Study On The Characteristic And Mechanism Of Cu Contaminated Soil Stabilized By Modified Red Mud With Cement

Red mud is a solid waste produced in the process of alumina production.Production of 1 tons of alumina will produce 0.8-1.5 tons of red mud.At present,the red mud mainly is deposited into dam for the opening storage in China,taking up enormous land resources,which affects human life and production.However,the level of massive red mud resource utilization is low,and the red mud processing technology is still outdated.Therefore,it is urgent to realize multi-channel and resource treatment of the red mud.In the meantime,with the rapid development of cities,a number of sites are polluted by wastes that enterprises generated,which has become a serious problem for the construction of cities.As an environmental problem,copper pollution is mainly caused from copper or zinc mine smelting,metal processing,machinery manufacturing and so on.Various forms of copper transform,disperse and enrich,which is finally harmful to human health through drinking,eating and other channels.Therefore,it is great significance of studying the treatment methods of copper contaminated soil.This work takes red mud in Liulin Shanxi as a raw material,using Ca O to stimulate the activity of the red mud,modifying the red mud with cement to cure high-concentration Cu²⁺contaminated soil,to study the variation rules and microscopic mechanism of the solidified soil by measuring and analyzing the parameters of unconfined compressive strength?_U?,electrical resistivity??,compression sensitivity that change with the content of red mud((8_RM),Cu²⁺concentration in soil((8_Cu)and the curing period??.In order to provide a theoretical basis for repairing the high-concentration Cu²⁺contaminated soil,the main research contents and results are as follows:?1?The CaO modified test data were analyzed,and a ratio scheme of curing agent made from the CaO modified red mud mixed with cement?RMCaC?ratio of were proposed.The mass ratio of cement and soil was 1:10,and the mass ratio of red mud and CaO was 3:1,the upper limit of red mud added into loess was 60%.Under the precondition that the solidified soil satisfies the strength requirements,the curing upper limit of content of Cu²⁺of contaminated soil was increased from 0.5%to 2.5%.Then,a leaching toxicity test was conducted on the contaminated soil samples with the content of curing Cu²⁺of 2.5%,the curing rate reached 99.99%,thus the corrosive and radioactive properties satisfy the relevant national standards.?2?The relationship between the compressive strength of the solidified soil and the content of the red mud were studied,it is found that as 45%?(8_RM?60%,the probability of a maximum of_U increases.After analyzing the strength that changes with the curing period,_U increases with the increase of.When<28 d,_U increased rapidly.but?28 d,the growth rate of_U tends to be slow.The red mud strengthening factor and curing enhancement factor were put forward,it is found that the curing strengthening effect of the RMCaC is better than that of the traditional cement,especially it can significantly improve the early age strength of the solidified soil.In the meantime,studies show that the variation trend that the electrical resistivity of the solidified soil varies with the current frequency was independent of(8_RM and(8_Cu.When the(8_Cu?0.25%,the resistivity decreases with the increase of(8_RM,while(8_Cu>0.25%,the resistivity increases with the increase of(8_RM.Moreover,the resistivity increases with the increase of curing period of the solidified soil.when<28 d,increased rapidly,and?28 d,the growth rate ofbecome slow.The prediction formula that the unconfined compressive strength and resistivity varies with(8_Cu,and(8_RM were proposed,it is found that there is a linear relationship for the variation of the unconfined compressive strength and the electrical resistivity.When(8_Cu?0.5%,thethat is corresponding to_U becomes small.The test results show that with the increase of strain,the resistivity change rate of the solidified soil gradually decreases.With the increase of(8_RM,the degradation range of the resistivity change rate increases.When(8_RM=zero,the variation range of the resistivity change rate of the solidified soil is from-30%to-50%,while that of the RMCaC solidified soil is between-40%and-70%.With the increase of curing period,the resistivity change rate of the cement stabilized soil progressively decrease,but the change of the RMCaC solidified soil is not obvious.?3?The strength of the cement stabilized soil is usually caused by the hydration reaction of cement,pozzolanic reaction,carbonization reaction and displacement reaction,which cementes the soil particles together to form a skeleton with a certain strength.There are few copper compounds in the cement stabilized contaminated soil.When solidified the high-concentration Cu²⁺contaminated soil,all types of compounds exist in a stacking state,which results in a high increase in porosity of the solidified soil and a decrease of the strength of the solidified soil in the macroscopic sense.Through microscopic test research,it shows that reaction mechanism of the RMCaC solidified soil are as follows,CaO suspended in pore solution to ensure that Ca²⁺is saturated;hydrolysis reaction of the red mud increased the content of active anion,unstable SiO₂ and Al₂O₃ minerals underwent pozzolanic reaction generating SiO₄^4-,SiO₂^2-and AlO₂^-;Ca²⁺displaced Na⁺,K⁺in the pore liquid improving the mineral composition of the solidified soil skeleton;The surface of the red mud and the loess particles adsorbed CaO and reacted with ions in the pore solution to generate cementing product.When(8_RM<45%,the concentration of OH^-increases with the increasing(8_RM,which increased the activation effect of active substances in the red mud;as 45%?(8_RM?60%,with the increase of(8_RM,the solubility degree of OH^-and Ca²⁺in the pore solution reached its upper limit,this is the reason that as(8_RM reaches a certain range,_U will be a maximum value.In the RMCaC solidified soil,the active hydrolysis mineral inside loess and red mud particles can be hydrolyzed into K⁺,Na⁺,and OH^-.Cement hydration reaction and CaO-water reaction causes that OH^-and Ca²⁺in the pore water maintained at a high concentration,the presence of these ions enhanced the conductivity of the pore water.The linear relationship between the strength of the solidified soil and the electrical resistivity is analyzed as follows,the strength is related to the cementation reaction and the composition and morphology of its solid product.The denser cementing product filling particle pores,the smaller the porosity,and the greater the resistivity.As the reaction progresses,the total content of the conducting particles in the pore water progressively decreased,the resistivity of the solidified soil gradually increased.In the process of compressing the test block,contact action of iron oxide and conducting channels of pore water change.In the meantime,the tunnel conduction effect and conductance seepage phenomenon exist in the test block,which jointly changed the resistivity change rate of the solidified soil.The increase of the red mud content and the concentration of the copper ion increases the conducting channels,and the presence probability of tunnel conduction and conductance seepage effect increases correspondingly,which macroscopically shows that the extent of the resistivity attenuation increases.