# A Comprehensive Review on Mine Tailings as a Raw Material in the Alkali Activation Process
## 2 Mineralogy of Mine Tailings
(1) Silicate minerals are the most abundant class of minerals in the Earth's crust and are composed primarily of silicon (Si) and oxygen (O) atoms combined with various cations (positively charged ions), such as aluminum (AI), iron (Fe), magnesium (Mg), and others. Silicate minerals include feldspars, quartz, micas, amphibes, and pyroxenes [67]. (2) Carbonate minerals are characterized by the carbonate ion (CO\({}_{3}\)\({}^{2-}\)) as a fundamental building block. They are primarily composed of carbon, oxygen, and various cations. Common carbonate minerals include calcite and dolomite [68]. (3) Oxide minerals are primarily composed of oxygen (O) combined with metal cations. These minerals often form as a result of the weathering of other minerals. Oxide minerals include magnetite, hematite, and cassiterite. (4) Sulfide minerals are composed of sulfur (S) combined with metal cations. These minerals often form in hydrothermal environments and are associated with ore deposits [69]. Common sulfide minerals include pyrite, galena, and chalcopyrite. Valuable metals, including gold (Au), copper (Cu), lead (Pb), and zinc (Zn), are commonly found in sulfide minerals. The mining industry extracts these valuable metals from sulfide ores, and as a result, a significant portion of mine tailings generated in mining operations are sulfur-rich [70]. However, this also poses environmental challenges. When sulfide minerals are exposed to air and water during mining operations or in tailing storage facilities, they can oxidize, producing sulfuric acid and releasing metals into the environment [71]. Pyrite, often called \"fool's gold\", is one of the most common sulfide minerals found on Earth and is widely distributed in various geological environments. The oxidation of pyrite (iron disulfide, FeS\({}_{2}\)) involves the reaction of pyrite with oxygen (O\({}_{2}\)) and water (H\({}_{2}\)O) to produce sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) and iron oxide (Fe\({}_{2}\)O\({}_{3}\)). The chemical reaction is represented by Equation (1) as follows:  
\[4\text{FeS}_{2}+14\text{O}_{2}+4\text{H}_{2}\text{O}\to 4\text{Fe}_{2}( \text{OH})_{6}+8\text{H}_{2}\text{SO}_{4} \tag{1}\]  
In this reaction, pyrite (FeS\({}_{2}\)) reacts with oxygen (O\({}_{2}\)) from the air and water (H\({}_{2}\)O) and produces iron hydroxide (Fe\({}_{2}\)(OH)\({}_{6}\)) as a solid product and sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) as a solution in water. This process produces acid mine drainage (AMD) when pyrite-containing rocks are exposed to air and water during mining operations [72]. The bioavailability of hazardous components in mine tailings is influenced by a complex interplay of factors, including the oxidation state of elements, mineralogy of tailings, grain size and surface area, morphology, chemical composition, environmental conditions, microbial activity, and hydraulic conditions [73]. When the leaching of harmful components from mine tailings surpasses the legally defined limits for waste, these tailings are classified as hazardous. When such tailings are disposed of in tailing ponds, extensive landfill spaces, along with meticulous construction and ongoing maintenance, are necessary, even after the closure of the mining operation. Carbonates (e.g., calcite and dolomite) and silicates (e.g., feldspars and olivine) are minerals that can neutralize acidic conditions in tailing ponds and should be characterized to understand the environmental behavior of mine tailings. They are used as neutralizing agents to mitigate the effects of acid mine drainage (AMD) [74]. Calcite (calcium carbonate, CaCO\({}_{3}\)) is highly effective in neutralizing acid due to its reaction with acidic water.