ZETA-POTENTIAL, CONTACT-ANGLE AND THE USE OF AMINES IN THE CHEMICAL DEWATERING OF FROTH-FLOATED COAL

The paper describes the historical development of coal preparation within the United Kingdom, highlighting the problems and economic implications associated with the dewatering of froth-floated coals. Theoretical considerations of the filtration process suggested that an increase in the receding contact angle would have beneficial effects on the residual moisture content and from a knowledge of the ionic characteristics, cationic reagents of the amine group were selected. Buchner funnel tests allowed the preliminary screening of some ten amine compounds; a diamine was shown to offer the most potential. This was examined in more detail to determine its effect on the zeta potential and contact angle of coal slurries, indications being that maximum dewatering (hydrophobicity) should be achieved at maximum contact angle and at the zero point of charge of the system. Pilot-scale filtration tests with the diamine confirmed the earlier Buchner funnel results and a reduction of approximately ten percentage points at a diamine dosage of 0. 4 kg/ton was indicated.