Al-Substituted Tobermorites: An Effective Cation Exchanger Synthesized from "End-of-Waste" Materials

Our plain-English summary of Al-Substituted Tobermorites: An Effective Cation Exchanger Synthesized from "End-of-Waste" Materials, by D. Malferrari, F. Bernini, D. Di Giuseppe, et al (ACS Omega, 2022).

The study

• Authors: D. Malferrari, F. Bernini, D. Di Giuseppe, V. Scognamiglio, A.F. Gualtieri
• Journal: ACS Omega
• Published: 2022;7(2):1694-1702
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The policies to meet the "zero waste" regime and transition to sustainable circular economy can no longer ignore the use of wastes in place of natural resources, and these daunting and vital societal challenges are nowadays being faced by several nations. The main objective of this work was to search waste materials suitable for a quick and environmentally friendly production of a nanoporous geomaterial able to trap toxic metals at the solid/liquid interface. More specifically, the end-of-waste from the thermal inertization of cement-asbestos and glass powder from domestic glass containers have been employed as sources for the hydrothermal synthesis of a tobermorite-rich material (TRM) successfully tested for the selective removal of Pb2+, Zn2+, Cd2+, and Ni2+ from aqueous solutions. The synthesis was carried out in alkaline solution under mild hydrothermal conditions (120 °C) within 24 h. The quantitative phase analyses of the TRM carried out by applying the Rietveld method showed the occurrence of a large amount of well-crystallized 11 Å Al-substituted tobermorites and an amorphous phase and a lower content of aragonite and calcite. Chemical analyses and thermogravimetric measurements coupled with simultaneous evolved gas mass spectrometry highlighted that Al3+ for Si4+ substitutions in the wollastonite-like tetrahedral chains of tobermorites are balanced by the occurrence of Ca2+, Na+, and K+ cations in the interlayer rather than by (OH)- for O2- substitutions in the CaO polyhedra. Time-dependent removal tests clearly indicated that metal cations are selectively adsorbed depending on their concentration in solution. Moreover, the kinetic curves showed that the removal of metals from solution is fast and the equilibrium is almost reached in the first 8 h.

© 2022 The Authors. Published by American Chemical Society.

In plain English

This was a laboratory chemistry study, not a health study. The authors used KRY·AS, made by heating cement-asbestos slates in industrial kilns at 1200 to 1300 °C, which the article describes as free of asbestos phases. They mixed it with recycled household glass powder and a little zeolitic tuff, then heated it in alkaline solution at 120 °C for 24 hours. The product was a tobermorite-rich material: 53.4 weight % 11 Å-tobermorite, 36.7 % amorphous material, 7.6 % aragonite and 2.3 % calcite. In water containing lead, zinc, cadmium and nickel, the material removed lead most readily, then zinc, cadmium and nickel. At 1 and 5 mmol/L, cadmium and nickel removal was comparable. Removal was nearly at equilibrium within the first 8 hours. Total metal removal ranged from 10 weight % at 100 mmol/L to 70 % at 1 mmol/L. The article does not say what these percentages are of. The authors concluded that tobermorite can be made from end-of-waste materials. They noted that the tests were laboratory scale, that waste composition varies by source, and that similar natural materials cost less.

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-synthesis and adsorption experiment (no human or animal subjects)
• Who was studied: No people studied. Test material was a mixture of KRY·AS (66.5 wt %), glass powder from domestic glass containers (31.5 wt %) and phillipsite-rich zeolitic tuff (2.0 wt %), made into a tobermorite-rich material (TRM).
• Exposure: No health exposure studied. The asbestos-related input was KRY·AS, the product of thermally treating cement-asbestos slates (CAS) in industrial kilns at 1200 to 1300 °C, described as free of asbestos phases. No fiber type is named. The TRM was then tested for removing Pb2+, Zn2+, Cd2+ and Ni2+ from multielement solutions at 100, 50, 10, 5 and 1 mmol/L.
• Main results:
  • Rietveld phase analysis of the TRM: 11 Å-tobermorite 53.4(6) wt %, aragonite 7.6(2) wt %, calcite 2.3(1) wt %, amorphous phase 36.7(7) wt %
  • The tobermorite in the TRM showed a high grade of crystallinity (Level D)
  • Metals were removed selectively: Pb2+ first, then Zn2+, Cd2+ and Ni2+
  • Cd2+ removal was comparable to Ni2+ removal only in the 1 and 5 mmol/L batches, while Zn2+ and especially Pb2+ removal stayed high and selective
  • Selectivity was greater at higher metal concentrations
  • Removal was fast, with equilibrium almost reached in the first 8 hours
  • Equilibrium, once reached, was preserved over almost 100 hours
  • Total metal removal by the TRM varied between 10 wt % at the highest concentration (100 mmol/L) and 70 wt % at the lowest (1 mmol/L). The article does not state what these percentages are of.
  • Except in the 1 mmol/L batch, more metal charge was removed than could be explained by exchangeable cations alone, which the authors took as a sign that surface adsorption also occurred
• The authors' conclusion: The authors concluded that tobermorite can be synthesized using end-of-waste materials (thermally treated cement-asbestos and waste glass powder).
• Limitations the authors state:
  • Tests were done only at laboratory scale
  • The chemical composition of the waste may vary depending on its source
  • Natural materials such as bentonites and zeolitic tuffs with similar properties are available; a cost-benefit and environmental analysis would be needed
  • The charge-balance interpretation assumes the amorphous phase contains no tobermorite-like compounds
  • Optimizing the synthesis to maximize tobermorite content was outside the aim of the study

Topics

Medical terms in this study, explained in our Lexicon: Cation, Wollastonite.

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