The solubility of La hydroxide and stability of La3+ and La hydroxyl complexes at acidic to mildly acidic pH from 25 to 250 °C

Batch-type hydrothermal solubility experiments were conducted using synthetic La hydroxide powders equilibrated in perchloric acid-based aqueous solutions at temperatures between 150 and 250 °C and starting pH of 2 to 5. The La hydroxide solubility is retrograde with temperature and displays a strong pH dependence with a decrease in La concentrations from acidic to mildly acidic pH spanning between 3 to 5 orders of magnitude (e.g. log La molality of -2.5 to -7.2 at 250 °C). Thermodynamic optimizations using GEMSFITS allow to retrieve the standard partial molal Gibbs energies for the La3+ aqua ion and the formation constants for the La hydroxyl species (i.e., LaOH2+, La(OH)2+, La(OH)30) between 25 and 250 °C.

采用合成的镧氢氧化物粉末，在150至250°C的温度范围内，以高氯酸基水溶液作为平衡体系，并在起始pH值介于2至5之间进行了一系列批处理型水热溶解度实验。镧氢氧化物的溶解度随温度升高而降低，并表现出对pH值的强烈依赖性，镧浓度从酸性至弱酸性pH值范围内的变化达到3至5个数量级（例如，在250°C时，镧摩尔活度的对数值从-2.5降至-7.2）。通过GEMSFITS软件进行的热力学优化，能够提取镧三价水合离子以及镧羟基物种（即，LaOH2+、La(OH)2+、La(OH)30）在25至250°C范围内的标准部分摩尔吉布斯能和形成常数。