Solid-liquid contact angle is an important parameter in many particulate processes of the mineral, ceramic and chemical industries. In particular, modification of the contact angle through surface active agents plays a crucial role in froth flotation of minerals. In the case of flat solid surfaces, direct measurement of the contact angle is possible. However, such flat surfaces can not be obtained with finely divided solids typically encountered in flotation applications. Then, indirect methods based on powder beds as thin layers of powders deposited on glass plates or packed columns are used for the determination of apparent contact angles. This thesis presents an alternative novel method based on the capillaric dewatering of filter cakes for the measurement of the receding contact angle and correlates the contact angles measured as such with column wicking and micro-flotation test results of zircon and rutile mineral particles. The experimental procedure is simple and fast. The results have proven that the proposed method is reliable and give a good measure of the contact angle in the absence and presence of surface active non-wetting agents.

[pt] A busca por novos reagentes de baixa toxicidade e de alta biodegradabilidade tem sido estimulada. Como resultado, diversas pesquisas vêm desenvolvendo biorreagentes, dentre eles os biossurfactantes. Os biossurfactantes são moléculas de origem microbiana que possuem ação superficial. Essas moléculas, com propriedades anfifílicas, são produzidas biologicamente e têm aplicação em diversos setores industriais. Assim sendo, esta pesquisa teve como objetivo estudar a flotação do sistema hematita-quartzo utilizando o biossurfactante solúvel produzido por Rhodococcus erythropolis como biorreagente coletor. O biossurfactante (BS) foi caracterizado por análises químicas para determinar a percentagem de proteínas, carboidratos e lipídeos e, suas propriedades físico-químicas foram determinadas por tensão superficial e concentração micelar crítica (CMC). Os minerais e sua interação com o BS foram caracterizados por medições de potencial zeta, medidas de ângulo de contato e espectroscopia no infravermelho (FTIR) para determinar suas propriedades eletrocinéticas, hidrofobicidade e grupos funcionais, respectivamente. Os resultados de adsorção revelaram maior adsorção do biossurfactante na superfície de hematita do que na superfície de quartzo e, isto foi confirmado por analises FTIR e testes de microflotação. Os resultados de microflotação de hematita e de quartzo foram maiores em pH 3 e com concentração de BS de 100 mg/L, com recuperações em torno de 99,88 por cento e 31,05 por cento, respectivamente e, os mesmos foram analisados estatisticamente para obter uma função polinomial representativa da microflotação. Os testes de microflotação do sistema hematita-quartzo mostraram que o biossurfactante é mais seletivo com hematita do que quartzo. O estudo cinético mostrou que os dados experimentais da microflotação de hematita foram ajustados quanto ao modelo cinético de primeira ordem como ao modelo cinético de ordem fracionária, enquanto os dados experimentais da microflotação de quartzo foram ajustados ao modelo cinético de ordem fracionária. Finalmente, os resultados deste trabalho evidenciaram que a utilização do biossurfactante solúvel produzido por Rhodococcus erythropolis como reagente coletor no sistema hematita-quartzo foi viável, demonstrando o seu grande potencial e mostrando- se bastante promissor para uma futura aplicação na indústria da flotação mineral. / [en] The search for new reagents of low toxicity and high biodegradability has been stimulated. As a result, several researches have been developing bioreagents, among them biosurfactants. Biosurfactants are molecules of microbial origin that have surface action. These molecules, with amphiphilic properties, are produced biologically and have application in various industrial sectors. Therefore, this research aimed to study the flotation of the hematite- quartz system using the soluble biosurfactant produced by Rhodococcus erythropolis as a collector bioreagent. The biosurfactant (BS) was characterized by chemical analysis to determine the percentage of proteins, carbohydrates and lipids and its physicochemical properties were determined by surface tension and critical micellar concentration (CMC). The minerals and their interaction with BS were characterized by measurements of zeta potential, contact angle measurements and infrared spectroscopy (FTIR) to determine their electrokinetic properties, hydrophobicity and functional groups, respectively. The adsorption results revealed higher adsorption of the biosurfactant onto the hematite surface than onto quartz surface and this was confirmed by FTIR analysis and microflotation tests. The results of hematite and quartz microflotation were higher at pH 3 and at the concentration of 100 mg/L, with recoveries around 99.88 percent and 