Fractal characteristics of Al-humic flocs

Abstract

The characteristics of Al-humic floes were studied through a series of experimental work using microscopic and online optical monitoring techniques.It was verified that AI-humic floes are of fractal nature and the two-dimensional fractal dimension Df derived from image analysis characterizes their morphological properties.At pH 5.0,the structure of Al-humic flocs formed was more compact with higher fractal dimension of 1.43 than that formed at pH 7.0 with lower fractal dimension Of 1.17.The difference in floc structure was considered to be related to the difierent characteristics of hydrolysis and precipiration of aluminum sulfate under these two typical pH values:at pH 5.0 with a low alum dose,the products of alurninum hydrolysis are mainly soluble maner,While at pH 7.0 at the same alum dose.precipitates form quicldv Alum dose also affected the structure Of Al-humic floes.Under pH 5.0 and at a dose to bring about charge-neutralization to 1.1<1OmV,floes formed are more compact with a fractal dimension ranging from 1.43 to 1.49.while at a higher dose when hydrolyzed aluminum precipitates form,flocs are more open and looser with a much lower fractal dimension.During growth.the fractal dimension of the floes decreased graduauY until an equilibdum state was reached.This implies a faster increase of floc volume than the number of primary particles the floc contains.