Industrial demonstration of indirect mineral carbonation in the cement and concrete sector

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This paper reports on the successful construction, commissioning and operation of a mobile indirect mineral carbonation (IMC) pilot plant in the concrete sector. This work confirms the technical feasibility of IMC at large scale, while producing precipitated calcium carbonate (PCC) and leached recycled concrete aggregate (RCA) as useful products. The plant is capable of handling industrial flue gas or pure CO2 as carbon feedstock, while processing around 80 kg/h of RCA as calcium feedstock, and storing around 0.9 kg/hr of CO2. Good recyclability of the aqueous ammonium nitrate mother liquor is suggested, although small changes occurred over time, with only small effects on the operation. Importantly, some CaCO3 precipitates in the dissolution reactor, especially at high CO2 feed rates; this does not decrease the CO2 storage rate, but it reduces the PCC production rate. The plant may be operated at a variety of operating conditions and it responds to them as expected from thermodynamic considerations. Similarly, the trade-offs in terms of performance parameters also change as expected. The observed calcium extraction efficiency is rather low due to the thermodynamic nature of the batch dissolution step. Also, the ammonium nitrate losses are rather high due to the plant not having a solvent recovery step integrated. Potentially alternative reactor concepts for the dissolution section can improve the calcium extraction efficiency while including a washing step, thus alleviating the main limitation. Material tests with the products of the process suggest that leached RCA is as good as, or even better than fresh RCA for use as aggregate in concrete; ground PCC performs similar as ground limestone in cement, however it is not the most attractive use of fine PCC, as higher value applications exist. Although improvements to the plant design are necessary to make the process economically and environmentally viable, this work represents an important steppingstone towards industrial implementation of IMC, and confirms its technical feasibility in the concrete sector.