Production of ultra clean coal: Part III. Effect of coalʹs carbonaceous matrix on the dissolution of mineral matter using hydrofluoric acid

An Australian bituminous coal was treated with increasing concentrations of hydrofluoric acid (HF), and the extraction levels of Al, Si, Fe, Ti, K, Na, Ca and Mg were determined. These extraction levels were compared to those obtained when the mineral matter alone, produced by ashing the coal at a low temperature, was treated with HF, in order to quantify the extent that the carbonaceous matrix inhibits extraction. The carbonaceous matrix inhibits the dissolution of Ti to a large extent. Si and Fe are the next most inhibited elements. It is proposed that the Ti is present as extremely small particles, of possibly less than 1 μm in length, which are finely disseminated throughout the coal.