The high efficiency of separation of fine (typically the -150 ~m fraction) particles achievable with column flotation technology is well established. The principal aim of this thesis is to investigate whether column flotation can be used to recover saleable, particularly low-ash quality, coal from South African coal fines which are presently discarded. Samples of thickener underflow fines from the Durnacol, Kleinkopje and Greenside Collieries were used in laboratory column testwork. In addition, on-line column trials were performed at the Kleinkopje Colliery. The effects of co 1 umn operating parameters were established using both one-variable-at-a-time testing and fractional factorial design experiments. An investigation into coal slurry conditioning using oil and oil-water dispersions was also undertaken. The results of laboratory and plant column testwork showed that it was possible to recover the desired quality products from all three of the coal fines samples investigated. For all the coals tested, better grades were obtained at any given yield from column cell flotation than with conventional (batch) froth flotation. The test results also demonstrated that the column cell is best suited to recovering and upgrading the finer (< 75 ~m) size fractions. Column performance was found to be strongly affected by the petrographic composition of the coal fines feed, i.e. by coal TYPE. Coals with high vitrinite and, conversely, low inertinite contents were found to be the most easily floatable. Depending on the coal TYPE, the rate of mass transport in either the pulp or froth phase was found to be rate limiting; this in turn dictated which operating parameters affected product yields and grades. Existing methods of conditioning coal slurries were found to be inadequate. Considerable scope for improvement in coal conditioning lies in better choice of collector and "promotor" reagents as well as in designing more energetically efficient conditioning vessels.

show more