Theoretical Foundation of Carbonation Pellet Process for Ferrous Sludge Recycling

For the recycling of ferrous sludge from steel industry, the carbonation pellet process should be considered as a “green” process, since no impurities are added as well as CO2 can be sequestrated and consumed. Through the thermodynamic calculation, the carbonation reaction can occur spontaneously and is an exothermic reaction. Based on the kinetic analysis through unreacted core model, the interfacial chemical reaction was the rate controlling step in the initial fast stage of carbonation, and the CO2 diffusion through the CaCO3 product layer was the rate controlling step in the following extremely slow stage. For the carbonation bonded mechanism, the pellet strength was gained by the formation and growing of CaCO3 product layer. Since the interfacial chemical reaction was the critical stage of the entire carbonation process, the emphasizes should be focused on the improvement of sorbent activity and the optimization of process parameters, such as pore structure, pore surface area, and total pressure, CO2 partial pressure, reaction temperature, etc to accelerate the reaction rate and to improve the quality of carbonation pellets.