Adsorption Behavior And Mechanism Of Sulfamethoxazole And Copper In Soil

With the intensive development of feed and livestock industry,antibiotics and heavy metals are widely used as feed additives in livestock and poultry farming,and most of these additives enter the soil environment in the form of their original forms or their metabolites.Heavy metals and antibiotics had increasing risks to the envi-ronment and human health as two kinds of agricultural soil pollutants that were paid close attention.In this paper,sulfanilamide antibiotics（SMZ）and heavy metals（Cu）with high detection rate,large carrying capacity and serious soil pollution were se-lected as target pollutant in livestock and poultry feces.Besides,two kinds of typical soils were choosen to be tested soil with the main adsorption matrix HA.Studied by tatic adsorption,XRD、FTIR and other characterization methods were used to char-acterize the adsorbens before and after adsorption,and the main results are as follows.（1）The adsorption kinetics of SMZ on black soil and brown soil could be fitted well by the second order kinetic equation.Therefore,it is inferred that the adsorption of SMZ in soil may contain multiple adsorption effects and most of them reached ad-sorption equilibrium after 72 hours of adsorption.（2）The Freundlich and Langmuir equations had fitted the adsorption isotherms of SMZ in black soil and brown soil well,and both of them were significantly corre-lated with each other（R²>0.997,P<0.01）.Besides,the adsorption intensity parameter1/n<1,which indicated that the adsorption of SMZ in these two soils is nonlinear.Then,the adsorption capacity of black soil is larger than brown soil’s.And it’sΔG（free energy of adsorption reaction）<40KJ/mol,which indicates both of the adsorp-tion with SMZ on black soil and brown soil were physical.（3）In the range of experimental pH,the adsorption capacity of SMZ decreased with the increase of pH.It appeared a balance of power platform first,and presented a downward trend later in the range of pH4.5-7.This is mainly related to the presence of SMZ at different pH conditions.（4）Examine the effect of soil clay minerals on adsorption.The result of XRD showed that H₂O₂ didn’t destroy soil structure significantly.It was found that the ad-sorption capacity of SMZ in black soil was greatly reduced after the removing organic matter.Fitting of the black soil after removing organic matter by Freundlich and Langmuir equations,and results showed that soil organic matter had a great effect on SMZ adsorption in soil.（5）In the HA-SMZ composite system,the kinetics show that the addition of HA can increase the adsorption rate of SMZ in soil and shorten the adsorption equilibrium time,and the adsorption effect is more significant with the increase of the concentra-tion of humic acid added.The composite of humic acid and soil has strong adsorption capacity,can effectively absorb antibiotics,and has a certain adsorption and fixation capacity,which can reduce antibiotics in soil migration and ecological risk,and rela-tively alleviate the problem of antibiotic contamination.（6）The presence of Cu²⁺increased the adsorption of SMZ in black soil and de-creased the adsorption of SMZ in brown soil.Because.Probably SMZ was adsorbed on the site of Cu which act as a bridge between SMZ and soil,increasing the adsorp-tion site for SMZ.At the same time,the SMZ and Cu²⁺in the solution might form a new composition-binary complex product,which had more positive charges than the SMZ itself.Therefore,it is easier to adsorb on the surface of black soil with negative charge.In addition,compared with the basic physical and chemical indexes of two soils,the cationic exchange capacity of black soil was higher than that of brown soil while the pH was lower than brown soil’s.And Cu²⁺would exchange the H⁺of soil surface to reduce the pH of equilibrium liquid.What’s more,SMZ was HAinated by cation in low pH solution.So,the lower the pH of solution,the greater cation ex-changing amount of soil adsorbed to the soil.（7）Studies by means of EDS characterization indicate that SMZ and Cu can be adsorbed on soil particles.Cu²⁺and SMZ appear co-adsorption in soil.According to the change of the peak value of FTIR of functional group,it is presumed that SMZ can be adsorbed on the soil particles through the bond bridge of hydrogen bond O-H,in which the anilino group mainly passes through the water molecule bridge.Studies have shown that in the presence of Cu²⁺,the adsorption of SMZ in the soil increases significantly,Cu²⁺can bridges the interaction between SMZ and soil particles,and SMZ-Cu-soil-tertiary complexes are formed during the adsorption process,increasing SMZ Adsorption in the soil.