Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan.
Department of Earth Sciences, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan.
J Hazard Mater. 2016 Mar 5;304:110-7. doi: 10.1016/j.jhazmat.2015.10.019. Epub 2015 Oct 17.
The metastability of monohydrocalcite (CaCO3·H2O: MHC) suggests high reactivity to dissolved trace elements. Using kinetic and isotherm sorption experiments with different reaction times (24h, 48h), As(V) sorption on MHC was examined to elucidate As(V) uptake by MHC. Although the MHC was transformed to aragonite with time, the MHC in higher As(V) loading conditions was able to persist longer than in lower loading conditions. Actually, As(V) uptake was negligible for samples in which the MHC remained. However, remarkable uptake of As(V) was observed for samples in which a complete transformation of MHC to aragonite occurred. Results of kinetic study confirmed that the timing of the MHC transformation coincided perfectly with that of As(V) removal from the solution. XAFS measurements showed that the local structure of As after the MHC transformation was almost identical to that of As in the As(V) coprecipitated aragonite. Sorption behavior of As(V) during the transformation is explainable theoretically by the substitution of As(V) into the aragonite structure. The distribution coefficient and (apparent) maximum sorption capacity of As(V) sorption on MHC after 48h at low-to-moderate As(V) concentrations are 500L/kg and 25μmol/g, respectively, which are much higher than those of simple adsorption of As(V) on calcite.
一水软钙石（CaCO3·H2O：MHC）的亚稳性表明其对溶解的微量元素具有高反应性。通过使用不同反应时间（24 小时、48 小时）的动力学和等温吸附实验，研究了 MHC 对 As(V)的吸附作用，以阐明 MHC 对 As(V)的摄取。尽管随着时间的推移，MHC 会转化为方解石，但在较高 As(V)负载条件下的 MHC 能够比在较低负载条件下更持久地存在。实际上，对于 MHC 仍存在的样品，As(V)的摄取可以忽略不计。然而，对于 MHC 完全转化为方解石的样品，观察到了显著的 As(V)摄取。动力学研究的结果证实，MHC 转化的时间与溶液中 As(V)去除的时间完全吻合。XAFS 测量表明，MHC 转化后 As 的局部结构几乎与共沉淀方解石中 As(V)的结构相同。MHC 转化过程中 As(V)的吸附行为可以通过 As(V)替代方解石结构来从理论上解释。在低至中等 As(V)浓度下，48 小时后 MHC 对 As(V)的吸附分配系数和（表观）最大吸附容量分别为 500L/kg 和 25μmol/g，这远高于方解石对 As(V)的简单吸附。
