Direct Aqueous Mineral Carbonation of Carbide Slag in a Bubble Column Reactor Under Ambient Conditions

The accelerated carbonation technology utilizing the alkaline minerals or alkaline wastes incurs high operation and investment costs, low conversion efficiency and high energy consumption. Due to the strong alkalinity of the carbide slag, good feedstock availability and great performance of the bubble column reactor, the direct aqueous mineral carbonation of the carbide slag in a bubble column at ambient conditions is evaluated. The impact mechanism of the liquid to solid ratio (5 mL/g - 50 mL/g) and gas velocity (0.0041 m/s - 0.205 m/s) on the reactions are investigated. The flow patterns are identified by EMD energy entropy, and carbonation efficiencies at different flow regimes are compared and illustrated. It is found that this route has a high carbonation efficiency and short reaction time. The maximum carbonation efficiency is 100% and the capture capacity is 214.05 g CO2 / kg carbide slag. The discrete bubble regime (DBR) and bubble coalescence regime (BCR) are observed, and the increase of the L/S ratio can promote the bubble coalescence. The hydrodynamics can influence the processes of the CO2 mass transfer from gas to liquid phase, Ca(OH)2 dissolution, reactant diffusion, collision and ionic reactions. At small L/S ratio, the greater carbonation efficiency is achieved in discrete bubble regime attributing to the longer gas residence time, larger gas-liquid interfacial area and better CO2 mass transfer than that in BCR. At large L/S ratio, the greater carbonation efficiencies are achieved both in DBR and BCR. It has good CO2 mass transfer in DBR and has the strong liquid turbulence intensity in BCR which is good for the reactant diffusion and collision. The enhancement factor increases when enhancing the L/S ratio in DBR. The 30 mL/g and the gas velocity operated in the discrete bubble regime are recommended considering the better three-phase contact, good carbonation conversion and low energy consumption.