Ma Chengyou, Nong Xiaoke, Xu Fan, Zhu Zongqiang, Nong Peijie, Luo Fei, Tang Shen, Zhang Lihao, Kang Zhiqiang, Zhu Yinian
College of Earth Sciences, Guilin University of Technology, Guilin, 541006, Guangxi, China.
College of Environmental Science and Engineering, Guilin University of Technology, Guilin, 541006, China.
Geochem Trans. 2024 Nov 29;25(1):13. doi: 10.1186/s12932-024-00096-6.
A series of the calcium-nickel carbonate solid solutions [(CaNi)CO] were synthesized and their dissolution in N-degassed water (NDW) and CO-saturated water (CSW) at 25 °C was experimentally investigated. During dissolution of the synthetic solids (Ni-bearing calcite, amorphous Ca-bearing NiCO and their mixtures), the Ni-calcite and the Ca-NiCO 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 (X), or 0.608-0.721 and 0.273-0.430 mmol/L for the solids with higher X, 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 K, Solubility product constants) were determined to be - 8.65 ± 0.04 and - 8.16 ± 0.11 for calcite [CaCO], respectively; - 8.50 ± 0.02 and - 7.69 ± 0.03 for the synthetical nickel carbonates [NiCO], respectively. In respect to the bulk composition of the (CaNi)CO solid solutions, the final log IAP showed the highest value when X = 0.10-0.30. Mostly, the mean values of log IAP increased with the increasing X 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 (CaNi)CO solid solution using the predicted Guggenheim parameters of a = 2.14 and a = - 0.128 from a miscibility gap of X = 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 Ni preferred to dissolve into the water solution and Ca preferred to remain in the solid, while during dissolution in CSW for the solids with higher X, the Ca preferred to dissolve into the water solution and Ni preferred to remain in the solid. These findings provide valuable insights into understanding the mechanisms governing Ni geochemical cycle in natural environments.
合成了一系列碳酸钙镍固溶体[(CaNi)CO]，并对其在25℃下于经氮气脱气的水(NDW)和二氧化碳饱和水(CSW)中的溶解情况进行了实验研究。在合成固体(含镍方解石、无定形含钙碳酸镍及其混合物)溶解过程中，镍方解石和钙镍碳酸镍先溶解，随后形成含镍文石结构相。在NDW中溶解240 - 300天后，对于镍/(钙 + 镍)摩尔比(X)较低的固体，水溶液中钙和镍的稳定浓度分别为0.592 - 0.665和0.073 - 0.290 mmol/L；对于X较高的固体，钙和镍的稳定浓度分别为0.608 - 0.721和0.273 - 0.430 mmol/L。在CSW中溶解240 - 300天后，水溶液中钙和镍的稳定浓度分别为1.094 - 3.738和0.831 - 4.300 mmol/L。对于在NDW和CSW中的溶解，方解石[CaCO]在最终稳定状态下log IAP(离子活度积)的平均值分别测定为 - 8.65 ± 0.04和 - 8.16 ± 0.11；合成碳酸镍[NiCO]的log IAP平均值分别为 - 8.50 ± 0.02和 - 7.69 ± 0.03。就(CaNi)CO固溶体的整体组成而言，当X = 0.10 - 0.30时，最终的log IAP显示出最高值。在含镍方解石、含镍文石和无定形钙镍碳酸盐方面，log IAP的平均值大多随X的增加而增加。利用从X = 0.238至0.690的混溶间隙预测的古根海姆参数a = 2.14和a = - 0.128，将实验数据绘制在(CaNi)CO固溶体的李普曼图上，结果表明固体发生不一致溶解，水溶液中最终的钙和镍浓度同时受到镍方解石、镍文石和无定形钙镍碳酸盐的最小化学计量饱和曲线的限制。在NDW中溶解时，镍更倾向于溶解到水溶液中，而钙更倾向于留在固体中；而在CSW中对于X较高的固体溶解时，钙更倾向于溶解到水溶液中，镍更倾向于留在固体中。这些发现为理解自然环境中镍地球化学循环的控制机制提供了有价值的见解。
