Macro-pore structure characteristics of a low-rank coal and its froth flotation fractions

A high pressure Mercury Porosimeter (M.P.) (max. oper. press: 2000 atm) and an optical microscope interfaced with a Quantimct image analyser were employed to investigate the internal macro-pore structure of froth flotation concentrates of low-rank coal. The objective of the froth flotation process is to produce a demineralized product from a pulverized low-rank feed coal suitable for use in industrial combustors as the solid component of a coal-oil mixture (COM). The effectiveness of the coal for this use is associated with a rapid rate of combustion for which a knowledge of macro-pore distribution is useful. It is also of interest to know whether the pore-size distribution of the treated coal influences in any way the froth flotation process, possibly leading to selective separation based on internal pore structure. The experimental distributions showed a bimodal configuration with maxima located at pore sizes of ≈ 10 and ≈ 5500 nm. Overall specific surface areas ranging between 3.50 and 11.80 m²/g_c are substantially higher in comparison with results from literature obtained by M.P. and N₂ adsorption at ?196 °C. M.P. hysteresis results are discussed and a low mercury entrapment of ≈ 5% of the ultimate detected porosity was observed on froth flotation tailings with an ash content approaching ≈ 77%.