Carbon Capture and the Aluminium Industry: Preliminary Studies

Environmental Context. Carbon dioxide concentrations in the atmosphere are rising every year by 1.5–3.0 ppm and there is now a general acceptance that increased efforts must be made to reduce industrial sources of this greenhouse gas. Carbonation of red mud wastes produced by aluminium refineries has been carried out to study the capacity of these wastes to capture carbon dioxide. Removal is very rapid, with the added carbon dioxide recorded as a large increase in bicarbonate alkalinity. Although these results can only be considered preliminary, the experiments indicate that these wastes can potentially remove up to 15 million tonnes of carbon dioxide produced in Australia per annum. Furthermore, the carbonated waste can be used in other industrial processes to add further value to these waste materials.

Abstract. Carbonation of raw red mud produced by aluminium refineries and a chemically and physically neutralized red mud (Bauxsol™) has been carried out to study the capacity of these wastes to capture carbon dioxide. After only 5 min of carbonation of raw red mud, total alkalinity dropped 85%. Hydroxide alkalinity was almost totally consumed, carbonate alkalinity dropped by 88%, and bicarbonate alkalinity increased to 728 mg L^–1. After 24 min carbonation, the bicarbonate alkalinity reached its maximum value of 2377 mg L^–1, and hydroxide and carbonate alkalinity were virtually absent. After 30 and 60 min carbonation, bicarbonate alkalinity started to decrease slightly as the pH of the slurry increased. After 5 min carbonation of Bauxsol™, total and bicarbonate alkalinity dropped 89% and 9%, respectively. After 20 min carbonation, bicarbonate alkalinity dropped another 11%, but after 30 min carbonation bicarbonate alkalinity increased 26% to levels found in the original Bauxsol material, and pH was stable. Based on these experiments, a calculation of the amount of carbon dioxide that could be removed annually at aluminium refineries in Australia is potentially 15 million tonnes, and suggests that further studies are necessary to maximize this carbon removal process. Furthermore, carbonation produces a product, which can potentially be used in other industrial and agricultural activities to remove toxic metals and nutrients.