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Searching for Acidity or the Case of the Missing Chlorine: An Option for a Global Closed Loop Alkalinity–Acidity Cycle for Bauxite Residue Neutralization Based on HCl from PVC Recycling

  • Marcel Schlaf
Research Article
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Abstract

The Bayer process depends on the large-scale use of caustic soda (NaOH)—produced at > 60 million tons/year from NaCl by the chlor-alkali process—and is thus one of the major consumers of the alkalinity generated by the latter. A part of this alkalinity then ultimately ends up in the bauxite residue from the Bayer process, arguably constituting one of the main chemical, technical, and environmental challenges for a valorization or long-term safe disposal and remediation of this material. By stoichiometric and chemical necessity, the complementary acidity resides in the Cl2 gas is also produced in the chlor-alkali process and is thus latent in the chlorinated compounds—notably polyvinyl chloride (PVC) and chlorinated solvents, such as dichloromethane or 1,1,1,-trichloroethane. Recapturing and recycling Cl2 from these uses in the form of hydrochloric acid (HCl) by means of a controlled thermal decomposition of the chlorinated hydrocarbons could—in principle—serve as a source of Brønsted acidity for the neutralization of bauxite residue (Red Mud) thereby transforming it into a nonhazardous material of much lower environmental concern limited to its NaCl content. This could establish a closed alkalinity–acidity cycle on a global scale while simultaneously addressing the end-of-life fate of environmentally persistent PVC that otherwise either is deposited in landfills or can end up in the oceans in form of dispersed microplastics.

Keywords

Bauxite residue Polyvinylchloride (PVC) Neutralization Recycling Synergistic co-processing 

Notes

Acknowledgements

The author thanks Dr. Jenny Cox (at the Dept. of Chem., Univ. of Guelph) for helpful suggestions.

Compliance with Ethical Standards

Conflict of interest

The author declares no Conflict of Interest with any of the stake holders and industries mentioned in this article.

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Copyright information

© The Minerals, Metals & Materials Society 2018

Authors and Affiliations

  1. 1.Department of Chemistry, Guelph-Waterloo-Centre for Graduate Work in Chemistry (GWC)2University of GuelphGuelphCanada

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