2017年06月23日 星期五
 
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我室在铁解作用对砷酸根化学行为的影响研究取得进展
发布时间:2017-05-02  来源:土壤与农业可持续发展国家重点实验室  浏览:289

    铁氧化物是可变电荷土壤中砷酸根的主要吸附载体,砖红壤发育的水稻土遭受风化淋溶作用导致氧化铁形态和数量发生强烈变化,然而我们对砷酸根化学行为如何响应这一过程知之甚少。
    我室徐仁扣课题组通过砷酸根吸附等温线、zeta电位、吸附动力学、pH影响和与磷酸根竞争吸附等实验,比较了砷酸根在水稻土和砖红壤上的亲和能力。结果表明,铁解作用导致水稻土中游离态氧化铁含量显著降低,而无定形氧化铁增加。由于无定形氧化铁活性更高,砷酸根在水稻土上吸附量的降低与游离氧化铁含量降低不成比例。吉布斯自由能、动力学吸附、zeta电位等数据证明砷酸根在水稻土和砖红壤上都发生了明显的专性吸附。吸附/解吸数据表明非静电吸附是砷酸根的主要吸附机制,占其吸附容量的91.42–94.65%。随着体系pH值的增加和磷酸根的加入,砷酸根的吸附受到强烈抑制。水稻淹水种植过程会导致酸性土壤pH值增加,以及大量磷肥的施入极可能造成已为土壤固定和吸附的砷酸根重新被激活释放到土壤溶液中,加剧砷污染危害,这点需引起我们的重视。上述研究结果发表在Chemosphere上。

Jiang J, Dai ZX, Sun R, Zhao ZJ, Dong Y, Hong ZN, Xu RK. Evaluation of ferrolysis in arsenate adsorption on the paddy soil derived from an Oxisol. Chemosphere, 2017, 179: 232-241

Abstract

Iron oxides are dominant effective adsorbents for arsenate in iron oxide-rich variable charge soils. Oxisol-derived paddy soils undergo intensive ferrolysis, which results in high leaching and transformation of iron oxides. However, little information is available concerning the effect of ferrolysis on arsenate adsorption by paddy soil and parent Oxisol. In the present study, we examined the arsenate affinity of soils using arsenate adsorption/desorption isotherms, zeta potential, adsorption kinetics, pH effect and phosphate competition experiments. Results showed that ferrolysis in an alternating flooding–drying Oxisol-derived paddy soil resulted in a significant decrease of free iron oxides and increase of amorphous iron oxides in the surface and subsurface layers. There were more reactive sites exposed on amorphous than on crystalline iron oxides. Therefore, disproportionate ratios of arsenate adsorption capacities and contents of free iron oxides were observed in the studied Oxisols compared with paddy soils. The Gibbs free energy values corroborated that both electrostatic and non-electrostatic adsorption mechanisms contributed to the arsenate adsorption by bulk soils, and the kinetic adsorption data further suggested that the rate-limiting step was chemisorption. The zeta potential of soil colloids decreased after arsenate was adsorbed on the surfaces, forming inner-sphere complexes and thus transferring their negative charges to the soil particle surfaces. The adsorption/desorption isotherms showed that non-electrostatic adsorption was the main mechanism responsible for arsenate binding to the Oxisol and derived paddy soils, representing 91.42–94.65% of the adsorption capacities. Further studies revealed that arsenate adsorption was greatly inhibited by increasing suspension pH and incorporation of phosphate.

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