Mineralogy and geochemistry of the coals from the Karmozd and Kiasar coal mines, Mazandaran province, Iran

The Karmozd and Kiasar mines are two major coal producing areas in the central Alborz coal-bearing field, northern Iran. This study focused on the mineralogy and geochemistry, with respect to the mode of occurrence of elements in feed coals and element partitioning during coal preparation. The low sulfur content in the coal seams indicates a non-marine origin, i.e. deposition in lacustrine and swamp environments. Detrital minerals in the coal seams are quartz, feldspar (albite and orthoclase), mica (muscovite and biotite), amphibole (hornblende), and kaolinite. Authigenic minerals include pyrite, calcite, and chlorite. The contents of most elements are within the general worldwide ranges (with the exceptions of Mn, Co, and Cr, in some coal seams). Correlation coefficients between elements and the ash yield identified four separate groups of elements. The sequential extraction results indicate that Al, Na, K, Zn, Cu, and Co principally occur in the silicates, whereas Pb and Cr mainly occur in the organic fraction. Calcium and Mg display strong affinities to the carbonate phase, while Cd mainly occurs in the water soluble and organic fractions. The calculated removability index shows that the coal cleaning method in Zirab not only removes mineral matter and pyritic sulfur, but also reduces the content of most inorganic elements.

► Total sulfur content in coal seams indicates a fresh water environment. ► This study demonstrates that coin-shape pyrite is the most abundant form of pyrite. ► It is indicated that Cd mostly occurs in the water soluble phase with serious environmental implications. ► Zirab coal cleaning plant is relatively efficient in removing mineral matter from the coal.