Ecological study of a mineral carbon capture and conversion process

The rise in carbon dioxide emissions is creating environmental problems of unprecedented magnitude and impact. Current total global emissions of CO2 from the fossil chemical use and industrial chemical processes are 38 GT CO2-eq per year with growth rate of 2.7 % during past decade. Due to COVID19 pandemic and its impact, a temporary decrease in the global emissions is expected. Carbon capture and utilisation (CCU) strategies can aid a potential mitigation option for the reduction of greenhouse gas emissions.
This study presents a mineral CCU process that employed flue gas and an alkaline solution to develop an integrated absorption-based carbon removal and conversion process and then used an ion exchange reaction by using available brines to produce a useful form of precipitated calcium carbonate (PCC). Furthermore, this study compared the environmental impact of proposed mineral carbonation process with other three mineral CCU processes reported in the literatures [15], [37]–[39] ; mineral carbonation processes from; 1) fly ash from powerplants, 2) mineral wollastonite rock (CaSiO3), and 3) steel slag using life cycle assessment (LCA) provided in ISO14044. The LCA was investigated using gate to gate (G-G) system boundary and 1 kg of CaCO3 product as functional unit for comparison.
Results indicate that the cost estimation of the process operational cost of PCC-NaOH based process is £ 446 per ton of CO2 removed and this is higher than other PCC based processes. The LCA results depict the PCC carbon capture technology using four different materials has a positive environmental impact. NaOH-based process has the lowest land use and water depletion impacts but it has the second largest global warming potential (GWP) within four options studied here due to NaOH solvent identified as the process hot-spot. The fly ash-based PCC has the highest environmental impact due to the process waste (direct emission), raw materials used and the energy consumption. The CaSiO3 and steel slag-based PCC have comparable low toxicity impact as low chemical consumption and the waste generation in the process capture system. The overall environmental impact of carbon capture into PCC indicated that while mineral CCU presents long-term carbon sequestration potential and scalable markets but all of the processes studied here are far from being carbon negative.