31.05 percent, respectively, and they were analyzed statistically to obtain a polynomial function representative of microflotation. The microflotation tests of the hematite-quartz system showed that the biosurfactant is more selective with hematite than quartz. The kinetic study showed that the experimental data of hematite microflocation were adjusted to both the first order kinetic model and the kinetic model of non-integral order, while the experimental data of the quartz microflotation were adjusted to the kinetic model of non-integral order. Finally, the results of this work showed that the use of the soluble biosurfactant produced by Rhodococcus erythropolis as a collector reagent in the hematite-quartz system was feasible, demonstrating its great potential and showing quite promising for a future application in the mineral flotation industry.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-04-28T15:55:34Z No. of bitstreams: 5 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (1).pdf: 14395227 bytes, checksum: 9f6b9fda10331302bb12ddd5bc52052a (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (2).pdf: 20512897 bytes, checksum: 4c247b49db05cc34da871ae9d8de8659 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (3).pdf: 19405428 bytes, checksum: 36b5a6102f851dcf63f4d358963cf425 (MD5) Dissertaação - Tatiane Carvalho Silva - 2014 - (4).pdf: 288725 bytes, checksum: 03b444b88f588991ca31e3bf8a83dc88 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-04-30T12:10:48Z (GMT) No. of bitstreams: 5 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (1).pdf: 14395227 bytes, checksum: 9f6b9fda10331302bb12ddd5bc52052a (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (2).pdf: 20512897 bytes, checksum: 4c247b49db05cc34da871ae9d8de8659 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (3).pdf: 19405428 bytes, checksum: 36b5a6102f851dcf63f4d358963cf425 (MD5) Dissertaação - Tatiane Carvalho Silva - 2014 - (4).pdf: 288725 bytes, checksum: 03b444b88f588991ca31e3bf8a83dc88 (MD5) / Made available in DSpace on 2015-04-30T12:10:48Z (GMT). No. of bitstreams: 5 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (1).pdf: 14395227 bytes, checksum: 9f6b9fda10331302bb12ddd5bc52052a (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (2).pdf: 20512897 bytes, checksum: 4c247b49db05cc34da871ae9d8de8659 (MD5) Dissertação - Tatiane Carvalho Silva - 2014 - (3).pdf: 19405428 bytes, checksum: 36b5a6102f851dcf63f4d358963cf425 (MD5) Dissertaação - Tatiane Carvalho Silva - 2014 - (4).pdf: 288725 bytes, checksum: 03b444b88f588991ca31e3bf8a83dc88 (MD5) Previous issue date: 2014-11-07 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / Pequi is an abundant fruit in the states that have the main phosphate concentration areas in Brazil. Fatty acids are substances that act as collectors in the phosphate flotation, and are present in vegetable oils. Pequi being an oleaginous fruit, its potential as a collector can be valued and explored in the region. In this context, this study aimed to apply the pequi’s oil, extracted from white and yellow pulp of the fruit, in apatite’s froth flotation, verifying its potential to be used as collector. This Brazilian fruit is rich in fatty acids with predominance of oleic and palmitic acids. For the white pulp (outer mesocarp) application, extraction procedures were performed using Soxhlet extractor, and subsequently was executed the separation of the solvent present in the extract. The yellow pulp (inner mesocarp) oil was obtained at Goiânia’s Central Market, and was produced by a specialized company. The pequi’s yellow pulp oil was subjected to chemical characterization, with the determination of its acidity, saponification, iodine and determination of unsaponifiable matter. The verification of this oil performance as collector was performed using microflotation in Hallimond tube, by varying the concentration of the collector and the pH of the solution. The microflotation was performed with samples of pure apatite. The mineral was subjected to chemical characterization and determination of density by pycnometry. Besides pequi’s oil, tests were performed with Flotigam 5806 collector, from the company Clariant, which was used as a comparative parameter. The collectors were previously submitted to alkaline hydrolysis (saponification) for its application in froth flotation. The microflotation results were statistically analyzed using analysis of variance - ANOVA, checking if the pH and concentration factors influenced mineral recoveries. It was observed that the white pulp extract was not effective in apatite’s froth flotation. It is believed that the methods of extraction and refining were not efficient to obtain the fatty acids present in this pulp. Pequi’s yellow pulp oil obtained high recoveries of apatite in microflotation tests, similar to the results of the industrial collector used as a parameter. Therefore, saponified pequi’s oil can be an