Division of Earth and Environmental Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan.
J Colloid Interface Sci. 2012 Oct 15;384(1):128-36. doi: 10.1016/j.jcis.2012.06.063. Epub 2012 Jul 2.
The sorption behavior and mechanism of phosphate on monohydrocalcite (CaCO(3)·H(2)O: MHC) were examined using batch sorption experiments as a function of phosphate concentrations, ionic strengths, temperatures, and reaction times. The mode of PO(4) sorption is divisible into three processes depending on the phosphate loading. At low phosphate concentrations, phosphate is removed by coprecipitation of phosphate during the transformation of MHC to calcite. The sorption mode at the low-to-moderate phosphate concentrations is most likely an adsorption process because the sorption isotherm at the conditions can be fitted reasonably with the Langmuir equation. The rapid sorption kinetics at the conditions is also consistent with the adsorption reaction. The adsorption of phosphate on MHC depends strongly on ionic strength, but slightly on temperature. The maximum adsorption capacities of MHC obtained from the regression of the experimental data to the Langmuir equation are higher than those reported for stable calcium carbonate (calcite or aragonite) in any conditions. At high phosphate concentrations, the amount of sorption deviates from the Langmuir isotherm, which can fit the low-to-moderate phosphate concentrations. Speciation-saturation analyses of the reacted solutions at the conditions indicated that the solution compositions which deviate from the Langmuir equation are supersaturated with respect to a certain calcium phosphate. The obtained calcium phosphate is most likely amorphous calcium phosphate (Ca(3)(PO(4))(2)·xH(2)O). The formation of the calcium phosphate depends strongly on ionic strength, temperature, and reaction times. The solubility of MHC is higher than calcite and aragonite because of its metastability. Therefore, the higher solubility of MHC facilitates the formation of the calcium phosphates more than with calcite and aragonite.
采用批量吸附实验研究了磷酸盐在一水碳酸钙（CaCO(3)·H(2)O：MHC）上的吸附行为和机理，考察了磷酸盐浓度、离子强度、温度和反应时间的影响。根据磷酸盐的负载量，PO(4)的吸附模式可分为三个过程。在低磷酸盐浓度下，通过 MHC 向方解石转化过程中磷酸盐的共沉淀去除磷酸盐。在低至中等磷酸盐浓度下的吸附模式很可能是吸附过程，因为在这些条件下的吸附等温线可以合理地与 Langmuir 方程拟合。在这些条件下的快速吸附动力学也与吸附反应一致。MHC 对磷酸盐的吸附强烈依赖于离子强度，但对温度的依赖性较小。从实验数据回归到 Langmuir 方程获得的 MHC 的最大吸附容量高于任何条件下稳定碳酸钙（方解石或文石）的报道值。在高磷酸盐浓度下，吸附量偏离 Langmuir 等温线，可拟合低至中等磷酸盐浓度。在这些条件下对反应溶液的形态饱和分析表明，偏离 Langmuir 方程的溶液组成相对于某种磷酸钙是过饱和的。所得到的磷酸钙很可能是无定形磷酸钙（Ca(3)(PO(4))(2)·xH(2)O）。磷酸钙的形成强烈依赖于离子强度、温度和反应时间。由于一水碳酸钙的亚稳性，其溶解度高于方解石和文石。因此，与方解石和文石相比，一水碳酸钙更高的溶解度更有利于磷酸钙的形成。
