Role of unfavorable impurities in CO2 mineralization process of industrial solid waste: Uncertainties in decarbonization potential

Using industrial solid waste to capture CO₂ by mineral carbonation is considered one of the promising technologies to prevent waste disposal while combating global anthropogenic CO₂ emissions. Especially, the carbonation reaction is spontaneous and the carbonated products are relatively stable; thus, mineral carbonation is an effective means of stabilizing CO₂ and valorizing industrial solid waste. Previous estimations report that a 4.02 Gt per year mitigation potential can be facilitated through CO₂ mineralization of industrial solid waste. However, existing estimates do not take into account the impacts of unfavorable impurities, which have broad uncertainty and variability due to different industrial processes and ore sources. The existence of certain impurities might influence the rate of the carbonation reaction and therefore, the amount of CO₂ captured and carbonates formed. For instance, some elements (e.g., Pb, Cd, and Mn in mine tailings) can enhance the CO₂ capture capacity due to the precipitation of heavy metal carbonates. While some organics (e.g., organic matter in sludge) and anions (e.g., phosphates in phosphogypsum) can influence the carbonation reactions negatively. Especially, the questionable releasing behavior of these potentially toxic elements can bring about new environmental issues when the deposited body reaches groundwater or aquifer resources. Therefore, in this work, we have attempted to clarify the roles of impurities in the mineralization process and the afterward usage period, including the accelerating or retarding effects of impurities in carbonation and the leaching behavior of potentially toxic elements. Industrial solid wastes from different sectors, such as typical mine tailings (e.g., copper mine tailings and nickel mine tailings), industrial by-products (e.g., phosphogypsum, fly ash, red mud, and coal gasification slag), and construction and demolition waste, are used for accelerated and atmospheric carbonation at ambient temperatures. Our study reveals that although mineralization and in-stu storage could turn industrial solid wastes into a global carbon mitigation sink, unfavorable impurities may curb abatement potential.