Mechanical Properties of Lightweight Aggregates Produced from Mine Tailings via Alkali-Activation
Authors: Asadizadeh M. , Hedayat A. , Tunstall L. , Taboada Neira M. , Vega González J. A. , Verá Alvarado J. W. 
Published: September 2023

ABSTRACT
This study investigated the production of lightweight aggregates (LWAs) from mine tailings (MTs) using an alkali activation approach. The main objective was to reduce the environmental and cost impacts of handling tailings while producing a useful material for the construction industry. The alkali activation process was used to activate the aluminum oxide and silicon dioxide in MTs to produce LWAs, which were then characterized for physical properties. A pelletization technique was practiced, using a disk granulator machine to spray a 10 M NaOH solution on the MTs with a liquid/solid ratio of 0.25. The produced LWAs were cured at temperatures 70 °C±2°C, and the properties of the resulting materials were assessed as a function of the type of fly ash used (class C and F fly ash). Results showed that using Class F fly ash is more successful for making LWAS, and its increasing percentage in the mixture led to increased compressive strength and relative and bulk densities and decreased water absorption and porosity. This study highlights the potential for producing sustainable construction materials from MTs using alkali activation, which could reduce the environmental impacts of MTs while producing useful materials for the construction industry.

INTRODUCTION
Minerals are in high demand, and as a result, mine tailings (MTs), a byproduct of the mining industry, are produced in high volumes. After the important metals have been extracted from ore through a process called mineral processing, the crushed waste rocks that remain are transferred to the tailings dam. Between 5 and 7 billion tons of tailings are made each year by the mining industry (Qi & Fourie, 2019; Wang et al., 2022). Large volumes of MTs with a high sulfide content can be produced during mining operations, especially from mines with low-grade ore deposits such as gold, and porphyry copper. This can cause several problems including occupation of large areas of land and leaching of contaminants into water sources. Some researchers have looked into ways to mitigate the negative effects of MTs on the environment, such as repurposing them as backfill material (Behera et al., 2021) or utilizing them in the form of supplementary cementitious materials (Ince et al., 2021) or alkali-activated binders (Koohestani et al., 2021). Alkaline activation has been proven as a promising method for production of geopolymers from raw tailings with aluminosilicate contents (Falayi, 2020; Tho-In et al., 2018; Zhang et al., 2021; Zhang et al., 2022a; Zhang, et al., 2022b). Geopolymers are a type of inorganic substance made by alkaline activation of aluminosilicate-rich source materials at temperatures typically below 100 °C (Davidovits, 2020; Zhang et al., 2022b). Aluminosilicate-based geopolymers rely heavily on the Si:Al ratio and are made up of the four cell structures, including sialate (Si:Al = 1), sialate siloxo (Si:Al = 2), sialate disiloxo (Si:Al =3), and sialate-multisiloxo (Si: Al&gt;3). The mechanical properties of geopolymers are controlled by the ratio of Si to Al, and MTs often don't contain sufficient amounts of reactive aluminosilicates (i.e., Si:Al &lt; 2). As a result, improving geopolymerization requires including reactive aluminosilicates and modifying the type of cell structures in alkali-activated materials (AAMs). Extensive studies have been conducted to improve the geopolymer's mechanical properties by adding amorphous aluminosilicates from other sources, such as fly ash (Farina et al., 2018; Jiao et al., 2013; Tian et al., 2020; Zhang et al., 2022b).