Scientists have presented a new set of guidelines in using solvents as recovery agents for calcium carbonate (CaCO3) from industrial wastes.
In recycling industrial wastes - which involves capture, use, and storage of atmospheric carbon dioxide (CO2). One option to achieve this is through indirect carbonation where calcium or magnesium is recovered from industrial waste compounds with the use of solvents, or chelating agents. The released carbon dioxide, as a byproduct of the chemical reaction, is then captured with an additional carbonation reaction.
Researchers from the Korea Maritime and Ocean University presented their guidelines for recovering CaCO3 of varying characteristics, meeting requirements of different industries. While a number of studies have already inquired about optimizing the efficiency from indirect carbonation of calcium, remarkably few studies explore the stability of the link between calcium and the ligand affects the resulting product of the reaction. This is a point of interest since calcium solvent, or ligand, stability constants affects not just the calcium extraction efficiency, but the carbonation efficiency as well.
Effects of Chelating Agent Choice
Professor Myoung-Jin Kim led the study that tested seven different chelating agents with different calcium-ligand stability constants, using them in an indirect carbonation process for paper sludge ash, a waste material generated by paper milling industries.
"Though paper sludge ash has not been used much for indirect carbonation, it is high in calcium and has a small particle size, making it an excellent raw material even without any form of pre-treatment," Kim explained in the choice for the waster product.
Their study, published in the Journal of CO2 Utilization, revealed that the choice and concentration of the chelating agent affects the volume of calcium from the chemical process, the among of CO2 captured, and the "purity" of the CACO3 obtained from the process. Kim explains that as an example, to attain CACO3 of 99% or higher purity, it is important to go with a chelating agent that has low calcium-ligand stability constant. Their experimental results revealed a trade-off between these factors: aiming for a higher Calcium extraction efficiency leads to lower carbonation efficiency. She also recommended that "to maximize CaCO3 yield regardless of purity, an agent with a stability constant similar to citrate is best."
Recovery of Paper-Based Waste
"We believe our guidelines will be quite helpful, both technically and economically, for the use of indirect carbonation technologies with chelating agents at industrial sites," Kim added. The team behind the study hopes that their work would help make the recovery and reuse of CaCO3 easier, creating more meaningful and responsible use of industrial waste.
Earlier this year, Belgian researchers published a paper in the journal Waste and Biomass Valorization, evaluating the feasibility of preserving recycled fillers, like kaolin and CaCO3, from deinking paper sludge used in newspaper production. The novel method proposed by the researchers included incinerating the deinked paper sludge, with the ash bleached using sodium dithionite. An analysis of the final product revealed that recycled paper from the new method showed an improved brightness and opacity, but with reduced porosity and breaking length.
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