The effect of flocculant anionicity on the resistance of quartz flocs to mechanical treatment

Five polyacrylamide (PAM)-based flocculants of similar molecular weights but different degrees of anionicity were selected to investigate the effect of physicochemical properties of the tested polymers on resistance of quartz flocs to mechanical treatment. The flocculated quartz suspension was prepared at two different flocculant dosages and each sample was subjected to either ultrasonication or screening to break the flocs. The tests were performed as a function of ultrasonication duration and screen size while settling rate of flocs, turbidity of supernatant and adsorption density of flocculants were measured as indices of strength of flocs. Adsorption studies showed that adsorption density of flocculants on fine quartz surface remained unaffected by ultrasonication and screening tests, indicating that the observed changes in floc sizes was not a result of desorption. It was found that ultrasonication not only breaks the flocs but also affects the polymer chain, while screening as a strength measurement technique only breaks the flocs. In relation to dewatering applications that rely on floc strength to allow water to flow freely, such as pressure filtration, it was found that at the same adsorption density of the flocculants, PAMs with flexible chains produced the most resistant flocs. These results are attributed to the ability of these flocculants to conform to the shape and size of the flocs. • Effect of five PAM samples on strength of quartz flocs was studied. • Polymer samples were of known molecular weight and degree of anionicity. • Ultrasonication and screening were used to break the flocs. • Screening was a more appropriate strength measuring technique than ultrasonication. • Correlation was shown between flocs strength and flexibility of polymers.