Role of pH and dissolved mineral species in Pittsburgh no. 8 coal flotation system — I. Floatability of coal

Abstract

The roles of pH and of dissolved mineral species on the floatability of Pittsburgh No. 8 coal was investigated. Isolation of the direct effect of pH from that of the interaction of the dissolved mineral species with OH − was achieved by the appropriate design of the experimental procedure. The effect of pH on flotation, determined using a washed coal sample, was found to be significant, especially above pH 8, with the floatability falling sharply with pH increase. The effect of interaction of the dissolved mineral species with OH − depended on the path of approach to the flotation pH. Under the conditions of increasing pH, precipitation/adsorption of Fe, Al, Ca and Mg species occurred, and the effect of interaction was marked with the floatability decreasing with pH increase. This was shown to be mainly due to precipitation/adsorption on the coal surface of dissolved Fe species which were the predominant inorganic species in the supernatant of the coal slurry. Under the conditions of decreasing pH, dissolution of Fe, Ca and Mg species and precipitation of Al species occurred as the pH is lowered, and the effect of the interaction between pH and the dissolved mineral species was marginal.