New Insights to the Formation of Dolomite and Magnesite Through Hydrothermal Alteration of Ca-Carbonates: An Experimental Approach

Isaac John Kell Duivestein, Martin Dietzel, Andre Baldermann, Vasileios Mavromatis, Albrecht Leis

Research output: Contribution to conferencePoster

Abstract

Hydrothermal precipitation experiments were performed to trace and quantify elemental (Ca, Mg and Sr) and stable isotopic δ18O signatures during the (trans)formation of intermediate aragonite and low-Mg calcite to more stable dolomite and magnesite in the presence of Mg-/Na-chloride rich brines by reacting 0.1M inorganic CaCO3 seed material (aragonite or calcite) with an artificial brine originally containing 0.2M MgCl2(aq) and 0.1 or 0.05M of NaHCO3 within Teflon-lined, steel autoclaves at temperatures of 150, 180 and 220°C over the course of 365 days. The evolution of reaction products and of the experimental solutions was monitored by ICP-OES, CRDS, FTIR, XRD, EMPA and SEM analyses as well as pH and alkalinity measurements. Based on apparent solid-phase compositions and reactive fluid chemistry the following sequence of mineral growth was established: aragonite and/or low-Mg calcite reacted with aqueous Mg2+ ions to form intermediate huntite, brucite and high-Mg calcite, subsequently altered to Ca-excess dolomite and Ca-rich magnesite and finally converted to nearly stoichiometric endmembers. A progressive evolution in the stoichiometry of dolomite (from 42 to 50 mol% MgCO3) and magnesite (from 80 to 98 mol% MgCO3) as well as the increase in the degree of cation order in dolomite (from 0.26 to 0.74) were observed during this reaction sequence, implying a kinetic drive towards the (thermodynamically stable) end members. Results from our study indicate that in the presence of Mg-rich brines metastable CaCO3 polymorphs are transformed into more stable magnesite and dolomite via the formation of intermediate Mg-Ca carbonates. The experimental results are discussed in the scope of dolomitization of limestone platforms in natural surroundings.
Original languageEnglish
Publication statusPublished - 2017
EventGoldschmidt Conference 2017 -
Duration: 14 Aug 201718 Aug 2017

Conference

ConferenceGoldschmidt Conference 2017
Period14/08/1718/08/17

Fingerprint Dive into the research topics of 'New Insights to the Formation of Dolomite and Magnesite Through Hydrothermal Alteration of Ca-Carbonates: An Experimental Approach'. Together they form a unique fingerprint.

  • Cite this

    Kell Duivestein, I. J., Dietzel, M., Baldermann, A., Mavromatis, V., & Leis, A. (2017). New Insights to the Formation of Dolomite and Magnesite Through Hydrothermal Alteration of Ca-Carbonates: An Experimental Approach. Poster session presented at Goldschmidt Conference 2017, .