基于透钙磷石向磷灰石转化的除氟过程及其机理

A study on the process and mechanism of defluorination based on the transformation of brushite to apatite

磷灰石的沉淀可以影响矿物相-水相之间氟化物的分配,在饮用水除氟以及延缓土壤中氟的迁移过程中扮演着重要角色。本研究通过共沉淀法制备了磷灰石的前驱体矿物透钙磷石,并将其转化为溶解度更低的磷灰石,以研究其转化过程中矿物相的演变及对氟的固定能力,并探讨了氟的固定机理。结果表明,溶液中的氟伴随着磷灰石的沉淀由液相转移至固相中,此过程对氟的固定量高达21.8 mg/g,是羟基磷灰石对氟吸附量的2.2倍。透钙磷石转化为磷灰石的过程为溶解-沉淀过程,氟在磷灰石的生长过程中进入磷灰石的结构中。此外,透钙磷石向磷灰石的转化过程对氟的去除具有高度选择性,溶液中共存的Cl^(-)、CO_(3)^(2-)、NO_(3)^(-)和SO_(4)^(2-)等阴离子几乎不影响其氟去除能力。研究结果表明,通过透钙磷石-磷灰石的转化可以将氟固定到磷灰石中,从而降低氟的可迁移性和渗入地下水造成的环境风险。

The precipitation of apatite could affect the distribution of fluoride between mineral and water phases.This mechanism plays a vital role in the defluorination of drinking water and the retardation of fluoride migration in soil.In this study,brushite,a precursor of apatite,was prepared by using the co-precipitation and was transformed into apatite which has relatively low solubility in order to investigate the evolution and fluoride removal capacity,and to discuss the fluoride removal mechanism of mineral phases during the transformation from brushite to apatite.The results show that fluorine in solution was transferred to the solid phase accompanied by the apatite precipitation,with a maximum fluorine removal capacity of 21.8 mg/g,which is 2.2 times higher than the adsorption capacity of fluorine by hydroxyapatite.The transformation process from brushite to apatite can be well explained by the dissolution-precipitation process,within which fluorine was incorporated into the structure of apatite crystal in its growth process.Furthermore,the fluoride removal by the transformation process of brushite to apatite is highly selective,as the fluoride removal capacity cannot be inhibited by other coexisted anions including Cl^(-),CO_(3)^(2-),NO_(3)^(-) and SO_(4)^(2-).Our results demonstrated that fluorine can be immobilized into apatite via the transformation of brushite to apatite,thereby the environmental risk caused by fluorine migration and infiltration into groundwater will be reduced.