Studies on flocculation of clay suspension by polyacrylamide

Abstract

The flocculation of dilute pottery clay suspension using polyacrylamide (PAM) was investigated. Different molecular weight PAMs were synthesized by free-radical polymerization initiated with the persulfate-bisulfate redox pair. The synthesized polyelectrolytes (PAM1, PAM2 and PAM3, from low to high molecular weight) and a commercial one (C-492) were used for flocculation studies. The flocculating performance of polyelectrolytes was measured on 3% w/v pottery clay suspension using settling tests and turbidity measurements. PAM2 at pH 5.0 showed the maximum settling rate, which is nearly three times that of C-492, and it also showed a better turbidity reduction. Molecular weight is the key factor in influencing settling and turbidity reduction. In the present study, increasing molecular weight enhanced settling rate and turbidity reduction to a certain level beyond which there is a decrease, suggesting an optimum molecular weight for the given application. PAM2, a medium molecular weight polyelectrolyte $(2.0.10^5 g/mol)$ has shown better performance than PAM1 $(1.3.10^5 g/mol)$, PAM3 $(6.0.10^5 g/mol)$ and the commercial polyelectrolyte C-492 (molecular weight of order 106)