Mechanochemical conversion of chrysotile/K2HPO4 mixtures into potential sustainable and environmentally friendly slow-release fertilizers

Our plain-English summary of Mechanochemical conversion of chrysotile/K2HPO4 mixtures into potential sustainable and environmentally friendly slow-release fertilizers, by R. Borges, L.M. Baika, M.T. Grassi, et al (Journal of Environmental Management, 2018).

The study

• Authors: R. Borges, L.M. Baika, M.T. Grassi, F. Wypych
• Journal: Journal of Environmental Management
• Published: 2018;206:962-970
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile fibers pose a threat to public health due to their association relation to respiratory malignant lung disease such as cancer. For this reason, they must be stored and discarded appropriately, including after treatment, which raises costs. In the present study, insoluble chrysotile fibers were milled in solid state with highly soluble K2HPO4, destroying both structures, making the chrysotile nontoxic and generating a new material with potential use as sustainable slow-release fertilizer (SSRF) containing mainly K and P. Based on the mills, milling conditions and chrysotile/K2HPO4 molar ratios used, Mg originating from chrysotile fibers reacted with K and P from dibasic potassium phosphate and were transformed into MgKPO4·H2O, MgKPO4·6H2O and probably a mixture of amorphous SiO2/MgO. In this study, a zirconia planetary mill and high-energy ball mill were used, both of them produced SSRF. In conclusion, it was possible to synthesize high-value and extremely useful materials for agriculture using a harmful waste. The release rate can be tailored by controlling chrysotile/K2HPO4 molar ratios, grinding speed and time, which makes the process even more promising for farming applications.

Copyright © 2017 Elsevier Ltd. All rights reserved.

In plain English

This was a laboratory chemistry study from the Federal University of Parana, Brazil. It involved no people or animals. The authors ground chrysotile fiber from a Brazilian mine together with a potassium phosphate salt (K2HPO4). Their aim was to break down the chrysotile and make a slow-release fertilizer. They used two types of mill and varied grinding time, mill speed, pretreatment in water, and the proportions of the mix. They examined the products with X-ray diffraction, electron microscopy and heating tests, and measured how much of the nutrients dissolved in water. Chrysotile was no longer detected in some samples but remained in others. Chrysotile fibers were seen in samples made with a 2:1 chrysotile-to-phosphate ratio. Two high-energy-mill samples (HEC3 and HEC4) showed no chrysotile fibers. Potassium and phosphorus were released slowly. For example, sample HEC3 released 19.9% of its potassium after 1 hour and 59.3% after 168 hours. The authors concluded that the process destroyed the chrysotile structure, reducing and/or eliminating its hazardousness, and could produce nontoxic fertilizers. Release was tested only in water.

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-chemistry experiment: chrysotile and K2HPO4 were milled together in two mills, with conditions varied in factorial experimental designs (eight combinations plus a central point run in triplicate). No human or animal subjects.
• Who was studied: Chrysotile fiber (length below 2.0 mm, product SAMA7ML) donated by SAMA, Minaçu, Goiás, Brazil, containing some talc and traces of iron oxides/hydroxides, mixed with commercial K2HPO4
• Exposure: Chrysotile was milled with K2HPO4. In the zirconia planetary (Z) mill, water pretreatment of 6, 9 or 12 h and milling of 6, 9 or 12 h were tested. In the high-energy (HE) ball mill, milling of 6, 9 or 12 h at 200, 400 or 600 rpm was tested. Both mills used chrysotile:K2HPO4 molar ratios of 1:2, 1.5:1.5 or 2:1.
• Main results:
  • In the Z mill, chrysotile diffraction peaks were absent only in samples ZC2, ZC3, ZC4 and ZC8.
  • Chrysotile fibers remained in samples made with a 2:1 chrysotile:K2HPO4 molar ratio, which the authors attributed to too little phosphate salt.
  • HE mill samples HEC3 and HEC4 formed dittmarite and showed no chrysotile fibers.
  • Potassium release in water for HE mill samples: HEC3 released 19.9% after 1 h and 59.3% after 168 h. HEC4 released 18.5% after 1 h and 42.8% after 168 h.
  • Potassium release in water for Z mill samples: ZC3 released 24.6% after 1 h and 55.2% after 168 h. ZC4 released 17.0% after 1 h and 55.1% after 168 h.
  • Magnesium release was very slow, and silicon release in water was close to zero.
  • In preliminary experiments with a high-speed mill (1420 rpm, about 5 g of material), 10 minutes was enough to destroy the chrysotile fiber structure. Similar results were reported with chrysotile/cement roofing tiles.
• The authors' conclusion: The authors concluded that milling with K2HPO4 destroyed the chrysotile structure, reducing and/or eliminating its hazardousness. They also concluded that the products could be used as nontoxic slow-release fertilizers whose release rate can be adjusted by the milling conditions.
• Limitations the authors state:
  • Release was tested only in water. The authors noted that silicon could be released under acidic conditions.
  • The contaminants in the raw chrysotile could not be identified by X-ray diffraction after milling.

Topics

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

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

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