Characterization, dissolution and solubility of the hydroxypyromorphite–hydroxyapatite solid solution [(PbxCa1−x)5(PO4)3OH] at 25 °C and pH 2–9

IF 0.9 4区地球科学 Q4 GEOCHEMISTRY & GEOPHYSICS

Geochemical Transactions Pub Date : 2016-05-06 DOI:10.1186/s12932-016-0034-8

Yinian Zhu, Bin Huang, Zongqiang Zhu, Huili Liu, Yanhua Huang, Xin Zhao, Meina Liang

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引用次数: 36

Abstract

The interaction between Ca-HAP and Pb²⁺ solution can result in the formation of a hydroxyapatite–hydroxypyromorphite solid solution [(Pb_xCa_1?x)₅(PO₄)₃(OH)], which can greatly affect the transport and distribution of toxic Pb in water, rock and soil. Therefore, it’s necessary to know the physicochemical properties of (Pb_xCa_1?x)₅(PO₄)₃(OH), predominantly its thermodynamic solubility and stability in aqueous solution. Nevertheless, no experiment on the dissolution and related thermodynamic data has been reported.

Dissolution of the hydroxypyromorphite–hydroxyapatite solid solution [(Pb_xCa_1?x)₅(PO₄)₃(OH)] in aqueous solution at 25?°C was experimentally studied. The aqueous concentrations were greatly affected by the Pb/(Pb?+?Ca) molar ratios (X_Pb) of the solids. For the solids with high X_Pb [(Pb_0.89Ca_0.11)₅(PO₄)₃OH], the aqueous Pb²⁺ concentrations increased rapidly with time and reached a peak value after 240–720?h dissolution, and then decreased gradually and reached a stable state after 5040?h dissolution. For the solids with low X_Pb (0.00–0.80), the aqueous Pb²⁺ concentrations increased quickly with time and reached a peak value after 1–12?h dissolution, and then decreased gradually and attained a stable state after 720–2160?h dissolution.

The dissolution process of the solids with high X_Pb (0.89–1.00) was different from that of the solids with low X_Pb (0.00–0.80). The average K _sp values were estimated to be 10^?80.77±0.20 (10^?80.57–10^?80.96) for hydroxypyromorphite [Pb₅(PO₄)₃OH] and 10^?58.38±0.07 (10^?58.31–10^?58.46) for calcium hydroxyapatite [Ca₅(PO₄)₃OH]. The Gibbs free energies of formation (ΔG ^o_f ) were determined to be ?3796.71 and ?6314.63?kJ/mol, respectively. The solubility decreased with the increasing Pb/(Pb?+?Ca) molar ratios (X_Pb) of (Pb_xCa_1?x)₅(PO₄)₃(OH). For the dissolution at 25?°C with an initial pH of 2.00, the experimental data plotted on the Lippmann diagram showed that the solid solution (Pb_xCa_1?x)₅(PO₄)₃(OH) dissolved stoichiometrically at the early stage of dissolution and moved gradually up to the Lippmann solutus curve and the saturation curve for Pb₅(PO₄)₃OH, and then the data points moved along the Lippmann solutus curve from right to left. The Pb-rich (Pb_xCa_1?x)₅(PO₄)₃(OH) was in equilibrium with the Ca-rich aqueous solution.

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羟基磷闪石-羟基磷灰石固溶体[(PbxCa1−x)5(PO4)3OH]在25℃和pH 2-9条件下的表征、溶解和溶解度

Ca-HAP与Pb2+溶液相互作用可形成羟基磷灰石-羟基磷灰石固溶体[(PbxCa1?x)5(PO4)3(OH)]，极大地影响有毒铅在水、岩石和土壤中的迁移和分布。因此，有必要了解(PbxCa1?x)5(PO4)3(OH)的物理化学性质，主要是其在水溶液中的热力学溶解度和稳定性。然而，没有关于溶解的实验和相关热力学数据的报道。羟基磷闪石-羟基磷灰石固溶体[(PbxCa1?x)5(PO4)3(OH)]在水溶液中25?°C进行了实验研究。固体的Pb/(Pb?+?Ca)摩尔比(XPb)对水溶液浓度有较大影响。对于高XPb固体[(Pb0.89Ca0.11)5(PO4)3OH]，水中Pb2+浓度随时间迅速增加，在240 ~ 720?H溶解，然后逐渐减少，在5040?h解散。对于低XPb固体(0.000 ~ 0.80)，水中Pb2+浓度随时间快速增加，在1 ~ 12℃时达到峰值。溶解度逐渐降低，在720 ~ 2160?h解散。高XPb固体(0.89 ~ 1.00)与低XPb固体(0.00 ~ 0.80)的溶解过程不同。羟基磷闪石[Pb5(PO4)3OH]的平均K sp值为10?80.77±0.20(10?80.57 ~ 10?80.96)，羟基磷灰石钙[Ca5(PO4)3OH]的平均K sp值为10?58.38±0.07(10?58.31 ~ 10?58.46)。Gibbs自由生成能(ΔG of)分别为?3796.71和?6314.63?焦每摩尔。随着(PbxCa1?x)5(PO4)3(OH)的Pb/(Pb?+?Ca)摩尔比(XPb)的增加，溶解度降低。25岁时离婚?在初始pH为2.00的条件下，在Lippmann图上绘制的实验数据显示，固溶体(PbxCa1?x)5(PO4)3(OH)在溶解初期呈化学量溶解，并逐渐向上移动到Lippmann溶质曲线和Pb5(PO4)3OH的饱和曲线，然后数据点沿着Lippmann溶质曲线从右向左移动。富铅(PbxCa1?x)5(PO4)3(OH)与富钙水溶液处于平衡状态。

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来源期刊

Geochemical Transactions 地学-地球化学与地球物理

CiteScore

3.70

自引率

4.30%

发文量

审稿时长

>12 weeks

期刊介绍： Geochemical Transactions publishes high-quality research in all areas of chemistry as it relates to materials and processes occurring in terrestrial and extraterrestrial systems.