DIFFERENCE OF IRON REMOVAL EFFICIENCIES FROM CIRCULATING FLUIDIZED BED FLY ASH AND PULVERIZED COAL FLY ASH BY MAGNETIC SEPARATION

Iron oxide in fly ash is the main impurity for its high value utilization process. Efficient removal of iron impurities is of great significance for the high value utilization of fly ash. In this paper, the wet magnetic separation method was used to remove iron from circulating fluidized bed fly ash (CFB ash), carbonthermal reduction circulating fluidized bed fly ash (R-CFB ash) and pulverized coal furnace fly ash (PC ash). Research and comparison of the existence forms of iron in different types of fly ash were studied and compared, and finally the removal of iron and recovery of aluminum in fly ash were examined. The results showed that the iron removal efficiency of CFB ash using direct magnetic separation method was only 17.6%, and the iron removal efficiency of PC ash using direct magnetic separation method could reach 55.8%. The iron in CFB mainly existed in the form of hematite, while iron was mainly related to the existence of magnetite in PC ash. The hematite in CFB ash was converted to magnetite after carbonthermal reduction, and the iron removal of R-CFB ash was 64.7%, with a magnetic field strength of 400 mT, magnetic separation 3 times and liquid-solid ratio of 20:1. The iron content was reduced from 3.4% to 1.2%, and the recovery of aluminum was 78.6%. Compared with the iron removal of PC ash, the carbonthermal reduction CFB ash could achieve higher iron removal efficiency.