alternative collector being applied on the froth flotation of phosphate minerals. / O pequi é um fruto abundante nos estados que possuem as principais áreas de concentração de fosfato no Brasil. Os ácidos graxos são substâncias que atuam como coletores na flotação de fosfato, e estão presentes nos óleos vegetais. Sendo o pequi um fruto oleaginoso, seu potencial como coletor pode ser valorizado e explorado na região. Nesse contexto, este trabalho teve como objetivo aplicar o óleo de pequi (Caryocar brasiliense), extraído das polpas branca e amarela do fruto, no processo de flotação de apatita, verificando seu potencial para ser utilizado como coletor. Este fruto, típico do Cerrado brasileiro, possui alta incidência dos ácidos graxos oleico e palmítico. Para a aplicação da polpa branca (mesocarpo externo), realizaram-se os procedimentos de extração (utilizando extrator Soxhlet) e separação do solvente presente no extrato. O óleo da polpa amarela (mesocarpo interno), produzido por empresa especializada, foi adquirido no Mercado Central de Goiânia. O óleo da polpa amarela do pequi foi submetido à caracterização química, com a determinação dos índices de acidez, saponificação, iodo e determinação da matéria insaponificável. A verificação do desempenho deste óleo como coletor foi realizada através dos ensaios de microflotação em tubo de Hallimond, variando-se a concentração do coletor e o pH da solução. A microflotação foi realizada com amostras puras de apatita. O mineral foi submetido à caracterização química e determinação da massa específica através da picnometria. Além do óleo de pequi, foram realizados ensaios com o coletor Flotigam 5806, da empresa Clariant, o qual foi utilizado como parâmetro de comparação. Os coletores foram previamente submetidos à hidrólise alcalina (saponificação) para sua aplicação na flotação. Os resultados de microflotação foram analisados estatisticamente através da análise de variância (ANOVA), verificando se os fatores concentração e pH influenciaram nas recuperações de mineral. Observou-se que o extrato da polpa branca não foi eficiente na flotação de apatita. Acredita-se que os métodos de extração e separação extrato/solvente não tenham sido eficientes para a obtenção dos ácidos graxos presentes nesta polpa. O óleo de pequi comercializado, extraído da polpa amarela do fruto, obteve altas recuperações de apatita nos testes de microflotação, com resultados similares ao coletor industrial utilizado como parâmetro. Portanto, o óleo de pequi pode constituir uma alternativa de coletor a ser aplicado na flotação de minerais fosfáticos.

Submitted by Franciele Moreira (francielemoreyra@gmail.com) on 2017-12-14T17:27:41Z No. of bitstreams: 2 Dissertação - Izabela Letícia Almeida de Moraes - 2017.pdf: 2791313 bytes, checksum: 95bb215d71f301f1f487b1e919c6304c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-12-18T13:41:37Z (GMT) No. of bitstreams: 2 Dissertação - Izabela Letícia Almeida de Moraes - 2017.pdf: 2791313 bytes, checksum: 95bb215d71f301f1f487b1e919c6304c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-12-18T13:41:37Z (GMT). No. of bitstreams: 2 Dissertação - Izabela Letícia Almeida de Moraes - 2017.pdf: 2791313 bytes, checksum: 95bb215d71f301f1f487b1e919c6304c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-06-01 / Brazilian soils present acidity and in some parts are deficient in nutrients such as Nitrogen (N), Phosphorus (P) and Potassium (K). For the soil to be arable it is indispensable the artificial fertilization. Brazil is known worldwide for being a major producer of grains, according to the National Company of Supply (CONAB), assuming the position of the second largest soybean producer in the world in the harvest years 2015/2016. Apatite is the main natural source of phosphorus recognized as a raw material for the manufacture of fertilizers. The origin of the phosphate rock in Brazil is predominantly igneous, presenting a mineralogy containing silicate and carbonate mineral particles. Due to these gangue minerals present in the phosphate rock the flotation process becomes indispensable during the processing, to separate the apatite from the contaminants and to obtain the minimum level of impurities so that the fertilizers are produced to the required specifications. The difficult separation of the silica-carbonate ores from apatite occurs in the similarity of surface chemistry. The collecting reagent is used in the flotation process to aid in the separation of barley ores, in which the fatty acids, among them the saponified fatty acids, are those traditionally used, and the fatty acids obtained from vegetable or animal oil are matter Collector master prime. Jatropha curcas L., known as jatropha (Jatropha curcas L.), has been arousing national interest in recent years because it is a species with excellent oil quality. The cultivation of this oleaginous species occurs in several Brazilian regions, is a perennial plant and