(533g) Accelerated CO2 Mineralization of Acid Mine Drainage Waste

Mining sector is one of the largest industrial CO₂ emitters in Canada. To support Canada’s commitment for the transition to net zero emissions by 2050, several regulations and approaches are recently taken into effect to this sector, trying to reduce CO₂ emissions and increase energy efficiency in mining operations. One approach to achieve this goal is the implementation of negative emissions technologies that can permanently store CO₂. One such carbon capture and sequestration strategy is mineral carbonation which involves reacting the CO₂ with an alkaline source to produce solid carbonate minerals. Application of the alkaline wastes have become increasingly more attractive than natural minerals, owing to their higher reactivity with the CO₂.Canada’s mining industry produces tonnes of mining wastes such as mine tailing and acid mine drainage (AMD) yearly, which are a potential secure source for CO₂ mineralization deployment. These wastes are rich in magnesium and calcium compounds, which are the promising candidates for sinking CO₂ through carbonation processes to produce solid stable carbonate products. On the other hand, the later source, AMD, is primarily one of the most hazards to ground and underground water sources on the mining sites and is characterized by low pH and high concentrations of heavy metals and sulfates. These contaminants can be easily leached out, having devastating effects on surrounding environment. On mining sites, AMD remediation is commonly achieved by the addition of lime that neutralizes the solution, consequently, makes the treated ADM solution rich in calcium species.

The current ex-situ solution-based CO₂ mineralization processes suffer from either low reaction rates or a need for expensive thermal pre-treatment that negatively affect the economy and environmental burdens of the system. Therefore, acceleration of involved reactions is a promising approach that could effectively enhance such CO₂ carbonation technology competitiveness. In this respect, the main goal of this work is to present a new mineralization process assisted by ultrasonic treatment that accelerates CO₂ reaction with active species of Canadian AMD solution, that is, magnesium and calcium compounds. Ultrasonic processing is a well established technology that can improve chemical reaction kinetics that are inherently slow towards gaining a higher product yield. Successful application of ultrasonic processing for producing precipitated calcium carbonate (PCC) and acceleration of calcium dissolution from the industrial slags has been addressed in the literature [M. Altiner et al, Ultrasonics Sonochemistry 72 (2021) 105421; A. Said et al. / Chemical Engineering and Processing 89 (2015) 1–8].

It is speculated that AMD-based CO₂ mineralization reaction integrated with ultrasonic processing is featured with a better CO2 gas dissolution and kinetics of carbonate precipitation which is slow in its nature. To this end, we developed a CO₂ mineralization test set-up, enabled us to apply different operation conditions for CO₂ carbonation study. Industrial AMD solution was subjected to CO₂ carbonation trials. The impact of solution pH, temperature, CO₂ partial pressure and the dosage of the alkaline agent were investigated to find the optimum conditions of operation for achieving a higher carbonation yield. The precipitate samples were characterized, and CO₂ carbonation efficiencies with and without ultrasonic processing were determined.