## 1 Introduction  
Loess, a predominant soil type in Northwest China, is characterized by large pores, weak cementation, and high collapsibility. These inherent properties lead to rapid reductions in soil strength when exposed to water infiltration or freeze-thaw cycles, often resulting in engineering challenges such as landslides and uneven settlement [1, 2]. Additionally, the region's significant diurnal temperature variations exacerbate issues like frost heave, making the optimization of soil thermal conductivity a crucial research focus [3]. Thermal conductivity is a key parameter influencing heat transfer efficiency and plays a pivotal role in the thermodynamic behavior of underground engineering, ensuring structural stability in cold regions. In such environments, soil thermal conductivity affects heat transfer during freeze-thaw cycles, impacting frost heave deformation and temperature distribution. Consequently, the application of additives to improve soil thermal conductivity has gained increasing attention in recent years. Traditional stabilizers such as cement and lime enhance thermal conductivity by modifying soil particle interactions, altering porosity distribution, and optimizing heat conduction pathways [4; 5]. Additionally, they improve soil properties, including strength and stability [6; 7; 8; 9]. However, these conventional methods pose challenges due to environmental pollution and significant CO\({}_{2}\) emissions [10; 11]. As the demand for sustainable development grows, research has increasingly focused on exploring novel eco-friendly soil stabilization materials to optimize thermal conductivity, while minimizing environmental impact. [PERSON] et al. [12] found that lignin possesses strong chelating properties, which can enhance the efficiency of nutrient utilization in plants, improve soil structure, and increase soil enzyme activity. Additionally, it adsorbs soil pollutants through ion exchange and complexation, promoting the degradation of organic pollutants by microorganisms, thereby facilitating the remediation of contaminated soils. [PERSON] et al. [13] studied the application of lignin-based adsorbents in alleviating soil heavy metal pollution (HMP), focusing primarily on their adsorption performance, mechanisms, kinetics, and thermodynamic models under different environmental conditions. The reusability of lignin-based adsorbents has been emphasized to improve their economic feasibility. [PERSON] et al. [14] demonstrated that reactive oxygen species generated by advanced oxidation technologies can degrade organic pollutants; simultaneously, the use of MgO and its hydrolysis product magnesium hydroxide (Mg(OH)\({}_{2}\)) can stabilize and immobilize heavy metal ions. Furthermore, this system can also serve as magnesium fertilizer, oxygen fertilizer, and nitrogen fertilizer, thereby increasing crop yields. [PERSON] et al. [15] concluded that MgO/magnesium hydroxide (Mg(OH)\({}_{2}\)) nanoparticles successfully combined with soil carbon to form magnesium carbonate (MgCO\({}_{3}\)), which mitigated CO\({}_{2}\) emissions. The high carbon retention of magnesium carbonate (MgCO\({}_{3}\)) increased cellulase activity, stimulated key carbon-cycling bacteria, and enhanced the expression of genes related to the degradation of starch, sucrose, amino sugars, nucleotide sugars, ascorbic acid, cellulose, and chitin, thus boosting organic carbon mineralization. Among the various stabilization methods, MgO carbonation technology has emerged as a promising solution due to its dual role as a carbon sequestration technique and soil stabilizer [16; 17]. This approach not only enhances soil strength, durability, and thermal conductivity but also reduces carbon emissions, positioning it as an environmentally friendly alternative for stabilizing underground soil environments. Lignin, the second most abundant biopolymer on Earth after cellulose, possesses a phenolic structure that endows it with superior ion-binding capacity and resistance to degradation [18].