Magnesium hydroxide extracted from a magnesium-rich mineral for CO2 sequestration in a gas-solid system

Our plain-English summary of Magnesium hydroxide extracted from a magnesium-rich mineral for CO2 sequestration in a gas-solid system, by P.C. Lin, C.W. Huang, C.T. Hsiao, et al (Environmental Science & Technology, 2008).

The study

• Authors: P.C. Lin, C.W. Huang, C.T. Hsiao, H. Teng
• Journal: Environmental Science & Technology
• Published: 2008;42(8):2748-52
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Magnesium hydroxide extracted from magnesium-bearing minerals is considered a promising agent for binding CO2 as a carbonate mineral in a gas-solid reaction. An efficient extraction route consisting of hydrothermal treatment on serpentine in HCl followed by NaOH titration for Mg(OH)2 precipitation was demonstrated. The extracted Mg(OH)2 powder had a mean crystal domain size as small as 12 nm and an apparent surface area of 54 m2/g. Under one atmosphere of 10 vol% CO2/N2, carbonation of the serpentine-derived Mg(OH)2 to 26% of the stoichiometric limit was achieved at 325 degrees C in 2 h; while carbonation of a commercially available Mg(OH)2, with a mean crystal domain size of 33 nm and an apparent surface area of 3.5 m2/g, reached only 9% of the stoichiometric limit. The amount of CO2 fixation was found to be inversely proportional to the crystal domain size of the Mg(OH)2 specimens. The experimental data strongly suggested that only a monolayer of carbonates was formed on the crystal domain boundary in the gas-solid reaction, with little penetration of the carbonates into the crystal domain.

In plain English

This was a laboratory chemistry study, not a study of health or asbestos exposure, and the article does not describe its serpentine sample as asbestos. The authors tested a way to extract magnesium hydroxide from serpentine mineral collected in Hua-Lien, Taiwan, and to use it to bind carbon dioxide (CO2) as a carbonate. They heated powdered serpentine in hydrochloric acid in a sealed vessel, then added sodium hydroxide to remove silica and precipitate magnesium hydroxide, recovering about 90% of the magnesium. The extracted powder had crystal domains of about 12 nm and a surface area of 54 m2/g. A commercial reagent-grade magnesium hydroxide had 33 nm and 3.5 m2/g. After 2 hours in 10% CO2 gas at 325 °C and normal atmospheric pressure, about 26% of the magnesium in the serpentine-derived powder was in carbonate form (4.4 mmol CO2 per gram), compared with 9% (1.6 mmol per gram) for the commercial powder. The authors concluded that the carbonate very likely formed only a single layer on the crystal domain boundaries, so powders with smaller crystal domains bound more CO2.

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 chemistry experiment (mineral processing and gas-solid carbonation tests), not a health study
• Who was studied: No people or animals were studied. The material was a serpentine mineral specimen from Hua-Lien, Taiwan, ground to about 50 µm. Magnesium hydroxide extracted from it was compared with a commercial reagent-grade magnesium hydroxide powder (Acros).
• Exposure: No human exposure was studied. The process was hydrothermal treatment of 2 g serpentine powder in 100 mL of 1 N hydrochloric acid at 150 °C for 24 h, followed by sodium hydroxide titration. The extracted magnesium hydroxide was then treated with 10 vol% CO2 in nitrogen at 325 °C for 2 h at atmospheric pressure.
• Main results:
  • The extraction process gave a magnesium yield of about 90%.
  • Mean crystal domain size was about 12 nm for the serpentine-derived magnesium hydroxide and about 33 nm for the reagent-grade specimen.
  • The serpentine-derived powder had an apparent surface area of 54 m2/g. The reagent-grade powder had 3.5 m2/g (Table 1).
  • After carbonation, about 26% of magnesium atoms in the serpentine-derived powder were in carbonate form (4.4 mmol CO2 per gram, against a stoichiometric limit of 17 mmol/g). The figure for the reagent-grade powder was 9% (1.6 mmol per gram).
  • The CO2 capacity of the serpentine-derived powder was about 2.8 times that of the reagent-grade powder, matching the estimated ratio of crystal domain-boundary area. The authors found that surface area measured by nitrogen adsorption was not a critical factor.
• The authors' conclusion: The authors concluded that carbonate very likely formed only a single layer on the crystal domain boundaries. They also concluded that restricted movement of carbonate into the crystal interior might have prevented a higher degree of carbonation.
• Limitations the authors state:
  • The authors noted that the calculated area per CO2 molecule (about 0.08 nm2) assumed perfectly spherical, smooth crystal domains, so the actual area should be larger.
  • The authors described their X-ray method for sizing crystal domains as giving only a qualitative description.

Topics

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

Medical terms in this study, explained in our Lexicon: Carbonate Mineral, Serpentine Group.

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