Characterizing dynamic segregation behavior in cemented paste during pipeline transport through electrical resistance tomography

Abstract

Cement paste backfill (CPB) technology is a key method for mine waste treatment, and pipeline transport is critical for safe and efficient waste transfer. Variations in raw material properties can cause slurry segregation, increase pipeline wear and resistance, raise the risk of blockages or bursts, and disrupt operations. To study CPB slurry segregation during transport, CPB was prepared using cement as the cementitious material and unclassified tailings as inert materials. A small annular-tube device using an electrical resistance tomography system was developed to analyze its flow characteristics, and quantitative segregation assessment methods were developed. The results indicated that CPB conductivity increases with transport time but decreases with higher solid mass content, with the latter having a greater impact. At a low solid content, solid particles migrated toward the bottom of the pipe as the flow time increased, and the migratory behavior of the particles diminished as the solid content increased. At a flow rate of 1.25 m/s, the heterogeneity index for CPB with 58wt% solid content increased by 1.24 in 20 min, whereas that for CPB with 62wt% solid content increased by 2.17. Higher solid mass content amplifies the effect of conveying time on segregation, emphasizing the need to balance these factors for minimizing segregation. These insights can guide the optimization of mine pipeline transport systems.

1. Introduction

The development of mineral resources has caused significant damage to the ecological environment through the destruction of vegetation, formation of waste-rock piles, accumulation of tailings, and relocation of river channels [1–4]. Meanwhile, geological disasters, such as subsidence, landslides, mudslides, and avalanches, induced by the numerous empty areas generated by ore mining pose a serious threat to human safety [5–9]. The cut and fill mining method protects the environment and fully utilizes mine waste materials. It mitigates the hazards caused by underground mining, such as surface subsidence. This achieves the purpose of controlling the ground pressure activities. Additionally, it reduces tailings discharge, avoids the dangers associated with tailings accumulation, and achieves a win-win outcome of safe underground mining and environmental governance [10–13]. Therefore, cut and fill mining is increasingly being used.

The backfilling mining method prepares cement paste backfill (CPB) through a backfilling system and transports the CPB to fill mine voids. The backfilling system consists of four key processes: full tailings concentration, aggregate mixing, pipeline transportation, and filling of underground mine voids [10–11,14]. The low-concentration tailings slurry from the mineral processing plant is thickened and mixed with binding materials (e.g., cement) to form CPB. After mixing and preparation, CPB is transported by gravity or pumping pipelines to underground mining areas for backfilling. CPB pipeline transportation plays a crucial role in mine backfilling [15–16]. CPB is a highly concentrated suspension of unclassified tailings, cement, and water that can be regarded as a non-Newtonian fluid with shear-thinning properties [17–19]. During pipeline transportation, CPB is subjected to shear, resulting in low viscosity; the floc structure composed of cement and fine particles cannot carry coarse particles, resulting in the precipitation of coarse particles (i.e., segregation), which reduces the homogeneity of the CPB [20]. There are two types of segregation in a pipeline: static and dynamic. Static segregation mainly occurs in the pump stopping stage, whereas dynamic segregation occurs in the transportation stage [21–22]. The dynamic segregation of CPB leads to pipe wear and increased transportation resistance, preventing the backfilling system from operating normally. This results in significant economic losses. Therefore, it is necessary to study the dynamic segregation of CPB in pipelines.

In previous studies, the segregation of cementitious materials was mainly assessed using the visual stability index (VSI) [23], electronic image analysis [24], the column method [25], the hydrostatic pressure tests [26], separation probes [27], the ultrasonic method [28], the visible slurry method [29], and the radioactive element labeling method [30]. However, each of these methods has limitations. VSI is not capable of quantitatively de