| The continuous development and utilization of low mineral resources leads to the decrease and exhaustion of high quality resources,which makes the development of resources face severe security,environmental protection and economic problems.Low cost green filling mining is the inevitable trend of resource development.The cemented tailings backfill with cement has high cost,poor economic benefit,low filling strength,high slurry viscosity and large pipeline transportation resistance,which are the main factors restricting the popularization and application of tailings cemented filling.Using low-quality solid waste to develop low-cost green filling cementitious material can not only effectively reduce the filling cost and promote the popularization and application of full tailings filling mining technology,but also explore a new way for the large-scale and high-value utilization of low-quality solid waste.In view of the problems of high filling mining cost and poor solidification effect of Huangtupo copper zinc mine of Xinjiang Xituo mining,this paper uses low-quality solid wastes such as slag,fly ash,magnesium slag and desulfurization gypsum in Hami area of Xinjiang to carry out the research on the development and filling application technology of fly ash-slag(FS)cementitious material.This paper carries out the following research work:(1)The field investigation,sampling analysis and quality evaluation of metallurgical slag of Da'an company and fly ash solid waste of power plant in Nanhu area of Hami,Xinjiang were carried out.In view of the low activity and poor quality of slag,the researches on activation and modification of physical and chemical activation were carried out respectively,and the activity of low-quality slag was increased to the requirement of S95 powder,which laid the foundation for the development of fly ash-slag(FS)composite cementitious materials.(2)Using clinker and desulfurized gypsum as composite activator,the proportioning test of clinker based FS composite cementitious material(ClinkerFly ash-Slag,CFS)was carried out.On the basis of exploratory experiments,researches were carried out on the optimization of the ratio of two clinker-based CFS cementitious materials with fly ash content of 40%and 45%(CFS-40 and CFS-45)respectively.The optimized proportion of CFS-40 was obtained as follows:40%fly ash,12%cement clinker,8%desulfurization gypsum and 40%modified slag.The strength of 7d and 28d are 1.69 MPa and 3.01 MPa respectively,and the material cost is ?160/t.The optimized proportion of CFS-45:45%fly ash,10%cement clinker,8%desulfurization gypsum and 37%modified slag powder.The strength of 7d and 28d are 1.581 MPa and 2.769 MPa respectively,and the material cost is ?155/t.(3)Based on the research of CFS cementing materials,in order to further reduce costs,magnesium slag was used to replace cement clinker and part of slag,that is,magnesium slag and desulfurized gypsum were used as composite activators to develop Magnesium-Fly ash-Slag(MFS)composite cementing materials.Through proportioning test and expansion test,the content of magnesium slag was determined to be 25%and 30%(MFS-25 and MFS-30),and the test and proportioning optimization of cementitious materials were studied by BP neural network.Through comprehensive analysis,it was determined that the optimal ratio of MFS cementitious material is:fly ash 40%,magnesium slag 30%,desulfurization gypsum 12%,modified slag powder 18%.The 7d strength and 28d strength meet the requirements respectively,and the material cost is ?82.62/t.(4)The hydration products and hydration mechanism of MFS cementitious materials were studied.By means of XRD,TG-DSC,FTIR,SEM and MIP,the types,micro morphology and structure of hydration products of MFS cementitious materials were studied,and the multiple coupling excitation mechanism of MFS cementitious materials was revealed.The results showed that the hydrated products mainly consisted of pine needles or elongated ettringite,amorphous C-S-H and CA-H gel.With the growth of curing age,ettringite and C-S-H gel are generated in large quantities,interlaced with each other and filled in the pores,which gradually reduces the number of harmful and multi-harmful pores and forms a dense network structure.Porosity gradually decreases,and the density of the gelling system gradually increases,as well as its strength.(5)Aiming at tailings-Gobi sand and tailings two kinds of filling aggregates,the preparation of MFS cementing material filling slurry was carried out,and the strength of the backfill,the working characteristics of the slurry and the rheological characteristics of the different slurry ratios were tested and analyzed respectively.The influence law of each factor was discussed,and the strength prediction model of the cemented backfill was established based on the strength test results.At the same time,the variation law of the slurry resistance along the pipe diameter and the average flow velocity was explored.The results show that filling slurry prepared by MFS cementitious material has good performance in terms of the strength of the backfill,the slurry fluidity stability.The cement sand ratio and slurry concentration are positively correlated with the strength of filling body.Proper addition of Gobi sand coarse aggregate can significantly improve the strength of backfill.The strength prediction model of MFS cemented backfill for 7d and 28d are as follows:R7d=0.167·?0.199·?0.289·Cw-4.59?R28d=0.502·?0.042·?0.225·Cw-17.20.The fluidity of filling slurry becomes worse with the increase of concentration,while the stability increases gradually.The rheological parameters of filling slurry are positively correlated with mortar ratio and negatively correlated with slurry concentration.The pipeline transportation resistance of filling slurry increases linearly with the increase of slurry velocity.(6)According to the test results of MFS cemented backfill strength and slurry fluidity,combined with the specific requirements of Xituo mine,the entropy weight multi-attribute decision-making model was used to optimize the slurry preparation parameters,and the slurry preparation parameters are obtained:Gobi sand/tailings=2:8 mixed aggregate,cement sand ratio 1:6 and mass concentration 72%.The semi industrial test is carried out with Xituo filling system.The results show that the strength,slurry fluidity and stability of the cemented backfill of MFS cementitious material meet the requirements of the mine,with low cost and significant economic and environmental benefits,which lays a foundation for the large-scale industrial application of MFS cementitious material in Xituo mine. |
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