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Alizadeh, Hamid

University of British Columbia

A series of flocculation, ultrasonication and screening tests were performed on dilute quartz suspensions with the use of five polyacrylamide (PAM)-based flocculants of similar molecular weights but of different degrees of anionicity (DA) to investigate the effects of physicochemical properties of the tested flocculants on flocculation performance and strength of the produced flocs. The tests were performed as a function of flocculant dosage, ultrasonication duration and screen size. The strength of flocs was assessed using ultrasonication and wet screening over a range of screen sizes, from 25 μm to 150 μm. Equal adsorption density of the tested PAMs on quartz did not correlate with settling rates of flocculated quartz. Using ratio of intrinsic viscosity ([η]) 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 and produced the most competent flocs. These most effective flocculants exhibited the greatest tendency to coil and stretch in solution, and therefore, could be viewed as the most flexible amongst the tested flocculants. [η] measurements showed that screening did not affect the [η] of the flocculants, while the results from size exclusion chromatography (SEC) demonstrated that ultrasonication caused breakage of polymer chains which led to degradation of flocculants. The results indicated that ultrasonication not only breaks the flocs but also affects the polymer chain while using screening as a strength measurement technique only breaks the flocs. Therefore, screening is a more appropriate technique than ultrasonication for measuring strength of flocs. An empirical stability index (SI) was defined as the ability of each flocculant to withstand degradation to facilitate comparisons between the effects of various handling methods on different polymers. The SI was correlated with the ratio of [η] in distilled water to those in a dilute electrolyte and the trends indicated that the most flexible polymer chains could withstand degradation better compared to the more rigid chains.

Text

2024-06-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88414

Mining Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/