Author:

Keywords:

mineral carbonation, carbon sink, thermal residues, process intensification, leaching, ultrasound, waste valorization, steel slags, alkaline minerals

Abstract:

Two of the largest and most important waste products from industrial the rmal processes are carbon dioxide gas and waste solid residues. Given th e high financial and environmental burden caused by these waste products , it is urgently desirable to industry and society alike to find a susta inable manner for managing them. The objective of this research project is the production of a carbon sink based on the process of mineral carbo n sequestration that provides a responsible and economical outlet for th ese waste products. Thermal processes are commonly applied in the production and refinement of metals, in waste incineration, energy generation, among other areas. The solid waste products typically produced include slag and fly ash, wh ich are composed primarily of oxides of silicon, calcium, magnesium, alu minum and iron, along other components such as heavy metals, chlorides a nd sulfates. Recently, due to rising production costs, increased regulat ory pressures and growing awareness towards environmental issues, there has been a change in the perception of these materials. It has been real ized that they can be regarded as potential products rather than simply as waste. This shift, however, still faces numerous challenges: unavaila bility of reliable low-cost technologies, variability of material qualit y, lack of legislation, underdeveloped markets for the resulting product s, and poor societal experience with closing material cycles. Thermal processes also generate a vast amount of carbon dioxide, which i s invariably emitted to the atmosphere. Concern regarding the role of ca rbon dioxide as a greenhouse gas in climate change is evolving rapidly, and it is evident that these emissions will become ever more regulated i n the future. In this regard, it will be of financial benefit to industr y to limit its net carbon dioxide emissions. Methods to sequester carbon dioxide gas currently being investigated included mineral carbon seques tration, which uses materials such as olivine and serpentine that must b e mined for use, and subsurface injection, which requires extensive geol ogical study and stewardship. An alternative method, sequestration in al kaline waste materials, is interesting due to the high reactivity of the material and the ease of on-site production, and is seen as potentially a low cost option. Further benefits include that fact that reaction of the alkaline waste with carbon dioxide stabilizes the material and often improves its environmental properties for disposal. This research project aims to investigate the use of alkaline waste mate rials in carbon dioxide sequestration and identify process properties su ch as sequestration load and yield efficiency, reaction kinetics, and li miting rate conditions. An optimized carbon sink should sequester a maxi mum amount of carbon dioxide without loss of reaction rate over time. Ai ming at the production of an improved carbon sink, two potential areas o f waste product improvement will be investigated: the first is to steer the functional properties of the cooled waste products during hot-stage residue processing; the second is to use physical-chemical methods for i mproving cold-product properties. Several carbonation strategies will be studied to overcome current process barriers and for optimization of th e concept, such as liquid-film carbonation and suspension carbonation. F or further sequestration process enhancement, a new approach will be int roduced by using localized energy for abrasion of the particles to obtai n new reaction surfaces and for enhanced diffusion.