Study On Mechanical Properties And Durability Of Cd-Cr Contaminated Soil Solidified By Composite Slag

The environment is often polluted by heavy metals due to factory relocation and sewage discharge.Cadmium(Cd)and chromium(Cr)are two common toxic heavy metals in metallurgy,chemical industry and other industries,which often cause soil pollution due to waste liquid leakage and so on.They have great environmental risks and need to be treated innocuously.Calcium carbide residue(CCR)and ground granulated blast furnace slag(GGBS)are two kinds of industrial by-products.Strong alkaline CCR can be used as activator to stimulate the hydration activity of GGBS,so as to form alkali activated slag cementitious material which can be used as treatment of heavy metal contaminated soil site.It can not only achieve "pollution control by waste",but also reduce the amount of cement,which is economic and green.This research is funded by research and development foundation of the Institute of Environment-Friendly Materials and Occupational Health of Anhui University of Science and Technology,Wuhu(ALW2020YF13).In this paper,the composite slag material was formed by CCR and GGBS and composite slag solidified cadmium and chromium contaminated soil is selected as the research object.The strength characteristics,carbonization durability and drying-wetting cycle durability of the solidified soil are studied through laboratory test and theoretical analysis.The solidification mechanism and carbonization mechanism of the solidified soil are studied based on X-ray diffraction(XRD)and scanning electron microscope(SEM).The main conclusions are as follows:(1)The strength test of solidified soil is carried out.The results show that the strength of solidified soil is positively correlated with curing age and dosage of curing agent.The longer the curing age and dosage,the higher the strength is.The influence of heavy metals Cd and Cr on the strength has duality.When the ion concentration is low,it can increase the strength,and when the ion concentration is too high,it can weaken the strength The influence of heavy metals on the strength of solidified soil is affected by the age and the amount of solidified agent;with the increase of heavy metal concentration,the failure strain of solidified soil increases and the plasticity increases.(2)The accelerated carbonation test of solidified soil is carried out.The results show that with the increase of carbonation time,the carbonation depth gradually increases,and there is a positive proportional function relationship between the carbonation depth and the square root of time.The longer the carbonation time is,the lower the strength of the sample is,and the strength degradation rate decreases obviously after 48 hours of carbonation.(3)The influence of the number of cycles on the mass loss,strength and stress-strain of the samples was studied through the drying-wetting cycle test.The results show that the mass loss and cumulative mass loss rate of the solidified soil samples increase with the increase of the number of cycles,and the cumulative mass loss rate reaches more than 35%at the end of the six cycles;the strength of the samples increases with the number of cycles With the increase of the number of cycles,the failure strain increases and the plasticity increases.(4)XRD and SEM tests showed that the main reason for the strength growth of solidified soil under standard curing was that the hydration of the curing agent produced a large amount of calcium silicate hydrate(C-S-H)and calcium hydrated calcium aluminate(C-A-H)and other gel products,which played the role of cohesive soil particles and filling pores,thereby enhancing the strength and reducing the strength of carbonization process.The reason is that the hydration product decarburizes,shrinks and decomposes after carbonization,and the calcium carbonate produced at the same time leads to micro cracking,so the strength of the solidified body decreases after carbonization.Figure[55]table[19]reference[148].