Surface complexation modeling of fluoride sorption onto calcite
Surface complexation modeling of fluoride sorption onto calcite
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DOI：
10.1016/j.jece.2015.06.027
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发表时间：
2015-09
影响因子：
7.7
通讯作者：
S. Padhi;T. Tokunaga
中科院分区：
文献类型：
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作者：
S. Padhi;T. Tokunaga
在许多国家，方解石和各种钙盐已被用来去除饮用水和废水中的氟化物，而钙质土壤阻碍了氟化物在土壤中的流动性。氟在方解石上的吸附在低氟浓度下可能是重要的。本研究采用方解石平衡溶液进行了一系列的批量实验，探讨了方解石对氟的吸收机理。初始氟浓度范围为2.5 ~ 10 mg/l。评价了pH值、离子强度和固体浓度的影响。氟的吸收被发现强烈依赖于pH值，而离子强度也影响氟的去除。采用恒电容模型模拟方解石对氟化物的吸附，其中氟化物吸附通过形成两个表面配合物> caf0和>CO3FCa0来描述。热力学方法证明了> co3fca0络合物的形成，而> co3fca0包合物是解释氟化物在方解石表面吸附的必要条件。在有沉淀和没有沉淀的情况下模拟氟化物的吸附。结果表明，在低氟浓度条件下，吸附是方解石除氟的控制机制，而在低pH和高氟浓度条件下，氟化物与方解石的相互作用需要吸附和萤石沉淀的联合机制。因此，在方解石丰富的适宜条件下，氟化物对方解石的吸附会影响氟化物在土壤中的迁移。此外，除沉淀法外，在使用方解石或石灰石作为除氟剂之一的除氟方法中，还应考虑表面吸附。
Calcite and various calcium salts have been used to remove fluoride from drinking water and waste water in many countries, and calcareous soils retard the mobility of fluoride in soil. Adsorption of fluoride onto calcite could be important at low fluoride concentration. In this study, a series of batch experiments with calcite equilibrated solutions was conducted to investigate the mechanisms of fluoride uptake by calcite. The range of initial fluoride concentration was from 2.5 to 10 mg/l. Effects of pH, ionic strength, and solid concentration were evaluated. Fluoride uptake was found to be strongly pH dependent whereas ionic strength also affected fluoride removal. A constant capacitance model was used to model fluoride sorption onto calcite, where fluoride adsorption was described by the formation of two surface complexes, >CaF0and >CO3FCa0. The formation of >CaF0complex was evidenced from thermodynamic approach, whereas inclusion of >CO3FCa0was necessary to explain fluoride sorption to calcite surface. Fluoride sorption was modeled with and without precipitation. The results showed that, at lower fluoride concentration, adsorption was the governing mechanism for fluoride removal by calcite whereas a combined mechanism of adsorption and fluorite precipitation was necessary to describe fluoride interaction with calcite at low pH and higher fluoride concentration. Thus, adsorption of fluoride to calcite can influence the mobility of fluoride in soil under suitable conditions where calcite is abundant. Also, surface adsorption should also be considered in addition to precipitation in defluoridation methods, which use calcite or limestone as one of the defluoridating agents.