Techn. Universiẗat, Diss., 2001--Freiberg (Sachsen).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 75-77). Also available via the Internet.

Thesis (MTech (Chemical Engineering))--Cape Technikon, 2000. / Internationally, there is an increase in the need for safer environmental processes that can be applied to mining operations, especially on a small scale, where mercury amalgamation is the main process used for the recovery of free gold. An alternative, more environmentally acceptable, process called the Coal Gold Agglomeration (CGA) process has been investigated at the Cape Technikon. This paper explains the application of flotation as a means of separation for the CGA process. The CGA process is based on the recovery of hydrophobic gold particles from ore slurries into agglomerates formed from coal and oil. The agglomerates are separated from the slurry through scraping, screening, flotation or a combination of the aforementioned. They are then ashed to release the gold particles, after which it is smelted to form gold bullion. All components were contacted for fifty minutes after which a frother was added and after three minutes of conditioning, air, at a rate of one I/min per cell volume was introduced into the system. The addition of a collector (Potassium Amyl Xanthate) at the start of each run significantly improved gold recoveries. Preliminary experiments indicated that the use of baffles decreased the gold recoveries, which was concluded to be due to agglomerate breakage. The system was also found to be frother-selective and hence only DOW-200 was used in subsequent experiments. A significant increase or decrease in the air addition rate both had a negative effect on the recoveries; therefore, the air addition rate was not altered during further tests. The use of tap water as opposed to distilled water decreased the attainable recoveries by less than five per cent. This was a very encouraging result, in terms of the practical implementation of the CGA process.

Este trabalho aborda a caracterização da matéria orgânica existente num ácido fosfórico de pureza industrial (AFPI), oriundo do Marrocos, objetivando sua remoção através de flotação por ar dissolvido (FAD). O AFPI é um líquido escuro que exibe densidade (2020 kg/m³) e viscosidade dinâmica (1,94 x 10-² Pa.s at 20°C) muito mais alta do que os tipos mais puros de ácido fosfórico, como o grau alimentar e o de pureza analítica. Por outro lado, o AFPI apresenta tensão superficial mais baixa que o ácido de grau alimentício (55,2 mN/m versus 63,7 mN/m a 25°C), indicando a presença de espécies surfactantes dissolvidas (ácidos carboxílicos de cadeia aromática). O teor de 447ppm de carbono orgânico total (TOC) evidencia a alta contaminação do AFPI marroquino por matéria orgânica, que pode ocorrer dissolvida (ácidos carboxílicos aromáticos) ou na forma de minúsculas placas que exibem diâmetro (média aritmética ponderada) de 4µm. Ensaios FAD foram executados usando ar pressurizado a 3,5kgf/cm², que após alívio de pressão, produziu uma população de bolhas com diâmetro de 2,41 x 10`POT´-5m (média aritmética ponderada) e altíssimo desvio padrão (2,94 x10`POT´-5m). A medida do diâmetro de bolhas (db), através de difração de laser, somente foi factível com mistura contendo 40% de ácido fosfórico grau alimentar e 60% de água. Devido a isto, os valores reais de db nos ensaios FAD podem diferir os valores medidos. Ensaios DAF foram executados sob diferentes tempos de flotação (15-60 minutos), todavia a mais alta remoção de TOC (somente de 17,7%) foi obtida com 45 minutos de flotação. A remoção muito baixa de TOC (e também de As, Mg e sulfato) gerada pelos ensaios FAD pode ser explicada pela baixa eficiência de colisão (EC) exibida por minúsculas placas (partículas orgânicas suspensas no AFPI) que precisam colidir com bolhas de ar muito maiores para que possam aderir às mesmas, flutuar e serem removidas do AFPI. Esta possibilidade foi corroborada por um valor de EC da ordem de 0,04 (EC~0,04), que foi determinada pelo modelo de Yoon-Luttrell. / This thesis approaches the characterization of the organic matter which exists in a Moroccan phosphoric acid of industrial grade (PAIG), aiming at its removal via Dissolved Air Flotation (DAF). PAIG is a dark liquid which exhibits specific gravity 2020 kg/m³ (26°C) and dynamic viscosity 1.94 x 10-² Pa.s (20°C) very much higher than other purified types of phosphoric acid (food or analytical grade). Conversely it presents surface tension lower than phosphoric acid food grade (55.2 mN/m versus 63.7 mN/m at 25°C), indicating the presence of dissolved surfactants (carboxylic acids bearing aromatic chains). The content of 447ppm of total organic carbon (TOC) evidences its high contamination by organic matter, which may occur either as dissolved species (aromatic carboxylic acids) or suspended platy-shaped particles (weighed average diameter of 4Êm). DAF experiments were conducted using an air pressurization of 3.5kgf/cm², which, after pressure release, yielded a bubble swarm of weighed average size of 2.41 x 10-5m and a large standard deviation of 2.94 x 10-5m. Because bubble size (db) measurements were conducted via laser diffraction with a mixture of 40% phosphoric acid food grade plus 60% of water, actual values of db may be different from the measured ones. DAF tests were conducted under different length of time (15-60 minutes), but the highest removal of TOC (17.7%) was accomplished at 45 minutes of flotation time. The very low removal of TOC (and also Mg, As and sulfate) yielded by DAF experiments may be explained by a low efficiency of collision (EC) exhibited by small platelets (suspended organic particles) which must collide with bigger air bubbles in order to attach to them and be floated. This possibility was corroborated by efficiency of collision (EC) = 0.04, determined by Yoon-Luttrell Model.

