## 1 Introduction  
Alum sludge (also known as red mud or bauxite tailings) is a byproduct of the alum used in the drinking water treatment process [1]. In recent decades, several studies have examined the use of alum sludge as a soil stabilizer [2]. As a soil stabilizer, alum sludge has the main advantage of improving the soil's physical properties, such as strength and stability [3]. The reason for this, is that alum sludge contains high levels of alum, which reacts with the soil to form a solid and stable structure [4]. As a result of this reaction, soil density and compaction increase, improving soil stability and reducing erosion sensitivity [4]. In addition, for pure aluminum sludge, the stability gained by adapted scheduling of bauxite tailings, is critical to warrant safe tailings deposition [5]. Alum sludge, a byproduct of the water treatment process, can be used as a soil stabilizer, providing several environmental benefits. Firstly, it can reduce soil erosion. The application of alum sludge to soil can help to reduce soil erosion by increasing its stability and reducing its susceptibility to erosion from wind or water [6]. Secondly, by improving soil structure, alum sludge can also help to reduce runoff [7], which can carry pollutants and sediment into nearby waterways, damaging aquatic ecosystems. Thirdly,alum sludge can reduce water usage in agriculture [8], by improving soil moisture retention, reducing the need for irrigation and saving water resources. Moreover, by improving soil structure and nutrient availability, alum sludge can reduce the use of fertilizers [9], which can contribute to water pollution and environmental degradation. Furthermore, using alum sludge can reduce greenhouse gas emissions [10] by reducing the emissions associated with the production and transportation of synthetic fertilizers and irrigation. Alum sludge offers another advantage from an environmental standpoint, which is a reduction in waste in landfills [11]. Alum sludge can be diverted from landfills and used as a soil stabilizer, reducing the amount of waste going into landfills and its associated environmental impacts. Finally, the utilization of alum sludge as a soil stabilizer promotes sustainable agriculture [12], by improving soil health and productivity while reducing environmental impacts. According to [PERSON] et al. [4], alum sludge as a soil stabilizer reduces the soil's flexibility and makes it less susceptible to deformation. This reduction in flexibility results in improved soil structure and increased stability [4]. Moreover, on the geotechnical side, [PERSON] et al. [4] showed that, the addition of sludge to the soil, increases the undrained compression strength (UCS) of the soil. In addition, several studies have demonstrated that alum sludge can be an effective alternative to traditional soil stabilizing agents, such as cement and lime [13; 14; 15]. Alum sludge as a soil stabilizer can have several environmental advantages [16]. The first benefit, is that it reduces the amount of waste produced by the alum production process, by recycling the sludge and reusing it for soil stabilization [16]. Furthermore, alum sludge reduces the need for conventional soil stabilizers, which are often derived from non-renewable sources and may emit large amounts of carbon dioxide [17]. In addition to improving soil stability, alum sludge can also improve soil chemical properties [16]. Studies have shown, that alum sludge can neutralize soil acidity and improve soil pH [18; 19]. The importance of this, is that soil acidity can inhibit plant growth and reduce crop yields [18]. As a result, better water infiltration and retention occurs in the soil, which is essential for the growth and development of plants. Additionally, improving soil permeability can reduce soil erosion and contribute to improving soil health [20]. Alum sludge is cost-effective when used as a soil stabilizer, compared to traditional soil stabilizers such as cement, coal, and fly ash [21].