Migration and transformation of water in paste and numerical deduction of its rheological behavior under pulse pumping environment

The development of green resources and deep mining face several challenges, including prominent safety hazards associated with deep mining and severe environmental pollution in mining areas. Paste-filling technology, designed to eliminate tailing ponds and control subsidence in mined-out regions, innovatively uses mined solid waste with the principle of "one filling for three wastes, one waste treatment for two harms," thus forming a mining approach characterized by a high recovery rate and low impoverishment rate. This technology possesses unique advantages in both mitigating environmental pollution and managing stress factors in deep mining. Paste filling has emerged as an effective solution for deep and green mining. Paste backfill technology, with its considerable potential, may become an impactful solution for future deep and green mining. However, it is difficult to accurately describe the rheological behavior and flow process of paste due to its diverse composition and variable transport environment. In this study, micro- and macrostructures and quantitative analysis of low-field nuclear magnetic resonance (LF-NMR) were employed to describe the existing form of cross-scale particle groups and the water occurrence state in a paste. In addition, the flow pattern evolution law of paste particles under the disturbance of pump pressure was analyzed using the finite element and discrete element coupling numerical analysis method. The results indicated that adsorption water, interstitial water, and weak free water in paste exhibited dynamic connectivity and transformation behavior, with water predominantly existing in an adsorbed state. According to the analysis of LF-NMR, the relaxation intensity and peak area of the adsorbed water were nonlinearly enhanced, demonstrating a pronounced positive correlation with the flow performance of the paste. The liquid network structure and the floc network structure reflected the activity of the water-flow channel and the strength of the force chain structure, respectively. These components together constituted a double-supported skeleton structure that determined the stability and fluidity of the paste. Furthermore, Fluent–EDEM coupling simulation was conducted to examine the particle movement behavior in a pulse-pumping environment; the velocity difference amplified the force chain contact effect, intensifying the impact disturbance of particles with high and low flow velocities, and considerably enhanced the flow uniformity and overall stability of particle motion. Generally, this study examined the mechanical response mechanism between particle groups and fluid drag in paste, establishing the intrinsic relationship between particle physical properties, spatial structure, and rheological characteristics. Furthermore, a constraint mechanism and control scheme were proposed for the long-distance and high-drop steady-state transportation of paste in a pulse compression environment. The results of this study provide valuable insight into the theoretical and engineering implications for achieving safe, environmentally friendly, economical, and efficient paste filling.