Bauxite Ore Deposits Research Articles

Chemical Fractionation of Trace Elements in Coal and Coal Ash

This article examines the chemical fractionation (leaching) of elements from the Whitewood Mine subbituminous coals and coal ashes at 120 C, 750 C, and 1000 C. The elements Ba, Zn, and Mn are easily leached from coal by water, ammonium acetate, and hydrochloric acid. Potassium is highly extractable by NH4O acetate but very little with HCl. Hydrochloric acid leaches most of Fe, whereas very small quantities of the element are leached by water or NH4O acetate. Low extractability from coal was noted for Si, Ti, and Cu, an indication of their association with detrital minerals. Extractability of Na from coal was low, which indicates an association with minerals rather than being in the form of exchangeable ions. High leachability for Ca, Sr, and to a certain degree, Mn, Mg, and Na were noted for the 120 C ash samples. Zinc, Ba, S, and P showed a wide variation, reflecting a complex association with carbonate, sulphate, sulphide minerals, and organic matter. Silica, Al, B, Li, Cu, and Mo were completely insoluble. Calcium, Al, Cu, Sr, and Mn were easily extractable from the 750 C coal ash. Copper in coal ash may be in the form of oxide, which is more leachable. High leachability for Al has an implication of potential extraction of the element from coal ash in countries that have no bauxite ore deposits. In the 1000 C ash, S, Zn, and Na were highly leached, whereas Ca, Ba, and Sr were moderately leached. Silica, Al, Fe, K, Mg, Ti, Mn, and Cu showed very low extractability.