Thesis (Ph.D.)(Metallurgical Engineering)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references.

D.Ing. / The use of dissolved air flotation (DAF) as a water clarification process has gained momentum over the past two decades. Despite its increased application there is a lack of information concerning the understanding of the underlying principles of the process. Plants are being designed based mainly on empirical guidelines, especially with respect to the bubble production system. Bubbles are generated in the DAF process when water, supersaturated with air under pressure, is released under atmospheric conditions. The efficiency of air dissolution and precipitation determines the quantity of air available for flotation and thus, to a large extent, the success of the whole DAF process. The first part of this thesis deals with a rational model for predicting the air transfer efficiency in packed saturators which are used in most modern DAF plants to dissolve air into water. The model assumes the Lewis-Whitman two-film theory for interfacial mass transfer and uses the Onda correlations to estimate the mass transfer coefficient. The model provides good insight into the effects of key design parameters on the air transfer efficiency. The experimental verification of the model required a method for predicting the saturator air composition and a technique to practically determine the air transfer efficiency in the packed bed of an operating saturator. Both methods are described in detail in this study. The verification of the mass transfer model showed a close agreement of experimental and theoretical results and the model thus provides a powerful tool for the design of packed saturators. The second part of the thesis deals with air precipitation and the quantity of air released after depressurization. Based on a literature review on this subject it was assumed that the air release is incomplete and that it would be a function of the operating conditions of the saturation system as well as of the design of the injection nozzle across which the pressure is released. Since the injection nozzles play an important role in the DAF process numerous experiments were carried out which measured the released air volume for different nozzle configurations and saturator pressures. The results of this study showed that the air release after depressurization is indeed incomplete and that it takes a long time for all the excess air to come out of solution. It was found that the efficiency with which the air was released is a function of the saturator pressure and the nozzle design. The experimental observations led to the formulation of a two-step air release model, which explains the precipitation process in terms of a slow and fast release step. The mathematical framework for quantification of the model is provided. Once the model is quantified it will be possible to compare the performance of different injection nozzles solely with regard to their design features and independent of any parameters influencing the air release downstream of the nozzle. This model may then help to further the understanding of the precipitation process and could lead to the development of some rational guidelines for nozzle design and prediction of nozzle performance.

D.Sc. (Chemistry) / The Phosphate Development Corporation (FOSKOR) recovers apatite from foscorite ore by a process of froth flotation. Four reagents are used viz. sodium hydroxide, water-glass, nonylphenol tetraglycol ether (EMU) and a fatty acid. The fatty acid is mainly composed of a mixture of oleic and linoleic acid in a ratio of 1,2:1. The aim of this study was to investigate the influence of the first three above-mentioned reagents on the adsorption of oleic, linoleic and linolenic acids on apatite and The Phosphate Development Corporation (FOSKOR) recovers apatite from foscorite ore by a process of froth flotation ...

The particle-bubble interaction is found in industrial applications with the purpose of selective separation of materials especially in the mining industry. The separation is achieved with the use of bubbles that collect particles depending on their hydrophobicity. There are few experimental studies involving a single interaction between a bubble and a particle. The purpose of this work is to understand this interaction by the study of a single bubble interacting with a single particle. Experiments were conducted using ultra-pure water, glass particles and air bubbles. Single interactions of particles with bubbles were observed using two high speed cameras. The cameras were placed perpendicular to each other allowing to reconstruct the three-dimensional position of the particle, the bubble and the particle-bubble aggregate. A single size of particle was used varying the size for the bubbles. It was found that the attachment of a particle to a bubble depends on its degree of hydrophobicity and on the relative position of the particle and the bubble before they encounter.

The effects SIBX/C10 (or C12) TTC mixtures on flotation response of pyrite, gold and uranium from Anglogold Ashanti’s No 2 Gold Plant feed were investigated. In batch flotation tests where TTC was dosed from aged 1% wt stock solutions, synergism was shown to occur in gold flotation at 25 mole percent C12 TTC and in uranium flotation at a similar dosage of C10 TTC. With commercial C12 TTC, 8 mole percent recorded the highest uranium and gold recoveries. The SIBX/C12 TTC mixture had a greater effect on gold than on uranium. When C12 mercaptan replaced the TTC in SIBX mixtures, rates and recoveries decreased at all levels. Kinetics and recovery with a mixture of 92 mole percent SIBX and 8 mole percent commercial C12 TTC gave a better flotation activity than obtained with SIBX alone. A combination of SIBX and an aged 1% wt solution of TTC lost activity when compared to that of SIBX and commercial TTC. This was attributed to the hydrolysis of TTC. Micro-probe analysis, back-scattered electron images, and EDS analysis showed that all the uranium recovered in flotation concentrates was associated with either pyrite, galena or a carbonaceous material (karogen). This was attributed to the flotation of the uranium oxide minerals brannerite and uraninite. Conditioning at pH values between 1.9-3.7 improved kinetics of gold, sulphur and uranium collection, but sulphur and uranium final recoveries were lower and gold final recovery was higher than the standard. In the presence of 0.001M cyanide, equivalent to 70g/t copper sulphate failed to activate pyrite at both pH 5.5 and pH 7.2. At a similar molar dosage lead nitrate did activate pyrite at pH 5.5 but not at pH 7.2. / Dissertation (MEng(Metallurgical))--University of Pretoria, 2005. / Materials Science and Metallurgical Engineering / unrestricted

