Production of carbon negative precipitated calcium carbonate from waste concrete

Abstract

Mineral carbonation can contribute to climate change mitigation through the production of synthetic limestone (CaCO3) from calcium silicate minerals and gaseous CO2. Some carbonates, such as Precipitated Calcium Carbonate (PCC), have industrial applications and may provide sufficient economic incentive for sequestering CO2 should the product be a marketable commodity. Cement is a suitable source of calcium and can be recovered from waste concrete. The production of cement accounts for 9.5 % of global CO2 emissions, however up to 50 % of the manufacturing emissions can be mitigated at the end of the materials service life through mineral carbonation.The objective here is to sequester CO2 through the production of PCC via the recovery and carbonation of calcium from waste cement. The calcium is suitable for mineral carbonation and can be effectively leached using an acid (e.g. HCl). When calcium is completely leached, the solution will be slightly acidic and contain impurities such as iron and silica. The impurities can be removed by adding alkalinity prior to CaCO3 precipitation, via reaction with Na2CO3 in a separate reactor. The Na2CO3 is produced by the absorption of CO2 using NaOH, while the resulting NaCl solution is recycled via bipolar membrane electrodialysis. Overall transportation emissions and costs are reduced and the process could enhance current waste concrete recycling practices. Furthermore, the low carbon intensity of electricity generation in Eastern Canada allows for capture of 444 kg CO2 per tonne of PCC.