Effect of Hydrodynamic Cavitation Assistance on Different Stages of Coal Flotation

Hua Han,Huaifa Wang,An Liu

doi:10.3390/min10030221

Abstract

In this study, the effect of hydrodynamic cavitation (HC) on the conditioning stage (HCCS), separation stage (HCSS), and whole stage (HCWS) of coal flotation was investigated by flotation tests, laser granulometry, and contact angle measurements. The flotation results indicate that compared to conventional flotation, all HC-assisted flotation methods can improve concentrate combustible recovery and flotation constant rate. HCCS and HCSS show similar levels of improvement, while HCWS has a better flotation efficiency. The screening tests demonstrate that HC has the advantage of being able to liberate coarse coal particles (+0.25 mm) prior to being combined with gangues. On one hand, HC promotes the dispersion of both particles and agents, while longer cavitation time in HCCS does not lead to better flotation performance. On the other hand, enhancement of the adsorption of the collector on the surface of coal particles in HCCS is confirmed by flotation concentrate contact angle tests. However, HCSS leads to a decrease in concentrate hydrophobicity, compared to conventional flotation. The micro-nanobubbles generated by HC play an important role in improving flotation performance. HCWS offers the advantages of both HCCS and HCSS, and the cooperated mechanism of different HC modes enhances the recovery of coal particles in flotation.

Highlights

Flotation has long been regarded as the most efficient method to separate fine mineral particles [1].The flotation process can be divided into two stages—the conditioning stage and the separation stage.In the conditioning stage, particles and reagents are sufficiently dispersed in the pulp and valuable mineral particles become more hydrophobic by enhancement of the adsorption of the collector on the particle’s surfaces
Hydrodynamic cavitation (HC) is defined by the appearance of vapor cavities when liquid flows through a pipe with increasing velocity; when the pressure at the contractive position is below the saturated vapor pressure of the liquid, cavities are generated in the liquid and suddenly collapse when the pressure recovers in the downstream position
The results show that it is easier for hydrodynamic cavitation (HC) to break up coarse coal particles than other gangue minerals

Summary

Introduction

Flotation has long been regarded as the most efficient method to separate fine mineral particles [1].The flotation process can be divided into two stages—the conditioning stage and the separation stage.In the conditioning stage, particles and reagents are sufficiently dispersed in the pulp and valuable mineral particles become more hydrophobic by enhancement of the adsorption of the collector on the particle’s surfaces. Flotation has long been regarded as the most efficient method to separate fine mineral particles [1]. The flotation process can be divided into two stages—the conditioning stage and the separation stage. Particles and reagents are sufficiently dispersed in the pulp and valuable mineral particles become more hydrophobic by enhancement of the adsorption of the collector on the particle’s surfaces. Hydrophobic particles adhere to the gas bubbles and form particle–gas aggregates. Due to the lower-than-normal density, particle–gas aggregates rise to the suspension surface by buoyancy and form the froth layer, while the hydrophilic particles fall down to the bottom of the flotation cell as tailings [2,3]. The gas dissolved in the liquid diffuses into the cavities and prevents collapse, which leads to the generation of tiny bubbles. The venturi tube is recognized as the most economic and efficient HC method [4]

Methods

Results

Conclusion