Dissolution behavior of mixed calcium‑cobalt carbonates at 25 °C in contact with different gas phases

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
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Abstract

The potential immobilization of cobalt in various environments can be achieved through the incorporation of Co into carbonate minerals, forming solid solutions of (Ca1-xCox)CO3. However, the thermodynamic properties of these minerals are not well-understood due to conflicting data from natural observations and experiments. In this work, a series of mixed calcium‑cobalt carbonates were prepared and their interaction with aqueous solution was investigated. Depending on the Co/(Ca + Co) mol ratio (XCo) of the mixed solution, ranging from 0.00 to 1.00, pure calcite, Co-bearing calcite, Co-bearing aragonite, Ca-bearing spherocobaltite and pure spherocobaltite were successively synthesized using a precipitation method. Upon dissolution of the Co-bearing solids (XCo = 0.10–1.00) in N2-degassed water (NW) and air-saturated water (AW), the Co concentration of the aqueous solutions increased gradually to a stable state of 0.017–0.191 and 0.018–0.186 mmol/L after 240–360 d dissolution, respectively. When the dissolution occurred in CO2-saturated water (CW), the Co concentration initially spiked to 0.372–2.258 mmol/L within 6 h ∼ 15 d and then decreased to a stable range of 0.030–0.559 mmol/L after 240–360 d. The Co/(Ca + Co) mol ratio in the aqueous solution (XCo2+,AS) was significantly lower than the Co/(Ca + Co) atomic ratio in the solids (XCo,SS), particularly when dissolved in NW and AW. During these dissolution processes in NW, AW and CW at 25 °C, the average log IAP values at the final stable state were determined as follows: for calcite (CaCO3), the values were −8.25 ± 0.03 in NW, −8.34 ± 0.11 in AW, and −8.10 ± 0.08 in CW; for spherocobaltite (CoCO3), they were −9.24 ± 0.26 in NW, −9.39 ± 0.23 in AW, and −9.38 ± 0.09 in CW. Furthermore, the log IAP values increased from those typical for calcite to −7.89 ± 0.01 ∼ −7.84 ± 0.10 for the solid with XCo,SS = 0.187 as XCo,SS increased, eventually aligning with those typical of spherocobaltite. Lippmann diagrams, constructed using the Guggenheim parameters a0 = 2.30 and a1 = 0.265 for the “subregular” calcite-spherocobaltite solid solutions [(Ca1-xCox)CO3] with a miscibility gap ranging from XCo,SS = 0.251 to 0.858, highlighted the “peritectic” point at XCo2+,AS = 0.0538 on the solutus. This analysis revealed that the solids dissolved non-stoichiometrically in water. Consequently, the Co-poor aqueous solution would reach equilibrium with the Co-rich calcite-structure phase at the solid surface.

钙钴混合碳酸盐在 25 °C 与不同气相接触时的溶解行为
钴在各种环境中的潜在固定化可通过将钴掺入碳酸盐矿物,形成(CaCo)CO 固溶体来实现。然而,由于来自自然观察和实验的数据相互矛盾,人们对这些矿物的热力学性质并不十分了解。在这项工作中,制备了一系列钙钴混合碳酸盐,并研究了它们与水溶液的相互作用。根据混合溶液中 Co/(Ca + Co)摩尔比(X)(0.00 至 1.00)的不同,采用沉淀法先后合成了纯方解石、含 Co 方解石、含 Co 文石、含 Ca 球钴石和纯球钴石。含钴固体(X = 0.10-1.00)在脱氮水(NW)和空气饱和水(AW)中溶解后,水溶液中的钴浓度逐渐增加,在溶解 240-360 d 后分别达到 0.017-0.191 和 0.018-0.186 mmol/L 的稳定状态。水溶液(X)中的 Co/(Ca + Co) 摩尔比明显低于固体(X)中的 Co/(Ca + Co) 原子比,尤其是在 NW 和 AW 中溶解时。在 25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C、25 °C和 25 °C的溶解过程中,最终稳定状态下的平均对数 IAP 值测定如下:方解石(CaCO)的对数值在 NW 中为 -8.25 ± 0.03,在 AW 中为 -8.34 ± 0.11,在 CW 中为 -8.10 ± 0.08;球钴石(CoCO)的对数值在 NW 中为 -9.24 ± 0.26,在 AW 中为 -9.39 ± 0.23,在 CW 中为 -9.38 ± 0.09。此外,随着 X 的增加,X = 0.187 固体的对数 IAP 值从方解石的典型值增加到 -7.89 ± 0.01 ∼ -7.84 ± 0.10,最终与球钴石的典型值一致。使用古根海姆参数 = 2.30 和 = 0.265 为 "亚规则 "方解石-球钴石固溶体 [(CaCo)CO]绘制的李普曼图,混溶间隙范围为 X = 0.251 至 0.858,突出显示了 X = 0.0538 处的 "peritectic "点。 该分析表明,固体在水中的溶解度不成正比。因此,贫钴水溶液将与固体表面富钴方解石结构相达到平衡。
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来源期刊
Journal of Geochemical Exploration
Journal of Geochemical Exploration 地学-地球化学与地球物理
CiteScore
7.40
自引率
7.70%
发文量
148
审稿时长
8.1 months
期刊介绍: Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.
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