Micromechanics: A New Approach to Studying the Strength and Breakup of Flocs

Micromechanical techniques were developed to pull apart single floc particles 6 to 40 μm in size in order to measure floc strengths and fractal dimensions. Flocs were formed by aggregating aqueous precipitated calcium carbonate sols with two water-soluble polymers. The tensile strengths ranged from 20 to 200 nN and showed no correlation with floc sizes when plotted on logarithmic scales. Flocs created by the two flocculant systems were found to have fractal dimensions of 1.8 and 2.4 based on analysis of fragment sizes. The compact flocs favored breakup by surface erosion, whereas flocs characterized by the lower fractal dimension tended to undergo large scale fragmentation. Comparison of the two polymeric flocculants revealed that both the fractal dimension and the tendency for ruptured fragments to reflocculate were sensitive to the polymer used.