Valorization of kaolin mining waste from the Amazon region (Brazil) for the low-carbon cement production

Abstract

The Amazon rainforest has 90% of Brazil's total kaolin reserves, and its mining is of great economic interest. However, the intense kaolin activity produces large quantities of deposited waste in tailing dams, generating a tremendous environmental and local economic liability. Such wastes have no economic value, but their high kaolinite composition can be interesting for the cement industry. Thus, this study aimed to valorize such material as a potential Supplementary Cementitious Material (SCM) in low-carbon cements. The calcined kaolin waste (KAW) was used with limestone and gypsum as clinker substitutes. Its performance was compared with calcined pure kaolin (KA) and an inert material (quartz powder, QP). The cements were evaluated regarding their setting times, water demand, rheological behavior, hydration and compressive strength at different ages. The most important results of the KAW are related to its better rheological behavior compared to KA and closer to QP when used in cement formulations. The kaolinite clay content played a significant role in the fresh properties assessed as well. The microstructural and mechanical performance of KAW cement is similar to KA, which highlights comparable reactivity. This study brings a new insight into the potential use of kaolinite-rich waste from the mining sector as SCM to be used in the local infrastructure of the Amazon region.