CO2 Capture by Aqueous NH3 Combined with High Quality CaCO3 Formation and Red Mud Neutralization

The reduction of anthropogenic CO2 emissions is an urgent challenge, and strategies must be adopted to improve the efficiency of CO2 capture and to reduce the costs of this technique. As an alternative to traditional processes, in our laboratory we developed a new concept of CO2 capture technology which combines the CO2 abatement with the production of useful compounds, in order to circumvent the energy costs of the traditional CO2 capture processes by virtue of the formation of valuable products. With this unconventional approach, we devised a process suitable for the aluminium production chain. The extraction of alumina from the bauxite ore by the Bayer process creates large quantities of a highly alkaline residue slurry, known as 'red mud'. The subsequent reduction of alumina to metallic aluminium requires electrical energy, produced on site by a fossil fuel fired power plant, with consequent emission of a large amount of CO2 into the atmosphere. Here we present a preliminary study for an innovative three steps procedure that combines: (1) the efficient CO2 capture from the flue gas of the power plant (CO2 15% v/v) with aqueous ammonia solutions; (2) the production of a valuable salt, the precipitated calcium carbonate (PCC) by using the cheap industrial by-products CaCl2; and (3) the regeneration of the sorbent solution by exploiting the alkalinity of the red mud, which is finally neutralized. The whole procedure configures a synergistic process able to transform an environmentally hazardous substance (the red mud) and a greenhouse gas (CO2) into a valuable substance.