BACKGROUND The interaction between Ca-HAP and Pb(2+) solution can result in the formation of a hydroxyapatite-hydroxypyromorphite solid solution [(PbxCa1-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 (PbxCa1-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. RESULTS Dissolution of the hydroxypyromorphite-hydroxyapatite solid solution [(PbxCa1-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 (XPb) of the solids. For the solids with high XPb [(Pb0.89Ca0.11)5(PO4)3OH], the aqueous Pb(2+) 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 XPb (0.00-0.80), the aqueous Pb(2+) 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. CONCLUSIONS The dissolution process of the solids with high XPb (0.89-1.00) was different from that of the solids with low XPb (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 f (o) ) were determined to be -3796.71 and -6314.63 kJ/mol, respectively. The solubility decreased with the increasing Pb/(Pb + Ca) molar ratios (XPb) of (PbxCa1‒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 (PbxCa1-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 (PbxCa1-x)5(PO4)3(OH) was in equilibrium with the Ca-rich aqueous solution. Graphical abstractLippmann diagrams for dissolution of the hydroxypyromorphite-hydroxyapatite solid solution [(PbxCa1-x)5(PO4)3OH] at 25 ˚C and an initial pH of 2.00.

中文翻译：

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羟基焦亚晶-羟基磷灰石固溶体[（PbxCa1-x）5（PO4）3OH]在25°C和pH 2-9下的表征，溶解和溶解度。

背景技术Ca-HAP与Pb（2+）溶液之间的相互作用可导致形成羟基磷灰石-羟基亚焦晶石固溶体[（PbxCa1-x）5（PO4）3（OH）]，这会极大地影响运输和分配在水，岩石和土壤中的有毒铅的含量。因此，有必要了解（PbxCa1-x）5（PO4）3（OH）的理化性质，主要是其在水溶液中的热力学溶解度和稳定性。然而，尚无关于溶出度和相关热力学数据的实验报道。结果研究了羟基焦亚晶-羟基磷灰石固溶体[（PbxCa1-x）5（PO4）3（OH）]在25°C的水溶液中的溶解情况。固体的Pb /（Pb + Ca）摩尔比（XPb）极大地影响了水的浓度。对于具有高XPb [（Pb0.89Ca0.11）5（PO4）3OH]的固体，Pb（2+）水溶液的浓度随时间迅速增加，在240-720 h溶解后达到峰值，然后逐渐降低，在5040 h溶解后达到稳定状态。对于低XPb（0.00-0.80）的固体，Pb（2+）的水溶液浓度随时间迅速增加，在溶解1-12 h后达到峰值，然后逐渐降低并在720-2160 h后达到稳定状态解散。结论高XPb（0.89-1.00）的固体与低XPb（0.00-0.80）的固体的溶解过程不同。羟基焦晶石[Pb5（PO4）3OH]的平均K sp值估计为10（-80.77±0.20）（10（-80.57）-10（-80.96））和10（-58.38±0.07）（10（- 58.31）-10（-58.46））的羟基磷灰石钙[Ca5（PO4）3OH]。形成的吉布斯自由能（ΔGf（o））分别确定为-3796.71和-6314.63 kJ / mol。溶解度随（PbxCa1x）5（PO4）3（OH）的Pb /（Pb + Ca）摩尔比（XPb）的增加而降低。对于在25°C且初始pH值为2.00的溶解，在Lippmann图上绘制的实验数据表明，固溶体（PbxCa1-x）5（PO4）3（OH）在溶解初期按化学计量溶解并移动。逐渐上升到Lippmann溶质曲线和Pb5（PO4）3OH的饱和度曲线，然后数据点沿着Lippmann溶质曲线从右向左移动。富含Pb的（PbxCa1-x）5（PO4）3（OH）与富含Ca的水溶液处于平衡状态。