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Coal Preparation

Improving The Treatment Of Clay Minerals In Coal Flotation Using Saline Water

Coal Preparation » Fine Coal

Published: April 13Project Number: C20042

Get ReportAuthor: Bo Wang, Di Liu, Yongjun Peng, and Sue Vink | The University of Queensland

Clay minerals present a widespread problem in the flotation of all kinds of minerals in that they can coat mineral surfaces resulting in low mineral flotation recovery, contaminate the flotation product through mechanical entrainment due to the small particle size and cause high pulp viscosity resulting in poor flotation hydrodynamics. These problems are exacerbated by saline water which changes the flotation chemistry and the interactions between bubbles/bubbles, bubbles/particles and particles/particles.

 

This project addressed the interaction between clay minerals and saline water with the objective of understanding the adverse effect of clay minerals in both pulp and froth phases and then developing new methodologies to improve the treatment of clay minerals in coal flotation. A range of techniques including Cryo-SEM characterisation of coal surfaces, viscosity measurement in pulp and froth phases, and froth property measurement were conducted and correlated with flotation performance indicated by combustible and ash recovery as well as water recovery.

 

The project started with mine site diagnostic tests conducted at coal site 1 and coal site 2. Pulp chemistry, water chemistry, froth stability and viscosity in the flotation plants were measured. This provides the physical and chemical conditions with which the mechanism understanding was undertaken in the laboratory.

 

It has been identified that clay minerals occur in the typical coal at both coal site 1 and coal site 2 and adversely affect coal flotation. In the flotation of the coal sample from coal site 1 with particles smaller than 150 μm, clay slime coating was detected on the coal surface and attributed to the low combustible recovery. While normal ionic dispersants could not improve the flotation using saline water, a non-ionic triblock polymeric dispersant successfully mitigated the slime coating and demonstrated a significant increase in the combustible recovery. In the flotation of the coal sample from coal site 2 dealing with a relatively coarser particle (-710 μm), clay minerals destabilised froth resulting in poor coarse particle flotation. In order to increase the coarse particle flotation of the coal from coal site 2, two approaches were applied. A polar collector was used to increase the coal surface hydrophobicity, while a stronger polyglycol-type frother was introduced to enhance the froth stability. Both methods demonstrated a great increase in the combustible recovery with little effect on the product grade. Plant trials of chemicals to improve coal flotation at both coal site 1 and coal site 2 are recommended.

 

This research also demonstrates a significant gangue entrainment as a result of the interaction between clay minerals and saline water at high electrolyte solutions.

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