Orientador: Matthieu Tubino / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T12:56:08Z (GMT). No. of bitstreams: 1 Queiroz_CarlosAlbertodaRocha_M.pdf: 1138911 bytes, checksum: 67f676e059efece3b6d64b209273d054 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho foram desenvolvidos dois procedimentos de análise quantitativa em fluxo, um para níquel e o outro para sulfato, usando a refletância difusa na região do visível. O primeiro sistema químico estudado faz uso da clássica reação de níquel (II) com dimetilglioxima em meio alcalino amoniacal, formando o precipitado de cor rosa forte, Ni(DMG)2. Este precipitado, como se sabe, é bastante volumoso e adere facilmente às paredes do recipiente onde se encontra. Também, coagula rapidamente formando aglomerados. Estas características já desqualificam, em princípio, este precipitado para uso em sistemas de fluxo, por anunciarem problemas de entupimento nas tubulações e problemas de aderência nas janelas da cela de medida colorimétrica, se esta for a técnica usada. No presente trabalho logrou-se contornar todos estes problemas utilizando-se um sistema de fluxo muito simples. A cela desenvolvida para medidas de refletância foi construída em PTFE branco, sendo nela inseridos o detector (LDR) e emissor de luz (LED verde). O LED foi alimentado com uma fonte com voltagem adequada e o LDR foi introduzido numa ponte de Wheatstone que forneceu as medidas analíticas. Dentro desta cela foi colocado um tudo de vidro, conectado à tubulação do sistema de fluxo, onde passava o precipitado suspenso no carregador. As medidas analíticas de refletância foram feitas na cela contendo esta suspensão. O segundo sistema químico estudado foi a reação de sulfato com íons bário, formando o precipitado branco de sulfato de bário. A aplicação desta reação de precipitação em sistemas de fluxo já foi estudada, por outros autores, em medidas turbidimétricas e nefelométricas. Nossa intenção, ao usar esta reação de precipitação, foi de verificar a coerência do sistema de fluxo desenvolvido neste trabalho com aqueles da literatura, particularmente com o procedimento turbidimétrico. A cela de refletância usada para o sistema com sulfato é semelhante àquela acima descrita para a determinação de níquel. A diferença é que no presente caso o PTFE usado para a confecção do corpo da cela é preto. Esta escolha teve por intenção diminuir a refletância da luz nas suas paredes internas. Nos dois sistemas estudados, os resultados foram muito satisfatórios inclusive quando aplicados em amostras reais. / Abstract: Two flow quantitative analytical systems were developed in this work, using the diffuse reflectance in the visible region of the spectrum: one for the analysis of nickel and the other for the analysis of sulfate. The first studied chemical system used the classical analytical reaction of nickel (II) with dimethylglyoxime in presence of ammonia, forming a pink precipitate, Ni(DMG)2. This precipitate, as currently known, is volumous and easily adheres to the walls of the recipient where it is placed. Also, it easily coagulates forming agglomerates. These characteristics are enough to disqualify this precipitate for application in flux analytical systems, as they announce problems with clogging of the tubes and problems with the adherence on the cell windows if this detecting technique was used. In this work, we succeeded avoid these problems using a very simple flux system. The developed reflectance cell was constructed in white PTFE. The light emitter (green LED) and the light detector (LDR) were placed in its body. The energy was furnished to the LED by a power supplier and the LDR was introduced in a Wheatstone bridge which gave the analytical signal. Into the PTFE cell was placed a glass tube, connected to the flow system, where flowed the carrier with the suspended precipitate. The analytical reflectance measurements were done in the cell containing this suspension. The second chemical system studied was the well known reaction of sulfate with barium ions, forming the precipitate of barium sulfate. The use of this reaction in flux systems was already studied by other authors, with turbidimetric and nephelometric measurements. Our intention, when we select this precipitation reaction, was to verify the coherence among the flux system developed in this work with those already related, particularly with the turbidimetric procedure. The reflectance cell used in the sulfate system is similar to that above described for the determination of nickel. The difference is that in this cell black PTFE was used in order to decrease the reflectance of the light in the internal walls. In the two studied systems the results were quite satisfactory, also when real samples were analyzed. / Mestrado / Quimica Analitica / Mestre em Química

