原位水解生成的羟基氧化铁凝聚吸附除磷效能与机制

Effectiveness and mechanism of the in situ formed iron hydroxide( FeO_xH_y ) towards the removal of phosphate by coagulation and adsorption

将不同摩尔比Fe3+与OH-([Fe3+]∶[OH-]=1∶0、1∶1、1∶2和1∶3)反应获得原位水解生成的羟基氧化铁(in situ FeO x H y),研究了具有不同水解程度的羟基氧化铁对凝聚吸附除磷效能与机制。研究显示,In situ FeO x H y对磷的去除率随铁投量增大而升高,且均在中性pH范围内具有最佳除磷效果;在相同铁投量条件下,磷去除率随着[OH-]∶[Fe3+]的升高而降低;当体系碱度较低时(pH<6),引入OH-可促进Fe3+水解而提高除磷效果。4种羟基氧化铁均可在15 s内可快速吸附磷,且吸附过程符合准二级动力学模型;Freundlich模型均可很好地描述磷在4种羟基氧化铁表面的吸附行为。磷酸盐吸附后,In situ FeO x H y表面Zeta电位明显降低,且[Fe3+]∶[OH-]为1∶0的羟基氧化铁降低最为显著。结合MINITEQ计算软件磷酸盐、铁盐形态分析结果显示,对于碱度较低的体系,通过投加一定量OH-可促进Fe3+水解,进而使得其更易与水中H2PO-4与HPO2-4结合,生成具有多核羟基的磷酸铁络合物,进而提高除磷效果。

We prepared the in situ formed iron hydroxide （In situ FeOxHy） by the interactions between Fe3 ＋ and OH - at different molar ratios of 1 ：0, 1 ： 1,1 ： 2, and 1 ： 3, and investigated the performance and mecha- nism involved in the removal of phosphate. The removal efficiency increased with elevated doses of FeOxHy and the maximum removal was observed to be in neutral pH ranges. The elevated ratios of OH - to Fe3＋inhibit the re- moval of phosphate whereas at low alkalinity, the introduction of OH- shows beneficial effects. The ahovemen- tioned four kinds of FeOHy can rapidly adsorb most phosphate within 15 s,and the adsorption process can be well described by the Pseudo-second-order kinetic model. Freundlich model can well describe the adsorption of phosphorus onto these four FeOxHy. The adsorption of phosphate significantly decreases the zeta potential of these in situ FeOxHy. The MINITEQ software can indicate the species distribution of phosphate and iron salts,and the theoretical calculation indicates that the introduced OH - can promote the hydrolysis of Fe3＋ especially in low al- kalinity system,which can easily adsorb H2PO/ and HPO42- and form the multinuclear hydroxy iron phosphate complexes thereafter.