A series of the calcium-nickel carbonate solid solutions [(Ca1−xNix)CO3] were synthesized and their dissolution in N2-degassed water (NDW) and CO2-saturated water (CSW) at 25 °C was experimentally investigated. During dissolution of the synthetic solids (Ni-bearing calcite, amorphous Ca-bearing NiCO3 and their mixtures), the Ni-calcite and the Ca-NiCO3 dissolved first followed by the formation of the Ni-bearing aragonite-structure phases. After 240–300 days of dissolution in NDW, the water solutions achieved the stable Ca and Ni concentrations of 0.592–0.665 and 0.073–0.290 mmol/L for the solids with lower Ni/(Ca + Ni) mol ratios (XNi), or 0.608–0.721 and 0.273–0.430 mmol/L for the solids with higher XNi, respectively. After 240–300 days of dissolution in CSW, the water solutions achieved the stable Ca and Ni concentrations of 1.094–3.738 and 0.831–4.300 mmol/L, respectively. For dissolution in NDW and CSW, the mean values of log IAP (Ion activity products) in the final stable state (≈ log Ksp, Solubility product constants) were determined to be − 8.65 ± 0.04 and − 8.16 ± 0.11 for calcite [CaCO3], respectively; − 8.50 ± 0.02 and − 7.69 ± 0.03 for the synthetical nickel carbonates [NiCO3], respectively. In respect to the bulk composition of the (Ca1−xNix)CO3 solid solutions, the final log IAP showed the highest value when XNi = 0.10–0.30. Mostly, the mean values of log IAP increased with the increasing XNi in respect to the Ni-calcite, the Ni-aragonite and the amorphous Ca-Ni carbonate. The plotting of the experimental data on the Lippmann diagram for the (Ca1−xNix)CO3 solid solution using the predicted Guggenheim parameters of a0 = 2.14 and a1 = − 0.128 from a miscibility gap of XNi = 0.238 to 0.690 indicated that the solids dissolved incongruently and the final Ca and Ni concentrations in the water solutions were simultaneously limited by the minimum stoichiometric saturation curves for the Ni-calcite, Ni-aragonite and the amorphous Ca-Ni carbonate. During dissolution in NDW, the Ni2+ preferred to dissolve into the water solution and Ca2+ preferred to remain in the solid, while during dissolution in CSW for the solids with higher XNi, the Ca2+ preferred to dissolve into the water solution and Ni2+ preferred to remain in the solid. These findings provide valuable insights into understanding the mechanisms governing Ni geochemical cycle in natural environments.

中文翻译：

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碳酸钙镍固溶体 [（Ca1−xNix）CO3] 在 25 °C 下的溶解度和溶解度


合成了一系列碳酸钙镍固溶体 [（Ca1−xNix）CO3]，并实验研究了它们在 25 °C 下在 N2 脱气水 （NDW） 和 CO2 饱和水 （CSW） 中的溶解情况。在合成固体（含镍方解石、无定形含钙 NiCO3 及其混合物）的溶解过程中，镍方解石和 Ca-NiCO3 首先溶解，然后形成含镍文石结构相。在 NDW 中溶解 240-300 天后，水溶液的 Ca 和 Ni 浓度稳定在 0.592-0.665 和 0.073-0.290 mmol/L（Ni 含量较低）的固体中，XNi 含量较高的固体分别为 0.608-0.721 和 0.273-0.430 mmol/L。在 CSW 中溶解 240-300 天后，水溶液分别达到 1.094-3.738 和 0.831-4.300 mmol/L 的稳定 Ca 和 Ni 浓度。对于在 NDW 和 CSW 中的溶解，最终稳定状态（≈ log Ksp，溶解度产物常数）的 log IAP（离子活性产物）的平均值分别为 − 8.65 ± 0.04 和 -8.16 ± 0.11方解石 [CaCO3];合成碳酸镍 [NiCO3] 分别为 − 8.50 ± 0.02 和 − 7.69 ± 0.03。关于 （Ca1−xNix）CO3 固溶体的本体组成，当 XNi = 0.10–0.30 时，最终对数 IAP 显示最高值。大多数情况下，对于镍方解石、镍文石和非晶态 Ca-Ni 碳酸盐，log IAP 的平均值随着 XNi 的增加而增加。使用预测的古根海姆参数 a0 = 2.14 和 a1 = − 0.128，从 XNi = 0.238 到 0 的混溶性间隙，在李普曼图上绘制 （Ca1−xNix）CO3 固溶体的实验数据。690 表明固体溶解不一致，水溶液中的最终 Ca 和 Ni 浓度同时受到 Ni-方解石、Ni-文石和非晶型 Ca-Ni 碳酸盐的最小化学计量饱和度曲线的限制。在 NDW 中溶解时，Ni2+ 倾向于溶解在水溶液中，Ca2+ 倾向于保留在固体中，而在 CSW 中溶解时，对于具有较高 XNi 的固体，Ca2+ 倾向于溶解在水溶液中，Ni2+ 倾向于留在固体中。这些发现为理解自然环境中控制 Ni 地球化学循环的机制提供了有价值的见解。