Study Of Evolution And Mechanism Of The Strength To Sulfur Content Lead-zinc Tailings Cemented Paste Backfill

With the increase of lead-zinc production,the problems of tailings disposal have seriously affected the sustainable development of lead-zinc mining.Tailings cemented paste backfill(CPB)is considers to be one of the best model for mining.High sulfur content is an obvious characteristic of lead-zinc tailings.The long-term strength and stability of high sulfur content tailings cemented paste backfill is an important prerequisite to ensure the safety of mining.Based on the study of lead-zinc tailings in Huludao,Liaoning Province,the paper revealed the evolution and mechanism of the mechanical and chemical properties of sulfur content cemented paste backfill by combining the method of macro-meso-micro experiments.The research not only provided reliable technical parameters for the filling of lead-zinc tailings,but also a necessary basis for the engineering stability.The main research contents and results were as follows.(1)According to the national standards,the basic physical parameters(e.g.,grain size distribution,permeability)and chemical parameters(e.g.,mineral composition,elements composition,static acid potential)of lead-zinc tailings were tested.Orthogonal experiments were carried out to optimize the matching ratio.The influence of the slurry concentration,cement-tailings ratio,fly ash content on the slump,bleeding rate,uniaxial compressive strength(7/28 days)were analyzed.The results showed that the slump and bleeding rate were mainly affected by slurry concentration and the compressive strength was mainly affected by cement-tailings ratio.The optimal matching scheme of lead-zinc tailings cemented paste backfill was that the slurry concentration was 74%,the cement-tailings ratio was 1:6 and the fly ash content was 15%.(2)Experimental study of uniaxial compressive strength and chemical properties of sulfur contents(2%,5%,10%,15%)lead-zinc tailings cemented paste backfill were carried out based on the optimal matching scheme.The long-term evolution laws of mechanical properties(e.g.,failure pattern,compressive strength,elastic modulus)and chemical properties(e.g.,pH of leaching solution,sulfate concentration)were analyzed in 28-360 days curing ages.Results showed that,with the increase of curing ages,compressive strength first increased and then decreased.When the sulfur content was 5%,the pyrite can show the early strength agent in 90 days.After 120 days,the strength decreased with the increase of sulfur content.The elastic modulus range was from 400 to 600 MPa,which had obviously positive correlation with compressive strength.The pH of leaching filtrate first increased then decreased with curing ages and decreased with sulfur content.After 360 days,the pH values were below 7 and lightly acidic.The sulfate concentration first decreased and then increased with curing ages,the higher sulfur content,the higher sulfate concentration.There was a negative correlation between the compressive strength and the sulfate concentration.(3)Mercury intrusion porosimetry tests were carried out with natural CPB specimens and sulfur content of 15% CPB specimens in different curing ages,pore structure characteristics were analyzed and the strength changes mechanism from the mesoscopic view was explored.Results showed that the total pore volume and macropore content increased with the increase of curing ages.The harmful pores of high sulfur CPB specimens were greater than the natural specimens'.The relationship between porosity and compressive strength was linear.(4)Based on SEM and XRD tests,the laws of the types and quantities of hydration products and corrosion products in different CPB specimens were observed and analyzed.The microcosmic mechanism of the strength change was studied.It showed that sulfide corrosion reduced the contents of the cementitious and alkaline minerals,while ettringite and gypsum contents increased significantly.Specimens had rich pore connectivity.Failure mode of high sulfur CPB changed from ettringite gradually damage into ettringite and gypsum composite damage.(5)Combining micro-meso-macro tests results,the dynamic relationship of cement hydration reaction and sulfide reaction to the mechanical and chemical parameters in sulfide CPB was explored.The main difference between sulfide corrosion and sulfate attack was analyzed.Based on the results of the study,the paper put forward some methods for backfill treatment of high sulfur tailings.The compressive strength of CPB had a negative exponential function relationship with its sulfur content and time.