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No description available.

Over the past 40 years, several procedures have been proposed for characterizing ideal flotation behavior. These procedures, known as release or tree analysis, generally involve multi-stage flotation in batch, laboratory flotation cells using various combinations of rougher, cleaner, and scavenger configurations. Although some of these procedures have been experimentally compared, there remains considerable controversy as to which approach best approximates the ideal flotation response. In this investigation, modeling and simulation techniques are used in conjunction with experimental studies to compare three procedures commonly used for characterizing flotation behavior. These procedures include timed release analysis, simplified release analysis, and tree analysis. Timed release analysis is shown to produce superior results to simplified release analysis and tree analysis; although simplified release analysis appears to be best suited for locating the "elbow" of the grade-recovery curve. In no case, do any of these techniques approximate a perfect separation. A novel technique, known as reverse release analysis, is described and demonstrated to be superior to the other three procedures. Finally, a theoretical methodology for obtaining the true ideal separation curve is presented. / Master of Science

The flotation of very fine ores is desirable because of the occurrence of some ores that require fine grinding to achieve liberation. The literature has been concerned with electrical and chemical effects at the interface of finely ground minerals. The writer proposed to investigate the effect of increasing gravity by the use of centrifugal force on the collection and separation of finely ground ores. The collection of minerals appeared to be hindered by increased gravity, but the separation was enhanced by increased gravity in the tests where conditions were conducive to froth flotation. / Master of Science

M.Sc. (Eng.), Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2012 / The aim of this research project was to test the response of ultra fine coal sourced at Klipspruit Colliery to froth flotation and the response of the froth flotation products to dewatering using two different types of filter presses, namely the Tecnicas Hidraulicas (TH) and the Ishigakhi presses. During test work, some difficulty was experienced with coarse material feeding the froth flotation pilot plant. This led to pilot plant modifications. Further process complexities necessitated laboratory scale flotation test work on the Klipspruit coal to be carried out. The results for both the laboratory scale and pilot plant test work for froth flotation indicated that froth flotation as applied to the Klipspruit fines was not economically feasible because neither the required quality of the product (calorific value of 27.80 MJ/kg) nor the product yield of 50% could be achieved when subjected to a primary and secondary stage of froth flotation. The coarse material, which fed the pilot plant and the Ishigakhi filter press, gave low moisture values (12.3%) not typical of ultra fine coal moisture values. However when fed with very fine particle size distributions, prior test work with the Ishigakhi showed that moisture values below 20% could be achieved. The moisture values obtained for very fine particles using the TH filter press on product thickener underflow material sourced at Goedehoop colliery reached values below 20%. Thus both of the two dewatering options, i.e. the Ishigakhi filter press equipment or TH filter press equipment for the ultra fine coal dewatering, can be utilized. Since the filter rate is the determining factor specifying filter press size, it was determined that a larger TH filter area is required in 1 comparison with the Ishigakhi press. Based upon the pilot and laboratory scale test work undertaken and the assessment of the results, it appears that both dewatering options could be successfully employed on a technical basis for the dewatering of coal flotation products, tailings and the arising raw ultra fine fraction. Froth flotation for Klipspruit ultra fine coal was deemed unfeasible for both pilot plant and laboratory scale tests conducted. For this reason a capital expenditure for the construction of a froth flotation plant at the Western Coal Complex Phola plant was not considered feasible since Klipspruit coal forms part of the feed that will feed the Phola plant. In conclusion, following dewatering using either the TH filter press or the Ishigakhi filter press, it was established that both froth flotation concentrate and unbeneficiated ultra fines gave acceptable total moisture results (below 20%). These dewatered raw ultra fines may therefore be blended into inland product as thermal coal to be utilised by Eskom for power generation. Based upon this premise, it is estimated that profits of 76.5 million Rand could be generated by blending Klipspruit ultra fine coal into thermal coal production at the new Phola plant.