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Title: Tank design modifications for the improved performance of froth flotation equipment
Author: Morrison, Angus James
ISNI:       0000 0004 7427 7053
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Froth flotation is a physico-chemical technique used to separate the constituents of a mixed mineral slurry by their relative surface hydrophobicity. In order to do so economically, it is necessary to treat large volumes of material in ever-larger and more efficient tanks. The efficiency and efficacy of such tanks can be enhanced through mechanical modifications designed to improve froth handling, increase the likelihood of bubble-particle interactions in the pulp, and increase the residence time of suspended solids in the tank. However, design modifications suggested by computational modelling or bench-scale experiments often do not realise performance improvements at pilot and plant-scale because of imperfect scale-up from bench-scale, and differences in the type and intensity of the sub-processes affecting performance at different scales. The first outcome of this thesis is an intermediate, laboratory-scale froth flotation circuit that more closely resembles continuously-operated pilot-scale equipment, but which is better instrumented and controlled. This work describes not only the laboratory-scale system, but also detailed regression models of its behaviour and performance based on extensive monitoring and instrumentation. The resultant performance models provide a baseline against which to test design modifications, and the resultant behaviour models inform the design of such modifications. The second outcome of this thesis, a performance-enhancing design modification, was prompted by the discovery that minimising the variability of the pulp-froth interface leads to an increase in both indicative grade and recovery. The resultant tank modification was a horizontal mesh inserted into the pulp below the pulp-froth interface, designed to isolate it from the turbulent region around the impeller. The mesh pore size and thickness, and the position at which it was installed in the tank, were taken as design variables to be optimised by the genetic algorithm method. The result is a grade-recovery curve corresponding to an optimal mesh pore size of 123.4 +/- 3.1 mm. From this curve it was found that increasing the mesh thickness from 33 mm to 47 mm yields a maximum improvement in the recovery of 18.9% without compromising the grade, and increasing the depth of the mesh from 200 mm to 250 mm below the pulp-froth interface yields a maximum improvement in the grade of 3.2% without compromising the recovery. This grade-recovery curve, and the insights gained during the process of design and refinement, provides the rationale for a proposed program of mesh tests at pilot-scale.
Supervisor: Cilliers, Jan ; Brito-Parada, Pablo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral