Extraction of High Grade Magnetic Material from Fly ash and its Evaluation for Dense Medium Coal Cleaning Application

摘要

On average,fly ash produced from burning high-sulfur coal in the U.S. contains 10 to 15% or more of magnetic materials, the majority of which are fine magnetite particles called fly ash derived magnetite (FAM). This study developed a proprietary processing scheme to economically extract high grade magnetite from high sulfur coal fly ash. A magnetite concentration of 17.5% (Davis tube measurement) in fly ash feed was enriched to 96% of magnetite in the FAM product. Feed solid content affected the FAM grade produced from the wet magnetic separator the most, whereas both feed solid content and water spray angle were equally important for magnetite recovery. The empirical models developed for both magnetite grade and recovery were validated and the highest grade of 96.5% was achieved at a reasonably high recovery of 83.7% by conducting tests at a feed solids content of 7% and a spray angle of 45°. In spite of the spherical shape and slightly coarser particle size distribution of the FAM particles in comparison to the NM particles, a relatively stable dense medium was successfully produced by the former apparently due to their lower density. The stability indices in the range of 30 to 40 for FAM medium densities from 1.3 to 1.6 compared favorably with those of NM based mediums. The coal cleaning performance, i.e., combustible recovery and ash rejection relationships, obtained from a 15-cm diameter dense medium cyclone using dense medium prepared from both FAM and NM, were quite similar.