Experimental Study On Red Mud-Fly Ash Synergistic Cement-Quicklime Solidification Of Copper Ion Contaminated Kaolin

Based on the concept of green development,adhere to the basic national policy of saving resources and protecting the environment,and the idea of"using waste to treat waste",use the two solid wastes of red mud and fly ash as well as a small amount of quicklime and cement as curing agents in the immobilized remediation of copper ion-contaminated kaolin,the effect of the curing agent on copper ion-contaminated kaolin was studied.In this paper,red mud and fly ash are used as the main curing agent components,together with cement and quicklime to cure and repair the copper ion-contaminated kaolin.The copper ion-contaminated kaolin after adding the curing agent is made into a cube specimen with a side length of 70.7 mm,called solidified body.Through the unconfined compressive strength test of the solidified body with different proportions and different ages,the influence of the red mud-fly ash mass ratio and curing age on the strength of the solidified body is analyzed;the impedance characteristics of the cured body is analyzed by electrochemical impedance spectroscopy test;Obtain the copper ion leaching concentration of the cured body through the toxicity leaching test,and evaluate the curing effect;at the same time,the relationship between the electrochemical impedance parameter and the unconfined compressive strength is established,and the microscopic image is used to verify The feasibility of electrochemical impedance spectroscopy as a quantitative evaluation of the solidification effect of heavy metal contaminated soil.The main conclusions are as follows:（1）Through the unconfined compressive strength test of the solidified body,the results show that as the mass ratio of red mud to fly ash increases,the strength of the solidified body first increases and then decreases.When the mass ratio of red mud to fly ash is 7:3,the strength reaches the maximum;as the curing age increases,the strength of the solidified body increases;the stress-strain curve of the solidified body is divided into four stages:compaction stage,elastic stage,plastic yield stage and failure stage.The peak strain of the cured body varies from 2% to 5%.Deformation modulus E₅₀ has a good linear correlation with strength,E₅₀=（20-45）q_u.（2）Through the electrochemical impedance spectroscopy test of the solidified body,the results show that the Nyquist diagrams of the solidified body specimens all show the capacitive reactance arc in the high frequency region and the diffusion slope in the low frequency region;with the increase of the red mud-fly ash content,the capacitive resistive arc radius first increases and then decreases;when the red mud-fly ash mass ratio is 7:3,the capacitive resistive arc radius is the largest;the impedance modulus value|Z|in the Bode diagram increases first and then decreases with the increase of the red mud-fly ash mass ratio;also at 7:3,the impedance modulus value is the largest;the equivalent circuit model of the cured body specimen isR_S(Q ₁(R_{ct 1}W)(Q₂ R _ct2);the impedance parameters R_s and R_ct1 first increase and then decrease with the increase of the red mud-fly ash mass ratio,and the maximum when the mass ratio is 7:3;R_s and R_ct1 both increase with the increase of the curing age.（3）Through the copper ion toxicity leaching test,the results show that the copper ion leaching concentration of the solidified specimen first decreases and then increases with the increase of the red mud-fly ash mass ratio,and it is the smallest when the mass ratio is 7:3;as the curing age increases,the leaching concentration of copper ions gradually decreases;the leaching concentration of copper ions in each ratio meets the copper leaching concentration limit of the relevant standards,which proves that the curing agent has a better curing effect on copper ion-contaminated kaolin.（4）Through the microscopic scanning electron microscope test,the results show that the change law of the microstructure of the solidified body reveals that when the mass ratio of red mud to fly ash is 7:3,the solidified body has a tight gel connection and a stable structure;the logarithmic relationship can be used to predict the strength of the cured body through R_s and R_ct1,so as to evaluate the curing effect;combined with the microscopic electron microscope image,it is proved that it is feasible to evaluate the curing effect by electrochemical impedance spectroscopy.