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Title: A study of the flocculation of mineral suspensions by polymers
Author: Slater, Robert Winston
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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The thesis opens with a review of the literature concerning flocculation of mineral suspensions by polymer compounds. Concepts of flocculation are considered from two points of view - namely, the physical and chemical aspects. The gaps and apparent contradictions found in the literature led to the greater part of the present study. An apparatus has been developed to determine, on the same sample, the several established empirical indices of flocculation. The polyacrylamide-fluorite system has been studied in detail. The results showed that, while the permeability of the filter-cake provides a comparative index of flocculation, the quantitative theory developed by La Mer, Smellie and Healy, relating the permeability to the degree of flocculation and polymer concentration, is invalid. This theory was shown to rest on an erroneous assumption about the origin of the permeability maximum and an incorrect physical model of flocculation. Further data obtained from the flocculation characteristics of fluorite and hematite suspensions, with a range of flocculants derived from polyacrylamide, provided support for the bridging theory of flocculation. The influence of the method of mixing and polymer addition was also investigated. A technique was devised to determine trace concentrations of an anionic polyacrylamide in solution, and this was used in a detailed investigation of the flocculation characteristics of the fluorite - hydrolysed polyacrylamide system. The effects of pH and of a neutral salt were determined and the results clearly indicated that, while adsorption was indispensable, optimum flocculation was obtained only with maximum extension of the polymer molecules. This property, itself, was strongly dependent on the pH and the ionic strength of the medium. The mechanism of adsorption of polyacrylamide on ionic crystals, such as calcium fluoride, has been considered and the possibility of dipole interaction of amide groups with the electro-static field of the lattice has been suggested. The flocculating action of anionic polyacrylamides with silica suspensions and of cationic polyacrylamides with alumina suspensions was found to be strongly influenced by the concentration of Ba++ and (HPO4)-- respectively. A possible adsorption mechanism has been suggested, based on the interplay of electrostatic forces of repulsion and attractive chemical forces.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available