resistant to several variations of soil and climate. Jatropha stands out for the production capacity of its oil, which reaches 50% of its seeds, and for the lipid composition rich in fatty acids; Its major acids are linoleic, oleic, and palmitic. This study aims to evaluate the selectivity of the jatropha oil used as collector in the apatite, calcite and quartz flotation. And to be used as a collector the jatropha oil was characterized and tested in two methods of saponification, and the plant species was saponified at a temperature of approximately 90 oC so that in the other method the oil was saponified at room temperature. The mineral samples were chemically analyzed by X-ray fluorescence, scanning electron microscope (SEM) images, X-ray dispersive energy (EDS) spectrometry and potential zeta measurements. The test conditions were obtained using the concentrations of 1.0; 2.5; 5.0; 7.5; 10.0 mg / L in pH's 8, 9 and 10. In order to evaluate the performance of saponified jatropha oil, tests were carried out under the same conditions with the industrial collector FLOTIGAM 5806 from Clariant. The results show that cold saponified jatropha oil (PMSF) was better than hot saponified jatropha oil (PMSQ) and, when compared to the Flotigam, the results showed a similar performance. The PMSF and PMSQ collectors showed selectivity for apatite and calcite and for quartz collectors did not achieve significant recovery of the mineral. Thus, it can be concluded that jatropha oil as a collector has a potential for apatite flotation. / Os solos brasileiros apresentam acidez e em algumas partes são deficientes em nutrientes, como Nitrogênio (N), Fósforo (P) e Potássio (K). Para o solo se tornar mais fértil é indispensável a adubação artificial. O Brasil é mundialmente conhecido por ser um grande produtor de grãos, de acordo com a Companhia Nacional de Abastecimento (CONAB), assumindo o lugar de segundo maior produtor de soja do mundo na safra anos 2015/2016. A apatita é a principal fonte natural de fósforo reconhecido como matéria prima para a fabricação de fertilizantes. A origem da rocha fosfática no Brasil é predominantemente ígnea apresentando uma mineralogia contendo partículas minerais de silicato e carbonato. Devido a esses minerais de ganga presentes na rocha fosfática o processo de flotação se torna indispensável durante o beneficiamento, para separar a apatita dos contaminantes e obter o nível mínimo de impurezas para que os fertilizantes sejam produzidos seguindo as especificações exigidas. A difícil separação dos minérios sílico-carbonatado da apatita se dá à semelhança da química da superfície. O reagente coletor é usado no processo de flotação para auxiliar na separação dos minérios de ganga, em que os ácidos graxos, dentre eles os ácidos graxos saponificados, são os tradicionalmente utilizados, sendo que os ácidos graxos obtidos de óleo vegetal ou animal são a matéria prima principal do coletor. O pinhão manso, vem despertando interesse nacional nos últimos anos por ser uma espécie que apresenta um óleo de excelente qualidade. O cultivo dessa espécie oleaginosa ocorre em várias regiões brasileiras, é uma planta perene e resistente a diversas variações de solo e clima. O pinhão manso se destaca pela capacidade de produção do seu óleo, que chega a 50% de suas sementes, e pela composição lipídica rica em ácidos graxos; seus ácidos majoritários são linoleico, oleico e palmítico. Este estudo tem como objetivo avaliar a seletividade do óleo de pinhão manso utilizado como coletor na flotação apatita, calcita e quartzo. E para ser utilizado como coletor o óleo de pinhão manso foi caracterizado e testado em dois métodos de saponificação, sendo que a espécie vegetal foi saponificada em uma temperatura de aproximadamente 90 oC de modo que no outro método o óleo foi saponificado em temperatura ambiente. As amostras minerais foram analisadas quimicamente por fluorescência de raios-X (FRX), imagens de microscópio eletrônico de varredura (MEV), espectrometria de energia dispersiva de raios-X (EDS), difração de raios-X (DRX) e medidas potencial zeta (PZ). As condições dos testes foram obtidas utilizando as concentrações de 1,0; 2,5; 5,0; 7,5; 10,0 mg/L em pH’s 8, 9 e 10. Com o objetivo de avaliar a performance do óleo de pinhão manso saponificado foram realizados testes nas mesmas condições com o coletor industrial FLOTIGAM 5806 da empresa Clariant. Os resultados mostram que os coletores do óleo de pinhão manso saponificado a frio (PMSF) apresentaram melhor performance que o óleo de pinhão manso saponificado a quente (PMSQ) e, quando comparados com o Flotigam, os resultados mostraram uma performance semelhante. Os coletores PMSF e PMSQ mostraram que existe seletividade para a apatita e calcita e para o quartzo os coletores não alcançaram recuperação significativa do mineral. Desse modo, conclui-se que o óleo de pinhão manso como coletor apresenta um potencial para a flotação de apatita.

