Impact Of Soil Colloid And Biochar On The Adsorption And Migration Of Cadmium In Porous Media

Soil and groundwater are important natural resources to human,which are of great significance to human survival and social development.However,with the development of economy,industry and agriculture,the threat of pollution in groundwater is becoming more and more serious as the wastewater and waste residue containing heavy metals enters the soil environment.Based on the key research project of the geological environment ecological restoration of typical mines in Qilian district of Qinghai Province,this paper the mechanism of remediation of heavy metal pollution caused by mining industry to local environment.The cadmium,on the one hand,accumulates in the plant body through plant roots,inhibits plant growth,and leads to the decline of crop quality and endangers food security.On the other hand,entering the human body through the air and food chain poses a threat to human health.Biochar is a kind of wide raw material sources,simple production technology,low cost of the new multi-functional materials,rich in contains a large number of negative charges and pore structure,surface functional groups and organic matter content of higher physical and chemical properties,make its can improve soil physical and chemical propertiesBiochar is a new multi-functional material with a wide range of raw materials,simple production process and low cost.It is rich in pore structure,a large number of negative charges and functional groups on the surface,as well as high content of organic matter,which can improve the physical and chemical properties of soil.It plays an important role in promoting plant growth,fixing soil pollutants and carbon cycle.It has great potential to repair materials,but its repair effect is comprehensive assessment should be carried out in combination with the actual environmental conditions.Cadmium,a heavy metal discharged from the mining process,migrates with a large number of soil colloids in the process of downward migration through the surface soil layer.A large number of studies have found that colloidal particles have a significant impact on the adsorption,migration and transformation behavior of heavy metals in saturated porous media.Based on this premise,a series of indoor simulation experiments were carried out to study the adsorption and migration process of cadmium in porous media under the joint action of soil colloid and biochar,in order to scientifically evaluate the application effect of biochar in the remediation of cadmium pollution in this area,and reasonable Suggestions for its remediation program were proposed.The main conclusions are as follows:?1?The results of lab batch experiments show that adding biochar can increase the adsorption capacity of Cd²⁺in soil,and properly increase the pH of colloidal solution can improve the adsorption capacity of Cd²⁺.When pH=7,the adsorption capacity of soil colloid to Cd²⁺is the largest.After adding the biochar colloid,the maximum adsorption capacity could be reached at pH=8.Reducing the ionic strength will increase the ability of soil colloid and biochar colloid to absorb Cd²⁺,and the effect is best when IS=3mm.?2?The results of the mathematical model fitting of the indoor soil column experiment are as follows:after the addition of biochar colloid,its irreversible colloid adsorption capacity on the porous media is larger,and the adsorption rate is faster.When the pH value increases,the irreversible adsorption rate of soil colloid and biochar colloid on the medium will decrease.However,the irreversible adsorption rate of soil colloid and biochar colloid increases with the increase of ionic strength.?3?The results of indoor soil column simulation experiments show that:biochar colloid is easier to adsorb on porous media than soil colloid.The larger the pH value,the stronger the migration ability of soil colloid and biochar colloid in porous media.At the same time,the pH value increases,which makes the migration ability of Cd²⁺decrease and reduces the threat to groundwater.In general,adding biochar will make the increase the adsorption effect of Cd²⁺.With the increase of ionic strength to 30 mM,the migration ability of soil colloid and biochar colloid in porous media decreased,and the amount of adsorbed Cd²⁺reduced,which enhanced the migration ability of Cd²⁺and increased the threat of heavy metal pollution to groundwater.Through the comparison of the results of the experimental group,it is found that biochar colloid solution has the best retention effect on Cd²⁺pollution in the soil when pH=8 and IS=0,and the reduction amount can reach about 80%.