Effect Of Biochars On The Adsorption Behaviou Of Pollutants In Heavy Metal PAEs Contaminated Soil

With the rapid development of global industry and agriculture,soil contamination has increasingly become more complicated and diversified.The problems of co-contamination by heavy metals and organic pollutants are particularly prominent,and have drawn widespread attention globally.Heavy metals can also enter the human body through the food chain,thereby threatening the environment and human health.As the most widely used plasticizer compounds,phthalic acid esters?PAEs?are applied in industrial production,medical materials and household goods,and released to soil,water and air with time.Therefore,co-contamination of the PAEs and heavy metals often occurs in soils which can adversely affect human food safety.Biochar typically has a porous structure,a high specific surface area,and large number of functional groups,and has been recognized as an emerging adsorbent for immobilization of heavy metals and organic contaminants in soils.However,most of the previous studies focused on the biochar remediation of soil contaminated either by organic compound,or by heavy metals.There is little information on using biochar for remediation of soils co-contaminated by heavy metal and PAEs.Therefore,biochars derived from dead pigs?PB?and the branches of Platanus orientalis Linn.?POB?were used to examine their effect on the behaviour of the contaminants in soils co-contaminated by cadmium?Cd?and zinc?Zn?and diethyl phthalate?DEP?by employing batch equilibrium method.The objectives of this study were to:?1?investigate the kinetics and thermodynamics associated with the adsorption,?2?explore the effect of different factors,such as temperature,time,biochar type,addition rate and contaminant type,on the heavy metals and PAEs adsorption in soil solution,and?3?investigate the adsorption mechanism and the interaction of contaminants.The main results of study are as follows:?1?Application of PB and POB enhanced the soil adsorption capacity of Cd²⁺,Zn²⁺and DEP,and the effect of PB application was greater than POB application.Under the heavy metals—DEP treatments,the soil adsorption capacity for Cd²⁺increased with increase of the biochars;the PB treatment significantly?P<0.05?increased the soil adsorption capacity for Zn²⁺,and greater increase was observed in the higher rate PB treatment.However,the POB addition rates had on significant influence on the soil adsorption capacity for Zn²⁺.Biochar application improved the adsorption capacity of co-contaminated soil for DEP.In the DEP treatments without heavy metals,only the PB application significantly?P<0.05?increased the soil adsorption capacity for DEP.?2?The contaminants interacted one other during the adsorption of Cd²⁺,Zn²⁺and DEP on soils.The presence of DEP could promote the soil adsorption capacity for Cd²⁺and Zn²⁺,particularly when the initial DEP concentration was higher.Cd²⁺and Zn²⁺in the soil solution could enhance the soil adsorption capacity for DEP,and the higher initial heavy metal concentration had greater effect.Therefore,there was a synergistic interaction between Cd²⁺,Zn²⁺and DEP in the adsorption processes.?3?When the adsorption time was extended,the process of soil adsorbed Cd²⁺,Zn²⁺and DEP may be divided into a fast adsorption stage and a slow adsorption stage.The adsorption sharply increased initially,then the adsorption rate slowed down and finally reached saturation equilibrium.Under the same adsorption period,the adsorption of PB-and POB-treated soil for Cd²⁺?Zn²⁺and DEP were higher than the untreated soil.Additionally,the adsorption of heavy metals—DEP treated soil were higher than the soil only treated with heavy metals or DEP.?4?The adsorption process could be described by pseudo-second order kinetics model,and the adsorption processes mainly included liquid film and intraparticle diffusions.The thermodynamic adsorption process was a spontaneous endothermic reaction,and the higher temperature was more conducive to spontaneous adsorption.