The performance of a growing sulphate reducing bacteria consortium for Sr2+, Co2+ and Cs+ removal from solution in a batch sulphidogenic bioreactor was investigated. Metal removal by the growing bacterial consortium, and microbial culture growth and metabolic activities (biological sulphate removal) were continuously monitored in the bioreactors over the duration of the treatment period. On the other hand, diversity changes within the bacterial consortium before and after bioreactor operation (28 days) were performed using the partial 16S rRNA fingerprinting method. In the original bacterial consortium, Enterococcus and Staphylococcus sp. were the dominant bacterial species. However, the presence of Sr2+, Co2+ and Cs+ in the growth media, resulted in the emergence of new bacterial species belonging to the Citrobacter, Paenibacillus, and Enterococcus and Stenotrophomonas genera, respectively. The Citrobacter and Paenibacillus sp. demonstrated high tolerance towards the presence of the divalent cations, Sr2+ and Co2+, respectively, while the Enterococcus and Stenotrophomonas sp., demonstrated Cs+ high tolerance. The bacterial growth and sulphate removal rate were significantly decreased at initial metal ion concentrations ≥100 mg/L. The toxicity and inhibitory effects of the metals on the present SRB consortium was observed in the order Sr>Co>Cs. The metal uptake capacity (qτ) of the bacterial consortium decreased with increasing initial metal concentration, and complete Sr2+, Co2+ and Cs+ removal was observed at initial metal concentrations ≤75 mg/L. Overall, the present SRB consortium demonstrated a superior Sr2+ removal capacity (qmax= 405 mg/g), and the least for Cs2+, where qmax = 192 mg/g. The present SRB culture exhibited a superior Sr+ and Cs+ binding capacity, compared to other studies in literature. Results from Sr2+, Co2+ and Cs+ biosorption kinetics indicate that initial concentration and solution pH played a vital role in determining the rate of metal removal kinetics. The experimental data was successfully analysed by the pseudo-second-order rate model, demonstrating that chemisorption is the main rate limiting step for the removal of Sr2+, Co2+ and Cs+ from solution. In this study, the adsorption behaviour of protons and of Sr2+, Co2+ and Cs+ onto the bacterial consortium cell surfaces was evaluated under anaerobic conditions as a function of pH (4-10), ionic strength (0.01, 0.05, 0.1M) and temperature (25, 50 and 75°C). Acid-base titrations of the bacterial suspension indicated that the titration data could be adequately described by a four site non-electrostatic model, with pKa values of 4.41, 6.69, 8.10 and 10. The Sr2+, Co2+ and Cs+ adsorption data could be fitted with a two site non-electrostatic model, involving the type 1 and 2 sites (carboxylic and phosphoryl sites). Increasing the ionic strength had a negative effect on the adsorption of metal ions from solution. There was no observed temperature dependence on the adsorption of Co2+ and Cs+ from solution. In summary, results obtained in this study have shown that the processes involved in microbial Sr2+, Co2+ and Cs+ removal from contaminated sources is a direct function of the microbial characteristics and efficiency, mass transfer and surface complexation effects under varying environmental conditions. One important goal to be achieved in future studies will be the determination of the intrinsic stability constants and the structure of the formed metal complexes species. These constants can be used directly in risk assessment programs. / Thesis (PhD(Eng))--University of Pretoria, 2011. / Chemical Engineering / unrestricted

This research project investigated the high concentration of sulphate in a tailing pond at LKAB and the characteristics and behavior of sulphate minerals in different areas of the pond. The sampling of the tailings was carried out at Nine stationary sampling points. Each sample was taken from the surface to a depth of one meter except for the underflow sample which was collected from the thickener in the processing plant (fresh tailings). Stereo microscopy and SEM-EDS analysis aid in identifying mineral grains and confirming the presence of Gypsum and/or Anhydrite, along with other minerals like Pyrite, Pyrrhotite, and Chalcopyrite. The difficulty in distinguishing between Gypsum and Anhydrite under SEM was noted due to their similar crystal shapes and chemical composition. Gypsum and/or Anhydrite were identified as the main minerals responsible for the high sulphate concentration based on elemental screening, sequential extraction, and mineralogical results. Sulfide minerals like Pyrite, Chalcopyrite, and Pyrrhotite were also present but did not show any signs of weathering characteristics and therefore probably not contributed to the high sulphate concentration in the pond. The quantitative mineralogy carried out confirmed the presence of Gypsum and/or Anhydrite, Pyrite, Pyrrhotite and Chalcopyrite as identified in the mineralogical analysis. The study concludes that Gypsum and/or Anhydrite are the main contributors to the high sulphate concentration in the LKAB tailings pond.

Graduation date: 1994

No description available.

No description available.

No description available.

