Effect of Impurities on the Decarbonization of Calcium Carbonate Using Aqueous Sodium Hydroxide

Decarbonizing calcium carbonate (CaCO₃) is a crucial step for a wide range of major industrial processes and materials, including Portland cement (PC) production. Apart from the carbon footprint linked to fuel combustion, the process CO₂ embodied within CaCO₃ represents the main concern for the sustainability of production. Our recent works demonstrated that it is possible to avoid both the fuel and process CO₂ by reacting CaCO₃ with aqueous NaOH and obtain Ca(OH)₂ and Na₂CO₃·xH₂O (x = 0 and 1). This present study provides a further understanding of the process by testing different raw calcareous sources. A high decarbonization (∼80%) of CaCO₃ was achieved for silica-rich chalk, whereas a lower extent was obtained (∼50%) for limestone. To understand the difference in their reaction behavior, the effect of impurities was studied. The effects of the major impurities (Si, Al, and Fe) were found to be marginal, which is advantageous to process industrial grade materials, while the morphology of the raw materials presents a significant impact. The applicability of our decarbonization technology was also demonstrated on magnesite (MgCO₃).