Effect of ultrasound on the flocculation-sedimentation and thickening of unclassified tailings

Environmental disposal of sulphide-rich and desulfurized tailings: Thickening, rheological, mechanical, and leaching performance

The surface disposal of sulphide-rich tailings (compared to ordinary tailings, it contains many sulphides) will cause environmental and groundwater pollution, and it is an eco-friendly method to prepare cemented paste backfill (CPB) from sulphide-rich tailings and backfill it into underground goafs. However, the thickening performance of sulphide-rich and desulfurized tailings is unclear, the sulphide-rich CPB strength cannot meet the standard. Therefore, a comprehensive study was conducted on its thickening performance through settling columns and dynamic thickening experiments, mechanics, and leaching tests were also conducted. The optimal flocculant conditions with different sulphide contents were obtained through settling column experiments. Meanwhile, it was found that turbidity and initial settling rate (ISR) were linearly related to tailings feeding concentration. Due to the higher specific gravity of sulphide-rich tailings, under different flocculation conditions, the higher the sulphide content, the higher the concentration, and there is a linear correlation between sulphide content and concentration. The results of dynamic thickening show that rake-shearing can improve the concentration and the shear yield stress, both of which increase rapidly at first and then slowly with the extension of shearing time. A logarithmic model of concentration based on shear yield stress was established. The unconfined compressive stress of the CPB prepared from tailings desulfurized to 20.7 wt%-S (S20.7) is much higher than that of 30.7 wt%-S sulphide content tailings (S30.7), which can meet the backfilling requirements. The concentration of metal ions in the soaking solution of S20.7 CPB is higher, and the environmental impact is small. Finally, it is recommended to choose S20.7 for backfilling. The study is significant for revealing the thickening and mechanical performance evolution of sulphide-rich tailings and environmental protection disposal.

Ultrasound Pretreatment for Enhancing Fine and Ultrafine Flake Graphite Flotation Beneficiation

With the severe depletion of coarse flake graphite (a critical raw material) resources, developing and utilizing fine and ultrafine graphite resources have recently attracted attention. Froth flotation is a widely used technique for the initial enrichment of graphite; however, the flotation selectivity decreases significantly along with particle size reduction. Ultrasound pretreatment would be a promising method to improve the flotation of fine particles. As an innovative approach to understand better the flotation response of different flake graphite sizes, this study conducted a comparative analysis based on flotation concentrate yield and ash as well as ash removal rate between the flake graphite with various particle sizes after ultrasound pretreatment. Particle size, X-ray powder diffraction, and scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were used to investigate the effect of ultrasound treatment on mineralogical properties of the flake graphite with varied particle sizes. Process outcomes indicated that the flotation performance of fine flake graphite (mean chord length: 62.63 μm) was significantly enhanced after ultrasound pretreatment. However, flotation of the ultrafine flake graphite (mean chord length: 24.97 μm) after ultrasound treatment was limited due to the difficulty of generating sufficient fragmentation and dissociation by microjets and shock waves formed by the cavitation effect. Compared with conventional flotation, the concentrate yield of ultrasound flotation increased from 88.95 to 94.98%, ash content decreased from 5.72 to 4.87%, and ash removal rate enhanced from 36.94 to 42.61%. Particle size and mineral property analyses confirmed that further crushing and dissociation of the larger flake graphite after ultrasound pretreatment would be the main factors contributing to improved flotation performance. Additionally, the formation of air flocs in the coarse flake graphite during the ultrasound pretreatment process facilitated the flotation recovery of the crushed graphite particles.

Efficient dewatering of unclassified tailings with flocculant: role of ultrasound

Flocculants play an important role in the solid-liquid separation of tailings slurry, and its dosage directly impacts on the dewatering efficiency of tailings. Herein, the influence of ultrasonication on flocculant dosage in dehydration process of unclassified tailings was studied. The effects of flocculant dosage on initial settling rate (ISR), underflow concentration, and effective settling time in the process were investigated in detail. The directivity characteristics of ultrasound transducers with different frequencies in unclassified tailings slurry was simulated by MATLAB. The morphologies of underflow tailings at different flocculant dosages were detected by environmental scanning electron microscope (E-SEM). The relationship between flocculant dosage and fractal dimension (D_F) was quantitatively analyzed based on fractal theory. The influence mechanism of flocculant on the settling and thickening of unclassified tailings was revealed. The results show that the optimum flocculant dosage for the ultrasonically treated tailings slurry is 40 g/t, at which the ISR reach a maximum value of 0.262 cm/min and the final underflow concentration (FUC) reach a maximum value in 60 min. Compared with settling without ultrasonication, the optimum flocculant dosage is reduced by 10 g/t, the ISR increases by 10.45%, the effective settling time is reduced by 50 min, and the FUC increases by 1.65%. The fractal dimension of underflow tailings first increases and then decreases with the increase in flocculant dosage, the relationship of which is in accordance with Lorentz model.

The Utilization of Ultrasound for Improving Oil Recovery and Formation Damage Remediation in Petroleum Reservoirs: Review of Most Recent Researches

The ultrasound method is a low-cost, environmentally safe technology that may be utilized in the petroleum industry to boost oil recovery from the underground reservoir via enhanced oil recovery or well stimulation campaigns. The method uses a downhole instrument to propagate waves into the formation, enhancing oil recovery and/or removing formation damage around the wellbore that has caused oil flow constraints. Ultrasonic technology has piqued the interest of the petroleum industry, and as a result, research efforts are ongoing to fill up the gaps in its application. This paper discusses the most recent research on the investigation of ultrasound’s applicability in underground petroleum reservoirs for improved oil recovery and formation damage remediation. New study areas and scopes were identified, and future investigations were proposed.

Mesoscopic Seepage Simulation and Analysis of Unclassified Tailings Pores Based on 3D Reconstruction Technology

Taking the unclassified tailings as the research object, the three-dimensional (3D) pore model was established using computed tomography (CT) scanning technology, image processing, and the 3D reconstruction method. The model was imported into Flac3D software for mesoscopic seepage simulation and analysis. Combined with the laboratory seepage experiment, the influence of tailings' mesoscopic parameters on permeability was explored. The results show that there is a high correlation between the fractal dimension and fragmentation index of tailings pores and the mesoscopic seepage coefficient, with correlation coefficients of 0.987 and 0.973, respectively. When the porosity difference of the pore model is small, the permeability is mainly affected by pore connectivity. The mathematical model between the permeability coefficient and the fragmentation index of tailings is established. The average error between the permeability coefficient calculated by the model and the measured value is reduced to 4.98%, which proves that the mathematical model has guaranteed reliability.