The direct dry mineral carbonation of selected mining and industrial wastes, using carbon dioxide derived from combustion flue gas, was evaluated. Specifically, coal fly ash from two Australian brown coal-fired power plants, red mud from the refinement of bauxite into alumina, and diamond tailings were considered, due to their relevant residual alkali content. These materials were tested in a laboratory-scale fluidized bed reactor at different temperatures (300–450 °C), in a reactive environment that simulated the typical CO₂ concentration in a combustion flue gas. The experimental results showed a low, but still appreciable, CO₂ capture capacity for three of the tested materials, which appears to be more favorable in the lower temperature range and with relatively fast kinetics, indicating the practical relevance of the process. One of the fly ashes exhibited a different behavior; starting at 350 °C, the sorbent began to release CO_2, rather than absorb it. This suggested that the sorbent was already extensively carbonated by weathering before the tests. This study provides some evidence for the possible viability of recycling mining waste and for the circular economy in offsetting carbon emissions in the mining industry.

The increase of capital investments and operation and maintenance (O&M) costs represents a current limitation to the diffusion of carbon capture systems for the clean combustion of fossil fuels. However, post-combustion systems, such as calcium looping (CaL), for CO₂ capture from flue gas are the most attractive carbon capture systems since they can be installed at new plants and retrofitted into existing power plants. This work investigates the pros and cons of employing a calcium looping system for CO₂ capture and also as a desulphurization unit. A preliminary techno-economic analysis was carried out comparing a base case consisting of a coal-based power plant of about 550MWe with a desulphurization unit (Case 1), the same plant but with a CaL system added for CO₂ capture (Case 2), or the same plant but with a CaL system for simultaneous capture of CO₂ and SO₂ and the removal of the desulphurization unit (Case 3). Case 2 resulted in a 67% increase of capital investment with respect to the benchmark case, while the increase was lower (48%) in Case 3. In terms of O&M costs, the most important item was represented by the yearly maintenance cost of the desulphurization unit. In fact, in Case 3, a reduction of O&M costs of about 8% was observed with respect to Case 2.