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2016-10-25T18:03:57Z No. of bitstreams: 2 Dissertação - Canuele Adamiane Tiago Pachêco - 2016.pdf: 5425547 bytes, checksum: 0db655cc600b41b3158eda2fce20cd1a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2016-10-27T17:28:23Z (GMT) No. of bitstreams: 2 Dissertação - Canuele Adamiane Tiago Pachêco - 2016.pdf: 5425547 bytes, checksum: 0db655cc600b41b3158eda2fce20cd1a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-10-27T17:28:23Z (GMT). No. of bitstreams: 2 Dissertação - Canuele Adamiane Tiago Pachêco - 2016.pdf: 5425547 bytes, checksum: 0db655cc600b41b3158eda2fce20cd1a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-09-13 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / The aim of this work was to evaluate the potential of macaúba’s pulp oil as anionic collector in flotation of apatite, comparing with industrial sinks (FLOMIN C9012 and FLOTIGAM 5806). Macaúba’s pulp oil was submitted to chemical characterization, with the determination of the levels of acidity and saponification, in addition to infrared analysis. The minerals were submitted to chemical characterization by x-ray fluorescence (FRX) mineralogical, by x-ray diffraction (DRX) and scanning electron microscope (MEV) with energy dispersive spectrometry (EDS). Zeta potential measurements were made also of minerals in solution of electrolyte indifferent (NaCl). The collectors were previously subjected to saponification by two methods, one hot and one cold. Microflotação tests were done in modified Hallimond tube with the use of pure minerals of apatite, calcite and quartz, varying the pH and the concentrations of the collecting solutions. Assessed the saponification method, times of conditioning and flotation, the recovery from the collectors, the selectivity between the minerals and the influence of pH. It was observed that the methodology of saponification by cold method proved to be more suitable. 7 min conditioning and flotation 1 min were more favorable times. Only macaúba’s pulp oil hit the recovery of 90 % established for the smallest reagent concentrations, in the three pHs. The reagents FLOMIN C9012 and FLOTIGAM 5806, reached the desired recovery using higher dosages to pick up. The apparent selectivity OPMSF introduced between the mineral apatite, calcite and quartz for the three pHs tested, and concentrations of 1.0 and 2.5 mg/L. Gave a consumption of about 842 g/t, concentrated to OPMSF and FLOMIN C9012 and 2105 g/t of concentrate to 5806 FLOTIGAM. The results of microflotação in Hallimond modified tube indicated that macaúba’s pulp oil can act satisfactorily in the flotation of apatite. The economic analysis showed that in addition to gains against the cost of industrial collectors the OPMSF has advantages over the volume of consumption to FLOTIGAM 5806. / O objetivo deste trabalho foi avaliar o potencial de aplicação de óleo da polpa da macaúba como coletor aniônico na flotação de apatita, comparando com coletores industriais (FLOMIN C9012 e FLOTIGAM 5806). O óleo da polpa da macaúba foi submetido à caracterização química, com a determinação dos índices de acidez e saponificação, além de análise por infravermelho. Os minerais foram submetidos à caracterização química por fluorescência de raios-X (FRX), mineralógica por difração de raios-X (DRX) e imagens de microscópio eletrônico de varredura (MEV) com espectrometria de energia dispersiva de raios-X (EDS). Também foram realizadas medidas potencial zeta dos minerais em solução de eletrólito indiferente (NaCl). Os coletores foram previamente submetidos à hidrólise alcalina por duas métodos, um a frio e outro a quente. Testes de microflotação foram feitos em tubo de Hallimond modificado com o uso dos minerais puros de apatita, calcita e quartzo, variando o pH e as concentrações das soluções coletoras. Avaliou-se o método de saponificação, os tempos de condicionamento e flotação, a recuperação obtida com os coletores, a seletividade entre os minerais e a influência do pH. Observou-se que a metodologia de saponificação pelo método a frio mostrou-se mais adequada. O condicionamento de 7min e 1min de flotação foram os tempos mais favoráveis. Somente o óleo da polpa de macaúba saponificados a frio atingiu a recuperação estabelecida de 90 % para as menores concentrações do reagente, nos