# Enhancing the Strength of Mine Residue Soil by Bioremediation Combined with Biopolymers
## 1 Introduction  
The global population growth has presented significant socio-economic challenges, particularly in terms of resource consumption and infrastructure development. The exponential increase in population has led to an excessive need for natural resources, resulting in the large-scale production of mining waste and associated environmental liabilities and safety risks (e.g., contaminant leaching, acid mine waters, and the collapse of tailing dams). Additionally, the expansion of societies has required the construction of extensive infrastructures, often in areas characterized by soils with poor mechanical properties (low bearing capacity, high compressibility, or poor drainage characteristics) [1; 2]. Both situations pose substantial engineering challenges that may be solved by ground improvement techniques. Ground improvement is a crucial aspect of geotechnical engineering, aimed at improving the mechanical properties and durability of soils [3; 4]. There is a wide range of ground improvement techniques for multiple applications. Within ground improvement techniques, soil stabilization has emerged as one of the most versatile and promising techniques, being applied all over the world [1; 5; 6]. Traditional soil stabilization methodsoften rely on chemical binders, which have demonstrated significant advantages but also pose environmental concerns. These binders, such as cement and lime, have proven effective in enhancing soil strength, reducing permeability, and mitigating environmental hazards [7]. However, the use of these binders raises concerns due to their high energy consumption, carbon emissions, and long-term environmental impact [4; 8; 9; 10]. To address these challenges, researchers have turned their attention to sustainable alternatives for soil stabilization. Indeed, recent developments in the field have explored the use of biopolymers and bioremediation techniques as eco-friendly alternatives to soil stabilization. Biopolymers, derived from natural sources, offer promising advantages in terms of their sustainability, biodegradability, and low environmental impact. Bio-techniques, such as biostimulation and bioaugmentation, utilize microbial activity to enhance soil properties and/or remediate contaminants. Biopolymers, such as xanthan gum, guar gum, carboxymethyl cellulose, and chitosan, have gained attention in geotechnical engineering due to their unique properties and environmental compatibility. These biopolymers, derived from natural sources, exhibit an ability to improve soil strength, reduce permeability, and control erosion [4; 11]. It is important to note that biopolymers differ in terms of their origins and specific characteristics [12]. The choice of biopolymer for soil stabilization depends, among others, on the type of soil and its compatibility with the biopolymer, biopolymer content, curing time, thermal treatment, and mixing methods [13]. The identification and efficient design of biopolymers for stabilized soil systems rely on the [PERSON] et al. [8] methodology: (1) a rapid membrane-enabled bio-mineral affinity screening approach, (2) supported by mineral binding characterization and complemented by geotechnical verification. Another aspect that should also be considered is the price of biopolymers, which can vary depending on factors such as production scale, purity, and market demand. Here, some results are highlighted for two of the most widely used biopolymers in soil stabilization, xanthan gum and carboxymethyl cellulose, due to their potential suitability to stabilize acid mine residue soils [8]. Xanthan gum (XG) is an anionic polysaccharide biopolymer produced by the bacterium _Xanthomonas campestris_[9; 14]. It is commonly used in various industries, including geotechnical engineering, where it is applied in contents ranging from 0.5 to 5% of the soil weight.