Effect of pH and Phosphate on Calcium Carbonate Polymorphs Precipitated at near-Freezing Temperature
Effect of pH and Phosphate on Calcium Carbonate Polymorphs Precipitated at near-Freezing Temperature
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DOI：
10.1021/cg500829p
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发表时间：
2015-04-01
影响因子：
3.8
通讯作者：
Nehrke, Gernot
中科院分区：
文献类型：
--
作者：
Hu, Yu-Bin;Wolthers, Mariette;Nehrke, Gernot
考察了pH值和磷酸盐对碳酸钙从水溶液中析出的影响。实验在接近冰点的温度和两种不同的pH条件(pH 13.4和9.0)下进行。在每种pH条件下，将不同浓度的CaCl2和NaHCO3溶液混合，在不同的泵送速率下，分别在有无磷酸盐的情况下获得1：1和10：1的Ca/CO3比。结果表明，在pH为13.4时，只有伊卡石生成，与泵速、Ca/CO3比和磷酸盐无关。在pH 9.0时，无论Ca/CO3的比例如何，无磷时的沉淀物主要为球状陨石，有磷酸盐时的沉淀物主要为伊卡石。这些结果表明，在低温和中等碱性条件下(pH 9.0)，磷酸盐可以起到转换伊开石和球泡石晶型的作用。相反，在更高的碱性条件下(pH 13.4)，磷酸盐不是必要条件，高pH本身就足以在球状陨石上触发伊卡石的形成。
The effects of pH and phosphate on the precipitation of calcium carbonate polymorphs from aqueous solution were investigated. Experiments were carried out at near-freezing temperature and two different pH conditions (pH 13.4 and 9.0). At each pH condition, solutions having different concentrations of CaCl2 and NaHCO3 were mixed to achieve Ca/CO3 ratios of 1:1 and 10:1 at different pumping rates with and without phosphate. Results showed that, at pH 13.4, only ikaite was formed, independent of pumping rate, Ca/CO3 ratio, and phosphate. At pH 9.0, the precipitate was predominantly vaterite in the absence of phosphate and ikaite in the presence of phosphate regardless of the ratio of Ca/CO3. These results indicate that at low temperatures and moderate alkaline conditions (pH 9.0), phosphate can act as a switch between ikaite and vaterite polymorphs. Contrastingly, at higher alkaline conditions (pH 13.4) phosphate is not prerequisite and the high pH in itself is enough to trigger ikaite formation over vaterite.