Blending of mining wastes from the Hammam Zriba mine (Northeast Tunisia) with the primary ingredients of clinkers: an evaluation of effects on gray Portland clinker properties

Abstract

The present work focuses on the effects of the blending of mining wastes from the Hammam Zriba mine (Northeast Tunisia) with the primary ingredients of Portland clinker properties. The raw mix was composed of limestone, sand, and clay sampled from the Sidi Bouzid area in Central Tunisia. The used mining wastes are composed essentially of barium, sulfur, and strontium and associated with calcium. Results show that it is possible to use these wastes to formulate an ecological clinker with high quality. The reference clinker is composed of C3S (67.8%), C2S (7.9% β-C2S and 7.15% α-C2S), and C3A (10.3%), associated with small quantities of C4AF. The incorporation of 2% of wastes does not lead to any significant change in mineral composition. The addition of 4% of wastes promotes the decomposition of alite into α-C2S (7.1 to 13.7%) and β-C2S (7.9 to 9.6%). In contrast, the clinker melt exhibits a slight drop of ferrite (5.3 to 3.1% C4AF) and a quasi-unchanged level of cubic-C3A. Greater incorporation of wastes tends to establish the mineral distribution as the reference. The amounts of free lime low when the addition of wastes is lower than 4% (< 2.28%). Higher addition (8%) shifts the free lime levels in particular for pure C3A and C3S (15.6 and 6% respectively). For the reference, free lime levels remain low (< 1%). This result bears relevant environmental and economic aspects by limiting greenhouse gas emissions, enhancing the production of low-cost gray cement, reducing the impacts of mining wastes, and opening an alternative for mining wastes management.