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Solubility investigations in the amorphous calcium magnesium carbonate system

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Abstract

Amorphous precursors are known to occur in the early stages of carbonate mineral formation in both biotic and abiotic environments. Although the Mg content of amorphous calcium magnesium carbonate (ACMC) is a crucial factor for its temporal stabilization, to date little is known about its control on ACMC solubility. Therefore, amorphous CaxMg1−xCO3·nH2O solids with 0 ≤ x ≤ 1 and 0.4 ≤ n ≤ 0.8 were synthesized and dispersed in MgCl2–NaHCO3 buffered solutions at 24.5 ± 0.5 °C. The chemical evolution of the solution and the precipitate clearly shows an instantaneous exchange of ions between ACMC and aqueous solution. The obtained ion activity product for ACMC (IAPACMC = “solubility product”) increases as a function of its Mg content ([Mg]ACMC = (1 − x) × 100 in mol%) according to the expression: log(IAPACMC) = 0.0174 (±0.0013) × [Mg]ACMC − 6.278 (±0.046) (R2 = 0.98), where the log(IAPACMC) shift from Ca (−6.28 ± 0.05) to Mg (−4.54 ± 0.16) ACMC endmember, can be explained by the increasing water content and changes in short-range order, as Ca is substituted by Mg in the ACMC structure. The results of this study shed light on the factors controlling ACMC solubility and its temporal stability in aqueous solutions.

Graphical abstract: Solubility investigations in the amorphous calcium magnesium carbonate system

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Publication details

The article was received on 18 Sep 2018, accepted on 16 Nov 2018 and first published on 20 Nov 2018


Article type: Paper
DOI: 10.1039/C8CE01596A
Citation: CrystEngComm, 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Solubility investigations in the amorphous calcium magnesium carbonate system

    B. Purgstaller, K. E. Goetschl, V. Mavromatis and M. Dietzel, CrystEngComm, 2019, Advance Article , DOI: 10.1039/C8CE01596A

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