土壤矿物和胡敏酸对阿特拉津的吸附-解吸作用研究

Effects of Humic Acids and Minerals on Adsorption-desorption of Atrazine in Soil

选取了6种土壤矿物(蒙脱石、高岭石、钙饱和处理蒙脱石、钙饱和处理高岭石、无定型氧化铁和无定型氧化铝),以及从土壤中提取纯化的3种胡敏酸为材料,采用批量吸附平衡法,研究土壤矿物和胡敏酸对阿特拉津的吸附特性。结果表明,各吸附剂对阿特拉津的吸附均能采用Frundlich方程进行较好地拟合(r≥0.982,p<0.01)。胡敏酸对阿特拉津具有最大的吸附性能,其固-液分配系数(Kd值)随平衡浓度(Ce值)的变化基本恒定,吸附等温线呈线性(Frundlich方程常数N≈1),吸附以分配溶解作用为主,吸附可逆性较高。黏土矿物(特别是蒙脱石)对阿特拉津也具有较强的吸附能力,Kd值随Ce值增加而增加,吸附等温线呈S型(N>1),吸附主要是通过表面亲水作用。无定型氧化铁铝的Kd值随Ce值增加而降低,当Ce达到一定水平后,Kd趋于恒定,吸附等温线呈L形(N<1),吸附主要是通过无定型氧化物表面的羟基与阿特拉津分子间的化学键合作用,吸附可逆性最差。

As a critical organic pollutant in soil environment,atrazine has aroused people’s concern about its fate and ecological risk in recent years. Adsorption-desorption behavior of atrazine is a key factor governing translocation,transformation,fate and bioavailability of the substance in the soil,while it is affected not only by physico-chemical properties of the soil,but also by some important components of the soil,such as minerals and organic matter（SOM）. There have been large volumes of studies demonstrating that SOM is the major factor governing adsorption of atrazine in the soil,and some others indicating that soil minerals may be almost equal to or higher than SOM in such an effect in the case that SOM is relatively low in content in the soil. However,most of the researches were concentrated merely on relationships of atrazine adsorption with soil minerals and content of SOM in natural soil. As soil is very diversified in type and very complex in composition,so far nothing has been done demonstrating quantitatively extents of the effects and contribution rates of SOM and minerals on and to atrazine adsorption. The aims of this study were to investigate characteristics of the adsorption-desorption of atrazine by SOM and minerals,so as to provide some theoretic basis for quantitative analysis of contribution rates of SOM and minerals in atrazine sorption,and some scientific evidence for better understanding and evaluating ecological risk of the organic pollutant in soils different in physic-chemical properties.Six pure minerals（montmorillonite[Mont],kaolinite[Kaol],Ca-saturated of montmorillonite[Mont-Ca] and kaolinite[Kaol-Ca],amorphous hydrated Al and Fe oxides[AHOs-Al,AHOsFe]）,and three types of soil humic acids（HAs）,which were extracted from soils and purified,were selected as the representative sorbents for the study. Structures and physico-chemical properties of the sorbents were analyzed with an X-ray diffractometer（XRD）,a surface area analyzer（BET）,and total nitrogen and total carbon analyzers. And then adsorption-desorption behaviors of atrazine on these soil minerals and HAs were analyzed with the isothermal batch equilibrium method. Results show that the isotherms of atrazine sorption to all the tested sorbents could well be described with the Frundlich equation（r≥0.982,p〈0.01）. Humic acid（HA）was the key factor influencing atrazine sorption in soils. A linear adsorption isotherm as was described with the Frundlich model was found（N≈1）,with Kd being nearly constant despite changes in Ce. The adsorption of Atrazine was controlled mainly by the mechanism of distributive dissolution and highly reversible. The effects of the three HAs on adsorption of Atrazine and the effect of delaying desorption of Atrazine were significantly related to content of TOC,N,or H in the HAs. Clay minerals（especially Mont）also showed strong Atrazine adsorption capacities,with Kd rising with increasing Ce and an isotherm being S-shaped（N〉1）,indicating that the adsorption is effected mainly by surface hydrophilic interaction. However,once saturated with Ca ions the clay minerals（Mont and Kaol）reduced their effective adsorbing sites on the surface and in the interlayer lattices and in turn their effects on adsorption and desorption ofAtrazine. Kd of AHOs decreased with increasing Ce values and leveled off when Ce reached a certain level. The isotherms all appeared in the shape of an L（N〈1）,indicating that the adsorption is effected mainly by chemical bonding between the hydroxy on the surface of AHOs and atrazine molecule and moreover,the lowest in reversibility.