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2 Physicochemical Problems of Mineral Processing

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Application of low-field NMR in the study of flocculant-aided filtration process of coal tailings

Guo Zhimin, Liang Long, Hu Pengfei

Physicochemical Problems of Mineral Processing

2021

Vol. 57, iss. 3

1--7

Preconditioning of coal tailings with flocculants is a useful technology to improve filtration performance. In this study, anionic and cationic polyacrylamides were used for the pretreatment coal tailings before filtration. Nondestructive and rapid measurement of the filter cakes of coal tailings at different filtration stages was conducted using a nuclear magnetic resonance (NMR). The transverse relaxation time (T2) results of NMR provided the information concerned the state of water in filter cake, showing that free water entrapped in larger pores was removed mainly during coal tailings filtration, and the pressure in this study cannot remove the inherent moisture of filter cake of coal tailings. The significant increase in the amplitude of T2 value between 0.1 and 1.0 ms revealed that the flocs collapsed into smaller ones with water entrapped in them during filtration. Comparing the NMR results with different flocculants shows that anionic polyacrylamide of 800 g/Mg produced a larger structure in the initial stage of filter cake formation. The final filter cake entrapped more water. The NMR results well validated the filtration experiments.

An investigation of continuous interaction process between air bubble and various roughness coal surfaces using microbalance

Guo Zhimin, Yang Jianguo, Wang Yuling

Physicochemical Problems of Mineral Processing

2020

Vol. 56, iss. 1

11--23

Surface roughness of particles plays an important role in bubble-particle interaction process. However, the continuous attachment and detachment process have rarely been characterized between the surface of different roughness and air bubble. In this study, the continuous attachment and detachment processes between the surface of different roughness and air bubble were investigated by a highly sensitive microbalance. The bubble–surface interaction process was monitored by a high-speed camera to analyze the geometry parameters, including distance, adhesion diameter, and contact angle. It was found that the bubble-particle attachment time increased with the increase of surface roughness. The magnitude of the repulsive force in the bubble-surface approaching process increased with the increase of surface roughness, while the attractive force in the bubble-particle retracting process decreased monotonically with the surface roughness. The force measured by microbalance was finally compared with the calculated one. The calculated force at the biggest force point also increased with the decrease of surface roughness. These results indicate that coal particles with lower surface roughness, which have less water-filled pores and pillars, is more conducive to flotation due to the lower repulsive force in the bubble-particle attachment process and higher adhesive force in the bubble-particle detachment process, and vice versa.