Characterization and elution behaviors of organically associated minerals in coals during acid treatment and solvent extraction

Mineral components bonded to organic parts in some Indonesian and Chinese coals were characterized by solid-state 29Si and 27Al NMR, inductively coupled plasma emission spectroscopy, and X-ray fluorescence before and after high temperature solvent extraction and acid treatments. In lower ranking coals such as South Banko and Berau coals, it was found that organically bonded Si species existed as siloxane-type from the solid-state 29Si NMR analyses. It was also found that some of aluminosilicates species were extracted by mild acid treatments with 2 M CH3COOH or HCl solution even at room temperature. Solvent extraction using N-methylpyrrolidinone (NMP) at 350 °C or with 1-methylnaphthalene(1-MN) at 360 °C was very effective for the production of coal extract (so-called hyper-coal: HPC) with high yields of ca. 60% and extremely low ash contents of ca. 200 ppm. It is noted that some organically associated Si, Al, Ca and Fe species still remained in the coal extract, especially siloxane-type Si species were concentrated in the extracts obtained from the lower rank coals. The same tendency was also observed for the higher rank coals such as Enshu and Nantun coals, although the contents of such organically associated minerals were lower than those of the lower rank coals.