Thesis (PhD)--University of South Australia, 1999

Thesis (PhD)--University of South Australia, 1999

Thesis (Ph.D.) --Murdoch University, 2003. / Thesis submitted to the Division of Science and Engineering. Includes bibliographical references (leaves 172-181).

Although the precipitation of aluminium trihydroxide as gibbsite, via the Bayer process has been widely studied, the mechanism of crystal growth is poorly understood. This work focus on the morphology of gibbsite and the relative growth rates of individual crystal faces.Initial work was carried out to characterize aluminium trihydroxide and it was found that bayerite, another polymorph, precipitated at temperatures below 50 [degrees] C and its morphology depended on the method of precipitation. Gibbsite however, precipitated above this temperature and its morphology depended on the type of alkali aluminate solutions used. The method of precipitation does not affect the morphology, only the size of the precipitate formed. The morphology of gibbsite can be altered by the addition of organic compounds which are known to inhibit gibbsite precipitation. Some of these compounds were found to selectively inhibit the growth of individual crystal faces, thus altering the overall morphology of gibbsite. Boehmite, a polymorph of aluminium hydroxide, can be produced by partial dehydration of gibbsite at 300T. The morphology of boehmite consisted of diamond shaped crystals.The influence of cation incorporation on the morphology of gibbsite was studied experimentally and computationally (molecular modelling). These studies showed that there is a linear relationship between the amount of cation incorporated and atomic radii and between the amount of cation incorporated and the defect energy calculated. The equilibrium morphology of gibbsite predicted in the absence of media matched the morphology of gibbsite grown slowly from sodium aluminate, implying that the amount of sodium incorporation is low in these crystals.The growth rates of individual crystal faces were measured in situ, and found to be a function of supersaturation squared for the prismatic faces, possibly indicating ++ / that E growth occurs by spiral growth mechanism. The growth of the basal face was found to follow the spiral growth mechanism below a relative supersaturation of 0.815 and the birth and spread mechanism above this level. The activation energies and kinetic coefficients for the individual prismatic faces were also determined.Growth rate dispersion was observed in these microscopic studies, but the question of size dependency remains unanswered.The overall growth rates of gibbsite crystal, determined using rapid dynamic light scattering, was found to be an exponential function of supersaturation indicative of a birth and spread growth mechanism.

Gibbsite scale growth in pipe fittings is a major problem for an alumina refinery. A recent investigation into the scale growth mechanism at an alumina refinery found almost 60 % more scale growth in a reducer when compared with the connecting straight pipe sections for similar flow conditions. Scale growth occurs where liquor (supersaturated solutions) come in contact with solid surfaces and it is affected by the liquor flow velocity besides other physical and chemical parameters. The present work is dedicated to study the hydro-dynamical aspects of the mechanism of scale growth. In particular, the role of the phenomenon of turbulent bursting, stream wise and cross stream fluctuating velocity components (Ux and Uy) was investigated as the flow moves through the reducer. Particle Image Velocimetry (PIV) technique was used to get a full view of the reducer and the readings close-to-the-wall of the reducer at Reynolds number of 27,000 and 44,000 upstream which corresponds to Reynolds number of 41,500 and 66,000 downstream of the reducer respectively. The results showed an increase in cross stream and a decrease in magnitude of stream wise fluctuating velocity components, whereby we presume that the increased cross stream fluctuating velocity component increases the frequency of impacts of the scaling particles on the wall thus initiating excessive scale growth in the reducer when compared with the connecting straight pipe sections, for similar flow conditions.

