AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP14
Tribocharging in Electrostatic Beneficiation of Coal: Effects of Surface Composition on Work Function as Measured by XPS and UPS in Air

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: S. Trigwell, University of Arkansas at Little Rock
Authors: S. Trigwell, University of Arkansas at Little Rock
M.K. Mazumder, University of Arkansas at Little Rock
R. Pellissier, RKI Instruments
Correspondent: Click to Email
The cleaning of coal by electrostatic beneficiation is based on tribocharging characteristics of pulverized (smaller than 120 µmm) coal particles. The variation in the charge distribution of electrostatically separated coal particles, as measured by an E-SPART analyzer, indicates that coal exhibits bi-polar charging. This appears to be in conflict with expectations in that the organic coal particles should charge positively, and the mineral particles, present as impurities such as pyrite, charge negatively, as predicted by the relative work functions of the particles (coal and mineral) and the metal surface (copper or stainless steel) used for tribocharging. UPS measurements in air on specimens of three different coal species showed the work function to be higher than predicted, approximately 5.4 eV. Determination of the coal surface composition by XPS showed the coal and the pyrite to be oxidized to different degrees. Studies by UPS and XPS, on copper, stainless steel, aluminium, and other commonly used tribocharging materials such as glass and PTFE, as well as pure pyrite, showed that the work function varied considerably as a function of surface oxidation. Therefore the reason for the bi-polar charging of the coal particles may be due a too small work function difference. The choice of a material for impaction triboelectric charging for coal or mineral separation should therefore depend upon the oxidized work function difference. The correlation between the charge distribution and work function is discussed.