Os depósitos de carvão no Brasil possuem conteúdos relativamente baixos de matéria orgânica. Aproximadamente 65% do carvão ROM (Run-of-min) extraído de minas subterrâneas na região carbonífera de Santa Catarina são descartados como resíduo em depósitos de rejeitos. Esse rejeito contem minerais sulfetados, principalmente a pirita, que oxida e pode gerar drenagem ácida de minas, com diversos impactos ambientais e custos econômicos. Entretanto, com o processamento do rejeito de carvão para concentração da pirita, esta pode-se tornar matéria prima para diversos produtos, entre eles o ácido sulfúrico (insumo deficitário no país, utilizado em grandes quantidades na indústria de fertilizantes). O objetivo deste trabalho foi caracterizar o rejeito de carvão para concentração da pirita proveniente da camada Bonito, no estado de Santa Catarina, avaliando-se o seu potencial uso na produção de ácido sulfúrico e os ganhos ambientais com a dessulfurização do material remanescente. Para isso, foram construídas as curvas de separabilidade densimétrica de uma amostra de rejeito grosso e de uma amostra de rejeito fino. Definiram-se densidades de cortes, de forma a recuperar um material carbonoso remanescente (d<2,2), um material dessulfurizado (2,2<d<2,7) e um concentrado de pirita (d>2,7). Efetuou-se a caracterização das frações densimétricas através de imagens fotográficas e análises de cinzas, enxofre, umidade, poder calorífico, difração de raio-x (DRX), fluorescência de raio-x (FRX) e análise termogravimétrica. As análises ambientais realizadas foram: classificação de resíduos conforme NBR 10.004 e teste estático de predição de acidez pelo método de contabilização de ácidos e bases. Estimou-se a produção de ácido sulfúrico a partir do concentrado piritoso obtido com o processamento do rejeito de carvão das camadas Barro Branco e Bonito e avaliaram-se os ganhos ambientais. Os resultados demonstraram que o rejeito proveniente do circuito de grossos (87,2% do material descartado) possui teor de enxofre de 7,8% e 79,9% de cinzas, já os finos (12,8% do material) tem um teor de enxofre de 4,9% e 70,8% de cinzas. Com a separação densimétrica do rejeito em 2,2 e 2,7, obteve-se uma fração d<2,2 g/cm³ com recuperação mássica de 20,7% para os grossos e 45,2% para os finos que só possui aproveitamento energético em termoelétricas se misturado com carvão de baixo enxofre. O material dessulfurizado (2,2<d<2,7 g/cm³) corresponde a 66% em massa do rejeito para os grossos, possui 3,8% de enxofre e potencial de geração de acidez 60% inferior ao rejeito original. Já a fração pirítica (d>2,7 g/cm³) possui recuperação mássica de 13% para os grossos e teor de enxofre de 33,1%. Quando comparada com a camada Barro Branco, a camada Bonito apresenta níveis superiores de S na fração intermediária, com maior potencial de geração de acidez. De qualquer forma, os rejeitos de carvão grossos, tanto da Camada Barro Branco como Bonito, são passíveis de beneficiamento por processos gravimétricos para obtenção de concentrados com no mínimo 30% de enxofre. Caso houvesse um planejamento global de aproveitamento da pirita na região carbonífera de Santa Catarina para produção de ácido sulfúrico, um acréscimo de 14% da demanda brasileira deste insumo poderia ser realizado com os atuais níveis de produção de carvão, reduzindo em até 75% o enxofre disposto no ambiente e trazendo benefícios econômicos e ambientais à região carbonífera de Santa Catarina. / The grade of coal deposits in Brazil is relatively low, and approximately 65% of the run-of-mine (ROM) coal extracted from underground mines in the carboniferous region of Santa Catarina is discarded as waste in dump deposits. These waste discards contain sulfide minerals, particularly pyrite, which oxidize and give rise to acid rock drainage (ARD) with recognized environmental impacts and economic costs. However, the coal waste could be gravimetrically processed to produce a pyrite concentrate to be used as a raw material for sulfuric acid production (an income with deficient production in the country, largely used in fertilizer industry). The aim of this work was to study the coal waste from the Bonito seam in the state of Santa Catarina, Brazil, evaluating its use for the production of sulfuric acid and the environmental implications of remaining material after the desulfurizing step. Washability curves of coarse and fine waste material from a coal preparation plant working with the Bonito seam was performed. Three different density fractions were separated: a carbonaceous material (d<2.2 g/cm3), a desulfurized material (2.2 and 2.7 g/cm³), and a pyrite concentrate (d>2.7 g/cm³). Characterization studies were carried out by photographic images and ash, sulfur, moisture, calorific value, X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermogravimetric analysis (TGA). Environmental classification of