pHs 8, 9 e 10. Os reagentes FLOMIN C9012 e FLOTIGAM 5806, atingiram a recuperação desejada utilizando dosagens superiores ao coletor pesquisado. O OPMSF apresentou seletividade aparente entre os minerais de apatita, calcita e quartzo para os três pH’s testados e, em concentrações de 1,0 e 2,5 mg/L. Obteve-se um consumo de aproximadamente 842 g/t de concentrado para OPMSF e FLOMIN C9012 e 2.105 g/t de concentrado para o FLOTIGAM 5806. Os resultados de microflotação em tubo de Hallimond modificado indicaram que o óleo da polpa da macaúba pode atuar satisfatoriamente na flotação de apatita. A análise econômica mostrou que além dos ganhos relação ao custo dos coletores industriais o OPMSF possui vantagens sobre o volume de consumo para o FLOTIGAM 5806.

Extensive research has been performed on the interaction of dithiocarbonates (xanthate) with a wide variety of substrates. This study the focuses on the interaction of trithiocarbonates (TTC) with pyrite and copper. The mechanism of adsorption of the xanthate is compared to that of the TTC. For the xanthate to adsorb it is necessary for an oxidant to be present, since xanthate adsorbs via charge transfer processes (electrochemical processes). It was found by the use of cyclic voltammetry and contact angle measurements that collector adsorption of the TTC can occur in both oxidising and reducing (thus the absence of an oxidant) conditions. Neither the TTC monomer nor the dimer could be detected on the surface by the use of Raman spectroscopy. The collector species on the surface was the TTC decomposition products namely the thiol or thiolate. Electrochemical impedance spectroscopy (EIS) confirmed that the TTC can interact under oxidising and reducing conditions. EIS showed that the rate of adsorption of the collector species for anodic currents increases relatively to the rate of adsorption for cathodic currents. Different adsorption mechanisms are realised for the different polarisation conditions. It is postulated that the TTC species serves as an intermediate for the adsorption of the thiol or thiolate on the surface, ultimately rendering the surface hydrophobic. Decomposition tests, performed by employing UV/Vis spectroscopy, indicated that the TTC is very unstable between a pH of 4 and 11. The thiol or thiolate however does not readily adsorb onto the substrates (indicated by the EIS measurements). Microflotation tests confirmed the thiolate’s inability to render pyrite hydrophobic. The microflotation tests also indicated that the TTC became less effective in recovering pyrite after it was left to decompose for a couple of hours. / Dissertation (MSc (Metallurgy))--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

Previous mineralogical investigations (QemSCAN) performed on all effluent flotation streams of Mimosa mine (Zimbabwe) indicated the presence of appreciable amounts of platinum group minerals (PGMs), which are not recovered. Most, generally in excess of 70%, of the liberated PGMs in these streams belonged to the Pt-Pd-Bi-Te class in all the samples investigated. In the first part of this work, electrochemical investigations, electrochemically-controlled contact angle measurements and Raman spectroscopy have been employed to investigate the interaction of ethyl xanthate with Pd-Bi-Te and PtAs2. Impedance measurements showed lower capacitance values in solutions containing KEX indicating the formation of a continuous surface layer. Anodic and cathodic polarization diagrams show the mixed potential to be higher than the reversible potential of the xanthate-dixanthogen equilibrium reaction, hence the formation of dixanthogen on the surface is possible. Electrochemically controlled in situ Raman spectroscopy has confirmed the co-presence of xanthate with dixanthogen indicating that xanthate retains its molecular integrity when it adsorbs on the surface of the Pd-Bi-Te. The result of this investigation has shown dixanthogen to be present on both the minerals (PtAs2 and Pd-Bi-Te) when the surfaces are anodically polarized. Chemisorbed xanthate could be identified within 120 seconds yielding a hydrophobic surface as indicated by electrochemically-controlled contact angle measurements. Maximum contact angles of 63o were measured in the case Pd-Bi-Te. As a result the mineral surface is expected to be hydrophobic