Accelerated CO₂ Mineralization of Acid Mine Drainage Assisted by an Ultrasound Technique: An Experimental Parametric Study

Among the wastes produced by the mining industry, acid mine drainage (AMD) is one of the most hazardous wastes for the environment because of its highly acidic nature and high concentration of heavy metals, which may lead to harmful effects in animals, plants, and humans. Various remediation technologies are available and have been applied to AMD treatment to meet mining effluent regulations. Remediation options are divided into those that use either chemical or biological mechanisms to neutralize AMD and remove metals from the solution. Among the chemical neutralizing methods, lime (calcium oxide) treatment is a cost-effective technology that has been widely used. The effluents from a lime treatment plant usually contain high concentrations of calcium (Ca) and magnesium (Mg), which are recognized as viable metal ion sources for mineral carbonation. This work presents an experimental study on the CO2 mineralization of AMD solutions with a simulated flue gas stream and its acceleration by ultrasound intensification. Two test methods are investigated: one involving the CO2 mineralization of previously demetallized AMD, and the other focusing on the one-pot demetallization of raw AMD and its CO2 mineralization. Furthermore, additional experiments are conducted by incorporating ultrasound intensification to accelerate the carbonation reactions. The effect of the temperature on the process is also investigated. The ultrasound-assisted experiments result in a higher CO2 sequestration capacity and Mg removal efficiency than those without ultrasound, indicating the corresponding process intensification and the enhancement effect of ultrasound on carbonation reactions and greater conversion. Moreover, the Mg removal rate is enhanced by increasing the operating temperature, while the Ca precipitation rate is not immensely sensitive to temperature variation. Additionally, the results indicate that one-pot AMD treatment and CO2 mineralization produce almost heavy metal-free effluents that comply with the Canadian Metal Mining Effluent Regulations. A maximum of 6.992 × 10–4 CO2 sequestration capacity (g-CO2/g-solution) at 80 °C is achieved for one-pot processing, which suggests that this method can be a viable approach for the mining industry, with the benefits of mitigating AMD effluent impacts and generating additional revenue through carbon credits or offsets.