A role of flocculant chain flexibility in flocculation of fine quartz. Part I. Intrinsic viscosities of polyacrylamide-based flocculants

Abstract

The intrinsic viscosities of five commercial polyacrylamide-based flocculants were measured as a function of pH, temperature (25–50°C), and the degree of anionicity of the polymers (from nearly 0 to almost 50%). The tests were carried out in distilled water and in a dilute background electrolyte (0.01mol/L sodium chloride). It was demonstrated that the raw viscosity data could accurately be described using the Fedors equation in order to obtain the intrinsic viscosity. Generally, the intrinsic viscosity increased with the degree of anionicity at any pH value although a plateau region was observed between degrees of anionicity of about 10% and 30%. It was also found that the ionic strength had a much more significant impact on the measured intrinsic viscosities than pH over the studied range of pH values (5.7–10.5). The results obtained in distilled water showed that temperature had a negligible effect on the intrinsic viscosity of any of the tested polymers, but a substantial decrease was observed at higher temperatures in the presence of sodium chloride for more anionic samples only. The data were discussed in terms of conformational changes of the flocculant chains. The background electrolyte primarily brought about coiling of the flocculant chains leading to a decrease in the intrinsic viscosity. It was also suggested that this main coiling effect promoted further intramolecular bonding for more anionic polymers at higher temperatures. An exceptional affinity of calcium ions towards anionic polyacrylamides was also demonstrated as even a small amount of calcium (0.001mol/L) was sufficient to reduce the intrinsic viscosity to a value indicating a physical limit of coiling.