无机磷酸盐离子对球霰石自发沉淀和球霰石向方解石转化的影响,Journal of Crystal Growth

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无机磷酸盐离子对球霰石自发沉淀和球霰石向方解石转化的影响
Journal of Crystal Growth ( IF 1.7 ) Pub Date : 1999-07-01 , DOI: 10.1016/s0022-0248(99)00174-8
Apostolis Katsifaras , Nikos Spanos

摘要在25°C、pH 9.0和10.0的恒定过饱和条件下，研究了碳酸钙沉淀过程中无机正磷酸根离子对球霰石沉淀和球霰石向热力学稳定方解石转变的影响。固体沉淀物的方解石含量通过粉末 X 射线衍射 (XRD) 使用以已知量混合的适当标准进行定量测定。发现非常少量的无机磷酸盐离子的存在会降低球霰石结晶的速率。将动力学数据应用于 Langmuir 型模型表明，在活性生长位点吸附磷酸盐是导致晶体生长速率降低的原因。在相对较高的过饱和比 (1.5–2.1) 下，其中转化率随着过饱和度的增加而降低，发现最初形成的球霰石向方解石的转化仅取决于过饱和度而不取决于发生沉淀的过饱和溶液的 pH 值。根据动力学结果表明，转变是通过球霰石溶解然后方解石结晶而发生的。在相对较高的过饱和比 (1.5-2.1) 下，转变由球霰石的溶解控制，而在较低的过饱和比 (1.1-1.5) 下，球霰石的溶解速率与相应的方解石结晶速率相当。最后，发现沉淀溶液中磷酸盐离子的存在稳定了最初形成的球霰石，通过显着降低其转化为方解石的速度。在磷酸根离子存在下球霰石的稳定性归因于球霰石溶解和方解石结晶的延迟，这是由于球霰石溶解和方解石结晶的活性位点被阻塞，由吸附磷酸盐。

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Effect of inorganic phosphate ions on the spontaneous precipitation of vaterite and on the transformation of vaterite to calcite

Abstract The effect of inorganic orthophosphate ions on both the precipitation of vaterite and the transformation of vaterite to the thermodynamically stable calcite was investigated during the precipitation process of calcium carbonate, under conditions of constant supersaturation at 25°C and at pH 9.0 and 10.0. The calcite content of the solid precipitates was determined quantitatively by powder X-ray diffraction (XRD) using the appropriate standards mixed at known amounts. The presence of very small amounts of inorganic phosphate ions was found to reduce the rate of vaterite crystallization. Application of the kinetic data to a Langmuir-type model suggested that adsorption of phosphate at the active growth sites was responsible for the reduction in the crystal growth rates. At relatively high supersaturation ratios (1.5–2.1), where the transformation rate decreases with increasing supersaturation ratio, it was found that the transformation of the initially formed vaterite to calcite depends only on the supersaturation ratio and not on the pH of the supersaturated solutions in which precipitation takes place. It was suggested on the basis of the kinetic results, that the transformation takes place through dissolution of vaterite followed by crystallization of calcite. At relatively high supersaturation ratios (1.5–2.1) the transformation is controlled by the dissolution of vaterite, whereas at lower supersaturation ratios (1.1–1.5) the rate of vaterite dissolution is comparable with the respective rate of calcite crystallization. Finally, it was found that the presence of phosphate ions in the precipitating solution stabilized the initially formed vaterite, by decreasing markedly the rate of its transformation to calcite. The stability of vaterite in the presence of the phosphate ions was ascribed to the retardation of both the dissolution of vaterite and of the crystallization of calcite, caused by blocking of the active sites for the dissolution of vaterite and for the crystallization of calcite, by the adsorbed phosphates.

更新日期：1999-07-01

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