The efficiency of flotation processes may be improved through an understanding of the flotation models. Two mathematical models, particle trajectory and mixing zone models, have been modified and used to describe flotation results obtained from a semi-continuous flotation rig. Two types of clay suspensions, kaolin and Wyoming bentonite, were used as representative raw materials treated with a cationic surfactant, hexadecyltrimethylammonium bromide (HT AB), and/or coagulants i.e. alum, ferric chloride and polyaluminium chloride (PAC). HT AB concentrations were varied in the range of I x 10-6 to 3 x 10-5 mol/L. Alum at a concentration of 40 mg/L, ferric chloride at 40 mg/L and PAC at 10 mg/L were the selected coagulant dosages to be used in flotation tests. For the clay-HT AB-coagulant system, a HT AB concentration of I x 10-s mol/L was used in the flotation tests. Suspension flow rate was chosen at 2 Llmin and recycle ratios were varied in the range of 6-40% at room temperature. Two categories, suspensions with and without flocs, have been considered. The trajectory model gave a good match even taking account of the decreases In flotation efficiency at high recycle ratios where flocs had been broken by shear gradients. This model included hydrodynamic and surface forces i.e. electrostatic, van der Waals and hydrophobic forces and was calculated by a Runge Kutta technique. The effect of the shear force on a size reduction was determined from particle size measurements (Lasentec apparatus) in a mixing tank and the results showed a decrease of floc sizes with increasing agitator speeds. Bubble zeta potentials obtained using a modified rectangular cell in a Rank Brothers' apparatus gave points of zero charge at concentrations of 1.61 x 10-9 mollL for HTAB, 1.69 x 10-8 mol/L for tetradecyltrimethylammonium (TTAB) and 2.37 x 10-7 mol/L for dodecyltrimethylammonium bromide (DTAB) at 2SoC respectively. Van der Waals and hydrophobic or hydration forces were obtained from contact angle measurements on solid surfaces. The hydrophobic forces were increased by increasing HT AB concentrations while the hydration effects occurred upon the addition of coagulants to the suspensions. A flocculation model using the extended-DLVO theory showed a good correlation when compared to experimental results. For the mixing zone model, an attachment efficiency for the aggregation of a particle and a bubble was proposed from a ratio between the energy barrier (E1) and the maximum free energy at equilibrium. When particle size is constant, the attachment efficiency values rise with increasing hydrophobic force levels. On the other hand, when floc sizes are increased, the attachment efficiencies are decreased due to the increase in the repulsive long range van der Waals force.

M.Ing. (Civil Engineering) / The dissolved air flotation process can be used for different functions in the drinking waterand sewage treatment fields. The focus for this study was on thickening of activated sludge. At first literature was studied to identify all possible parameters. Then five plants were visited periodically and the physical layout and operating parameters were documented. With the examination of the data the different existing models were evaluated, and new relationships were investigated.

