Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The restoration of bauxite residue disposal areas (BRDA) is one of the most important environmental challenges that the aluminium industry faces. It must take into consideration several factors including country regulations and standards, social acceptability, and the climatic zones in which the industry operates. Rio Tinto operates the only alumina refinery in Canada, the Vaudreuil refinery, located in the province of Quebec. The BRDA is nearly at full capacity and will have to be reclaimed in the coming years. The overall objective of this research project is to develop a cover layer favourable to plant growth conditions for the BRDA ecological restoration. This cover should be composed of a mixture of bauxite residue (BR), inorganic and organic residual materials from local industries and woody plants native to the province. Before creating composite soils from bauxite residue, it is essential to understand the hostile environment conferred by these residues, so as to create an ecosystem in which plants and microorganisms can grow. Since each bauxite residue has its own characteristic properties, the aim of this paper is to describe the results of the first phase of the research project (acidification) for Vaudreuil BR, i.e. the behaviour of residue chemical species under different pH conditions (target pH of 5-9) using hydrochloric acid (HCl). Preliminary results of bauxite residue acidification with HCl indicate that fluoride (F-) and trace metal elements are present mostly in the solution at basic pH, and that the ideal pH for compliance with the agri-environmental standards is neutral-basic. Following these results, the challenge will then be to create fertile soil while maximizing the proportion of bauxite residue to enhance plant growth while satisfying environmental and geotechnical criteria.