Soil reconstruction and water-salt transport mechanism of waste dump in arid open-pit coal mine in Northwest China

Abstract

The ecological restoration of mine dump is a major environmental problem faced by open-pit mining, and it is an important factor restricting the construction of green open-pit coal mine. Soil reconstruction is an important step in the ecological restoration of dumps. The northwest coal base, represented by Xinjiang, is characterized by water scarcity and salinization. Soil water and salt migration is a key indicator to determine the success of soil reconstruction. At present, the research focuses on the surface soil reconstruction to improve soil nutrients and promote plant growth. There are few studies on the functional soil reconstruction of water and salt control, and the mechanism of water and salt transportation under different soil reconstruction methods is still unclear. Based on the characteristics of coal resource endowment in Xinjiang, from the perspective of coal circular economy, this study used coal gasification slag (CGS), a by-product of energy and chemical industry, as a reconstruction material. Through a capillary water rising-evaporation experiment, the vertical migration of water and salt and water supply capacity after CGS reconstruction were analyzed. The Van Genuchten model was used to fit the soil water characteristic curve, analyzed the soil water holding capacity after CGS reconstruction, and studied the feasibility of CGS as an aquifer reconstruction material. The red mudstone associated with coal mining was used as the reconstruction material. Through the soil column infiltration evaporation experiment, the water and salt changes at different soil depths after the reconstruction of red mudstone were analyzed, and the feasibility of mudstone as the reconstruction material of aquiclude was studied. The results showed that the CGS reconstruction improved soil texture, optimized pore structure, promoted soil water and salt transport, enhanced capillary action, promoted the upward supply of water in the lower layer, and also increased salt surface accumulation. The reconstruction changed the parameters of soil water characteristic curve, increased θs, decreased a and n, and improved soil water holding capacity. The higher the amount of CGS added, the greater the fine slag content, the more obvious the effect. The CGS was feasible as a material for reconstructing aquifer. The red mudstone had high clay and secondary mineral content, rich pore structure and good physical adsorption. After reconstruction, the soil water content at 0−24 cm depth was higher than that of the control group, and the salt reached the highest value at 20−24 cm after evaporation. The red mudstone effectively blocked the upward movement of salt. Red mudstone was feasible as a material for reconstructing aquifuge. The research explores a suitable soil reconstruction model for the waste dump in western coal base.

Keywords

• soil reconstruction
• water and salt transport
• coal gasification slag
• red mudstone
• capillary water rising