Mineral carbonation is a carbon sequestration technology that entails the reaction of CO2 with oxides or silicates of magnesium, calcium or iron to produce stable carbonate compounds. Magnesium-rich tailings from the platinum industry in South Africa have been identified as a potentially viable and attractive feedstock for CO2 sequestration through mineral carbonation. Many of the strategies proposed to enhance the dissolution kinetics of silicate minerals, such as the use of elevated temperatures and pressures and chemical additives, as well as pretreatment through mechanical and thermal activation, are energy intensive and will thus reduce the net CO2 sequestration capacity of the overall mineral carbonation process. As a result, there is growing recognition of the need to evaluate the processes using life-cycle based approaches and tools to ensure they result in net CO2 reduction. However, to date, research and development has focused primarily on the optimisation of extraction and/or carbonation efficiencies, with specific emphasis on the relatively reactive silicate minerals, such as olivine and serpentine. This project seeks to investigate the viability of using pyroxene-rich PGM tailings for the sequestration of CO2, with specific emphasis on net carbon neutrality. Promising mineral carbonation processes have been identified on the basis of an extensive literature review, and include the: ammonium salts pH swing, Lackner’s HCl multi-stage, gas-solid Åbo Akademi University process, direct aqueous process, and mineral acid pH swing. Material and energy balances were then conducted for these processes on the basis of the sequestration of 1 ton of carbon dioxide, using Aspen Plus v8 simulation software package. The material and energy data were then used to determine the total carbon footprint contributions, through the use of SimaPro v 7.7.3. life cycle assessment software. The selected carbonation processes were found to release more carbon dioxide than the process sequesters. The carbonation process resulting in the most emissions released was found to be Lackner’s multi-stage process (18 295 kg-CO2e), followed by the ammonium salts process (8 798 kg-CO2e), per ton carbon dioxide sequestered. The carbonation process resulting in the least emissions released was the solid Åbo Akademi University process (1 354 kg-CO2e), followed by the gas-solid direct aqueous process (2 364 kg-CO2e), as well as the mineral acid pH swing process (3 126 kg-CO2e). The most carbon emissions intensive contributions to the carbon footprint were found to be heat requirements and chemical reagent make-up, which generally accounted for more than 85% of total emissions when combined. Aqueous processes generally incurred a much higher carbon footprint, despite using relatively lower temperatures than the gas-solid ÅAU process. This was attributed to the higher quantities of water used in the aqueous processes that, in some cases, were subject to phase change via, for example, evaporation. Additionally, the production of make-up chemical reagent, alone, was found to result in emissions that exceeded the carbon dioxide sequestered for four of the five selected processes (ammonium salts process, Lackner’s HCl multi-stage, direct aqueous, mineral acid pH swing). The potential to reduce emissions associated with heat generation could be achieved through the exploration of heat integration and cleaner alternative sources of heat, for the potentially feasible processes. On the other hand, the carbon dioxide emissions associated with make-up reagent could be reduced through the use of cleaner input materials as well as by increasing the recycle ratios to reduce external reagent requirement.

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