Wet Carbonation of Recycled Cement Paste Fines: Controlling Vaterite and ACC Precipitation with Ethylenediamine

The sequestration of CO2 into mineral carbonates via wet carbonation offers a promising pathway for carbon capture and storage, particularly when it is applied to recycled cement paste (RCP) materials. Traditionally, this involves a two-step process: Ca2+ extraction using additives such as amines, followed by carbonation. In this study, we explored a one-step direct wet carbonation method using ethylenediamine (EDA) at dosages of 1, 5, and 10% to control the crystallization behavior and polymorphism of calcium carbonate. A high degree of carbonation, approximately 0.9, was achieved at 5 and 10% EDA. Amorphous calcium carbonate (ACC) formed at all dosages, with the highest amount observed at 5%. Depending on EDA concentration, ACC subsequently transformed into calcite (1%) or vaterite (5 and 10%). This polymorphic evolution is governed by Ca2+-EDA complexation, which modulates calcium supersaturation and thus affects carbonation kinetics and crystallization pathways.