Transformation of Silicate Ions into Silica under the Influence of Acid on the Structure of Serpentinite

Our plain-English summary of Transformation of Silicate Ions into Silica under the Influence of Acid on the Structure of Serpentinite, by A. Auyeshov, K. Arynov, C. Yeskibayeva, et al (Molecules, 2024).

The study

• Authors: A. Auyeshov, K. Arynov, C. Yeskibayeva, A. Dikanbayeva, D. Auyeshov, Y. Raiymbekov
• Journal: Molecules
• Published: 2024;29(11)
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The process of transformation of the silicate components of the crystal lattice structure of chrysotile during its quantitative interaction with aqueous solutions containing various stoichiometrically required amounts of sulfuric acid (SRA H2SO4) calculated with respect to the magnesium content in the composition of chrysotile is investigated. It has been shown by IR spectroscopic, X-ray phase, thermal and chemical methods of investigation and analysis that, with quantitative interactions of chrysotile and sulfuric acid, first of all, the "brucite layer" of the molecular structural structure of chrysotile is exposed to acid at SRA H2SO4 = 0.1-0.3. As a result of ion exchange processes, acidic silanol (≡Si-O-H) or disilanol (=Si=(O-H)2) bonds are formed. These acid groups form one-dimensional silicate chains with transverse bridges (≡Si-O-Si≡), where the angles (Si-O-Si = 180 °C) straighten, which are recorded in the IR spectra in the region of characteristic absorption of 1220-1250 cm-1 silica. The association of the resulting acid groups into silicate chains, dimers, and trimers with transverse bridges, leads to the appearance of colloidal silica particles in the system, which cause some inhibition of the dissolution of layered magnesium hydrosilicate in sulfuric acid solutions containing H2SO4 ˃ 0.3 SRA.

In plain English

This was a laboratory chemistry experiment on the mineral itself, not a study of people, animals or health. The authors used chrysotile (grade A-4-20) from Kostanay Minerals JSC in Zhitikara, Kazakhstan. They mixed 10-gram samples with sulfuric acid solutions at 96 degrees Celsius for 10 minutes. The acid amount was expressed as a fraction, from 0.1 to 1.0, of the amount needed to react with all the magnesium in the chrysotile. They then examined the undissolved residue using infrared spectroscopy, X-ray analysis and chemical analysis. Up to 0.3 of the required acid, magnesium dissolved in almost equivalent proportion. Above that the proportion fell behind, and at 0.7 to 1.0 no more than 0.45 to 0.7 of the magnesium was extracted. From about 0.3 to 0.4, the infrared spectra showed silica-forming products on the fiber surfaces, and these signals grew stronger with more acid. The main chrysotile signals remained throughout, which the authors took to mean that only the surface of the particles changed. The authors concluded that the silicate part of chrysotile turns into silica, and that this somewhat slows further dissolution.

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: acid leaching of a chrysotile mineral sample, with the undissolved residue analysed by infrared (IR-Fourier) spectroscopy, X-ray phase analysis and chemical analysis
• Who was studied: 10-gram samples of crushed chrysotile, grade A-4-20, from Kostanay Minerals JSC, Zhitikara city, Kazakhstan. The particle fraction was under 0.14 mm and contained 26.42% magnesium by weight. No people or animals were studied.
• Exposure: Chrysotile was treated with 118 cm3 of aqueous sulfuric acid solution at 96 degrees Celsius, stirred at 350 rpm for 10 minutes. The acid was given as 0.1 to 1.0 of the stoichiometrically required amount (SRA), calculated from the magnesium content of the chrysotile.
• Main results:
  • From 0 to 0.3 SRA of sulfuric acid, magnesium passed into solution in almost an equivalent amount. Beyond that, proportional extraction gradually became impaired.
  • At 0.7 to 1.0 SRA of sulfuric acid, the magnesium extracted did not exceed 0.45 to 0.7 of the total magnesium in the chrysotile.
  • The filtration rate of the acid suspension fell sharply, from 28·10−2 to 16.2·10−2 mL/min·cm2. The article states the condition as an SRA 'less than 0.4', which appears inconsistent with the surrounding text.
  • Residues treated with 0.1 and 0.2 SRA showed no significant infrared changes in the OH-group range.
  • From 0.3 to 0.4 SRA, infrared spectra showed silica-forming products. The authors described a broad absorption 'step' in the 1120 to 1250 cm−1 region that grew more intense as acid increased, and they attributed it to acid groups of silica on the surface of the chrysotile fibers.
  • X-ray analysis after treatment with 0.4 SRA showed no significant changes in the chrysotile and antigorite peaks. The authors stated that complete destruction of the silicate structure did not occur.
  • The three main chrysotile infrared peaks kept their positions after treatment with up to 1.0 SRA. The authors interpreted this as changes affecting only the surface of the particle, with the interior remaining intact.
• The authors' conclusion: The authors concluded that the silicate component of chrysotile is transformed into silica, increasingly so as the amount of sulfuric acid rises. They concluded that this leads to some inhibition of chrysotile dissolution.

Topics

Medical terms in this study, explained in our Lexicon: Silicate, Serpentinite, Chrysotile, Brucite Layer.

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