the waste was conducted in terms of NBR 10.004 and static acid prediction test by the acid-base accounting method. It was also estimated the production of sulfuric acid from Barro Branco and Bonito seams as well the environmental benefits of such desulfurization procedures. The results showed that the coarse fraction of coal tailing from Bonito seam (87.2% of the discarded mass) presents 7.8% sulfur and 79.9% ash. The fine waste fraction from the spirals circuit (12.8% of the discarded mass) showed 4.9% sulfur and 70.8% ash. Both materials were subjected to density separation. The fraction d<2.2 g/cm³, with a mass recovery of 20.7% for the coarse fraction and 45.2% for the fine fraction, could be only used for energy production if a moisture with low sulfur coal was provided. The intermediate density material (2.2<d<2.7 g/cm³), which corresponds to a 66% of the mass coarse mass fraction and presents 3.8% sulfur, have a 60% lower acid generation material than the raw waste. The pyrite concentrate (d>2,7) reached a 13% mass recovery with 33.1% sulfur. Comparing the Barro Branco and Bonito seams, the Bonito seam showed superior levels of sulfur in the 2.2<d<2.7 g/cm³ fraction, with a higher an acid generation potential. Nevertheless, the coarse fraction of both seams can be processed for pyrite concentration, reaching the minimum of 30% sulfur necessary for sulfuric acid production by roasting. Considering the levels of coal production in the carboniferous region of Santa Catarina, an input of 14% in the national demand of sulfuric acid would by supplied. This procedure will also reduce in 75% the pyrite disposed in landfills, bringing economic and environmental benefits to the local coal chain production.

O presente trabalho teve como objetivo desenvolver um protótipo para a produção hidrometalúrgica de sulfato ferroso heptahidratado (FeSO4.7H2O – melanterita). A matéria prima foi um concentrado de pirita obtido a partir de rejeitos do beneficiamento de carvão mineral. Construiu-se, em escala piloto, uma planta de lixiviação com 300 kg de um concentrado com 73,2% de pirita. Nesta unidade, realizou-se uma etapa de lixiviação com água, em circuito fechado, sob condições aeróbias, com o intuito de se obter um extrato aquoso rico em íons férrico e sulfato. A seguir, procederam-se mudanças no sistema de forma a estabelecer uma condição anaeróbia ao meio, transformando os íons férricos em ferrosos. O lixiviado, rico em Fe2+, foi precipitado na forma de sulfato ferroso heptahidratado pela adição de etanol. Esse precipitado foi submetido a uma etapa de recristalização, obtendo-se cristais de melanterita de maior pureza. Ambos os produtos foram caracterizado por análise química elementar e difração de raios X. Os cristais de melanterita recristalizados apresentaram alta pureza, com qualidade para uso químico e farmacêutico. Assim, desenvolveu-se uma nova rota para produção de sulfato ferroso tendo como matéria-prima um concentrado de pirita da mineração de carvão (usualmente o sulfato ferroso é produzido como coproduto da produção de ilmenita e aço). A tecnologia apresenta uma elevada conversão do ferro lixiviado em melanterita e os insumos necessários são pirita, água e álcool etílico. A proposta abre uma nova possibilidade de uso dos rejeitos de carvão e a possibilidade de comercialização de outro produto na cadeia produtiva de carvão mineral. / The aim of this work was to develop a prototype for hydrometallurgical production of ferrous sulfate heptahydrate crystals (FeSO4.7H2O – melanterite). The raw material was a pyrite concentrate obtained from a coal tailing. The leaching system was assembled in pilot scale with 300 kg of a concentrate with 73.2% pyrite. Initially, it was carried out a leaching step in aerobic conditions with the purpose to obtain an aqueous solution rich in ferric ions and sulfate. Next, modifications were proceeded to establish an anaerobic condition in the reactor, converting the ferric to ferrous ions. Ethanol was added to the leaching solution to provide the precipitation of the Fe2+ and sulfate as ferrous sulfate heptahydrate. The ferrous sulfate precipitate was recrystallized, allowing producing melanterite crystals of higher purity. The crystals were characterized in terms of chemical and mineralogical composition. The process allowed producing crystals with a high purity attending chemical and pharmaceutical purposes. Thus, it was developed a process to produce ferrous sulfate from coal wastes (usually, ferrous sulfate crystals are produced as a co product from titanium dioxide and steel production). The technology presents a high conversion factor of soluble Fe2+ to melanterite and the necessary incomes are pyrite, water, and ethylic alcohol. The hydrometallurgical technique applied in this study allowed production of a commercial grade product from coal mining waste material.

