Exploration of the role of heat activation in enhancing serpentine carbon sequestration reactions

Our plain-English summary of Exploration of the role of heat activation in enhancing serpentine carbon sequestration reactions, by M.J. McKelvy, A.V. Chizmeshya, J. Diefenbacher, et al (Environmental Science & Technology, 2004).

The study

• Authors: M.J. McKelvy, A.V. Chizmeshya, J. Diefenbacher, H. Béarat, G. Wolf
• Journal: Environmental Science & Technology
• Published: 2004;38(24):6897-903
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

As compared with other candidate carbon sequestration technologies, mineral carbonation offers the unique advantage of permanent disposal via geologically stable and environmentally benign carbonates. The primary challenge is the development of an economically viable process. Enhancing feedstock carbonation reactivity is key. Heat activation dramatically enhances aqueous serpentine carbonation reactivity. Although the present process is too expensive to implement, the materials characteristics and mechanisms that enhance carbonation are of keen interest for further reducing cost. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) of the serpentine mineral lizardite was used to isolate a series of heat-activated materials as a function of residual hydroxide content at progressively higher temperatures. Their structure and composition are evaluated via TGA/DTA, X-ray powder diffraction (including phase analysis), and infrared analysis. The meta-serpentine materials that were observed to form ranged from those with longer range ordering, consistent with diffuse stage-2 like interlamellar order, to an amorphous component that preferentially forms at higher temperatures. The aqueous carbonation reaction process was investigated for representative materials via in situ synchrotron X-ray diffraction. Magnesite was observed to form directly at 15 MPa CO2 and at temperatures ranging from 100 to 125 degrees C. Carbonation reactivity is generally correlated with the extent of meta-serpentine formation and structural disorder.

In plain English

This was a laboratory materials-chemistry experiment on a mineral sample; it did not study people. The authors examined how heating changes the serpentine mineral lizardite so that it reacts more readily with carbon dioxide to form a carbonate, a proposed way of permanently storing carbon. The lizardite came from the Philips Mine, Arizona. Microscope examination found trace levels of chrysotile fibers (about 1 percent by volume), with most of the material having the platy form typical of lizardite. Samples were heated at 2 °C per minute to temperatures up to 1100 °C and cooled rapidly. Loss of hydroxyl (OH) groups began at about 350 °C. By 650 °C, 10% of the hydroxyl groups remained and the crystalline lizardite features had disappeared. Forsterite had begun to form by 780 °C. In carbonation tests under 15 MPa of carbon dioxide, the unheated lizardite showed no reaction up to 185 °C. The heated samples formed magnesite directly; those heated to 650 and 720 °C began reacting at 100 and 105 °C. The authors concluded that the structural disorder created by heating is strongly associated with the enhanced carbonation reactivity.

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 materials experiment: lizardite was heated to a series of temperatures and the products were analysed (thermal analysis, X-ray powder diffraction, infrared spectroscopy); selected products were then reacted with CO2 while being monitored by in situ synchrotron X-ray diffraction
• Who was studied: a mineral sample, not people: lizardite (a serpentine mineral) from the Philips Mine, Arizona, containing trace chrysotile fibers (about 1 vol %); four heat-activated samples were used in the carbonation tests
• Exposure: heat activation of lizardite at temperatures up to 1100 °C, followed by reaction of selected products with CO2 at 15 MPa in a 0.64 M sodium bicarbonate and 1.0 M sodium chloride solution; the feedstock contained trace chrysotile fibers (about 1 vol %)
• Main results:
  • Loss of hydroxyl groups (dehydroxylation) from the lizardite began at about 350 °C
  • At 580 °C, with 45% of the hydroxyl content remaining, a new partly ordered meta-serpentine component appeared in the X-ray pattern
  • By 650 °C, 10% of the hydroxyl groups remained and the crystalline lizardite features were gone, leaving a poorly ordered material with a strong amorphous component
  • Above 610 °C the ordered component disappeared, while the amorphous component reached its maximum at 795 °C
  • Forsterite had begun to form by 780 °C
  • In infrared spectra the hydroxyl bands weakened as hydroxide was lost but did not shift position
  • The unheated lizardite showed no carbonation up to 185 °C
  • In each heat-activated sample tested, magnesite formed directly, with no crystalline intermediate
  • The sample heated to 580 °C showed only trace carbonation at 120 °C
  • The sample heated to 610 °C showed substantial carbonation at 125 °C
  • The samples heated to 650 and 720 °C began carbonating at 100 and 105 °C, respectively, with good reaction progression
• The authors' conclusion: The authors concluded that the structural disorder produced as meta-serpentine forms during heating is strongly associated with the enhanced carbonation reactivity caused by heat activation
• Limitations the authors state:
  • Direct magnesite formation may not occur for materials reacting at lower temperatures and pressures, where other carbonate phases such as hydromagnesite may form
  • The estimates of the relative amounts of each component carry an overall error of about plus or minus 10%
  • The amount of meta-serpentine in the X-ray sampling area during reaction was difficult to quantify, which can cause sample-to-sample differences in peak intensity
  • The energy cost of heat activation is currently too high for the process to be put into use

Topics

Medical terms in this study, explained in our Lexicon: Serpentine Group, Lizardite, X-Ray Diffraction (XRD).

Related studies

• Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions — L.C. Pasquier, G. Mercier, et al. (2014)
• Carbon dioxide sequestration using NaHSO4 and NaOH: A dissolution and carbonation optimisation study — A. Sanna, L. Steel, et al. (2017)
• Free radical activity of natural and heat treated amphibole asbestos — C. Otero Areán, F. Barceló, et al. (2001)
• Effect of heat on the identification of asbestos by x-ray diffraction — C. Plowman (1973)
• 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)
• Students' Perceived Heat-Health Symptoms Increased with Warmer Classroom Temperatures — S. Bidassey-Manilal, C.Y. Wright, et al. (2016)

Browse more research in Environmental Science & Technology, or return to medical research.