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This paper investigates the feasibility of mechanical activation as a pre-treatment method as part of an integrated mineral carbonation process for a nickel mining operation in British Columbia. The physical, structural and chemical characteristics of forsterite and lizardite in mine waste rock after mechanical activation were monitored to determine their CO 2 sequestration efficiency for a direct aqueous carbonation process. Economic analysis on the process was developed through considering the energy requirements, cost modeling and carbon balance. Mechanical activation on mining residue reduced the particle size, enlarged the surface area, distorted the crystal structure of forsterite, and enhanced the CO 2 sequestration efficiency. However, it didn't create new phase or induce phase transfer between forsterite and lizardite, and distort the crystal lattice of lizardite. The optimum condition for 60% CO 2 sequestration efficiency was found at mechanical activation for 210 kWh t −1 ore and carbonation for 260 kWh t −1 ore, which had an operating cost of 104.1–107.1 $ t −1 CO 2 avoided. Using mechanical activation, the integrated mineral carbonation plant in the mine can potentially sequester 14.62 Mt y −1 CO 2 using mine waste rock and tailings during the 28-year life of mine. [ABSTRACT FROM AUTHOR]

Converting industrial wastes into value-added building products in an environmental management strategy is a challenging yet vital component of the industrial process. Steel slag (SS), an industrial waste by-product from the steel-making process, is typically disposed of in landfill which consumes land resources and pollutes the environment. This paper explores the possibility of a closed-loop system to convert steel slag into a cement material through carbonation activation, thereby significantly reducing the amount of steel slag waste sent to landfills across Canada. The production of this cementing material can occur next to the steel mill, utilizing steel slag and carbon dioxide collected on-site to fabricate carbon-negative products. To save energy and allow production to be feasible on an industrial scale, ambient pressure (AP) carbonation is developed to reduce carbon emissions while improving their performance. High pressure (HP) carbonation curing and normal hydration (NH) references were also implemented at the same time to justify the application of AP carbonation in reducing CO 2 emission. The results of this study found AP carbonation-activated SS compacts have comparable CO 2 uptake (about 7.5 tons CO 2 /100 tons slag) and mechanically compressive strength values as those subjected to HP carbonation, suggesting that AP could be used to replace HP in carbonation curing to ensure a lower energy input. Additionally, AP seemed to possess as effective carbonation as HP. The studies investigated by multiple techniques including X-ray diffractometer (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopic analysis, and scanning electron microscopy (SEM) aim to identify the microstructure development of carbonated SS paste to assess carbonation results. Developed with life cycle assessment (LCA), environmental impact evaluation shows that AP presents a smaller global warming potential (GWP) value than HP. The comparable CO 2 sequestration, satisfactory engineering properties, enhanced microstructure and lesser environmental impact in AP carbonation confirm the feasibility of replacing high pressure with extremely low pressure to cure concrete products. The use of AP carbonation for cement material created using steel slag reduces carbon emissions, energy usage, and natural resource consumption. • Ambient pressure can be used to replace high pressure in early carbonation curing. • Ambient pressure carbonation can turn steel slag into a clean cementing material. • The production of carbon-negative products can be set next to the steel mill. • Ambient pressure carbonation presents a relatively uniform and effective reaction. • Life cycle assessment confirms ambient pressure carbonation reduces CO 2 emission. [ABSTRACT FROM AUTHOR]

Two experimental small-scale cells have been constructed in the field to better understand passive mineral carbonation under natural atmospheric conditions in the ultramafic milling wastes of Thetford Mines (Québec, Canada). The magnesium-rich milling wastes mainly consist of poorly sorted grains and fibers of lizardite and chrysotile, with smaller amounts of antigorite, brucite and magnetite. These wastes could serve as significant and long-term CO 2 sinks but the mechanisms and rates of mineral carbonation are not well understood. In this paper, the design of the experimental cells along with observations on gas composition, gas pressure, soil temperature, volumetric water content and mineral composition are presented with the objective to better understand the mineral carbonation processes under natural conditions and to propose a conceptual model for mineral carbonation at the field cell scale. Low CO 2 concentrations (5–50 ppm) measured in the experimental cells and the presence of hydromagnesite suggest that natural and passive mineral carbonation is a significant process occurring in the magnesium-rich wastes (4 kg/m 3 /year of sequestrated CO 2 ). In the proposed conceptual model, atmospheric CO 2 (∼400 ppm) dissolves in the hygroscopic water of the piles, where weathering of magnesium silicates forms magnesium carbonates. Water saturation in the cells is relatively stable over time and varies between 0.4 and 0.65, which is higher than optimal saturation values proposed in the literature, reducing CO 2 transport in the unsaturated zone. Gas-phase CO 2 concentrations along with gas flow rate measurements in the cells suggest that the reaction is most active close to the surface and that diffusion of CO 2 is the dominant transport mechanism in the wastes. Although the carbonation reaction is exothermic, no evidence of thermal convection has been observed in the experimental cells. This conceptual model will serve to support a reactive transport model in order to quantify and optimize the amount of CO 2 that can be captured in chrysotile milling waste piles. [ABSTRACT FROM AUTHOR]

Polyvinyl chloride plastics (PVC), made flexible through the addition of di-2-ethylhexyl phthalate (DEHP) also known as di- octyl phthalate (DOP), are used in the production of a wide array of medical devices, toys, etc. During the past many years, concern has been voiced by public interest groups and regulatory agencies in Europe, Canada, and the United States regarding the potential adverse health effects of DOP migrating from children's toys during mouthing activities. Concern has focused on potential chronic effects on the kidney and liver. Therefore phthalate based plasticizers are facing ban in majority of the countries owing to its carcinogenic properties. Hence, the use of natural and/or biodegradable plasticizers, with low toxicity and good compatibility with several plastics, resins, rubber and elastomers in substitution of conventional plasticizers, such as phthalates and other synthetic conventional plasticizers attracted the market. Many modified vegetable oils are being used as partial replacement of DOP, but none of them has the historical record of acceptable performance comparable with phthalate plasticizers. In this study, cyclic carbonated soyabean oil(CSBO)was prepared by reacting epoxidised soyabean oil (ESBO) under pressure in presence of CO2. Reaction of ESBO to CSBO was confirmed by 13C-nuclear magnetic resonance (13C- NMR) and Fourier transform infrared spectroscopy (FTIR). The CSBO was used as plasticizer in PVC in various proportions for replacement of DOP in samples as prepared from PVC-DOP-ESBO combination, keeping ESBO proportion constant in all samples. The incorporation of CSBO resulted in, increase in viscosity but reducing viscosity pick-up, improved tensile strength, exudation, and chemical resistance properties, with decreased elongation. The presence of CSBO showed reduction in whiteness index due to brownish color of the product. Shore D hardness was found to be increased with increase in CSBO content. The results of thermal analysis showed no significant variation in properties when compared to those of DOP-ESBO plasticized sheets which can contribute to the conclusion that CSBO can be used as a plasticizer in PVC with ESBO as a co-plasticizer to replace DOP. [ABSTRACT FROM AUTHOR]