No description available.

The use of dissolved air flotation (DAF) for drinking water treatment has steadily grown in popularity in Atlantic Canada for the treatment of low turbidity water supplies with high levels of algae or dissolved organic matter. Runoff from high intensity rainfall events may cause a rapid increase in turbidity and dissolved organic matter in rivers and lakes used for drinking water. A technical evaluation of a DAF water treatment plant (WTP) was conducted to determine the contributing factors to clearwell turbidity increases resulting from increased raw water turbidity and colour during intense rainfall and runoff events. The effect of chemical and operational factors on treatment of a low turbidity and colour water source as well as a high turbidity and colour water source were examined, including coagulant dose, coagulation pH, polyaluminum chloride (PACl) coagulant basicity and DAF recycle rate. In response to deteriorating water quality, it was found that increased coagulant addition inadvertently caused the loss of coagulation pH control in a full-scale DAF WTP, resulting in potentially elevated dissolved aluminum residuals entering the clearwell. This would have led to excessive aluminum hydroxide precipitation in the clearwell, and resulted in turbidity increases above the acceptable limit of 0.2 NTU. Turbidity was found to be better removed, and dissolved aluminum residuals minimized, when coagulation pH was set to the pH of minimum aluminum solubility vs. a lower pH of 6.0 during bench-scale DAF testing. A higher dose of coagulant was required to produce optimal removal of turbidity and dissolved organics at the pH of minimum solubility. The difference in bench-scale DAF treatment performance was found to be minimal when comparing sulphated PACl coagulants with 50 and 70+ % basicity. Charge analysis parameters zeta potential and streaming current were found to have a strong correlation in bench-scale testing, though the relationship between the two was affected by the coagulation pH. The results suggest that utilizing streaming current for coagulant dose control at a full-scale WTP would be best accomplished by establishing a consistent relationship between raw water quality, pH and other factors with streaming current experimentally before relying streaming current targets for dose control. Equivalent or improved DAF efficacy for solid-liquid separation was found when the recycle rate was lowered from 12 to 6 % in bench-scale tests and 12 to 8% in full-scale tests. The results suggested that maintaining an optimum air:solids ratio improved treatment performance, possibly by providing adequate bubble contact opportunities while minimizing excess shearing of the sludge blanket. The most significant finding of this research was that maintaining the coagulation pH in WTPs utilizing PACl coagulants is of utmost importance during source water quality deterioration in order to optimize treatment performance as well as prevent excess dissolved and precipitated aluminum from entering a public drinking water supply.

No description available.

No description available.

Frothers are used in flotation to aid generation of small bubbles, but little is known about the mechanisms that take place in the flotation machine to produce such an effect. Coalescence prevention is the common explanation, although the exact mechanism is obscure and almost no attention has been paid to a frother effect on bubble break-up, the other possible mechanism. This thesis presents a technique to study the effect of frothers on bubble coalescence at the generation stage (at a capillary tube) and a technique to study the effect of frothers on bubble coalescence and break-up in a turbulent field. The first technique is based on the sound bubbles emit when they form and coalesce. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has a resolution capable of detecting coalescence events that occur within 1-2 ms. The second technique allows discriminating between coalescence and break-up and is based on the exposure of a mono-size distribution of bubbles to a turbulent field generated by a three-bladed axial flow impeller. Analysis of bubble size distributions after contact with the turbulent field gives the coalescence and break-up fraction. The results show frothers reduce coalescence and alter the bubble size distribution of bubbles generated by break-up. / In the course of high-speed imaging an effect of frother on bubble shape and motion after formation was detected. Analysis of this forms the third major component of the work. A dependence of velocity on bubble aspect ratio is shown, which is in line with recent literature.

No description available.

No description available.

A comprehensive model of particle collection in flotation is developed from a rigorous analysis of the relative motion between a particle and a bubble prior to and during particle-bubble contact. Collection efficiency E(,K) is derived as a product of collision efficiency E(,C) and attachment efficiency E(,A). From trajectory calculations E(,C) is correlated to the bubble Reynolds number and the Stokes number, a dimensionless inertia term. E(,A) is calculated as the fraction of particles which reside on the bubble for a time greater than the induction time. As a result of the velocity gradient are the bubble surface E(,A) decreases with increasing particle size. The model explains the peak in size-by-size recovery data that is often observed at intermediate particle sizes. The peak location is shown to shift to smaller sizes as induction time increases. / A scale-up model for flotation columns is also developed. The model uses measured values of collection rate constants and an experimental correlation of plant column mixing parameters to calculate collection zone recovery R(,K). R(,K) is interfaced with a variable cleaning zone recovery to yield a grade-recovery relationship for the plant column. The onset of bubble loading is accounted for.