The control of flotation circuits is a complicated problem, since flotation circuits are nonlinear multivariable processes with a significant degree of interaction between the variables. Isolated PID controllers usually do not perform adequately. The application of a nonlinear model predictive algorithm based on second order Volterra models was investigated. Volterra series models are a higher order extension of linear impulse response models. The nonlinear model predictive control algorithm can also be seen as a linear model predictive controller with higher order correction terms. A dynamic model of a flotation circuit based on the governing continuity equations was developed. The responses obtained represented the qualitative relationships between the model inputs and the controlled variables. This model exhibited strong nonlinearities, including asymmetrical responses to symmetrical inputs and gain sign changes. This dynamic model was treated as the plant to be identified and from which second order Volterra models were obtained. Full Volterra models required excessively large data sets, but significant reductions in the size of the required data set could be achieved if some of the second order coefficients were constrained to zero. These "pruned" Volterra models represented the plant dynamics significantly better than linear models. In particular, these second order Volterra models were able to model asymmetrical responses including gain sign changes. A special case of "pruned" second order Volterra models are diagonal second order models, where all the off-diagonal coefficients (hij where i ≠ j) are constrained to zero. These models required less data than pruned Volterra models containing off-diagonal coefficients, but were less accurate. The performance of nonlinear model predictive controllers based on a pruned second order and diagonal second order Volterra models was evaluated. The performance of these controllers was also compared to the performance obtained with a first order (linear) Volterra model. All three controllers gave equivalent results for large manipulated variable weights. However, when the controllers were tuned more aggressively, results obtained from the three controllers differed considerably. The pruned nonlinear controller performed well even when tuned aggressively while the performance of the linear controller deteriorated. For the case of disturbance rejection, the linear controller performed slightly better than the nonlinear controllers. / Dissertation (MEng (Control Engineering))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

Please read the abstract in the 00front part of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

The techniques of X-ray photoelectron spectroscopy (XPS), secondary ionization mass spectroscopy, chemical abstraction analysis and microelectrophoresis were used to confirm the existence of iron films on cassiterite grains recovered from the tin concentrator of Renison Limited (Australia). All analyses indicated the level of surface iron contamination to be far in excess of that characteristic of the bulk mineral lattice. No evidence was found in XPS analyses to support the contention that this iron represented lattice iron that had accumulated on the surface due to migration through the lattice, as has been suggested to be the case for certain sulphide minerals. Instead, all of the experimental data supported the hypothesis that the surface film was the result of previous adsorption of hydrous ferric oxide sols onto the cassiterite surface in the plant environment but which had undergone fundamental structural changes when the sample was dried. Specifically, the presence of the iron film did not change significantly the electrokinetic properties of cassiterite, as is known to be the case for other insoluble oxide minerals in the presence of freshly precipitated hydrolyzed metal ionic species. To reconcile these observations, it was shown independently that drying, both thermally and under vacuum, caused the charge reversal phenomena related to hydrolyzed metal ion adsorption either to diminish or disappear. In the presence of styryl phosphonic acid, the iron contaminated cassiterite exhibited a microflotation response that corresponded remarkably with the actual flotation observed in the plant from which it was taken. A critical examination of the literature revealed that this behaviour was indicative of that reported for other cassiterites in both batch and plant flotation of ores. Most notably the mineral floated strongly between pH 4.0 and 7.5. However, after acid leaching, the pH of maximum recovery moved to more acidic values around pH 2.0 and the mineral floated much less strongly in the slightly acidic to alkaline range. This latter behaviour correlated with a large body of published data for which it was known that the cassiterite used was either a high purity sample, not exposed to solutions containing dissolved metal ionic species, or had been acid cleaned prior to test work. Conversely, results from fundamental studies, where this was known not to be the case, exhibited remarkable consistency with the data obtained for the untreated cassiterite sample. The principal influence of the iron species adsorbed onto the surface of cassiterite was shown to be flotation activation in the pH range where the adsorbed species were not extensively solubilized. In the acidic range below pH 4.0, solubilization of the surface iron entities occurred which caused a severe flotation depressant effect. This solubilization was promoted in the presence of sodium fluoride, a known complexing agent for iron in acidic solutions, and the phosphonic acid. In the latter case, evidence was found for the formation of a soluble iron phosphonate complex. Independent confirmation was also sought and obtained from light scattering photometry to verify the strong affinity of phosphonic acids for hydrous ferric oxide species. Other ionic entities, such as those of magnesium and calcium were found to interact far less strongly. On the basis of this research, it has proven possible to provide a rational interpretation of all previously existing data pertaining to cassiterite flotation with phosphonic acids, for which reasonable sample description and preparation information exist. Such a reconciliation has not previously been provided, either through studies on the effects of cassiterite mineral lattice impurities or other work with dissolved metal ionic species. Furthermore, a significant link has been established between the results of fundamental analyses and industrial related observations. In particular, commercially successful practices, such as fluoride pretreatment of ore slurries prior to cassiterite flotation, now can be interpreted successfully in terms of fundamental ion solution chemistry. The evidence is that such processes involve the solubilization under acidic conditions of adsorbed iron hydroxy sols from the surface of minerals prior to cassiterite flotation. A bulk rejection of the complexed metal ionic species is then made in the water split of the desliming circuit that precedes flotation. The solution chemical evidence obtained supporting such a mechanism is considerable and no finding, in this work or elsewhere, refutes it. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

M.Sc. (Chemistry) / Please refer to full text to view abstract