Abstract：
This research aimed to introduce a novel method for the valorization of mineral waste, focusing on the development of hydroxyapatite (HAP) as an effective and economical adsorbent for immobilizing fluoride ions (F-) in soil. Hydroxyapatites were produced through the reaction between potassium dihydrogen phosphate (KH2PO4) and calcium-abundant limestone soil (CLS). X-ray diffraction analyses revealed that the primary phases in HAPCLS were brushite (CaHPO5·2H2O) and hydroxyapatite (Ca10(PO4)6(OH)2). The FTIR spectra exhibited characteristics akin to natural HAP, including the presence of orthophosphate groups (PO43-), hydroxyl groups (OH-), and both A/B types of carbonates in the apatite structure. The morphology of the synthesized HAP, as observed through SEM-EDS, was consistent with that of phosphocalcic hydroxyapatite crystals. The EDS results indicated a Ca/P atomic ratio of 1.7 for HAPCLS, aligning closely with the typical hydroxyapatite stoichiometry (Ca/P = 1.67). The application of HAP to reduce fluoride (F-) levels in soil proved to be successful; introducing 1% of various HAP formulations reduced the fluoride concentration from 51.4 mg/kg in untreated soil to levels below the IWSI limit (10 mg/kg), achieving a reduction to 8.1 mg/kg for HAPCLS. The sequential extraction of fluoride demonstrated that after soil treatment, fluoride was predominantly removed from the residual fraction (Fraction 4) and was effectively sequestered by the hydroxyapatites (Ca10(PO4)6(OH)2) through anionic exchange with hydroxide ions (OH-), resulting in the formation of stable and insoluble fluorapatite (Ca10(PO4)6F2).
摘要：
本研究的目的是介绍一种新的矿物废物的价值化方法，重点开发羟基磷灰石（HAP）作为一种有效和经济的吸附剂，用于固定土壤中的氟离子（F-）。羟基磷灰石是通过磷酸二氢钾（KH2PO4）与富钙石灰岩土壤（CLS）之间的反应产生的。X射线衍射分析表明，HAPCLS中的主要相是透钙磷石（CaHPO5·2H2O）和羟基磷灰石（Ca10（PO4）6（OH）2）。FTIR光谱表现出类似于天然HAP的特征，包括正磷酸基团（PO43-）的存在，羟基(OH-),和磷灰石结构中的两种A/B型碳酸盐。合成的HAP的形态，如通过SEM-EDS观察到的，与磷钙羟基磷灰石晶体一致。EDS结果表明，HAPCLS的Ca/P原子比为1.7，与典型的羟基磷灰石化学计量(Ca/P=1.67)密切相关。应用HAP降低土壤中的氟化物（F-）水平被证明是成功的；引入1％的各种HAP配方将未处理土壤中的氟化物浓度从51.4mg/kg降低到IWSI限值（10mg/kg）以下，实现HAPCLS降至8.1mg/kg。氟化物的顺序提取表明，经过土壤处理后，氟化物主要从残留部分（馏分4）中去除，并通过与氢氧根离子（OH-）的阴离子交换被羟基磷灰石（Ca10（PO4）6（OH）2）有效地隔离。导致形成稳定且不溶的氟磷灰石(Ca10(PO4)6F2)。
