| The rapid development of the national economy increases the demand for mineral resources.The problems caused by mining,such as the collapse of the goaf,the accident of the tailings dam collapse,and various environmental pollution caused by the accumulation of tailings,have become more and more serious.Therefore,based on the concept of sustainable development,the government promotes the use of green mining technology.Cemented tailings backfill(CTB)mining technology,which can utilize a large number of tailings to mitigate the hazards of tailings accumulation and reduce the risk of ground collapse in the goaf,has become the green mining technology adopted by a large number of mining enterprises.CTB mining technology has attracted the attention of relevant scholars.Currently,the research of tailings binders is an important research content in the field of cemented backfill technology.The application of tailings binders is mainly limited by cost and performances in CTB mining technology.The cost of CTB is generally high.Especially,when the ultrafine tailings with high moisture content are used in CTB,the cost rises sharply.When the moisture content and fine particle content of the tailings are too high,it has a significant negative influence on the workability and stability of fresh CTB.When general binders are used in CTB with ultrafine tailings with high moisture content,the UCS of hardened CTB cannot meet the requirements of the CTB mining.In this paper,the type of binders suitable for ultrafine tailings with high moisture content were designed and optimized.Then the particle size distribution of CTB was modified and chemical admixtures were added to improve the performances of CTB,and binders with improved performances were designed.The mechanisms of binder improved the workability of fresh CTB and binder cemented and solidified tailings were clarified,which indicated the direction for the design and optimization of binders with improved performances.The main research content of this thesis includes the following aspects.(1)types of binders suitable for tailings were designed and optimized.In order to seek the binders suitable for ultrafine tailings with high moisture content,the physical and chemical properties of the tailings are charaterized,and three types of binders are selected for tailings bindering texts based on the CTB evaluation system.The type of slag-based binders suitable for the tailings was selected via the comprehensive evaluation of performances of CTB.Furthermore,the type of slag-based binders was further optimized by adjusting the parameters of the binders and improve the performances of slag-based binders.The UCS of hardened CTB made by the slag-based binders on 3d,7d and 28 d age was 0.32MPa?0.52 MPa and 0.72 MPa,with satisfied workability and stability of fresh CTB.(2)The slag-based binders were modified by physical and chemical methods,and two slag-based binders with improved performances were designed.In order to further improve the performances of slag-based binders,the particle gradation adjustment and chemical activation methods were used to modify the binders.The particle gradation of CTB made by slag-based binders was adjusted by the incorporated coarse-grained material ceramsite and super absorbent polymer(SAP),medium-grained material ground quartz sand and fine-grained material bentonite and ultrafine cement and slag of slag-based binders.It was found that the method of adjustment of particle gradation modification by ultrafine slag can significantly improve the mechanical properties of hardened CTB and stability of fresh CTB.The binders were chemically activated by adding quicklime,desulfurized gypsum,sodium sulfate and alum in the binders.It was found that Sodium sulfate has a good activity effect on the slag-based binders,and desulfurized gypsum can improve the UCS of hardened CTB on early age.Based on the modification effects,the design idea of slag-based binders with improved performances was proposed,and two slag-based binders with improved performances were designed.It was found that the CTB prepared by the slag-based binders with improved performances had excellent mechanical properties which met the requirements of UCS of hardened CTB,and had better workability and stability.More importantly,the slag-based binders with improved performances had high cost performance.(3)The microscopic composition and structure of the CTB and their relationship with the macroscopic performances of the CTB were analyzed,and the improvement mechanism of workability of fresh CTB made by slag-based binders and the hardening mechanism of hardened CTB caused by the slag-based binders were explored.The Zeta potential and resistivity of the fresh CTB were characterized,and their effects on the workability and stability of fresh CTB were studied.It was found that the slag-based binders with the same symbol of positive or negative of Zeta potential as the tailings in the fresh CTB improved the workability and stability of fresh CTB,which was conducive to improving the mechanical properties of hardened CTB.The hydration process of the slag-based binders,the composition of the hydration products of the slag-based binders,and the microstructure and morphology of hardened CTB were characterized,and their relationship with the mechanical properties of hardened CTB was clarified.It was found that large amounts of C-S-H gel,ettringite,calcium hydroxide and other hydration products,which were generated by the hydration reaction of the binders in the hardened CTB,overlapped and cross-linked with the tailings to form a microscopic network structure,which improved the UCS of hardened CTB.In this research,based on the ultrafine iron ore tailings with high moisture content and requirement of low binder-sand ratio(1:8)for preparation of CTB,slag-based binders with improved performances were prepared.The improvement mechanism that the slag-based binders improved the workability of fresh CTB and the hardening mechanism that the slag-based binders cemented the tailings to form the hardened CTB were clarified.The results can provide theoretical foundation and technical support for the CTB with a larger amount of ultrafine tailings with high moisture content,and effectively promote the green mining technology,resulting in numerous economic,social and environmental benefits. |
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