Development of a process for separating and dewatering fine particles

Various beneficiation processes are employed for upgrading Australian raw coals over a broad size range. Among the beneficiation processes widely used in Australian coal preparation plants are dense medium separation and froth flotation. A common feature for these separators is the use of a lifting force (buoyancy force exerted on particles alone or particle-bubble aggregates) to allow lighter coal particles to move upward and denser mineral matter to move downward. A lifting force for particles in water can also be generated using acoustic waves, where these waves can exert radiation force on particles. The correlation of the acoustic radiation force with the size, density, and compressibility of the particles enables selective separation of particles according to their physical properties.

The aim of this work was to develop and evaluate a process based on acoustic particle manipulation for beneficiation of Australian raw coals at laboratory scale. We examined the potential of this process for upgrading coals of different sizes. The report provided detailed information on how machine design and operating variables would affect the particle separation efficiency.

A flow tubing system with an ultrasound transducer was designed and used to test the effectiveness of this beneficiation process for raw coals in the ultrafine and fine size fractions. Results show that coal particles can be manipulated by acoustic radiation force to form large aggregates and be trapped or floated in the water in the tubing. Good separation of coal particles from quartz particles using the designed separator was achieved, with high combustible recoveries being achievable over a broad size range tested. The acceleration of the sedimentation of coal particles in slurry for dewatering was also obtained using this device.