The preparation and ageing of acrylamide/acrylate copolymer flocculant solutions

Abstract

The flocculation activity achieved with aqueous solutions of polyacrylamide and acrylamide/acrylate copolymers is shown to be highly dependent upon the solution age. Continuous flocculation with a standard kaolin slurry in a Couette mixing device, giving settling rate and in-line chord length distributions, allows the comparison of different flocculant properties and make-up conditions. The multiple-stage ageing process proposed by Owen et al. [Owen, A.T., Fawell, P.D., Swift, J.D. and Farrow, J.B. (2002), The impact of polyacrylamide flocculant solution age on flocculation performance. Int. J. Miner. Process., 67, 123–144.] for nonionic flocculant stock solutions is found to also apply for the wider range of products, although the relative effects of each stage varies, depending on the flocculant form and molecular weight. For powder-based products, the initial wetting, swelling and dispersion of the solid polymer is influenced by the powder size, such that activity may be extremely poor even after several hours. Emulsion-based flocculants effectively eliminate this stage, but both forms of the high molecular weight flocculants require at least an additional 24 h to achieve maximum activity. This is attributed to the slow disentanglement of highly agglomerated polymer. The practical implications for flocculant make-up and use in mineral processing are discussed.