Study On Mechanical-Chemical Activation Process And Mechanism Of High Silicon Iron Tailings Powder

High-silicon iron tailings account for a large part of the existing tailings reservoirs in China.The main feature is that the chemical composition Si O₂is mostly more than 70%,and it has the characteristics of being a volcanic ash raw material.At present,the stockpiling waste of iron tailings is increasing rapidly,and its utilization rate is still not improved in China.In this regard,in order to stimulate the activity of iron tailings to the greatest extent,apply more dosage to building materials,and improve the added value and utilization rate of iron tailings,this thesis aims to better stimulate the potential pozzolanic activity of iron tailings.The effects of mechanical activation and chemical activation of additional activators on the activity of iron tailings were systematically studied,and the hydration and hardening mechanism of iron tailings composite cementitious system was revealed.The results of mechanical activation showed that the particle size changed rapidly 20 min before grinding,and the specific surface area increased rapidly from59 m²/kg to 721 m²/kg.After mechanical activation to 60 min,the specific surface area and particle size change tend to be stable,the particle size distribution is mainly concentrated below 10μm,the particle proportion exceeds 80%,the specific surface area is 1470 m²/kg,and the median D50 is 2.4μm.When the iron tailings with specific surface area of 1470 m²/kg were mixed with 30%mechanical activation for60 min,the highest 28 d flexural strength was 7.1 MPa,the highest 28 d compressive strength was 53.1 MPa,and the activity index was 84.7%.With the progress of mechanical activation grinding,the peak intensity of XRD diffraction quartz peak of iron tailings powder gradually decreases,the FWHM half peak width gradually increases,and the crystallinity of iron tailings gradually decreases.Through the ZETA potential and microscopic electron microscopy images,mechanical grinding will change the particle surface charge,long time grinding will enhance the electrostatic adsorption,aggravate the agglomeration between particles.The chemical activation study of adding activator shows that under the action of single activator alone,sodium carbonate can reduce the surface hardness of particles.The optimum dosage is 1%.At this time,the specific surface area of iron tailings is1504 m²/kg,the 28 d compressive strength of the test block is 54.3 MPa,and the activity index is 86.6%.Sodium silicate can weaken the agglomeration effect,increase the specific surface area of grinding particles,but will reduce the strength of the test block.Calcium oxide will increase the concentration of Ca²⁺in the slurry and the alkalinity of the solution,and accelerate the formation of hydration products.The optimum dosage is 1%,the specific surface area is 1523 m²/kg,the 28 d compressive strength of the test block is 55.8 MPa,and the activity index is 89%.Gypsum can improve the dispersion of particles and can participate in the hydration reaction of Al₂O₃in the system.The 28 d compressive strength of the test block under the optimal yield is 55.4 MPa and the activity index is 88.4%.Under the combined action of two optimal activators,when the activator ratio is 0.5%Ca O+1%Ca SO₄,the specific surface area reaches the maximum value of 1614 m²/kg,and the 28 d compressive strength of the test block is 60.2 Mpa,the activity index reaches the maximum value of 96%,which is significantly improved compared with the mechanical activation activity index.The research on hydration mechanism of iron tailings composite cement cementitious material shows that chemical activation improves the sphericity of particles to a greater extent,enhances the fluidity of the system,and reduces the water demand compared with mechanical activation of iron tailings.The results of XRD analysis show that the hydration products of iron tailings composite cementitious materials mainly include Ca（OH）₂,AFt and C-S-H.In the later stage of hydration,the hydration product Ca（OH）₂undergoes secondary hydration reaction with iron tailings,which weakens the peak intensity of Ca（OH）₂.The DSC-TG results show that through the analysis of weight loss,with the increase of age,the content of C-S-H in hydration products gradually increases,and the content is the highest when the chemical activation is 28 d,and the dehydration endothermic peak of Ca（OH）₂gradually decreases,which also confirms the occurrence of secondary hydration reaction.