Carbon dioxide sequestration of iron ore mining waste under low-reaction condition of a direct mineral carbonation process

Limited reactivity of pyroxene and plagioclase in batch experiments with supercritical CO2 in the presence of NaCl and NaHCO3 in the context of CO2 sequestration via carbonation

One-step high-pressure and high-temperature direct aqueous mineral carbonation of tailings derived from mining of Platinum Group Metals in South Africa requires a fundamental understanding of the reactivity of the most dominant mineral phases, i.e. pyroxene and plagioclase (66 wt. % and 12 wt. % of the bulk rock respectively) that are typically found in these tailings. The silicate minerals pyroxene and plagioclase were sampled from a pyroxenite footwall mined with the ore-bearing UG2 and from the Merensky Reefs outcropping in the eastern limb of the Bushveld Complex. These pyroxene and plagioclase grains were concentrated by gravity separation from the orthopyroxenite bulk rock and batch-reacted in a sodium chloride (NaCl) brine saturated with pure carbon dioxide (CO2) gas-only or seeded with sodium bicarbonate (NaHCO3; as an additional CO2 source) for 13 days at 100 °C and 10 MPa. Pyroxene dissolved slightly but no weathering features were observed in plagioclase. Analyses of the filtrates obtained from the pyroxene sample in the absence of NaHCO3 showed an increased concentration of magnesium and calcium ions in the solution. However, they had also reached a cation saturation sealing. On the other hand, liquid samples from reactions where both CO2 gas and NaHCO3 were added to the solution exhibited a pronounced decrease in dissolved magnesium and calcium ions. XRD patterns of some of the post-reaction solids collected from the cation-depleted solution aliquots showed peaks of newly formed secondary magnesite and vermiculite. Moreover, the presence of magnesite was further confirmed by Raman shift analysis of the dried solid products. The formation of secondary magnesite was observed only in the experiments seeded with NaHCO3, specifically where the pre-reaction solid was pyroxene rich. Some of the resultant fluid chemistry was corroborated by the geochemical model that simulated the reaction parameters using the Geochemist Work Bench (GWB) software. Overall, the results indicate low pyroxene dissolution, which leads to limited carbonation. These findings suggest that the carbonation of PGM tailings may be constrained under the evaluated physicochemical conditions.

Potential of major by-products from non-ferrous metal industries for CO2 emission reduction by mineral carbonation: a review

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO₂ through the mineral carbonation process. This review discusses the potential of these by-products for CO₂ reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO₂ equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO₂ emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO₂ emissions from the non-ferrous industries could be reduced by up to 9-25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries.