# Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder
## 1 Introduction  
Sustainable development is increasingly essential worldwide, and the study of innovative alternatives to long-used high environmental impact materials and products is essential to promote a more sustainable future [1]. The amount of mining waste generated worldwide makes this industry the top producer globally, with 5 to 7 billion tons produced annually [2]. Mine tailings can harm ecosystems due to their chemical, mineralogical composition, physical properties, and surface volume [3, 4]. Tailings are considered acidic, especially those generated by metals such as copper and zinc; when placed in landfills, toxic elements are leached, creating severe risks of pollution to the environment. Hence, it is imperative to discover new methods to reuse excessive volumes of mining waste generated and deposited [5]. Additionally, the deposition of the tailings in landfills implies the need to increase the mechanical properties, generally performed by mixing the tailings with a conventional binder such as Portland cement. Stabilizing mine tailings with Portland cement as a binder generates a high amount of carbon dioxide (CO\({}_{2}\)); for each ton of Portland cement produced, a ton of CO\({}_{2}\) is generated, making the cement industry responsible for about 7% of the world's total greenhouse gas emissions [6]. Therefore, it is crucial to discover new sustainable solutions comparable to solutions that use Portland cement as a binder from a mechanical and environmental point of view. Consequently, chemical stabilization through the alkaline activation of industrial wastes has emerged. Alkaline activation (AA), also known as geopolymerization, is a chemical reaction produced by an aqueous solution, the mixture having materials as a solidprecursor rich in silica (SiO\({}_{2}\)) and alumina (Al\({}_{2}\)O\({}_{3}\)) and an activator with high pH, based on sodium (Na) or potassium (K) [7]. Binders obtained by alkaline activation are a more sustainable solution in environmental terms and reduce the amount of emitted CO\({}_{2}\), e.g., using fly ash as a binder leads to a 45% reduction in CO\({}_{2}\) release compared to chemical stabilization with cement [8]. Generally, any material that contains a certain amount of alumina and silica is a potential precursor to being used in the AA process [9]. Most available aluminosilicates have a crystalline structure, making them stable to interact with any chemical reaction. However, the sources of aluminosilicates can be of natural origins, such as kaolins, resulting from a chemical process of feldspathic rocks undergoing heat treatment or industrial waste such as slag (obtained in blast furnaces), coal fly ash (thermal power plants), volcanic ash (heat treatment) and dust tiles or brick (industrial baking ovens) [10]. One proposed suggestion is the implementation of FA as a geopolymer binder since it is mainly composed of silica and alumina, in the amorphous state, with a shape and size favorable to AA [11]. In addition, FA is more susceptible to combination with alkaline activators based on sodium and potassium [12]. The polymeric gel originates immediately after the activator comes into contact with the silica/alumina source, having a Si/Al ratio of 1.0 [13; 14; 15]. The Si/Al ratio that best suits the use of fly ash as a precursor is 2.0 [16]. More homogeneous and dense reaction products form with an increase in Si/Al ratio [17]. The most frequently used chemical activators are sodium hydroxide (NaOH) and potassium hydroxide (KOH). The dose of the alkaline activator used is crucial and contributes to the hydration kinetics; impacting the hardening processes related to the strength of the geopolymer material and its durability [18; 19]. Alkaline activation process using class F fly ash as a precursor and sodium hydroxide with 10, 12.5, and 15 molal concentrations as the activator was studied.