One hundred billion tons of mine solid waste are estimated to be produced worldwide each year. In Canada, the mining and oil industries produce the most solid and semi-solid waste in the country, with more than a billion tons each year. In the earlier days of mining, the initial practices that were used to contain these waste materials consisted of surface storage, river dumping or just simple abandonment, while the more recent practices include dam impoundment and underground waste fill. These methods however can potentially cause environmental hazards and geotechnical problems. Against this context and as a result of stricter environmental regulations, cemented paste backfilling has been developed as a solution. This relatively new technology uses the produced waste tailings to backfill the mine stopes, greatly reducing their environmental impact while offering proper structural support in an efficient manner. However, the cost of cemented paste backfill (CPB) is greatly impacted by the binder content which can constitute up to 75% of its total cost. Additionally, the binder is usually mostly composed of ordinary Portland cement, and its production is highly energy-intensive and generates a large volume of carbon dioxide (CO₂). Indeed, it is estimated that the cement industry accounts for approximately 7% of the global anthropogenic CO₂ emissions, which is expected to increase on an annual basis. All of these factors have compelled the mining industry to seek alternatives for cement to enhance CPB strength, in hopes of reducing its carbon footprint.
Against this context, this study investigates the effect of the addition of nanoparticles, namely nano silica (SiO₂) and nano-calcium carbonate (CaCO₃), on the strength development of CPB cured at a constant room temperature and in non-isothermal conditions. Nanoparticles have been studied and used as chemical admixtures in different cementitious materials with promising results; non-isothermal curing conditions better reflect the in-situ thermal curing conditions of CPB. Thus, numerous different laboratory tests and analyses, including uniaxial compressive strength (UCS), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests, thermogravimetric/derivative thermogravimetric (TG/DTG) analyses and electrical conductivity monitoring, have been conducted on CPB samples with or without nanoparticles, and cured at room temperatures or under non-isothermal conditions. The non-isothermal conditions replicate the development of temperature in two different sizes of CPB structures in the field. The results show that CPB that contains nanoparticles show a higher UCS over the entire period of curing in all of the tested conditions. The mechanical performance is further enhanced when tested under higher temperatures in non-isothermal temperature profiles. Most of the strength increase takes place at the early ages (3 days) of the testing. The reason for the improvement in the mechanical strength is linked to accelerated binder hydration and the nucleating and filler effects of the nano-material, which is corroborated by results obtained through microstructural analyses and EC monitoring. The use of natural gold tailings affects the mechanical performance of CPB and the accelerating effect of the nanoparticles due to sulphate attacks. Overall, these promising findings can help to contribute to reducing the carbon footprint of mining activities, and improve the efficiency and cost-effectiveness of mine backfilling processes.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/44548 |
| Date | 20 January 2023 |
| Creators | Benkirane, Othmane |
| Contributors | Fall, Mamadou |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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