Role of ettringite formation in the stabilizationsolidification of sulphide-bearing mine waste

Disposal of acid generating sulphidic tailings is a major environmental problem facing the Canadian as well as the international mining and mineral industries. If the deposited tailings are not treated the sulphide minerals oxidise and create an acidic environment. The leachate from such a site is rich in soluble heavy metals and has the potential to contaminate the groundwater as well as the local surface watercourses. This thesis explores an alternative treatment method via ettringite formation, which stabilises and solidifies these highly reactive tailings.Ettringite has the capacity of uptaking other metals into its structure by isomorphous substitution. Ettringite has also a negative surface charge, which makes it a good adsorbent for positively charged cations. Furthermore, the high pH solution required for ettringite formation will cause the precipitation of heavy metals from the solution. Therefore, ettringite in a lime-remediated sulphate rich acid mine drainage system could serve as a physical and chemical stabilization agent, which could also reduce the remediation costs over other commercially available stabilization technology.In order to assess the feasibility of forming ettringite in sulphide rich tailings, a thermodynamic model was used to investigate the optimal geochemical parameters. The model predicts that ettringite is stable over a wide range of compositions and pH. Results presented in this thesis show that the sulphate content of the tailings samples could limit the precipitation of ettringite, and monosulphate could be the end-precipitate.Long-term leachability and durability analysis showed that ettringite can be formed as a stable mineral in lime, fly ash, and aluminum rich sulphidic tailings samples. Ettringite formation reduced the leachability of the heavy metals and improved the geotechnical characteristics of the treated samples. Freeze and thaw analyses showed that formation of ettringite produce a low permeability and high strength tailings sample capable of withstanding harsh environmental fluctuations