Thesis (PhD)--University of South Australia, 1997

Sodium oxalate is one of the many organics present in Bayer liquor. Due to its limited solubility, sodium oxalate can co-precipitate with alumina trihydrate during precipitation. This can have detrimental effects on the final product quality, especially if it occurs in the initial stages of precipitation.Quaternary amine type cationic surfactants can prevent sodium oxalate co-precipitation and increase the tolerable concentration of sodium oxalate in Bayer liquor. Their action is via the inhibition of nucleation or/and the inhibition of crystal growth. This study presents work detailing the effect of quaternary amines on sodium oxalate crystal growth in Bayer liquor.A series of quaternary amines were tested and classified as strong, medium or weak crystal growth inhibitors in plant liquor. The octadecyltrimethylammonium bromide was found to be the most effective under plant conditions.Results will show that while quaternary amines inhibit crystal growth in Bayer liquor, they have no effect on crystallization in synthetic liquor. It has been postulated that the presence of certain organic molecules is required for quaternary amines to crystallization and therefore stabilize the liquor. The inhibition of oxalate crystal growth in Bayer process liquors is due to the plant organics present, and the stabilizing effect of quaternary amines is the result of an interaction between quaternary amines and plant humic material on the oxalate surface. A series of organics, anionic macromolecules and anionic surfactants, have been tested to simulate the behaviour of plant humates, and their inhibitory effect on sodium oxalate crystal growth has been measured.A method for the analysis of the strongest quaternary amine has been adopted, improved and modified in order to fulfil experimental conditions.The CMC of quaternary amines has been determined in liquor. Surface tension ++ / measurements revealed relationships between certain liquor components and quaternary amines.Adsorption isotherms of quaternary amines have been successfully generated in Bayer liquor. Investigations with quaternary amines and plant humics reveal a synergy between the two. Co-adsorption of quaternary amines and plant humates onto the oxalate surface has been found, and the effect of the components on the adsorption behaviour will be discussed. The inhibitory effect and the adsorbed amount of components have been compared. Results revealed a relationship between the amount of plant humates on the surface and the crystal growth inhibition.The nature of the adsorption has been investigated with confocal laser scanning microscopy. These results will show that humic material adsorbs at the edges and in the corners of the crystals. In the presence of quaternary amines, the humic material occupies the main crystal faces as well. The nucleation of sodium oxalate from humic solution and from a mixture of humates and quaternary amine resulted in crystals with different morphology.Fourier Transform Infrared Attenuated Total Reflection Spectroscopy investigations will present the adsorption of quaternary amine on oxalate, and will indicate that the adsorption is pH dependent.

In this study, effects of changes in various parameters of the Bayer process on the amount of &ldquo / red mud&rdquo / , which has many environmental drawbacks, were examined in accordance with the principles of &ldquo / sustainable development&rdquo / . The production process of SeydiSehir Aluminum Plant is modeled as a case study. First a steady-state mass balance calculation is carried out by incorporating sequential modular approach. Then a model of the Bayer process digester is programmed and several simulations are carried out using this model. Results of the mass balance calculation revealed that changes in the extent of the digestion reaction, which is a function of temperature and caustic concentration, and washing efficiency may have a 2.07% decrease on the amount of red mud produced,which implies nearly 10,000 tons of decline per annum, while amount of hydrate produced is increased by 4.52%. A 7.40 % decrease on the amount of red mud produced on dry basis per kg of hydrate was found to be achievable. Optimum operating temperature for the digester was calculated as 277.3 &deg / C.