and a lack of collector interaction with the mineral is not the reason for low PGM recoveries experienced. Secondly, the flotation recovery of synthetically prepared Pd-Bi-Te was compared with that of chalcopyrite (a typical fast-floating mineral) and pyrrhotite (a typical slow-floating mineral), with microflotation tests. These indicated Pd-Bi-Te to be a fast-floater with flotation rates exceeding that of chalcopyrite. Predicted flotation rate constants (from the Ralston model) were significantly lower for small particles (with diameters similar to those lost to the effluent streams) compared with those of particle with intermediate sizes. This supports the suggestion that losses to effluent streams are caused by particle size effects. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

Extensive research has shown that electrochemistry is one of the factors that govern the flotation of sulfide minerals. Flotation is often adversely affected by uncontrolled oxidation, which is also an electrochemical process. The interest in pyrrhotite recovery arose after observing that there is a substantial loss of PGM due to the depression of pyrrhotite and the subsequent loss of any PGMs associated with it. The first part of this study focuses on the influence of chemical composition and crystal structure on the electrochemical behaviour of pyrrhotite in a 0.05 M Na2B4O7 solution. Rest potential and polarisation resistance measurements, as well as anodic polarisation diagrams, showed that the magnetic 4C type pyrrhotite is anodically more reactive than the non-magnetic 6C type pyrrhotite. It was also shown in cathodic polarisation diagrams that the non-magnetic 6C type pyrrhotite is a better substrate for oxygen reduction and is less susceptible to oxidation. ToF-SIMS showed the formation of an oxide layer on the pyrrhotite surface after oxidation. In the second part of this work, the influence of galvanic interactions on the electrochemical behaviour of pyrrhotite in contact with pentlandite was investigated. It was observed that, under oxygen-saturated conditions, as the amount of pentlandite increases, the reactivity towards oxidation of the mixed mineral system is reduced. Impedance measurements showed a decrease in capacitance values, indicating the formation of a continuous oxide layer on the surface and an increase in oxide layer thickness with decreasing pentlandite content. Anodic polarisation diagrams showed that under oxygen-deficient conditions and in the low potential region, pentlandite behaves as an inert material and does not have an influence on the oxidation behaviour of pyrrhotite. Hence, the anodic activities of the different magnetic 4C type pyrrhotites from Sudbury Gertrude, Phoenix and Russia were compared. It was shown that the oxidation reactivity decreased in the following order: Sudbury Gertrude magnetic 4C pyrrhotite > Phoenix magnetic 4C pyrrhotite > Russian magnetic 4C pyrrhotite; it also varied according to location. In the transpassive region, higher anodic currents were observed on the mixed samples because both pentlandite and pyrrhotite reacts. The reactivity increased in the order: pure pyrrhotite (Russia) < medium-pentlandite (Sudbury Gertrude) < high-pentlandite (Phoenix). In the presence of potassium ethyl xanthate, there was no change in the initial anodic reactivities of the different pyrrhotites. The anodic polarisation diagrams of the pure and mixed samples showed a reduction in the maximum anodic peak current, suggesting the presence of xanthate on the surface, which hinders oxidation of the mineral surface. In addition, the influence of cleaning of oxidised pyrrhotite with gaseous carbon dioxide was studied, using electrochemical and microflotation measurements. Electrochemical measurements indicated that CO2 treatment resulted in depassivation of the oxidised surfaces; this was supported by ToF-SIMS measurements that demonstrated a reduction in the oxide layer thickness after CO2 treatment. Anodic polarisation diagrams showed a higher anodic peak current, indicating that the surface is more reactive. Gaseous carbon dioxide conditioning of oxidised pyrrhotite resulted in improved flotation response of pyrrhotite with the aid of copper activation and higher air flow rate. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted