title: Optical monitoring of particle aggregates.
abstract: Methods for monitoring particle aggregation are briefly reviewed. Most of the techniques are based on some form of light scattering and may be greatly dependent on the optical properties of aggregates, which are not generally known. As fractal aggregates grow larger their density can become very low and this has important practical consequences for light scattering. For instance, the scattering coefficient may be much less than for solid objects, which means that the aggregates can appear much smaller than their actual size by a light transmission method. Also, for low-density objects, a high proportion of the scattered light energy is within a small angle of the incident beam, which may also be relevant for measurements with aggregates. Using the "turbidity fluctuation" technique as an example, it is shown how the apparent size of hydroxide flocs depends mainly on the included impurity particles, rather than the hydroxide precipitate itself. Results using clay suspensions with hydrolyzing coagulants and polymeric flocculants under different string conditions are discussed.
authors.affiliation: Department of Civil, Environmental and Geomatic Engineering, University College London, Gower Street, London WCIE 6BT, UK. j.gregory@ucl.ac.uk
authors.forename: John
authors.initials: J
authors.lastname: Gregory
mesh_terms: D000534:Alum Compounds / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D000077215:Clay; D005290:Ferric Compounds / Q000737:chemistry; D005427:Flocculation; D017709:Fractals; D006878:Hydroxides / Q000737:chemistry; D007616:Kaolin / Q000737:chemistry; D008027:Light; D009391:Nephelometry and Turbidimetry; D010316:Particle Size; D012542:Scattering, Radiation; D014867:Water / Q000737:chemistry
chemical_list: D000534:Alum Compounds; D000538:Aluminum Silicates; D005290:Ferric Compounds; D006878:Hydroxides; D014867:Water; D007616:Kaolin; C041524:aluminum sulfate; C024823:ferric sulfate; C031356:hydroxide ion; D000077215:Clay