Progress in recyclable chemicals for sustainable ex-situ CO2 mineralisation

The 21st century grapples with rising atmospheric CO2 and anthropogenic solid waste. Ex-situ CO2 mineralisation, converting CO2 into stable carbonates via reacting with solid waste, shows great promise. However, concerns over the extensive consumption of chemicals urge sustainable and recyclable alternatives. This paper critically reviews recyclable chemicals for CO2 mineralisation with various industrial solid wastes, and systematically examines their efficacy and reaction mechanisms. This study offers a comprehensive comparison of these chemicals and outlines clear future research directions. The main findings are briefed below: first, we emphasize the pivotal role of trapping and recycling NH3 gas for achieving effective and efficient CO2 mineralisation using ammonium salts. Second, scaling up amines-based mineralisation could be feasible by replacing conventional strippers with mineralisation units. This transition is contingent upon resolving technical challenges such as amines' low leaching capacity and limited applicability to solid feedstocks that contain water-soluble Ca/Mg-bearing species. Third, leveraging their unique zwitterionic structures, amino acids may cater to diverse industrial needs and achieve a satisfactory CO2 mineralisation efficiency with good recyclability at low temperatures. Fourth, a novel HCl regeneration technology known as ‘oxy-pyrohydrolysis,’ can achieve simultaneous CO2 mineralisation and HCl regeneration in a single step. However, both amino acids-based mineralisation and oxy-pyrohydrolysis are nascent technologies requiring further research to ascertain their applicability and advance their development. Fifth, despite employing recyclable chemicals, operational costs of mineralisation could remain significant when high temperatures are used. Thus, energy optimization strategies should be explored, such as exploring low-energy consumption chemicals and integrating waste energy harvesting units. This review paper aims to delineate potential avenues for cost-effective CO2 mineralisation facilitated by recyclable chemicals, thereby alleviating post-processing costs and environmental concerns associated with chemical residues.