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The stabilities of calcium arsenates at 23 ± ldeg.C

机译:砷酸钙在23±1摄氏度下的稳定性

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The stabilities of calcium arsenate compounds were established by analysis of suspensions made with varying molar Ca/As ratios. Solution chemistry analyses determined the concentrations of calcium and arsenic and pH. The phases that were shown to form in order of descending pH were Ca_4(OH)_2(AsO_4)_2. 4H_2O, Ca_5(AsO_4)_3OH (arsenate-apatite), Ca_3(AsO_4)_2 3 2/3H_2O, Ca_3(AsO_4)_2 4 1/41H_2O, Ca_5H_2(AsO_4)_4 9H_2O -- ferrarisite, Ca_5H_2(AsO_4)_4 9H_2O -- guerinite and CaHAsO_4 H_2O. The analytical concentrations of calcium and arsenic and pH were used in estimating solubility products. The estimated values were then refined through the comparison of the analytical data with calculated K_sp, values using the computer program PhreeqC. From the refined solubility products, the free energies of formation of the calcium arsenate hydrates were calculated as follows: Ca_4(OH)_2(AsO_4)_2 4H_2O (--494l kJ/mol), Ca_5(AsO_4)_3OH (--5087 kJ/mol), Ca_3(AsO_4)_2 3 2/3H_2O (-- 3945 kJ/mol), Ca_3(AsO_4)_2 4 4/1H_2O (--4085 kJ/mol), Ca_5H_2(AsO_4)_4 9H_2O -- ferrarisite (-- 7808 kJ/mol), Ca_5H_2(AsO_4)_4 9H_2O -- guerinite (--7803 kJ/mol), and CaHAsO_4 H_2O (-- l533 kJ/mol). Unlike other solubility studies on arsenate immobilization, this study was the first to consider the complete array of calcium arsenate hydrates that can form and to use the associated ions, CaAsO_4, CaHAsO_4 and CaH_2AsO~+_4 in determining their solubility products.
机译:砷酸钙化合物的稳定性是通过分析以不同摩尔Ca / As比制成的悬浮液来确定的。溶液化学分析确定了钙和砷的浓度以及pH值。所示的按pH降序形成的相为Ca_4(OH)_2(AsO_4)_2。 4H_2O,Ca_5(AsO_4)_3OH(砷酸磷灰石),Ca_3(AsO_4)_2 3 2 / 3H_2O,Ca_3(AsO_4)_2 4 1 / 41H_2O,Ca_5H_2(AsO_4)_4 9H_2O-铁酸盐,Ca_5H__2(AsO_4) -钙质沸石和CaHAsO_4 H_2O。钙,砷和pH的分析浓度用于估算溶解度产物。然后通过使用计算机程序PhreeqC将分析数据与计算得出的K_sp值进行比较,从而对估计值进行细化。从精制的溶解度产物中,砷酸钙水合物的形成自由能计算如下:Ca_4(OH)_2(AsO_4)_2 4H_2O(-494l kJ / mol),Ca_5(AsO_4)_3OH(--5087 kJ / mol),Ca_3(AsO_4)_2 3 2 / 3H_2O(-3945 kJ / mol),Ca_3(AsO_4)_2 4 4 / 1H_2O(--4085 kJ / mol),Ca_5H_2(AsO_4)_4 9H_2O-铁酸盐( -7808 kJ / mol),Ca_5H_2(AsO_4)_4 9H_2O-钙钠石(--7803 kJ / mol)和CaHAsO_4 H_2O(-1533 kJ / mol)。与其他关于砷酸盐固定化的溶解度研究不同,该研究是第一个考虑可形成的完整砷酸钙水合物的阵列,并使用相关离子CaAsO_4,CaHAsO_4和CaH_2AsO〜+ _4确定其溶解度产物。

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