###### Abstract  
As an organic material with large reserves and environmental protection, the application of lignin in loess improvement can greatly improve the engineering properties of loess, such as water loss disintegration and water collapsibility. This paper summarizes the main achievements of lignosulfonate in improving loess over the past five years and discusses and analyzes its microstructure, mechanical properties, and mechanism of action. The microscopic results show that the incorporation of lignosulfonate produces a three-dimensional network structure, which can effectively cement loess particles and improve soil strength and impermeability, and the Quantity of this network structure depends on the amount of lignosulfonate. An excessive amount of lignosulfonate preferentially combines with itself due to its cohesive and chelating properties, resulting in an increase in soil porosity and a decrease in the improvement effect. Based on the macroscopic and microscopic tests, it was concluded that the optimal dosage reference range of lignosulfonate-improved loess is mostly between 1% and 1.5%. However, considering the limited number of references in this paper, the differences in physical properties of the experimental loess used in the literature, and the different curing ages, the optimal dosage needs to be further studied. The discussion and analysis in this paper provide a reference for research on lignosulfonate-improved soil, as well as new knowledge and information for more efficient engineering applications of lignin-improved loess. lipsin; lignosulfonate; loess; curing agent; mechanical properties; microstructure; improvement mechanism +
Footnote †: journal: Applied sciences  
The curing agent is the product of the combination of new materials and new technologies in the field of engineering and construction. It is widely used in today's geotechnical reinforcement and geological disaster management [12]. The improvement of curing agents is mainly divided into inorganic, biological, and organic types. Inorganic curing agents, such as cement, lime, and fly ash, have a good curing effect and low cost, but they are used in large quantities and often cause damage to the loess structure and cause environmental pollution [13]. The brittle failure is mainly caused by tensile cracking. The lime-improved soil is easily softened when in contact with water and generates a lot of dust during construction. The fly-ash-improved soil has low early strength and poor water stability and requires strict humidity and alkaline conditions control. The biological curing agents have the advantages of less pollution and low cost, but the design life of its improved soil is low, the strength is reduced after immersion in water, and the catalysis of biological enzymes is greatly affected by environmental conditions, and thus, it has poor applicability to soils in some cold regions [14; 15]. Most of the organic curing agents are liquid, and they are mainly prepared from one or more combinations of modified water glass, epoxy resins, polymer materials and ions, etc. [14], in which lignin as an environmentally friendly polymer organic curing agent has received close attention in recent years. With the rapid development of China's social economy, environmental problems have become one of the important factors restricting development. The research on improving loess in a green economy has become a new topic in the field of geotechnical engineering. Lignin is widely present in plant xylem, accounting for 15-35% of the typical dry lignocellulosic biomass [16]. The Chinese paper industry produces about 50 million tons of lignin per year, and the output will continue to increase [17; 18]. Lignosulfonate is based on lignin as raw material and the principle of the sulfite pulping process. It is the most abundant industrial lignin that is currently available. It has the advantages of stability, large reserves, environmental protection, and low cost.