Study On Cleaning Mechanism Of Magnetic Separation Pre-combustion And Experimental Research

Trace elements removal can be achieved while pyrite and ash-related minerals were removed from coal, so as to achieve the purpose of coal cleaning. But the research is still at an experimental stage and the mechanism is not fully understood; so experiment were done by raw coal from YiLuo and HeBi to research the purification mechanism.Setting the non-magnetic materials cumulative yield as vertical axis and plotting conventional coal quality indexes such as ash and sulfur versus cumulative production rate of non-magnetic materials. The function relations of cumulative production rate of non-magnetic materials versus magnetic susceptibility, as well as coal quality index versus cumulative production of non-magnetic materials were established. From the function relations quantitative assessment of magnetic separation washability can be carried out. Taking YiLuo coal for example, when the theoretical separation magnetic susceptibility is -0.92×10^-8m³Â·kg^-1, the corresponding ash and yield of fine coal is 12.58 percent and 72.78 percent respectively, the yield of tail coal is 26.63 percent, the corresponding result of fine coal from is 7.24 percent and 68 percent; the yield of magnetic materials is 32 percent, the test result fit well with figures in the curve. The ash has deviation with the result but it is in the error limit.The fine coal's dry permanent magnetism high gradient magnetic separation experiment was made by self-made apparatus. Results showed that desulphurization and deashing effect can be achieved by magnetic separation. YiLuo coal of 120¹60 mesh reached 33.12 percent and 22.78 percent respectively, yield of fine coal was 78.82 percent under these conditions, meanwhile HeBi coal was 16.24 percent and 7.28 percent, the cleaned yield was 75.11 percent. The contents of trace elements were analyzed by ICP-MS and SYG-I intellectualized cold vapor atomic fluorescence mercury analyzer based on experiment and the majority trace elements were removed. The trace elements were preferred to enrich in the tailings. The removal efficiency of Cd,Cr,Se,Hg,Pb and As,Hg,Cr,Se,Pb is above zero for YiLuo and HeBi coal respectively. Modes of occurrence of trace elements were analyzed by sequential chemical extraction; migration mechanism of hazardous trace elements in coal were discussed by analyzing the relation between trace element and coal component, especially morphologic sulphur and ash using mathematical statistics. Results showed that Hg,As,Se,Pb,Cr have a linear correlation with ash and Cd is unrelated with ash; Hg,As,Se,Pb,Cr,Cd meet a significant correlation with pyrite sulfur. Pb and Hg have strongest affinities with ash and pyrite sulfur respectively. The removal rate of Hg is best. The mechanism of trace elements removal by magnetic separation lies in occurrence of majority trace elements in coal; most showed a strong affinity with sulfides, especially Hg,As,Se. There were many factors effect hazardous trace elements in coal in the magnetic separation migration, but the modes of occurrence is the mainly influence factors.