Solubilité de différents minéraux aluminosilicatés en vue de leur contribution à la géopolymérisation dans les remblais miniers en pâte

Cemented paste backfills (CPBs) have become common practice in many modern underground hard-rock mines, primarily due to increasing ore recovery and the safety of mine workings, as well as reductions in the amount of tailings requiring surface storage. However, the constant increase in the costs of Portland cement and other cementitious additives (e.g. blast furnace slag) makes CPB more expensive. In most cases, the cost of the binder (e.g. Portland cement or other additives) exceeds 75% of backfilling operation costs. To address this constraint while ensuring the performance of CPBs, there is a need for alternative binders that result in acceptable technical properties and lower costs. One potential solution is the geopolymerisation of mine tailings. The geopolymers are obtained by polycondensation of aluminosilicates species originating form dissolution of aluminosilicates materials at strongly alkaline medium in the presence (or not) of soluble silicates. Mine tailings, mostly rich in aluminosilicates minerals, could be a potential raw material for geopolymerisation and thus for the manufacture of geopolymer paste backfill (GPB). This new type of backfill is anticipated to be less expensive than the CPB and could develop very good geomechanical and chemical stabilities and better encapsulation of toxic metals. The main objective of this project is to evaluate the geopolymerization potential of mine tailings (with or without additives) to synthesis mine paste backfill. More specifically, the project aims to: (i) study the alkaline dissolution of various pure aluminosilicate minerals (frequent in mine tailings). The experiments aimed in selecting the most favorable silicate to geopolymerization and finding the factors that control the alkaline dissolution of these minerals. (ii) Study the enrichment effect of tailings by these selected mineral phases (or other aluminosilicates materials, if necessary) on the mechanical strength of geopolymer backfills, (ii) select an optimal geopolymer backfill recipe and make a brief economic comparison with the reference backfill recipe (backfill based blended binder 20%GU/80%SLAG). The results of alkaline dissolution tests of pure minerals and geosynthesis tests (by alkaline activation) of pure tailings-based backfill have shown that the geopolymerization potential in mine backfills is significant; however, reaction (geopolymerization) kinetic is slow. Indeed, the developed strength by geopolymer backfill is appreciable in the mining context but is only obtained in the long term (beyond 28 days). Therefore, to ensure the required strength of the backfill in the short term (≤28 days), several geopolymer binder formulations were tested on a synthetic backfill (based on fine sand instead of mine tailings). These binders are obtained by alkaline activation (by NaOH) of the mixtures GGBFS/FA_F (ground granulated blast furnace slag/type F fly ash). This study identified geopolymer binder formulations that could provide short-term backfill strength (≤28 days). The results of this study are not reported in this report and will be the subject of a future publication. Finally, in the light of the above results, different mine backfill formulations were tested according to standards design of experiments (Taguchi method). These formulations were based on the Goldex mine tailings for their aluminosilicate minerals content. The analysis of the results of these designs of experiments concluded that geopolymerization in mine backfill is very promising and that the substitution of Portland cement is possible. The cost of new backfill remains, however, highly dependent on the price of NaOH. Keywords: Alkaline dissolution, geopolymerization, aluminosilicates, mine tailings, alternative binders, mine paste backfill.