Removal Mechanism Of Roxarsone And Arsanilic Acid In Water By Iron Based Thermal Modified Attapulgite

Roxarsone（ROX）and p-arsanilic acid（p-ASA）are two organic arsenic feed additives commonly used in the livestock and poultry breeding industry to promote the growth and development of farmed animals and enhance immunity.However,it is difficult to metabolize and transform in animals,and most of them are excreted into the environment through livestock and poultry manure,and are transformed into the more toxic As（III）and As（V）under some conditions.This will lead to soil and water pollution,and bring ecological and environmental risks.As a clay mineral,attapulgite（ATP）has abundant reserves in China and is often used as an adsorbent for the treatment and disposal of industrial wastewater and waste liquid and for water purification;in agriculture and industry,it is also used as carriers for pesticides,fungicides,catalysts,etc.In this study,four kinds of modified ATP materials,which called thermally modified ATP,Fe₃O₄-ATP,Fe S-ATP,and Fe-C-ATP were prepared by pickling,high temperature treatment,and iron-based loading,respectively.SEM-EDS,XRD,XPS were performed for characterization and Analysis of Materials.The modified ATP was used for the adsorption of two kinds of organic arsenic compounds,ROX and p-ASA in water,and the adsorption behavior and mechanism of the modified ATP on the organic arsenic compounds were studied by controlling different temperatures,ATP dosage,and initial pH of the solution.The main results are as follows:（1）Fe₃O₄-ATP,Fe S-ATP and Fe-C-ATP were prepared by loading ATP with different iron groups after acid washing and high temperature activation.SEM-EDS analysis showed that ATP was partially dissolved and the pore structure was opened after acid washing.After loading different iron groups,the iron content of modified ATP increased from 0.83%initially to 5.73%（Fe S-ATP）,12.77%（Fe₃O₄）,and 2.17%（Fe-C-ATP）,respectively.The most abundant elements are still O and Si,which are related to the basic structure of ATP.XRD analysis showed that the iron-based modified ATP well retained the original diffraction peaks of ATP,and the diffraction peaks of various iron-based groups appeared in the corresponding positions after modification,indicating that the basic structure was not damaged and iron groups were successfully loaded on ATP.（2）The adsorption kinetics fitting results showed that the adsorption behaviors of ROX and p-ASA on the modified ATP surface were suitable for the second-order kinetic model,and the adsorption was chemical adsorption.（3）Both the Freundlich and the Langmuir adsorption isotherms can well describe the adsorption behavior of ROX and p-ASA on the modified ATP surface.Compared with thermally modified ATP,the adsorption performance of ATP for ROX and p-ASA was significantly improved after loading iron-based modification（p<0.1）.The maximum adsorption capacities for ROX of thermally modified ATP,Fe₃O₄-ATP,Fe S-ATP and Fe-C-ATP were 39.39 mg/g,239.23 mg/g,178.87 mg/g,70.22 mg/g,while the maximum adsorption capacities for p-ASA were 32.79 mg/g,97.09 mg/g,62.89 mg/g,and 50.25mg/g,respectively.In the range of 25～45℃,the effect of temperature change on the adsorption of ROX and p-ASA by modified ATP was not significant（p>0.1）.（4）The adsorption mechanism of modified ATP for the adsorption of ROX and p-ASA is that the arsine groups on ROX and p-ASA are chemically combined with the iron groups supported on the surface of ATP.This process is affected by the modified ATP and ROX and p-ASA.The electrostatic interaction between them is extremely influential,thus favoring the occurrence of ROX and p-ASA adsorption at lower solution pH.