Research On Key Technologies For The Preparation Of Mineral Admixtures And Recycled Aggregates From Iron Ore Tailings

Low-silicon iron ore tailings ultra-fine sand was taken as the research object and studied from two aspects.For one thing,three activation methods were used to activate iron ore tailings in order to prepare iron ore tailings powder,which can be utilized to prepare concrete as mineral admixtures.For another thing,studies were carried out to explore the feasibility of using iron ore tailings as aggregates in cement-based materials.Firstly,iron ore tailings as fine aggregates were used to prepare concrete.Then improved pelletizing technology was employed to prepare iron ore tailings-based recycled coarse and fine aggregates that referred to as recycled aggregates,which were applied to prepare mortar and concrete respectively.Firstly,three activation methods were used to activate iron ore tailings,which included mechanical activation,mechano-chemical activation,and mechano-thermal activation.By testing the particle characteristics,specific surface area and activity index of iron ore tailings powder,and hydration heat of iron ore tailings powder-cement system,results show that when grinding time is 30minutes,the dosage of organic grinding aid triethanolamine and chemical activator calcium hydroxide are 0.050%and 3.0%of iron ore tailings mass,respectively,and their 28 days strength activity index are 76%and 74%,respectively.Mechano-thermal activation has no obvious effect on improving pozzolanic activity of iron ore tailings,so this activation method is of little significance.The maximum dosage of iron ore tailings powder with best activity is 30%when the concrete is prepared,and its 28 days compressive strength is 58.1 MPa,which is 2.3%higher than that of reference concrete.Secondly,iron ore tailings were compounded with natural sand to form compound sand that meets the current standard.When the dosage of iron ore tailings sand is 10%～20%,the compressive strength of concrete at different ages are all higher than those of reference concrete.The concrete mixed with 10%iron ore tailings sand generates plenty of hydrated cementitious substances,which significantly reduce the number of micro-cracks and porosity of the system,so the structure is denser than reference concrete.Finally,the improved pelletizing technology was utilized to prepare recycled aggregates,suitable preparation conditions of which are:the concentration of surface pretreatment solution is0.5%～1.0%of cement mass,the mass ratio of cement to iron ore tailings sand is 5:8 and the crushing indexes of recycled coarse and fine aggregates by standard curing are 5.1%and 5.3%,respectively,and the water absorption rate of the both aggregates are 7.7%.Except that the gradation does not meet the standard,other properties of recycled fine aggregate do.Recycled fine aggregate and natural sand are compounded into a grade-matched compound sand,when the replacement rate of recycled fine aggregate is 10%,the 28 days compressive strength of the mortar is 56.8 MPa,which is 2 MPa higher than that of reference mortar.The microscopic morphology and pore structure of recycled coarse aggregates under different curing methods were analyzed through scanning electron microscope（SEM）and mercury intrusion porosimeter（MIP）test.The water absorption rate of recycled coarse aggregates by CO₂ curing is the smallest,and the crushing index of steam-cured recycled coarse aggregates is the smallest of all curing methods.