Coal Preparation » Fine Coal
This project aimed to develop and assess a method combining the use of oscillatory air supply and acoustic sound for improving coal flotation. The approach was based on the dynamic stabilisation effect induced by exposing the froth phase to low frequency acoustic sound and the decrease in the size of bubbles using oscillatory air supply to replace conventional steady air supply.
Pilot scale column flotation tests in semi-continuous and continuous modes were carried out to evaluate the proposed method. Results showed that use of the combined method could reduce product ash content without decreasing yield or combustible recovery.
Fundamental studies were carried out to improve understanding of the effect of acoustic sound on flotation process. Laboratory scale flotation tests in semi-continuous mode were done to examine the effect of acoustic sound on froth carry rates with varying feed rate and aeration rate. In these tests, quartz particles were used as model particles. Results showed that applying the acoustic sound to the column flotation could increase froth carry rate by as much as 20% and mass pull by up to 19%. Furthermore, a study of the bubble-particle interaction with or without acoustic sound found that the use of acoustic sound at a range of frequencies and amplitudes could destabilise the wetting films confined between particles and bubbles, in favour of particle flotation. This finding suggested that the improvement of coal flotation by acoustic sound could be due to the cooperative effect of improved froth stability and enhanced bubble-particle interaction.
Successful implementation of the method is expected to improve product grade while keeping the yield or combustible recovery the same.