Magnesium and silicon recovery from chrysotile asbestos waste of the deposit Zhitikara, Kazakhstan

Our plain-English summary of Magnesium and silicon recovery from chrysotile asbestos waste of the deposit Zhitikara, Kazakhstan, by R.A. Shayakhmetova, A.A. Mukhametzhanova, D.N. Akbayeva, et al (Scientific Reports, 2024).

The study

• Authors: R.A. Shayakhmetova, A.A. Mukhametzhanova, D.N. Akbayeva, A.Z. Terlikbaeva, P.A. Osipov, A.M. Alimzhanova, A.A. Zharmenov
• Journal: Scientific Reports
• Published: 2024;14(1):31866
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Waste generated during asbestos manufacturing contains substantial quantities of iron, nickel, magnesium, and silicon. The existing techniques for processing chrysotile-asbestos waste (CAW) cannot fully recover these elements. Therefore this paper presents a hydrometallurgical method for processing the CAW of the Zhitikara deposit in the Kostanay region of Kazakhstan. Batch reactors are used in both laboratory and pilot experiments, and initial trials are conducted in a recently constructed industrial Ti reactor at the Kostanay Minerals JSC plant in the Kostanay region of Zhitikara. The primary benefits of the industrial reactor include operation without excessively grinding the feedstock and creation of a pulp with enhanced filtration properties. A moderate agitation speed (10 rpm) helps ensure a consistent pulp density and prevent the production of silica gel. Optimal leaching conditions are determined as a fraction size of CAW between - 1.25 and 0.25 mm, hydrochloric acid concentration of 18 wt%, temperature of ~ 85-90 °C, pressure of 1 atmosphere, and duration of 2 h. An investigation of the process kinetics reveals that diffusion is the rate-controlling step. Further, the activation energies are determined to be 54.4 kJ.mol- 1, and the leaching rates of Mg, Fe, and Ni under these conditions are 96.0, 87.8, and 81.3%, respectively. Washing and recycling water enhances helps to increase the recovery of magnesium chloride. Implementing pilot-scale hydrometallurgical processing of CAW can effectively address environmental issues that pose a threat to human health and provide commercial advantages.

© 2024. The Author(s).

In plain English

This was a laboratory and pilot-scale processing experiment. The authors tested a five-step method for recovering magnesium, silicon, iron and nickel from chrysotile asbestos waste from the Zhitikara deposit in Kazakhstan, supplied by the Kostanay Minerals JSC plant. After magnetic separation, the non-magnetic part of the waste was leached with 18% hydrochloric acid at about 85–90 °C for 2 hours with slow stirring. Iron and nickel were then precipitated, and a magnesium chloride (bischofite) solution was produced. In the pilot reactor, leaching rates were 96% for magnesium, 87.8% for iron and 81.3% for nickel. From 175 kg of non-magnetic waste, the process yielded 100 kg of silica-rich cake, 45 kg of iron-rich cake, 42 kg of nickel-rich cake and 334 kg of bischofite solution. After a second acid leaching, the silica product contained up to 98% silica, and X-ray analysis showed chrysotile remaining in trace amounts. The authors concluded the method was feasible for extracting these elements with relatively low energy and cost.

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 and pilot-scale chemical processing experiment (hydrochloric acid leaching of asbestos waste in batch reactors); not a health study
• Who was studied: Chrysotile asbestos waste left after serpentinite enrichment, supplied by the Kostanay Minerals JSC plant (Zhitikara deposit, Kostanay region, Kazakhstan). The pilot run used 210 kg of waste, split into 35 kg magnetic and 175 kg non-magnetic fractions.
• Exposure: Chrysotile asbestos waste was treated by a five-step process. The non-magnetic fraction was leached with 18% hydrochloric acid at a solid-to-liquid ratio of about 1 to 3, at about 85–90 °C for about 2 hours, with stirring at 10 rpm. Iron and nickel were then precipitated with hydrogen peroxide and magnesium oxide, and the remaining solution was evaporated to bischofite.
• Main results:
  • In the pilot-scale reactor, the leaching rate was 96% for magnesium, 87.8% for iron and 81.3% for nickel.
  • In the pilot run, 175 kg of non-magnetic waste yielded 100 kg of silica-rich cake, 45 kg of iron-rich cake, 42 kg of nickel-rich cake (187 kg dry solids in total) and 334 kg of bischofite solution, with 95% magnesium recovery.
  • In laboratory beaker tests, faster stirring raised magnesium leaching from 11% at 20 rpm to 98% at 300 rpm. However, filtration slowed substantially at 300 rpm.
  • The kinetics study gave an activation energy of 54.4 kJ per mole. The authors suggested that diffusion may be the step that controls the rate of the process.
  • A second hydrochloric acid leaching of the silica cake produced a silica content of up to 98% and reduced magnesium oxide by almost 6.5 times.
  • X-ray diffraction of the silica residue after the second leaching showed amorphous silica, with chrysotile remaining in trace amounts.
  • In a simplified economic estimate for a 200 tons per year facility, the projected operating cost was 153 USD per ton of product.
• The authors' conclusion: The authors concluded that the method was feasible for extracting magnesium, silicon, iron and nickel from chrysotile asbestos waste with relatively low production energy and cost.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile.

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