羟基磷灰石除氟的实验地球化学研究

Macroscopic and Spectroscopic Study on Fluoride Sorption by HAP

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(p H≥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(R^2=0.89)同时也满足Freundlich等温模式(R^2=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、^(19)FNMR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 problemsthat drinking water contains excess F concentration. In this research, we adopted low-cost non-metal mineral hydroxyapatite (HAP) asadsorbent to study the geochemical behavior and mechanism of F adsorption as a function of reaction time, pH, and initial Fconcentration. After 48 hours, the reaction reached equilibrium and yielded a maximum adsorption amount of 21.6 mg/g at pH 6through regression analysis using Langmuir equation. To further understand the mechanisms of F adsorption on HAP, we employedadvanced geochemical approaches, such as XRD, SEM, HR-TEM, and 19F solid state NMR, to characterize the sorption products beforeand after reaction. It can be concluded that formation of F-Hap (s) solid-solution is the dominant mechanism at high F initialconcentration (>10 ppm). This study demonstrates that hydroxyapatite is a good candidate material for fluoride removal.