Study On Engineering Characteristics Of Solidified/Stabilized Chromium-contaminated Soil By Soil Stabilizer And Biochar

Heavy metal pollution in soils has become an increasingly problem that has bad influence on human life.After heavy metals enter soils,they will be absorbed by human being through water,atmosphere and food,which threatens the health of human.On the other hand,heavy metals will change the physical,chemical,and mechanical properties of soils which do harms to the security and stability of related buildings.Therefore,it is of both academic and realistic value to study the remediation of heavy metal-contaminated soil.This study firsty used cement as the main curing agent,calcium oxide,calcium sulfate,sodium silicate,sodium sulfateas as activators to solidify Yangling loess.By doing orthogonal experiments,we selected the unconfined compressive strength as an indicator to formulate a cement-based soil stabilizer with high strength.Then,the Influence of engineering characteristics with chromium content,biochar content,and curing age were studied by unconfined compressive strength test,compression test,permeability test,toxicity leaching test and SEM.Illustrate the mechanisms of biochar and cement-based soil stabilizer co-repairing the chromium-contaminated soil.The conclusions of study are as follows:(1)The results of the unconfined compressive strength test show that calcium oxide,calcium sulfate,sodium silicate,sodium sulfate can effectively improve the mechanical strength of cement-soil.When the cement content is 12%,determined by study on the formula of soil stabilizer,the excitants content is: calcium oxide 8%,calcium sulfate 8%,sodium silicate 0.4%,sodium sulfate 0.6%(each component content is based on the quality of cement).The strength of solidified soil with 28 curing age is 40.4% higher than cement-soil.(2)The experimental results of engineering properties of solidified chromium-contaminated soil show that the compressive strength,compressive modulus,and permeability coefficient of the solidified soil increase first and then decrease,and the compressibility decreases first and then increases with increasing content of chromium Ion.The increase of biochar content will decrease the compressive strength,compressibility,and permeability coefficient of solidified soil,while increasing the compression modulus.However,the biochar content of 3% is beneficial to the strength of solidified soil in the later period.Curing age will increase the compressive strength and compressive modulus and decrease the compressibility and permeability coefficient of solidified soil.(3)The toxicity leaching test results show that the increase of chromium ion will increase the chromium ion concentration in the leachate of solidified soil;cement-based soil stabilizer can decrease the chromium ion of the soil;besides,because of the synergistic effect of cement-based soil stabilizer and biochar,chromium ion concentration of solidified soil leachate dramatically decrease with the increase of biochar content.The concentration of medium chromium ions decreases sharply with the increase of curing age.(4)The experimental results of electron microscopy scanning show that CSH,CAH,Ca(OH)2,AFt produced with the hydration reaction,formation of consolidate,cation adsorption and pozzolanic reaction of cement-based soil stabilizer.Those materials can improve engineering properties by physico-chemical actions of adsorption cementation and reinforcement.Biochar has strong adsorption characteristics due to its porous structure and can adsorb heavy metal ions such as chromium ions.The mechanism of biochar and cement-based soil stabilizer co-repairing the chromium-contaminated soil manifests in biochar`s adsorption and cement-based soil stabilizer`s solidification.