Thermal activation of antigorite for mineralization of CO2

Our plain-English summary of Thermal activation of antigorite for mineralization of CO2, by R.D. Balucan, B.Z. Dlugogorski (Environmental Science & Technology, 2013).

The study

• Authors: R.D. Balucan, B.Z. Dlugogorski
• Journal: Environmental Science & Technology
• Published: 2013;47(1):182-90
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This contribution demonstrates the sensitivity of antigorite dehydroxylation to treatment conditions and discusses the implications of the observations for scientific (i.e., dehydroxylation kinetics) and technological (i.e., energy efficient conditions and design of practical activation reactors) applications. At present, the energy cost of dehydroxylation of serpentinite ores represent the most important impediment for a large scale implementation of sequestering CO(2) by mineralization. We have analyzed changes in antigorite's derivative thermogravimetric curves (DTG) and deduced factors affecting the mass loss profiles. The imposed heating rate, type of purge gas, type of comminution and sample mass all influence the dehydroxylation curve. However, the results show no influence of material of construction of the heating vessel and flow rate of the purge gas. We report an important effect of oxidation of Fe(2+) under air purge gas that occurs prior to dehydroxylation and leads to formation of hematite skins on serpentinite particles, slowing down subsequent mass transfer and increasing the treatment temperature. From the process perspective, 75 μm particles afford optimal conditions of temperature and rate of dehydroxylation. Overall, the practical considerations, in thermally activating serpentinite ores for storing CO(2) by carbonation, comprise rapid heating, proper size reduction, prior demagnetisation, and fluidization of the powder bed.

In plain English

This laboratory study examined how antigorite, a serpentine mineral, loses bound water when heated. The authors framed this heating as preparation for storing carbon dioxide (CO2) as a mineral. It did not study people or health. The authors heated samples from near Bingara, New South Wales, Australia, under varied conditions. Most water loss took place between about 500 and 800 °C, though full water loss required temperatures above 850 °C. An alumina versus platinum crucible, argon flow of 20 versus 200 mL per minute, and ground samples with d80 particle sizes of 31 to 75 μm gave similar weight-loss curves. Using air instead of argon raised the temperature of fastest water loss by 17 °C and lowered its rate by 10%. The authors attributed this to a hematite (iron oxide) layer forming on the particles. Heating at 20 and 30 instead of 10 °C per minute raised that temperature by 11 and 22 °C but increased the rate by 89% and 192%. The authors concluded that practical activation calls for rapid heating, proper size reduction, prior demagnetisation and a fluidized powder bed.

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 using thermogravimetric analysis (measuring weight loss during controlled heating) of a natural mineral under different conditions
• Who was studied: Antigorite collected near Bingara in the Great Serpentinite Belt, New South Wales, Australia, prepared into five sample fractions (A to E) by crushing and by wet or dry grinding
• Exposure: Heating from 30 to 1000 °C. The control run used 5.5 mg of wet-ground, demagnetised antigorite (d80 of 75 μm) in an alumina crucible, heated at 10 °C per minute under argon flowing at 20 mL per minute. The conditions varied were: platinum crucible; gas flow of 200 mL per minute; d80 particle sizes of 31 and 52 μm; sample masses of 2.75 to 37.7 mg; CO2 or air purge gas; heating rates of 20 and 30 °C per minute; and dry-ground or dry-crushed samples.
• Main results:
  • In the control sample, the main water loss occurred from about 500 to 800 °C. Structurally bound water made up 11.43 ± 0.03% of the antigorite by weight.
  • Full loss of bound water was reached only at temperatures above 850 °C.
  • Under the tested conditions, three comparisons gave similar weight-loss curves: alumina versus platinum crucibles, argon flow of 20 versus 200 mL per minute, and ground samples with d80 particle sizes of 31, 52 and 75 μm.
  • In the control run, the temperature of fastest water loss was 725 ± 2 °C. Every condition change that altered the curves raised this temperature, by 11 to 39 °C. Depending on the condition, the rate of water loss fell by as much as 10% or rose by as much as 192%.
  • Increasing the sample mass by about 600% raised the temperature of fastest water loss by 11 °C and increased the rate by 10%.
  • Using air as the purge gas delayed the temperature of fastest water loss by 17 °C and lowered the rate by 10%. The samples turned reddish, and the authors suggested that a hematite layer limited the escape of water.
  • Raising the heating rate to 20 and 30 °C per minute raised the temperature of fastest water loss by 11 and 22 °C, and increased the rate of water loss by 89% and 192%.
  • Compared with the ground sample, the crushed, unground sample lost water 35% faster, but at a temperature 36 °C higher.
  • The weight-loss profiles did not differ significantly between wet-ground and dry-ground samples.
• The authors' conclusion: The authors concluded that particles of less than 75 μm give optimal temperature and rate of water loss. Because oxidation of iron forms hematite layers on the particles, they suggested CO2 as the preferred purge gas. They also called for fluidizing the powder bed and recommended rapid heating.
• Limitations the authors state:
  • The small 5.5 mg samples produced weight-loss curves that were less smooth than those obtained with samples above 30 mg.
  • The authors stated that kinetic results can ideally be compared only between studies that use the same experimental conditions.

Topics

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

Medical terms in this study, explained in our Lexicon: Antigorite, Dehydroxylation, Serpentinite, Hematite.

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