铁（氢）氧化物悬液中磷酸盐的吸附-解吸特性研究

铁（氢）氧化物对P的吸持和释放在一定程度上决定着P的生物有效性和水体富营养化。以两种环境中常见晶质铁氧化物（针铁矿和赤铁矿）为对照，采用X射线衍射（XRD）、透射电镜（TEM）、热重分析（TGA）和孔径分析以及动力学和吸附-解吸热力学平衡等技术方法，研究了弱晶质水铁矿对P吸附-解吸特性，并探讨了相关机制。实验表明，三种矿物对P的吸附分为起始的快速反应和随后的慢速反应，它们均符合准一级动力学过程，反应中OH释放明显滞后于P吸附，P吸附经历了从外围到内囤配位、单齿到多齿配位过渡的过程，与晶质氧化铁比，水铁矿吸附容量和OH释放量更大、慢速吸附反应更快、存在缓慢扩散反应阶段，吸附容量依次是：水铁矿（436μmol／m^2）〉针铁矿（262μmol／m^2）〉赤铁矿（228μmol／m^2），针铁矿和赤铁矿吸附P符合L（Langmuir）模型，而水铁矿更符合F（Fremldlictl）模型。中性盐介质（KCl）中在最大吸附量时P的解吸率依次为：水铁矿（85％）〈针铁矿（10％）〈赤铁矿（125％），柠檬酸通过配体解吸和诱导溶解两种机制促进P的解吸，最大吸附量时解吸率依次是：针铁矿（25％）〈水铁矿（32％）〈赤铁矿（50％）。

The P adsorption-desorption characteristics on ferrihydrite and crystalline Fe oxides suspension

The retention and release of P onto iron oxides influence and determine the bioavailability and eutrophication of R We study the adsorption-desorption characteristics of P onto ferrihydrite and explore the relevant mechanisms compared with two common crystalline Fe oxides （goethite and hematite）, using the techniques of X-ray diffraction （XRD）, transmission electron microscopy （TEM）, thermal gravimetric analysis （TGA）, porosity structure analysis and the methods of kinetics and adsorption-desorption equilibrium. Results show a fast initial adsorption took place in a few minutes followed by a slow reaction process, both of which can be well fitted by first order kinetics. During the reaction, the release of OH lags behind P adsorption and increases step by step, indicating that P adsorption may go through complexation from outer-sphere to inner-sphere, from monodentate to bidentate coordination. Compared with goethite and hematite, ferrihydrite has higher amount of P adsorption and OH release, faster slow reaction process, and exhibits slow diffusion reaction stage. The maximum adsorption capacities are in order of： ferrihydrite （4.36μmol/m^2） 〉〉 goethite （2.62 μmol/m^2） 〉 hematite （2.28μmol/m^2）; adsorption isotherms of goethite and hematite agree well with Langmuir model while ferrihydrite exhibits an adsorption isotherm of Freundlich type. Desorption percentage of adsorbed P by neutral electrolyte at maximum adsorption capacities is in order of： ferrihydrite （8.5%） 〈 goethite （10%） 〈 hematite （12.5%）. Relatively, citric acid significantly promotes the desorption reaction. Desorption percentages at the maximum adsorption capacity are in order of： goethite （25%） 〈 ferrihydrite （32%） 〈 hematite （50%）.