Net-Zero-Based Chemical Recirculation for Greener Hydrometallurgy
摘要
While Canada’s Critical Minerals Strategy focuses on the mineral extraction, processing, advanced manufacturing, and recycling of such metals and materials, the contribution of chemicals used in those processes to net-zero calculations and the waste generated are to be addressed. As part of objective two of the strategy, the waste reduction innovative technologies, and processing techniques can also lift part of the GHG emissions, enhance process circularity, and augment autonomy through onsite recycling. One such innovative technology and processing technique is the use of electrodialysis processes. The electrodialysis processes could, by using electricity, recover spent acids/caustic used in processes, separate waste such as sodium sulfate into sulfuric acid and caustic soda to be used back into the generating processes, and be transformed into acid-base flow batteries to store excess electricity production on remote locations. Some problems were addressed. First of all, membrane technologies in such processes suffer from high concentrations (high osmotic pressures) achieved in the lixiviates. This high osmosis pressure causes the transfer of cations through anionic membranes and anions through cationic membranes, causing contamination. Another example is that membranes chosen for their permeation selectivity can improve or decrease the whole cell voltage. For instance, there is less contamination with thicker membranes, but this makes the resistivity of the whole cell higher, increasing energy demands. This presentation surveys technologies that have the potential to lower energy consumption in the electrodialysis process, hence greatly lowering GHG emissions and decreasing contamination problems, while limiting waste production.