Preparation And Performance Control Of Low Alkali Backfill Materials Based On Activity Optimization Of Fine-grained Tailings

With the continuous exploitation of mineral resources,the quality of ore continues to decrease.The exploitation of low-grade ore produces a lot of fine-grained tailings.The utilization of fine-grained tailings is difficult and the utilization rate is low.The storage of fine-grained tailings has high-security risks and occupies a lot of land resources.Therefore,using fine-grained tailings to prepare backfill materials with high workability,high strength,and low environmental load is an effective way to promote efficient and green production in mines,and it is also an inevitable requirement to promote social "green development,circular development,and low-carbon development".This paper is based on the National Nature Fund "Rheological properties and consolidation behavior of green disposal of metal ore full tailings paste",and the horizontal project“Study on the preparation of high value-added materials by comprehensive utilization of fine tailings of baixiangshan iron mine".In this paper,aiming at the high-efficiency,green and high-performance backfill of fine-grained tailings,on the basis of the optimization study on the activity of fine-grained tailings,low-alkali composite cementitious materials(KPM)were prepared from multi-component solid wastes such as slag and phosphogypsum,the theoretical models of compressive strength and alkali dissolution of KPM were established,and the hydration hardening mechanism of KPM was revealed.The problems of poor mechanical properties,segregation and bleeding of backfill materials prepared by fine tailings were solved,and the performance control method of backfill materials prepared by KPM and fine tailings was put forward.The curing method and mechanism of alkaline ions were clarified,and the backfill materials meet the requirements of service safety and environmental protection.The main research contents and conclusions are as follows:(1)The composition and surface characteristics of screened and unscreened fine tailings were studied by X-ray diffraction(XRD),Fourier transforms infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),and Zeta potential analysis.In the process of ultra-fine grinding of tailings,the crystal structure of minerals such as biotite and chlorite is destroyed,resulting in a large number of Si-O and Al-O bond breakage and lattice defects,and the number of surface charge increases,which improves the activity index of fine tailings.The activity index of unscreened tailings is 70.1%,the increase of fineness of tailings to the activity index is limited,and the activity index of 0-0.045 mm graded iron tailings is only 77.8%.Through the coupling excitation of OH-and SO42-and the synergistic effect of mineral powder,a large number of ettringite and silica-alumina gel minerals are formed,and the activity index can reach 95.1%.(2)Based on the experimental results of the effects of lime,desulphurization gypsum,ordinary Portland cement(OPC),and mineral powder on the activity index of fine tailings,and the effects of magnesia,phosphogypsum and potassium dihydrogen phosphate on the compressive strength of cementitious materials,through orthogonal experimental design and response surface interaction model.The effects of the interaction of single material and multiple materials on the compressive strength of cementitious materials and the pH value of solution after 28 days of curing were studied,and the prediction models of compressive strength and pH value were obtained.the experimental values were consistent with the predicted values,and the optimal ratio of KPM was obtained.The mass ratio of slag:OPC:lime:desulphurization gypsum is 82:3:6:9,magnesium oxide replaces 20%lime,and phosphogypsum replaces 75%desulphurization gypsum.The cementitious material prepared with a molecular ratio of magnesium oxide to potassium dihydrogen phosphate with a molecular ratio of 24:1 has the highest compressive strength and lower pH value after 28 days of curing.(3)The hydration mechanism of KPM was analyzed by scanning electron microscope(SEM),XRD,FTIR,inductively coupled plasma emission spectrometer(ICP),and heat of hydration.Under the excitation of OH-and SO42-,Ca2+,Mg2+,[AlO2]-and[SiO4]4-in the slag are dissolved,ettringite,C-A-S-H gel,hydrotalcite and other products are formed by hydration reaction,and a small amount of K-struvite is formed under the action of PO43-.With the increase of hydration age,the number of Ca(OH)2 decreases and the number of other hydration products increases.Different hydration products interweave into a dense structure to fill pores.Increase the compactness,improve the expansion rate and enhance the volume stability.(4)Based on the study of fine tailings backfill,polycarboxylic acid superplasticizer(PCE)and ternary copolymerized modified sodium polyacrylate(PAAM)with high carboxyl density were prepared,and composite inorganic salts and ultra-fine glass beads were mixed as admixtures.After adding admixture,the bottom flow concentration of fine-grained tailings is increased by 3-4%,the bleeding rate of fine-grained tailings backfill material is reduced by 10%,and the transportation and mechanical properties are significantly improved.at the same time,reduce the environmental sensitivity of the backfill material and improve the adaptability of hydration time.Through the analysis of X-ray-computed tomography(X-CT),organic carbon adsorption(TOC),and Zeta potential,it is clear that the admixture can improve the performance of the backfill material by increasing the water conduction path,increasing the electrostatic repulsion and steric hindrance,generating ettringite and consuming free water.(5)Through ion dissolution and pH dynamic monitoring of different systems,sulfate resistance,and life cycle analysis,the environmental compatibility of backfill materials prepared by KPM and fine tailings was studied.By adding phosphogypsum and potassium dihydrogen phosphate to neutralize Ca(OH)2 in the hydration system and produce insoluble Ca3(PO4)2 and Ca(PO3)2 which is beneficial to plant growth,the alkali dissolution of backfill material is reduced and the harm to the environment is reduced.The backfill material prepared with KPM and fine tailings has lower porosity and better sulfate resistance.The impact of KPM-CPB on the environment is quantified by life cycle assessment.Compared with the backfill materials prepared by OPC,the impact of global warming and particulate matter emissions can be reduced by more than 70%.Comprehensive analysis of KPM-CPB has good environmental compatibility.