Geochemical study of the inorganic constituents in some low-rank coals

Abstract

Because lignites contain acidic and other functional groups, the inorganic matter associated with them can consist not only of discrete mineral phases but also of cations associated with the organic matter. That much of the inorganic matter can be held in the latter way is likely to have an important influence on the role or fate of inorganic matter in processes utilizing lignites. A number of elements (Ca, Mg, N, K, Sr, Ba, and Mn) were found to be present in all samples largely or partly in ion-exchangeable form, little variation with depth in the seam being observed. In particular, 70 to 90% of the calcium in all samples was ion-exchangeable, so that the formation of calcite deposits in liquefaction reactors is likely to be a general phenomenon when low-rank coals are used. Certain elements (Be, V, Al, Ti, Fe) appeared to be present largely or partly as chelated organic complexes decomposable by acid. Since such complexes will often be soluble in organic liquids, poisoning of liquefaction catalysts by Ti is likely also to be a common phenomenon. A number of elements (Si, Al, K, Mg, Zr, Ti) were largely or partly associated with detrital mineral phases. A variety ofmore » trace elements (e.g., Be, V, Cu, Yb, Sc, Ge, Ga), and also acid-soluble Ti, showed major enrichments in the margins of the seams, implying important influences of the organic matter on the trapping of the elements. It also follows that the concentration of a number of elements that may be deleterious to a process or environmentally hazardous could be materially reduced by a selective mining process that rejected, or diverted to other use, a relatively small fraction of a seam near the margins.« less

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