Study On Adsorption Of Organic Arsenic Drugs By Typical Soil Minerals

In recent years, the livestock emissions generated containing organic arsenic and heavy metals pollutants due to the extensive use of compound feed including organic arsine additives, copper and zinc, has already been a the presence of a potential threat to the ecological environment and human health and caused the extensive concern. Therefore, it is necessary to carry out a research of migration and transformation of organic arsine and its fate in environment. Roxarsone and arsanilic acid were taken as typical organic arsine with nan-alumina, goethite and kaolinite as typical soil mineral adsobents, to systematically study the adsorption behavior of two kinds of organic arsine on typical soil minerals surface.The effects of pH value, cation, heavy metal ions and the dissolved organic matter (DOM) on adsorption have been investigated as well, and the results are shown as follows:(1) Adsorption behavior of organic arsine on goethite. The adsorptions of two kinds of organic arsine on goethite conform to pseudo-second-order model and Langmuir isotherm model.The initial absorption rates of roxarsone and arsanilic acid were 81.97 and 50.00 mg·g-1·h-1, respectively, and the adsorption capacity of roxarsone on goethite was stronger. With the increase of pH, the adsorption of organic arsine on goethite remained unchangedfirst and then decreased. Background of metal cation with bigger atomic radius and higher valence would increase the adsorption of organic arsine on the surface of goethite. Mg2+, Ca2+, and heavy metal ions Cu2+, Zn2+ can enhance the adsorption of organic arsine on goethite by bridge bond effect, and the enhancement effect of Zn2+ was more obvious. Presence of dissolved organic matter (DOM) would reduce the adsorption capacity through electrostatic interaction to occupy the adsorption site of goethite. The main adsorption mechanism of organic arsine on goethite was the coordination effect on the surface.(2) Adsorption behavior of organic arsine on kaolin. The adsorption kinetic and isothermal of roxarsone and arsanilic acid on kaolin conformed to pseudo-second-order model and Freudlich isotherm adsorption model. The initial adsorption rate of roxarsone and arsanilic acid, valued 0.72 and 0.67 mg·g-1·h-1 respectively, indicating that the adsorption capacity to roxarsone was stronger than arsanilic acid. With the increase of pH value, the adsorbance of two kinds of organic arsine on kaolin tended to first increase and then decrease, and the maximum values occured at pH= 7 for roxarsone and pH= 5 for arsanilic acid. Background cations have no obvious effects on the organic arsine adsorptionon kaolin. Heavy metal ions Cu2+, Zn2+could enhance the adsorptionby bridging between organic arsine and kaolin, and Zn2+made more obvious change. Dissolved organic matter (DOM) could reduce the adsorption by taking up adsorption sites on kaolin and interaction settlement with kaolin under acidic conditions.(3) Adsorption behavior of organic arsine on nan-alumina. The adsorption kinetic features of roxarsone and arsanilic on Nano-alumina were characterized by pseudo-second-order model. The initial adsorption rate of roxarsone and arsanilic acid, valued 12.92 and 10.37 mg·g-1·h-1, respectively, which indicated that the adsorption capacity of roxarsone on nano-alumina was stronger than arsanilic acid. Nano-alumina adsorption isotherm of organic arsine conformed to Freudlich model and nonlinear adsorption mechanism. With the increase of pH value, the adsorbance of two organic arsine on nano-alumina increased first and then decreased, and peaked at pH= 5, which is related to the morphology of organic arsine and surface charge properties of nano-alumina. Background cation with higher atomic radius and valence can increase the adsorption of organic arsine on nano-alumina. Cu2+, Zn2+also can significantly change the adsorbance by bridging between organic arsine and nano-alumina, between them, enchancement effect of Zn+was more obvious. With the increase concentration of dissolved organic matter (DOM), adsorbance of organic arsine on nano-alumina decreased significantly. With DOM concentration increase, the adsorbance of organic arsine on nano-alumina reduced, which was due to the competitive adsorption between organic arsine and DOM on nano-alumina.