羟基磷灰石除氟的实验地球化学研究

中国和世界上许多国家（地区） 都面临着饮用水氟含量超标的问题，因此研究氟的环境地球化学行为以及探索除氟 技术和原理至关重要。本实验采用廉价的非金属矿物羟基磷灰石作为吸附材料，研究羟基磷灰石吸附溶解态F-的地球化学 行为和机制，考察反应时间、pH、初始F-浓度等环境参数对吸附反应的影响。实验结果发现羟基磷灰石对F-的吸附反应需 进行到48 h以上时才接近反应平衡。在实验条件下（pH≥4），F-的吸附量随pH升高而降低，羟基磷灰石对F-的吸附受pH 调控。同时还发现羟基磷灰石在pH=6条件下对F-的吸附等温线既满足Langmuir等温模式（R2=0.89） 同时也满足Freundlich 等温模式（R2=0.99），并推导出该条件的理论最大吸附量为21.6×10-3。本研究还进一步采用了先进的XRD、SEM、 HR-TEM、19F NMR手段，系统地表征了反应前后吸附产物的形态和成分变化，发现在高F-浓度条件下，F-在羟基磷灰石表 面的吸附机制不再是单层的表面配位。核磁共振的结果表明F-可部分取代羟基磷灰石结构中的隧道羟基而形成含氟羟基磷 灰石。研究结果表明羟基磷灰石是一种相当具有潜力的除氟材料，值得进一步开发。
Geologic fluoride pollution is a worldwide environmental problem, as numerous countries and regions are facing problems that drinking water contains excess F concentration. In this research, we adopted low-cost non-metal mineral hydroxyapatite (HAP) as adsorbent to study the geochemical behavior and mechanism of F adsorption as a function of reaction time, pH, and initial F concentration. After 48 hours, the reaction reached equilibrium and yielded a maximum adsorption amount of 21.6 mg/g at pH 6 through regression analysis using Langmuir equation. To further understand the mechanisms of F adsorption on HAP, we employed advanced geochemical approaches, such as XRD, SEM, HR-TEM, and 19F solid state NMR, to characterize the sorption products before and after reaction. It can be concluded that formation of F-Hap (s) solid-solution is the dominant mechanism at high F initial concentration (>10 ppm). This study demonstrates that hydroxyapatite is a good candidate material for fluoride removal.