基于不同分析方法研究磷酸根在矿物表面吸附机制的进展

磷素是植物生长必需的营养元素,也是联系生态系统中生物与非生物作用的关键元素。对磷酸根在矿物表面吸附反应机制的深入认识,有助于了解其在陆地和水环境中的形态、迁移、转化和生物有效性。本文主要综述了磷酸根在常见(土壤)矿物表面吸附机制的研究进展。各种分析技术或方法,如OH–释放量分析、Zeta电位分析(电泳迁移率测试)、等温滴定量热法、原子力显微镜、X射线光电子能谱、红外光谱、核磁共振波谱、X射线吸收光谱、表面络合模型、量子化学计算等,均以不同方式揭示磷酸根在不同矿物体系的吸附机制。磷酸根在矿物(尤其是铁、铝氧化物)表面的吸附通常伴随着水基和羟基的交换。一般认为磷酸根在矿物表面主要形成双齿双核、单齿单核内圈络合物,且受pH的影响较大。pH以及磷酸根在矿物表面的吸附密度影响内圈络合物的质子化状态。在低pH、高磷浓度、较高反应温度、较长吸附时间,以及弱晶质矿物吸附等条件下矿物表面吸附的磷可在矿物表面转化形成含磷的表面沉淀,造成矿物溶解转化以及磷生物有效性的进一步降低。最后展望了磷酸盐在矿物-水界面吸附有关的研究热点和方向。

Progresses in Studies on Sorption Mechanisms of Phosphate on Minerals Using Multiple Analytic Approaches

Phosphorus is a nutrient element essential to plant growth and a key one linking biological and abiotic interactions in ecosystems. An in-depth knowledge of sorption mechanism of phosphate on mineral surface is helpful to understanding the speciation, translocation, transformation, and bioavailability of phosphate in terrestrial and aquatic environments. In this paper, a review is presented of progresses in researches on phosphate sorption on mineral surface and its mechanism. Various analytical techniques or methods, such as quantitative analysis of OH- released, Zeta potential measurement (electrophoretic mobility measurement), isothermal titration calorimetry, atomic force microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, surface complexation model, and quantum chemical calculation have been used to analyze adsorption mechanism of phosphate on mineral surface from different angles. Adsorption of phosphate on the surface of minerals (e.g., iron and aluminum oxides) is usually accompanied by exchange of aqueous and hydroxyl groups. It is generally believed that phosphate mainly forms bidentate binuclear, monodentate mononuclear inner-sphere complexes on the surface of minerals, which is greatly affected by pH. Both pH and adsorption density of phosphate on the surface of minerals affect its protonation state. Under special conditions (i.e., low pH, high phosphorus concentration, high reaction temperature, long adsorption duration, and adsorption by weak crystalline mineral), phosphate adsorbed on the surface of minerals may transform into phosphate-containing surface precipitates, thus resulting in mineral dissolution and conversion, and further decrease of phosphate bioavailability. In the end, prospects are discussed about hot spots and orientation of future researches related to phosphate sorption on the surface of minerals.