Abstract

Defluoridation of groundwater was performed in a batch reactor using bivalve shell powder (BSP) as adsorbent. The physicochemical characteristics of BSP, studied by Fourier Transform Infrared, X-ray Diffraction and Inductively Coupled Plasma-Optical Emission Spectrometry after dissolution, have shown that BSP was mainly composed of crystalline CaCO₃ (∼97.8%). The effects of pH, initial fluoride concentration, adsorbent dose and contact time on the adsorption capacity of BSP were investigated. For an initial fluoride concentration of 2.2 mg/L and with 16 g/L of BSP, after 8 hours of treatment, 27.3% were eliminated at pH 7.5 versus 68% at pH 3, highlighting the efficiency of the adsorption process. The difference in adsorption capacity as a function of pH was correlated to the pHpzc of the BSP, which was equal to 8.2. Thus, at pH below pHpzc, electrostatic attraction between the fluoride anions and the positively charged adsorbent could justify the adsorption mechanism. Fittings of experimental data have evidenced that the adsorption kinetics were of pseudo-second order whereas the adsorption isotherms were of Langmuir type. The chemical precipitation of calcium fluoride was also revealed to occur upon release of Ca²⁺ from partial dissolution of CaCO₃ in acidic conditions.

摘要

使用双壳壳粉 (BSP) 作为吸附剂在间歇反应器中对地下水进行脱氟。通过傅里叶变换红外光谱、X 射线衍射和电感耦合等离子体发射光谱法研究 BSP 溶解后的理化特性，表明 BSP 主要由结晶 CaCO ₃组成(~97.8%)。研究了pH值、初始氟化物浓度、吸附剂量和接触时间对BSP吸附能力的影响。对于 2.2 mg/L 的初始氟化物浓度和 16 g/L 的 BSP，处理 8 小时后，在 pH 7.5 时去除了 27.3%，而在 pH 3 时去除了 68%，突出了吸附过程的效率。作为 pH 函数的吸附容量差异与 BSP 的 pHpzc 相关，其等于 8.2。因此，在低于 pHpzc 的 pH 值下，氟阴离子和带正电的吸附剂之间的静电吸引力可以证明吸附机制是合理的。实验数据拟合表明吸附动力学是准二级的，而吸附等温线是朗缪尔型的。²⁺来自 CaCO ₃在酸性条件下的部分溶解。