A presente pesquisa teve por objetivo a análise do comportamento de diferentes combinações de liners de um determinado solo com e sem cimentação, submetidos à percolação de líquidos ácidos, com o objetivo de simular o comportamento de campo de liners de aterros especiais, que recebem resíduos à base de pirita. Tal resíduo em contato com água e oxigênio forma solução de ácido sulfúrico. Assim sendo, as pretensões deste trabalho foram a análise do comportamento compressivo de liners formados por um dado tipo de solo compactado, com e sem a adição de cimento, através do emprego de um equipamento de adensamento modificado desenvolvido especialmente para esta pesquisa. Da mesma forma, procedeu-se o estudo dos fenômenos de transporte de contaminantes por meio do liner em estudo, basicamente daqueles que comandam o transporte (difusão, advecção, sorção, retardamento da frente de contaminação e grau de afinidade entre o contaminante e o liner). Ensaios isotrópicos a altas tensões de confinamento também foram realizados a fim de se estudar a possível desestruturação dos liners quando percolados por resíduos ácidos. Os resultados obtidos destacam a desestruturação de amostras naturais do solo estudado quando percolado por rejeitos ácidos, em todas as concentrações estudadas, tanto em ensaios triaxiais isotrópicos quanto em ensaios de carregamento axial com deformações laterais nulas. Conclui-se que as águas ácidas quando percoladas por meio de um solo com presença de finos, tende a proporcionar um efeito de carreamento de partículas, aumentando conseqüentemente a porosidade, fator este que poderia proporcionar a falha operacional de um liner. / The objective of this work is to analyse the behavior of a liner formatted by different combinations of soil and cement, percolated by low pH waters under different hydraulic gradients and concentration of acid in the percolant, aiming to simulate in laboratory what would happen in the field to liners in contact with pyrite wastes, from mineral coal mining. Pyrite wastes in contact with water and oxygen result in sulphuric acid, what makes the objective of this research the study of the compressive behavior of the liner submitted to the percolation of acid waters, by means of a special column equipment developed during this research, which allows applying an axial load to the sample under flux. Also, the variation of the transport of contaminants values were investigated, basically diffusion, advection, sorption, retardation coefficient, distribution coefficient, hydrodynamic dispersion, ground water velocity and hydraulic conductivity). Triaxial Isotropic tests were carried out under high confinant pressures in order to verify the volume changes of the samples due to the low-pH contamination. The results show that liners formatted only by soil had rearrange of their structure due to acid percolations, according to both column and isotropic tests. The value of the hydrodynamic dispersion was considerated being totally dependent on the diffusion, because the hydraulic conductivity of the differente combination was low. The results also show that low-pH percolations make a rearrange of the fine particles into the sample, because after a grain size distribution test, the fine particles from the top of the samples were detected on the bottom of the sample, what increase the porosity on the top of the samples, what could lead the liner to a failure.

