The Effect Of Biochar On Adsorption And Migration Of Tetracycline And Copper Ions In Saline Soil

The problem of farmland salinization has always been one of the major problems restricting the sustainable development of agriculture in Xinjiang.With the rapid development of breeding industry,animal manure is gradually increasing.Most of the manure is applied to the soil to improve the basic physical and chemical properties of the soil.Therefore,the pollution of heavy metals and antibiotics in the soil is becoming increasingly prominent.At present,the mechanism of migration and transformation of antibiotics,heavy metals and other pollutants in saline soil is not clear.In this study,the adsorption and migration laws of tetracycline（TC）and copper ion(Cu²⁺)in saline soil added with two different sources of biochar（pig manure biochar（PMBC））and cotton straw biochar（CSBC）were investigated through adsorption and migration experiments/models,The mechanism of exogenous biochar affecting the migration of TC and Cu²⁺in saline soil was clarified.The results provide a theoretical basis for the compound pollution control of antibiotics and heavy metals in saline soil,and are of great significance to the safety of agricultural ecological environment in Xinjiang.The main conclusions are as follows:（1）The equilibrium adsorption capacity of TC by saline soil treated with different biochar was as follows:pig manure biochar（Soil+PMBC）（1.099 mg/g）>cotton straw biochar（Soil+CSBC）（1.045 mg/g）>saline soil（Soil）（0.930 mg/g）.The higher the initial concentration of TC,the greater the adsorption capacity of Soil+CSBC/PMBC on TC,and the maximum adsorption capacity of Soil+CSBC is 1.24 times of that of Soil+PMBC（25℃）;The adsorption amount of TC on the tested soil sample is positively correlated with temperature and negatively correlated with p H value.The effects of four cations on the adsorption of TC by Soil+CSBC/PMBC showed inhibition,mainly Na⁺<K⁺<Ca²⁺<Mg²⁺,and the inhibition was positively correlated with the ionic strength.（2）The equilibrium adsorption capacity of the saline soil treated with different biochar was as follows:Soil+CSBC（3.135 mg/g）>Soil+PMBC（2.933 mg/g）>Soil（2.805 mg/g）;Langmuir model can better describe the isothermal adsorption process,and the n value is greater than 1,indicating that the addition of two kinds of biochar is conducive to Cu²⁺adsorption.At 25℃,the adsorption capacity of Cu²⁺increased with the increase of initial concentration until equilibrium;The increase of temperature is beneficial to the adsorption of Cu²⁺;When p H=1.0,the adsorption capacity is the smallest and is:Soil+PMBC>Soil+CSBC>Soil.When p H=6.0,the adsorption capacity is the largest and there is no significant difference between the tested soil samples;The four cations have inhibitory effects on the adsorption of Cu²⁺by different treatments.The order of inhibition is Na⁺<K⁺<Ca²⁺<Mg²⁺,and the adsorption capacity is inversely proportional to the ionic strength.The adsorption of Cu²⁺and TC in saline soil can promote each other.The main results are as follows:the maximum adsorption capacity of Cu²⁺under the coexistence of 80 mg/L TC is more than 2.27 times that of the treatment without TC;Compared with no addition of Cu²⁺,the addition of 80 mg/L Cu²⁺increased the TC adsorption capacity of Soil,Soil+CSBC and Soil+PMBC by 19.3%,20.9%and 12.7%respectively.This interaction was related to the cation exchange and complexation reaction between Cu²⁺and TC.（3）The migration of TC/Cu²⁺in saline soil is closely related to the physical and chemical properties of saline soil,the amount of biochar added and the types of biochar.The peak value of TC relative concentration breakthrough curve（BTCs）is:Sand>Sand+2%CSBC（Sand+1%PMBC）>Soil>Soil+2%CSBC（Soil+1%PMBC）.The content of biochar in soil was negatively correlated with the migration capacity of TC.The R_dand K_dof Soil+2%PMBC were greater than that of Soil+2%CSBC.The migration of Cu²⁺and TC in saline soil was inhibited by each other;However,dissolved organic matter（DOM）can promote the migration of TC in saline soil.DOM concentration is positively correlated with the migration capacity.The difference in the retardation effect of Soil+1%PMBC and Soil+2%CSBC on TC and Cu²⁺is related to the concentration of TC,Cu²⁺and DOM in the coexisting solution.