(35f) Production of Carbonates from Alkaline Industrial Waste Via Carbon Mineralization Towards a Circular Economy

Carbon mineralization is a process to fix CO₂ into solid carbonates for permanent storage. This process has been proposed as an efficient approach to achieving the goal of net-zero greenhouse gas emissions. Mineralization reaction could happen spontaneously from the thermodynamic perspective, but the kinetic is very slow and can be accelerated via engineered techniques. Industrial wastes (e.g. demolition & construction materials, coal fly ash, steel slags, etc.), which contain a high concentration of alkaline earth metals (i.e. calcium) can be used as sources to produce calcium carbonates instead of landfilling them.

Herein, we present studies focusing on the utilization of alkaline industrial wastes to produce different polymorphs of calcium carbonates for different industrial applications. We propose a multiple-stage process to treat the feedstock to obtain high purity carbonates. First wastes are dissolved in an acidic solution to extract out Ca, and followed by an impurities removal (Fe, Al and partial Si) via pH swing process, and finally a crystallization reaction is occurred by bubbling CO₂. In this research, we also apply an in-situ observation of the dissolution and carbonation process by an optical advanced probe from BlazeMetrics, and we can monitor the particle size and polymorphs variations in real-time, facilitating us to better understand the kinetics and mechanisms of these reactions. It was found that dissolution process is a diffusion-controlled reaction and different high purity polymorphs of calcium carbonates (vaterite, calcite and aragonite) could be synthesized by controlling operating conditions. We also scaled up this process to a 20L reaction with this mild reaction condition. These produced carbonates can be used as supplementary cementitious materials or fillers to achieve a circular economy by eliminating the industrial waste and converting them into feedstock. In order to achieve a greener and sustainable process, we will utilize electrolysis of salty solution to produce acid and base in our process in the future, and renewable energy will be used to activate this reaction. Life cycle assessment and techno economic assessment are used to evaluate the process from environmental and economic perspectives.