A role of chain flexibility of polyacrylamide-based flocculants in flocculation of fine quartz
Hamid Alizadeh, Vivian Ferrera Leon, Esau Arinaitwe, Marek Pawlik
Abstract
A series of flocculation and adsorption tests were performed on dilute quartz suspensions using five polyacrylamide (PAM)-based flocculants of similar molecular weights but of different degrees of anionicity (DA). The tests were performed as a function of pH at a constant ionic strength. It was demonstrated that adsorption density of the tested PAMs on quartz did not clearly correlate with settling rates of flocculated quartz, and adsorption densities of the polymers under similar flocculation conditions were nearly equal. Using ratio of intrinsic viscosity in distilled water to that in a dilute electrolyte as a measure of flexibility of the flocculant chain, it was shown that the flocculating efficiency of the PAMs was related to their ability to coil or stretch in solution. PAMs with DA of 10–18 % showed the highest flocculating efficiency in terms of settling rates and turbidity. These most effective flocculants exhibited the greatest tendency to coil and stretch in solution, and therefore, could be viewed as the most flexible among the tested flocculants. This result suggests that flocculating power of a flocculant is determined not only by its ability to adsorb onto particles but also by its ability to conform to the shape of the resulting flocs.