The Effects of Cationic Polymers on Flocculation of a Coal Thickener Feed in Washery Water as a Function of pH CHANDRA W. ANGLE, 1 TRUIS SMITH-PALMER, 2 BYRON R. WENTZELL 2, * 1 CANMET, Natural Resources Canada, Western Research Centre, P.O. BAG 1280, Devon, Alberta, Canada 2 Chemistry Department, St. Francis Xavier University, Antigonish, Nova Scotia, Canada B2G 2W5 Received 13 March 1996; accepted 28 August 1996 ABSTRACT: The flocculation of a thickener feed using three cationic polyacrylamide copolymers of high molar mass and different charge densities was studied at three pHs in washery water. The binding capacities were very dependent on pH but only slightly dependent on the polymeric charge density. The reverse was true for the settling rates. At pH 7, all three polymers were equally effective at clarifying the suspensions, but there were marked differences at pH 4 and 9. For the polymers of highest charge density, reducing the pH increased their effectiveness; for the polymer of lower charge density, changing the pH had little effect on the residual turbidity.  1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 783–789, 1997 Key words: cationic copolymers of polyacrylamide; flocculation; adsorption; turbidity INTRODUCTION resultant of all these parameters. In particular, we were interested in the effect of varying the charge density of the polymer, as previous floc- Processing and beneficiation operations involving the interaction of coal thickener feed (TF) with culations involving kaolin and cationic polymers have given conflicting results. 2,3 These conflicting polymers are usually geared towards either selec- tively removing the clean coals from the rest, or results also suggest that factors other than the charge density may be quite critical in determin- towards the removal of the fines, and hence, the recovery of the water. The interactions of the poly- ing the nature of the interaction. This article describes the interactive influence mers with the solids are dependent on many fac- tors, which are for the most part interactive. The of molecular weight, charge density, and pH on the flocculation of a TF in washery water by three nature of the water that interacts with both solids and polymer, its temperature, pH, and ionic com- cationic polymers. Polymers were chosen with a wider range of charge densities than had been position influence not only the solids’ surfaces but the polymer conformation and, hence, adsorption used previously. 2,3 The flocculations are moni- tored in terms of settling rate, turbidity, and ad- properties as well. 1 Mixing, shearing by flow, and other mechanical influences in a processing opera- sorption. tion are also important. Flocculation becomes a EXPERIMENTAL * Now at Diagnostic Chemicals, West Royalty Industrial Park, Charlottetown, PEI, C1E 1BO, Canada. Correspondence to : T. Smith–Palmer. Materials Contract grant sponsor: Engery Mines and Resources, Can- ada. Medium volatile bituminous coal and its associ- Contract grant number: 20ST. 23440 – 6-9213.  1997 John Wiley & Sons, Inc. CCC 0021-8995/040783-07 ated clays in a TF was obtained from a Western 783 / 8E84$$4073 02-27-97 14:50:33 polaa W: Poly Applied