Study On The Collaborative Preparation Of Filling Materials With Low Quality And Multi-solid Wastes And Their Pressure Drop In Pipeline Transportation

At present,high quality blast furnace slag have been fully developed and utilized.In contrast,steel slag,copper tailings and other low quality solid wastes have a low utilization rate due to the technical difficulties and poor economic benefits.With China’s efforts to strengthen environmental protection,backfill mining is vigorously promoted,particularly the technology of cemented tailings backfill which provides an excellent opportunity for the recycle of low quality solid wastes.Therefore,this paper studies the utilization of low quality solid wastes in backfill mining.This article focused on backfill cementitious material development with low quality solid wastes as well as backfill slurry performance improvement with solid waste aggregate addition.The procedure is focused on the low reactivity and fine particle size improvement for the solid wastes.The optimal mixing ratios of the cementitious material and aggregates are obtained.Besides,experimental study on pipeline flow ability and friction head loss of the mixture was carried out.The main research contents and results of this paper are as follows:Firstly,a cementitious material using low quality and low-reactive steel slag and desulfurization gypsum was carried out in collaboration with high quality slag.The filling body strength at 28d curing is 1.4 times than that of the ordinary portland 42.5 cement.Additionally,a binder material with large amount of steel slag(50%)addition was developed,which meets the strength requirements for the subsequent second step backfilling.The utilization rate of low-quality solid waste exceed 70%,while the cost is less than 50%than that of cement.Furthermore,another fly ash binder material was developed for backfill with the cost of only 70%of that ordinary Portland 42.5 cement.Secondly,in order to inspect the hydration mechanism of the developed binder materials,tests of XRD,TG/DTG,SEM and mercury injection experiment were carried out to reveal the hydration products,micro structure and filling body pore development of the two binders respectively.The results show that the difference of hydration products in cementitious materials has little contribution to the strength,and the influence of component dosage on the strength mainly lies in the pore structure,the threshold size can reasonably characterize the strength of filling body.Thirdly,research on utilization of non-reactive copper nickel slag as filling aggregate was carried out.Tests on filling body strength and grain size optimization with variant copper nickel slag addition were conducted.A strength model was obtained based on the impacts of aggregate density and water cement ration.The Particle Swarm Optimization was applied for mixing proportion optimization.The optimal aggregate of waste rock-copper tailings ratio was obtained,which reduced the cost by 30.5%compared to traditional aggregate of rod mill sand.The slurry has a reasonable bleeding rate and high stability,meeting the flowability requirements of gravity transport of Jinchuan mine.Fourthly,the rheology of the backfill mixture with the developed binder and combined aggregates was studied as well as the friction head loss calculated.The swamee-aggarwal friction factor correlation was used to calculate the pressure drop in the practival application.The results showed that the pressure drop of the mixture was less than that of cement based mixture.The incorporation of low quality fine aggregates can significantly reduce the pressure drop in pipe transport,that is,improving the flowability of the mixtures.Finally,industrial and semi industrial experiments on the applying the backfilling mixtures with low cost solid wastes were carried.Slump,bleeding,fluidity,and segregation properties were inspected with the impacts of solid waste adding amount.A particle-fluid two phase flow numerical analysis was conducted to simulate the pipe flow performance.Furthermore,a L pipe flow and industrial tests in a real backfill system were performed to verify the pressure drop.A relation between the pressure drop and backfill mixture components was established.The relative error of the prediction result of the model was within 4%.To sum up,the utilization of low-quality solid waste in filling mining was studied as cementitious materials and as fine aggregate,the results contribute to exploring a way for low-quality solid waste utilization.