Experimental Study On Solidification Of Iron Tailings With Carbonated Steel Slag And Granulated Blast Furnace Slag Powder

At present,China’s granulated blast furnace slag is basically fully utilized,while the utilization rate of steel slag tailings is less than 30%.Over the past three decades,the cumulative stock of steel slag and tailings has reached nearly 2 billion tons.In2019,the national development and Reform Commission and the Ministry of industry and information technology jointly issued a document to actively promote the in-depth research,graded utilization,high-quality and large-scale utilization of steel slag and tailings,so as to fully realize the"zero emission"of steel slag.Therefore,it is of great significance to improve the comprehensive utilization of steel slag and tailings by using carbon dioxide maintenance system,whether from the secondary utilization of resources or reducing carbon dioxide emission,and finally realize"carbon neutralization".In order to improve the solidification treatment technology of iron tailings in China,to promote energy saving,emission reduction and sustainable development of metal mines and iron and steel metallurgy industry,this paper takes low-carbon,environmental protection and efficient green iron tailings solidification technology as the goal,this paper studies the reinforcement effect and mechanism of carbonated pretreatment steel slag and slag powder instead of cement.The main research contents are as follows:（1）The compressive strength test of single influencing factor is carried out,and the results show that the compressive strength of steel slag-slag-tailings composite sand（CS）specimens increases first and then decreases with the increase of water cement ratio,proportion in cement and carbonation time,and decreases with the increase of steel slag ratio;Orthogonal tests were carried out,and the results showed that the influencing factors of the compressive strength of CS specimens from large to small were as follows:water cement ratio>steel slag ratio>proportion in cement>carbonization time,the optimal mix ratio is:water cement ratio is 1.25,steel slag ratio is 3:7,proportion in cement is 50%,carbonization time is 15min,the maximum compressive strength is 3.19 MPa at 7d and 5.26 MPa at 28d.（2）Triaxial compression tests were carried out to study the shear properties of CS specimens.By drawing the stress-strain curve,it is concluded that carbonation treatment specimen（CCS specimens）and specimen without carbonation treatment（DCS specimens）show strain hardening under different confining pressures;Through the molar stress circle,the effective cohesion of CCS specimens is 19.07k Pa and the effective internal friction angle is 11.91°;the effective cohesion of DCS specimens is2.25k Pa and the effective internal friction angle is 34.10°.（3）The freeze-thaw cycle test was carried out to study the frost resistance of composite soil.Under the same cycle times,the mass loss rate and strength loss rate of CCS specimens were less than those of DCS specimens,indicating that CCS specimens had stronger frost resistance;the permeability test was carried out to study the impermeability of composite soil,by controlling single factor,the permeability coefficient decreases with the increase of water cement ratio,increases with the increase of steel slag to blast furnace slag ratio,and increases with the increase of steel slag and blast furnace slag to cement ratio,with the increase of carbonization time,it first decreases and then increases。When the water cement ratio is 1.25,mass ratio of steel slag to blast furnace slag is 3:7,steel slag and blast furnace slag to cement quality ratio is 50%,carbonization time is 15min,the permeability coefficient reaches a minimum of 6.29×10^-5cm/s.The main reason for the high frost resistance and impermeability of CCS specimens is that carbonation treatment makes free calcium oxide,free magnesium oxide and other substances in steel slag produce small particles of calcium carbonate and magnesium carbonate,which fill the pores in the sand,so as to make the soil particles closer and increase the compactness of samples.Therefore,the impermeability is improved by an order of magnitude.（4）The microstructure test was carried out,and the specimen was characterized by XRD and SEM,it is found that there are more hydration products in the CCS specimens,and the slurry structure is more dense and firm.On the one hand,carbonation promoted the hydration of tricalcium silicate and dicalcium silicate,on the other hand,free calcium oxide is carbonized into calcium carbonate,which eliminates the later expansion harm of steel slag.At the same time,calcium carbonate participates in the hydration reaction,provides location space for the nucleation and growth of hydrated calcium silicate,and improves the compressive strength of composite tailings sand.（5）ABAQUS simulation test was carried out to study the slope stability of CS materials,and the results show that the safety factor increases with the increase of the unit side length and the shear expansion angle,and decreases with the increase of the slope toe angle;Carbonation treatment can increase the safety factor of CS specimen by 39.6%at the maximum,and greatly improve the safety,so that the solidified tailings can meet the requirements of higher-level soil materials and adapt to more complex geological engineering environment.