The mode of occurrence and concentration of trace elements in coal

Abstract

The mode of occurrence and concentration of trace elements in bituminous and sub-bituminous coals have been examined in terms of chemical characteristics of the coal substance and mineral matter. The reactive and porous fuel matrix of lignites and sub-bituminous coals can incorporate a large number of light elements and transition metals in organic acid salts and organo-metal complexes. The bituminous coal trace elements are present chiefly in the mineral matter fraction; in particular the sulphide species host a large number of chalcophilic elements. The average concentrations of most trace elements in coals mined in different countries tend towards the same levels, but there are some differences. The marine trace elements, chromium, copper, nickel, rubidium and vanadium show some enhanced concentrations in British coals whereas the high sulphur coals in the U.S.A. are relatively rich in cadmium and zinc. The chalcophilic trace elements are preferentially removed on coal cleaning. Between 40 and 50% of beryllium, cadmium, copper, lead, mercury and zinc are removed by reducing the ash content of cleaned coals below 15%.