Submitted by Dilene Paulo (dilene.fatima@ufcg.edu.br) on 2018-02-05T15:39:20Z No. of bitstreams: 1 LUIS EDUARDO MEDEIROS FROTA – DISSERTAÇÃO PPGEQ 2012.pdf: 1801644 bytes, checksum: 1d91f3ec19c316106682f868684e0357 (MD5) / Made available in DSpace on 2018-02-05T15:39:20Z (GMT). No. of bitstreams: 1 LUIS EDUARDO MEDEIROS FROTA – DISSERTAÇÃO PPGEQ 2012.pdf: 1801644 bytes, checksum: 1d91f3ec19c316106682f868684e0357 (MD5) Previous issue date: 2012-05-16 / O Oxido de alumínio, Al2O3, comumente chamado de alumina se trata de um composto químico de ampla utilização na indústria estando presente em pastas de dente, tinta, aditivos para tratamento de água dentre outros. Porém sua principal utilização é na indústria do Alumínio onde representa a principal material prima para a obtenção deste metal. A maior parte do Oxido de alumínio produzido no mundo hoje tem como fonte primária a Bauxita. O Alumínio está presente nesse minério na forma de óxi-hidroxidos de alumínio onde os principais são: gibbsita Al(OH)3, diasporo AlO(OH) e boehmita AlO(OH). O processo de refino para obtenção da Alumina a partir da Bauxita mais comumente aplicado atualmente é o processo Bayer no qual o minério é atacado com uma solução cáustica a base de hidróxido de sódio (NaOH) a fim de solubilizar o Alumínio para posterior recristalização. As várias etapas do processamento do minério são definidas e ajustadas em virtude das peculiaridades da bauxita utilizada como, por exemplo, composição química, granulometria e composição mineralógica. Bauxitas com características diferentes pedem processamento diferenciado. Com a demanda por alumina crescente, novas fontes de Bauxita necessitam ser exploradas e uma preocupação é que tipo de mudanças um minério de uma nova fonte pode causar ao processo. Este trabalho teve como objetivo avaliar a bauxita proveniente de uma nova fonte seus impactos no processo servindo como embasamento para tomada de decisão sobre a viabilidade da abertura de uma nova mina e um aumento de capacidade de processamento por parte da Refinaria. Caracterização química e simulação do processo Bayer em bancada mostraram que o material proveniente da nova fonte de bauxita não apresenta diferenças significativas em relação ao minério já utilizado embasando assim os investimentos para abertura e uma mina com capacidade de 4 milhões de toneladas de minério por ano e um aumento de capacidade de produção na refinaria de 2 milhões de toneladas de alumina ao ano. / The aluminum oxide, Al2O3, commonly called alumina it is a compound widely used in chemical industry and is present in toothpastes, ink, water treatment additives and others. However aluminum industry is the principal client where is the main raw material for production of this metal. Most of the aluminum oxide produced today has Bauxite as the main source. The aluminum is present in this ore as oxi-hydroxides which are the main: gibbsita Al(OH)3, diasporo AlO(OH) and boehmita AlO(OH). The refining process for obtaining alumina from bauxite most commonly is the Bayer Process where ore is attacked with a caustic solution based on sodium hydroxide (NaOH) in order to solubilize the aluminum subsequent to recrystallization. The various steps of ore processing are set and adjusted based on the characteristics used as, eg, chemical, mineralogical composition and particle size. Bauxites with different characteristics require different processing. With the increasing demand for alumina, new bauxite sources need to be explored and to know what kind of changes new ore source could require is fundamental. This work aimed to evaluate possible impacts caused by a new source and use this information to evaluate a new mine operation and increase processing capacity at Refinery. Chemical characterization and reproduction of some stages of the Bayer process in bench showed that material from the new source of bauxite does not differ significantly in relation to the first ore confirming investments for opening a anew mine with a capacity of 4 million tons per year supporting production increase refinery production capacity of 1,5 million tons of alumina per year.

The goal of this project was to develop novel bacterial biomarkers for use in an industrial context. These biomarkers would be used to determine aluminium industry activity impact on a local ecosystem. Sediment bacterial communities of the Saguenay River are subjected to industrial effluent produced by industry in Jonquière, QC. In-situ responses of these communities to effluent exposure were measured and evaluated as potential biomarker candidates for exposure to past and present effluent discharge. Bacterial community structure and composition between control and affected sites were investigated. Differences observed between the communities were used as indicators of a response to industrial activity through exposure to effluent by-products. Diversity indices were not significantly different between sites with increased effluent exposure. However, differences were observed with the inclusion of algae and cyanobacteria. UniFrac analyses indicated that a control (NNB) and an affected site (Site 2) were more similar to one another with regard to community structure than either was to a medially affected site (Site 5) (Figure 2.4). We did not observe a signature of the microbial community structure that could be predicted with effluent exposure. Microbial community function in relation to bacterial mercury resistance (HgR) was also evaluated as a specific response to the mercury component present in sediments. Novel PCR primers and amplification conditions were developed to amplify merP, merT and merA genes belonging to the mer-operon which confers HgR (Table 5.6). To our knowledge, the roles of merP and merT have not been explored as possible tools to confirm the presence of the operon. HgR gene abundance in sediment microbial communities was significantly correlated (p < 0.05) to total mercury levels (Figure 3.4) but gene expression was not measurable. We could not solely attribute the release of Hg0 from sediments in bioreactor experiments to a biogenic origin. However, there was a 1000 fold difference in measured Hg0 release between control and affected sites suggesting that processes of natural remediation may be taking place at contaminated sites (Figure 3.7). Abundance measurements of HgR related genes represent a strong response target to the mercury immobilized in sediments. Biomarkers built on this response can be used by industry to measure long term effects of industrially derived mercury on local ecosystems. The abundance of mer-operon genes in affected sites indicates the presence of a thriving bacterial community harbouring HgR potential. These communities have the capacity to naturally remediate the sites they occupy. This remediation could be further investigated. Additional studies will be required to develop biomarkers that are more responsive to contemporary industrial activity such as those based on the integrative oxidative stress response.