Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions

Our plain-English summary of Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions, by L.C. Pasquier, G. Mercier, J.F. Blais, et al (Environmental Science & Technology, 2014).

The study

• Authors: L.C. Pasquier, G. Mercier, J.F. Blais, E. Cecchi, S. Kentish
• Journal: Environmental Science & Technology
• Published: 2014;48(9):5163-70
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mineral carbonation is known as one of the safest ways to sequester CO2. Nevertheless, the slow kinetics and low carbonation rates constitute a major barrier for any possible industrial application. To date, no studies have focused on reacting serpentinite with a relatively low partial pressure of CO2 (pCO2) close to flue gas conditions. In this work, finely ground and heat-treated serpentinite [Mg3Si2O5(OH)4] extracted from mining residues was reacted with a 18.2 vol % CO2 gas stream at moderate global pressures to investigate the effect on CO2 solubility and Mg leaching. Serpentinite dissolution rates were also measured to define the rate-limiting step. Successive batches of gas were contacted with the same serpentinite to identify surface-limiting factors using scanning electron microscopy (SEM) analysis. Investigation of the serpentinite carbonation reaction mechanisms under conditions close to a direct flue gas treatment showed that increased dissolution rates could be achieved relative to prior work, with an average Mg dissolution rate of 3.55 × 10(-11) mol cm(-2) s(-1). This study provides another perspective of the feasibility of applying a mineral carbonation process to reduce industrial greenhouse gas (GHG) emissions from large emission sources.

In plain English

This laboratory chemistry study tested whether serpentinite mining residue could capture carbon dioxide from a gas like cement plant exhaust (18.2% CO2). The residue came from an old chromite mining site in Coleraine, near Thetford Mines, Quebec. It was ground and heat-treated; its main mineral was lizardite. Reactions ran in a stirred reactor near room temperature, alongside computer modeling. Modeling indicated more CO2 dissolved with the solid present than in pure water. Magnesium release rose with dissolved carbon. The average magnesium dissolution rate was 3.55 × 10^-11 mol per square centimetre per second. After six gas batches, no more magnesium was released. After regrinding and reheating, CO2 removal matched that of fresh solid. Microscopy showed grain surfaces depleted in magnesium and enriched in silica. In solutions held at 40 °C, 95 wt % of the magnesium formed solid carbonates within 18 hours, partly attributed to evaporation. The only crystalline phase detected was nesquehonite. The authors concluded that, despite needing optimization, the results open new possibilities for cutting industrial CO2 emissions. It did not measure asbestos fibers, exposure, or health outcomes.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory experiment (batch reactor tests with heat-treated serpentinite) combined with geochemical computer modeling
• Who was studied: serpentinite mining residues sampled near Thetford Mines, southern Quebec, at the old American Chrome chromite mining site in Coleraine; main crystalline phases lizardite, magnetite and chromite
• Exposure: ground serpentinite (median grain size 28.4 ± 1.8 μm), heat-activated at 650 °C for 30 min, reacted in water with a gas of 18.2 vol % CO2 and 4 vol % O2, balance nitrogen, similar to cement plant flue gas
• Main results:
  • In simulations, more CO2 was lost from the gas with lizardite present than with pure water, indicating the solid favors CO2 solubility
  • In the experiments, the solution pH was around 10.5 after the solid was added and fell to between 7.5 and 8.5 after reaction
  • In the experiments, 85 ± 2% of the carbon lost from the gas was still in the liquid after 15 min; the authors took this to mean carbonate precipitation is much slower than CO2 dissolution
  • Across experiments at different CO2 pressures, magnesium leached from the solid showed a linear relationship with dissolved inorganic carbon
  • In the kinetic experiment (global pressure 10.5 bar, CO2 partial pressure 1.91 bar), the average magnesium dissolution rate was 3.55 × 10^-11 mol per square centimetre per second
  • The initial dissolution rate rose linearly with CO2 partial pressure up to 4 bar; the authors interpreted the lower rate at 8 bar as solution saturation
  • When the same solid was reused, no more magnesium was leached after six gas batches; after regrinding and reheating, CO2 removal efficiencies equivalent to fresh solid were achieved, for a total of 12 batches
  • Electron microscopy of the solid after 12 batches showed a surface layer with more silica and less magnesium than the grain core
  • Reaction solutions held at 40 °C precipitated 63 wt % of the magnesium within 3 h and 95 wt % as solid carbonates within 18 h; X-ray diffraction detected only one crystalline phase, nesquehonite
• The authors' conclusion: The authors concluded that, although experimental conditions require further optimization, their observations open new possibilities for using mineral carbonation to reduce industrial CO2 emissions
• Limitations the authors state:
  • The tests were run batchwise, so the reaction may also have been limited by CO2 diffusion from the gas-liquid interface; rates under continuous gas flow might differ
  • The high final carbonate yield was partly attributed to solution evaporation
  • The model describes the system at equilibrium, while the experiments were far from equilibrium

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group, Serpentinite, Scanning Electron Microscopy (SEM).

Related studies

• Direct gas-solid carbonation of serpentinite residues in the absence and presence of water vapor: a feasibility study for carbon dioxide sequestration — S.P. Veetil, L.C. Pasquier, et al. (2015)
• Exploration of the role of heat activation in enhancing serpentine carbon sequestration reactions — M.J. McKelvy, A.V. Chizmeshya, et al. (2004)
• Morphological changes during enhanced carbonation of asbestos containing material and its comparison to magnesium silicate minerals — G. Gadikota, C. Natali, et al. (2014)
• Magnesium hydroxide extracted from a magnesium-rich mineral for CO2 sequestration in a gas-solid system — P.C. Lin, C.W. Huang, et al. (2008)
• Disordered biopyriboles, amphibole, and talc in the Allende meteorite: products of nebular or parent body aqueous alteration? — A.J. Brearley (1997)
• Microbial diversity and mineral composition of weathered serpentine rock of the Khalilovsky massif — I.V. Khilyas, A.V. Sorokina, et al. (2019)

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