Pb²⁺,it goes: the composite gel material,the lead-zinc tailings and the slags.The amount of Pb²⁺ dissolved from the above three matrices all decreased when the pH value went up.The dissolution amount of Pb²⁺ could remain at a low level?about 0.90mg/g?in a large pH scale?pH?7?,which was particularly conducive to controlling the influence of the dissolution of Pb²⁺ on the natural underground water.The mechanism of the fixation was supposed to be the coordination between Pb²⁺ and silicate ion.Investigating the application of mining subsidence lead-zinc tailings and metallurgical slags solid waste in the preparation of filling materials has vast importance and a number of applications to the high efficiency and comprehensive utilization of tailings and metallurgical slags and environmental protection.