The pollution of South Africa’s water resources puts a strain on an already stressed natural resource. One of the main pollution sources is industrial effluents such as acid mine drainage (AMD) and other mining effluents. These effluents usually contain high levels of acidity, heavy metals and sulphate. A popular method to treat these effluents before they are released into the environment is lime neutralisation. Although this method is very effective to raise the pH of the effluent as well as to precipitate the heavy metals, it can only partially remove the sulphate. Further treatment is required to reduce the sulphate level further to render the water suitable for discharge into the environment. A number of sulphate removal methods are available and used in industry. These methods can be divided into physical (membrane filtration, adsorption/ion exchange), chemical (chemical precipitation) and biological sulphate reduction processes. A literature study was conducted in order to compare these different methods. The ABC (Alkali – Barium – Calcium) Desalination process uses barium carbonate to lower the final sulphate concentration to an acceptable level. Not only can the sulphate removal be controlled due to the low solubility of barium sulphate, but it can also produce potable water and allows valuable by–products such as sulphur to be recovered from the sludge. The toxic barium is recycled within the process and should therefore not cause additional problems. In this study the sulphate removal process, using barium carbonate as reactant, was investigated. Several parameters have been investigated and studied by other authors. These parameters include different barium salts, different barium carbonate types, reaction kinetics, co–precipitation of calcium carbonate, barium–to–sulphate molar ratios, the effect of temperature and pH. The sulphate removal process was tested and verified on three different industrial effluents. The results and conclusions from these publications were used to guide the experimental work. A number of parameters were examined under laboratory conditions in order to find the optimum conditions for the precipitation reaction to take place. This included mixing rotational speed, barium–to–sulphate molar ratio, initial sulphate concentration, the effect of temperature and the influence of different barium carbonate particle structures. It was found that the reaction temperature and the particle structure of barium carbonate influenced the process significantly. The mixing rotational speed, barium–to–sulphate dosing ratios and the initial sulphate concentration influenced the removal process, but not to such a great extent as the two previously mentioned parameters. The results of these experiments were then tested and verified on AMD from a coal mine. The results from the literature analysis were compared to the experiments conducted in the laboratory. It was found that the results reported in the literature and the laboratory results correlated well with each other. Though, in order to optimise this sulphate removal process, one has to understand the sulphate precipitation reaction. Therefore it is recommended that a detailed reaction kinetic study should be conducted to establish the driving force of the kinetics of the precipitation reactions. In order to upgrade this process to pilot–scale and then to a full–scale plant, continuous reactor configurations should also be investigated. The sulphate removal stage in the ABC Desalination Process is the final treatment step. The effluent was measured against the SANS Class II potable water standard and was found that the final water met all the criteria and could be safely discharged into the environment. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

The pollution of South Africa’s water resources puts a strain on an already stressed natural resource. One of the main pollution sources is industrial effluents such as acid mine drainage (AMD) and other mining effluents. These effluents usually contain high levels of acidity, heavy metals and sulphate. A popular method to treat these effluents before they are released into the environment is lime neutralisation. Although this method is very effective to raise the pH of the effluent as well as to precipitate the heavy metals, it can only partially remove the sulphate. Further treatment is required to reduce the sulphate level further to render the water suitable for discharge into the environment. A number of sulphate removal methods are available and used in industry. These methods can be divided into physical (membrane filtration, adsorption/ion exchange), chemical (chemical precipitation) and biological sulphate reduction processes. A literature study was conducted in order to compare these different methods. The ABC (Alkali – Barium – Calcium) Desalination process uses barium carbonate to lower the final sulphate concentration to an acceptable level. Not only can the sulphate removal be controlled due to the low solubility of barium sulphate, but it can also produce potable water and allows valuable by–products such as sulphur to be recovered from the sludge. The toxic barium is recycled within the process and should therefore not cause additional problems. In this study the sulphate removal process, using barium carbonate as reactant, was investigated. Several parameters have been investigated and studied by other authors. These parameters include different barium salts, different barium carbonate types, reaction kinetics, co–precipitation of calcium carbonate, barium–to–sulphate molar ratios, the effect of temperature and pH. The sulphate removal process was tested and verified on three different industrial effluents. The results and conclusions from these publications were used to guide the experimental work. A number of parameters were examined under laboratory conditions in order to find the optimum conditions for the precipitation reaction to take place. This included mixing rotational speed, barium–to–sulphate molar ratio, initial sulphate concentration, the effect of temperature and the influence of different barium carbonate particle structures. It was found that the reaction temperature and the particle structure of barium carbonate influenced the process significantly. The mixing rotational speed, barium–to–sulphate dosing ratios and the initial sulphate concentration influenced the removal process, but not to such a great extent as the two previously mentioned parameters. The results of these experiments were then tested and verified on AMD from a coal mine. The results from the literature analysis were compared to the experiments conducted in the laboratory. It was found that the results reported in the literature and the laboratory results correlated well with each other. Though, in order to optimise this sulphate removal process, one has to understand the sulphate precipitation reaction. Therefore it is recommended that a detailed reaction kinetic study should be conducted to establish the driving force of the kinetics of the precipitation reactions. In order to upgrade this process to pilot–scale and then to a full–scale plant, continuous reactor configurations should also be investigated. The sulphate removal stage in the ABC Desalination Process is the final treatment step. The effluent was measured against the SANS Class II potable water standard and was found that the final water met all the criteria and could be safely discharged into the environment. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

External sulphate attack on concrete can lead to cracking, expansion and sometimes loss of cohesiveness of hardened cement paste. Therefore, aside from using sulphate resistant cementitious binders, it is important to design concrete which can resist sulphate penetration. In this research, both ASTM C1202 and NT Build 492 electrical migration tests were modified such that sulphate rather than chloride penetration resistances were measured. Modifications included exposing concrete specimens to Na2SO4 rather than NaCl solutions and measuring the depth of sulphate penetration visually using BaCl2+KMnO4 rather than AgNO3 solution. Nine concrete mixtures of varying w/cm, slag replacement and cement types were tested in both original standard tests and modified tests to evaluate the influence of these material variables on test results and compare chloride to sulphate results. It was found that while migration coefficients and total charge passing were lower for sulphate, the influence of material variables were relatively similar.