Arsenite and arsenate adsorption on ferrihydrite:: Surface charge reduction and net OH- release stoichiometry
Arsenite and arsenate adsorption on ferrihydrite:: Surface charge reduction and net OH- release stoichiometry
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DOI：
10.1021/es980722e
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发表时间：
1999-04-15
影响因子：
11.4
通讯作者：
Loeppert, RH
中科院分区：
文献类型：
--
作者：
Jain, A;Raven, KP;Loeppert, RH
亚砷酸盐[As（III）]和砷酸盐[As（V）]是高毒性无机砷物种，对环境和人类健康构成潜在威胁。铁氧化物，包括结晶性差的氧化物，例如，水铁矿在控制溶解As浓度和限制As（III）和As（V）的移动性和生物有效性方面起重要作用。吸附发生的配体交换的作为物种的OH 2和OH-在表面结构的Fe原子的配位球。本研究的目的是评估H+/OH-释放的化学计量和表面电荷性质的吸附剂在吸附过程中的亚砷酸盐和砷酸盐的水铁矿在pH值为4-10的变化。这些信息，这是不能直接通过光谱研究，提供了重要的线索，键合机制。而砷酸盐吸附导致在pH 4.6和9.2的OH-的净释放，亚砷酸盐吸附导致在pH 9.2的净OH-释放和净H+释放在pH 4.6。H+或OH-释放量每摩尔的吸附As的变化与As表面覆盖，表明不同的机制，砷吸附占主导地位，在低与高覆盖。实验观察到的表面电荷减少和净OH-释放的化学计量进行了比较，与可能发生的表面吸附反应的理论化学计量。结果表明，在低pH条件下，pH 4.6时，Fe-O-As键的氧仍部分质子化为FeO（H）-As。有证据表明，单齿键合机制可能发挥越来越大的作用，在砷酸盐吸附在水铁矿的pH值增加（在pH > 8）。本研究的结果提供了辅助证据，以支持实验观察到的低pH值和高pH值的砷酸盐的吸附减少。
Arsenite [As(III)] and arsenate [As(V)] are highly toxic inorganic arsenic species that represent a potential threat to the environment and human health. Iron oxides including poorly crystalline oxides, e.g., ferrihydrite, play a significant role in controlling dissolved As concentration and limit the mobility and bioavailability of As(III) and As(V). Adsorption occurs by ligand exchange of the As species for OH2 and OH- in the coordination spheres of surface structural Fe atoms. The objective of this study was to evaluate H+/OH- release stoichiometry and changes in surface charge properties of the adsorbent during the adsorption of arsenite and arsenate on ferrihydrite in the pH range of 4-10. This information, which is not directly accessible through spectroscopic studies, provides important clues to bonding mechanism. While arsenate adsorption resulted in the net release of OH- at pH 4.6 and 9.2, arsenite adsorption resulted in net OH- release at pH 9.2 and net H+ release at pH 4.6. The amount of H+ or OH- release per mole of adsorbed As varied with the As surface coverage, indicating that different mechanisms of arsenic adsorption predominate at low versus high coverage. The experimentally observed surface charge reduction and net OH- release stoichiometry were compared with the theoretical stoichiometry of the surface adsorption reactions that might occur. The results provide evidence that during arsenite adsorption at low pH, i.e., pH 4.6, the oxygen of the Fe-O-As bond remained partially protonated as FeO(H)-As. There is evidence that the monodentate bonding mechanism might play an increasing role during arsenate adsorption on ferrihydrite with increasing pH (at pH > 8). The results of this study have provided ancillary evidence to support the experimentally observed reduced adsorption of arsenite at low pH and of arsenate at high pH.