One of the problems in the flotation of copper sulphide ores in moderately alkaline pH conditions is the misreporting of iron sulphide minerals into copper concentrates, which results in low copper grades. The relatively strong flotation of iron sulphides is caused by their copper activation from copper species dissolved from copper minerals present in the ore. In this study, several methods were used to reduce copper activation of pyrite during grinding or to minimise its effect on the flotation of pyrite at pH 9.0. Various surface analytical techniques were used to identify the mechanism of these methods and to optimise their performance. / First, it was confirmed that strong pyrite floatation at pH 9.0 in the presence of xanthate was caused by copper activation during grinding with copper sulphate or in the presence of chalcopyrite in single or mixed mineral flotation experiments, respectively. It was found that pyrite flotation is Eh dependent with low flotation for pulp oxidation potential, Eh, values lower than 7 mV (SHE), strong flotation between 7 and 50 mV, and flotation decreasing above 50 mV. The sharp increase in pyrite flotation around neutral Eh values was associated with high copper and xanthate adsorption while the decreased flotation at higher Eh values was caused by the formation of ferric hydroxide at the pyrite surface which in turn reduced copper adsorption but also reduced hydrophobicity. From the measurement by X-ray photoelectron spectroscopy (XPS) of the type and proportion of surface species, it was possible to calculated a hydrophobicity index at each step in the grinding discharge, during conditioning, in each flotation concentrate and finally in the tailing. A satisfactory agreement was obtained between this XPS hydophobicity index and the flotation recovery in each concentrate. / It was found that pyrite could be separated from chalcopyrite at pH 9.0 by controlling the pulp Eh value with maximum mineral separation and chalcopyrite flotation occurring at an Eh of 275 mV. This mineral separation could be further increased with the addition of zinc sulphate which selectively adsorbs or precipitates on the pyrite surface as zinc hydroxide via electrostatic interaction. The selectivity of this adsorption, and therefore larger pyrite depression, is the result of the larger amount of ferric hydroxide formed on the pyrite surface because of the more cathodic nature of this mineral. Thioglycolic acid (TGA) was also found to selectively depress pyrite flotation when added during grinding but, if added during conditioning, its effect on pyrite depression was only observed in the presence of citric acid (CA). This depression was related to the removal of copper hydroxide from the pyrite surface as both TGA and CA are strong complexants of cupric hydroxide (but also ferric hydroxide); as a result, fewer sites are available for xanthate adsorption. Citric acid is a weaker complexant than TGA, especially in the presence of xanthate; its role is to mop up the surface ferric hydroxide so that TGA is free to react with copper hydroxide. More importantly, in less oxidising conditions and with no Eh control, addition of zinc sulphate or TGA increased chalcopyrite flotation but had no effect on pyrite flotation. Pyrite flotation could also be reduced with addition of xanthate during grinding. In this case, the selective depression of pyrite flotation was attributed to the immobilisation of copper by xanthate at the chalcopyrite surface or its removal from solution, both mechanisms resulting in a reduced copper activation of pyrite. Pyrite depression and chalcopyrite flotation, and therefore mineral separation, were optimised with collector addition in both the grinding and conditioning stages. / Finally, the efficacy of these methods has been substantiated by comparing their effects on iron sulphide depression in two copper sulphide ores and with more common methods of iron sulphide depression. / Thesis (PhDAppliedScience)--University of South Australia, 2006

In this study the unique Magotteaux Mill® system was used to control the grinding chemical conditions, which may be adjusted by varying grinding media, purging gas and pH, during grinding. An electrochemical apparatus was used to investigate oxidation-reduction behaviour of grinding media and sulphide mineral electrodes, as well as their galvanic interaction in-situ of the Magotteaux Mill®. Galvanic interaction between the grinding media (mild steel, 15% chromium, 21% chromium and 30% chromium media) and the sulphide minerals (bornite, arsenopyrite and pyrite) was initially quantified in-situ of the mill by electrochemical techniques under different grinding atmospheres (nitrogen, air and oxygen). An innovative mathematical theoretical model was developed to describe the effect of galvanic interaction on oxidation rates of the grinding media during grinding, which was verified by the experimental data. Galvanic interaction enhanced the oxidation of the grinding media and produced more oxidized iron species in the mill discharge. It was observed that oxidized iron species (EDTA extractable iron) was linear with galvanic current between the grinding media and the sulphide minerals, in agreement with the prediction of the theoretical model. The effect of grinding conditions on pulp chemistry, surface properties and floatability was investigated by the measurement of dissolved oxygen (DO), pH, pulp potential (Eh), ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and floatation recovery. / Thesis (PhDAppliedScience)--University of South Australia, 2005.