Effect of Cement Type on Compacted Iron Ore Tailings-Binder Response Blends: Comparative Study

Abstract

Lately, dry stacking of filtered tailings has emerged as a safer alternative to traditional slurry disposal in ponds as it comprehends the compaction of the unsaturated cake to form piles. A cementing agent can be added to the mixture to improve the mechanical properties of the compacted tailings; however, it is essential to understand its response under different conditions. The present study examines the mechanical behavior of compacted iron ore tailings (IOT)-binder blends for dry stacking purposes, highlighting the effect of the cement type on the behavior of the tailings: two commercially available types of binders, portland pozzolan cement (PPC) and high early-strength portland cement type III (PC III); and one green alkali-activated cement (AAC). A full factorial design approach was used to study the influence of the following parameters on the strength and stiffness of the studied mixtures: dry unit weight (γd), cement content (C), type of cement (TC), and curing period (CP). To do so, a set of unconfined compression, ultrasonic pulse velocity, and consolidated drained triaxial tests were carried out. To compare the microstructural and compositional characteristics of the three different cement types, secondary scanning electron microscopy (SSEM) and backscattered scanning electron microscopy (BSEM)/energy dispersive spectrometry (EDS) analyses were performed. The stiffness and strength results have been successfully correlated to the porosity/cement index (η/Civ) and the statistical analysis has unveiled the great effects attributed to the cement content, type, and CP. Additionally, microstructural and macrostructural observations revealed that after seven days of curing, the IOT mixtures stabilized with PC III exhibited more robust microstructures and superior mechanical performance: around five times greater strength and stiffness than AAC-containing samples and two times higher considering the PPC-containing specimens. With extended CPs (90 days), the performances of PC III and PPC samples are equivalent, whereas the strength is around three times greater than that of the AAC samples. That is, there was a notable enhancement in the cementitious matrix for IOTs stabilized with PPC and AAC for a more extended CP.