Magnetic separation of coal fly ash from Bulgarian power plants.

Fly ash from three coal-burning power plants in Bulgaria: 'Maritza 3', 'Republika' and 'Rousse East' were subjected to wet low-intensity magnetic separation. The tests were performed at different combinations of magnetic field intensity, flow velocity and diameter of matrix elements. It was found that all parameters investigated affected the separation efficiency, but their influence was interlinked and was determined by the properties of the material and the combination of other conditions. Among the fly ash characteristics, the most important parameters, determining the magnetic separation applicability, were mineralogical composition and distribution of minerals in particles. The main factors limiting the process were the presence of paramagnetic Fe-containing mineral and amorphous matter, and the existence of poly-mineral particles and aggregates of magnetic and non-magnetic particles. It was demonstrated that the negative effect of both factors could be considerably limited by the selection of a proper set of separation conditions. The dependences between concentration of ferromagnetic iron in the ash, their magnetic properties and magnetic fraction yields were studied. It was experimentally proved that, for a certain set of separation conditions, the yields of magnetic fractions were directly proportional to the saturation magnetization of the ferromagnetic components of the ash. The main properties of typical magnetic and non-magnetic fractions were studied.