Spectrometric determination of minor, trace and ultra-trace elements in coal

Complete text of publication follows. Coal, in South Africa, is a major source of energy. All power stations, with exception of one, are coal-driven. The result is that large quantities of material enter the atmosphere and may cause pollution. Acid mine drainage may leach elements from coal which will enter the water systems. The determination of the levels of minor, trace and ultra-trace elements in coal is consequently of major importance. Most laboratories make use of X-ray fluorescence spectrometry (XRF), but the technique is limited to trace elements at best. An alternative technique which will determine elements in the desired range would assist environmentalists in assessing the impact of the coal-fired stations. A slurry technique using N,N-dimethylformamide (DMF) has been established and trace elements determined by ICP-OES. Minor elements Al, Ca, Fe, Mg, S, Si and Ti, and trace elements Ba, Mn, Ni, Sr, V, Zn and Zr were successfully measured using ICP-OES. Elements present at the ultra-trace level As, Cd and Pb were determined by ET-AAS using a filter furnace. A variety of dispersants, grinding methods and acids were investigated. The stability of the slurry was studied using a SEM, particle analyzer, viscosity and surface area. Physisorption studies indicated that ground coal had up to ten times higher surface areas than coarse coal. The higher surface areas for fine ground coals suggested why they were better dispersed and thus better transported into the plasma, resulting in higher emission signals. Zeta potentials indicated that for all dispersants, the coal particles were well repelled from each other, although SEM pictures indicated better dispersion for 0.1% Triton X-100 with 10% DMF. It was demonstrated that higher intensities and higher precision could be obtained with well dispersed and stable coal slurries. Accuracy of both instrumental techniques was confirmed by the analysis of several certified reference materials using slurry introduction.