A presente pesquisa teve por objetivo a análise do comportamento de diferentes combinações de liners de um determinado solo com e sem cimentação, submetidos à percolação de líquidos ácidos, com o objetivo de simular o comportamento de campo de liners de aterros especiais, que recebem resíduos à base de pirita. Tal resíduo em contato com água e oxigênio forma solução de ácido sulfúrico. Assim sendo, as pretensões deste trabalho foram a análise do comportamento compressivo de liners formados por um dado tipo de solo compactado, com e sem a adição de cimento, através do emprego de um equipamento de adensamento modificado desenvolvido especialmente para esta pesquisa. Da mesma forma, procedeu-se o estudo dos fenômenos de transporte de contaminantes por meio do liner em estudo, basicamente daqueles que comandam o transporte (difusão, advecção, sorção, retardamento da frente de contaminação e grau de afinidade entre o contaminante e o liner). Ensaios isotrópicos a altas tensões de confinamento também foram realizados a fim de se estudar a possível desestruturação dos liners quando percolados por resíduos ácidos. Os resultados obtidos destacam a desestruturação de amostras naturais do solo estudado quando percolado por rejeitos ácidos, em todas as concentrações estudadas, tanto em ensaios triaxiais isotrópicos quanto em ensaios de carregamento axial com deformações laterais nulas. Conclui-se que as águas ácidas quando percoladas por meio de um solo com presença de finos, tende a proporcionar um efeito de carreamento de partículas, aumentando conseqüentemente a porosidade, fator este que poderia proporcionar a falha operacional de um liner. / The objective of this work is to analyse the behavior of a liner formatted by different combinations of soil and cement, percolated by low pH waters under different hydraulic gradients and concentration of acid in the percolant, aiming to simulate in laboratory what would happen in the field to liners in contact with pyrite wastes, from mineral coal mining. Pyrite wastes in contact with water and oxygen result in sulphuric acid, what makes the objective of this research the study of the compressive behavior of the liner submitted to the percolation of acid waters, by means of a special column equipment developed during this research, which allows applying an axial load to the sample under flux. Also, the variation of the transport of contaminants values were investigated, basically diffusion, advection, sorption, retardation coefficient, distribution coefficient, hydrodynamic dispersion, ground water velocity and hydraulic conductivity). Triaxial Isotropic tests were carried out under high confinant pressures in order to verify the volume changes of the samples due to the low-pH contamination. The results show that liners formatted only by soil had rearrange of their structure due to acid percolations, according to both column and isotropic tests. The value of the hydrodynamic dispersion was considerated being totally dependent on the diffusion, because the hydraulic conductivity of the differente combination was low. The results also show that low-pH percolations make a rearrange of the fine particles into the sample, because after a grain size distribution test, the fine particles from the top of the samples were detected on the bottom of the sample, what increase the porosity on the top of the samples, what could lead the liner to a failure.

O presente trabalho teve como objetivo desenvolver um protótipo para a produção hidrometalúrgica de sulfato ferroso heptahidratado (FeSO4.7H2O – melanterita). A matéria prima foi um concentrado de pirita obtido a partir de rejeitos do beneficiamento de carvão mineral. Construiu-se, em escala piloto, uma planta de lixiviação com 300 kg de um concentrado com 73,2% de pirita. Nesta unidade, realizou-se uma etapa de lixiviação com água, em circuito fechado, sob condições aeróbias, com o intuito de se obter um extrato aquoso rico em íons férrico e sulfato. A seguir, procederam-se mudanças no sistema de forma a estabelecer uma condição anaeróbia ao meio, transformando os íons férricos em ferrosos. O lixiviado, rico em Fe2+, foi precipitado na forma de sulfato ferroso heptahidratado pela adição de etanol. Esse precipitado foi submetido a uma etapa de recristalização, obtendo-se cristais de melanterita de maior pureza. Ambos os produtos foram caracterizado por análise química elementar e difração de raios X. Os cristais de melanterita recristalizados apresentaram alta pureza, com qualidade para uso químico e farmacêutico. Assim, desenvolveu-se uma nova rota para produção de sulfato ferroso tendo como matéria-prima um concentrado de pirita da mineração de carvão (usualmente o sulfato ferroso é produzido como coproduto da produção de ilmenita e aço). A tecnologia apresenta uma elevada conversão do ferro lixiviado em melanterita e os insumos necessários são pirita, água e álcool etílico. A proposta abre uma nova possibilidade de uso dos rejeitos de carvão e a possibilidade de comercialização de outro produto na cadeia produtiva de carvão mineral. / The aim of this work was to develop a prototype for hydrometallurgical production of ferrous sulfate heptahydrate crystals (FeSO4.7H2O – melanterite). The raw material was a pyrite concentrate obtained from a coal tailing. The leaching system was assembled in pilot scale with 300 kg of a concentrate with 73.2% pyrite. Initially, it was carried out a leaching step in aerobic conditions with the purpose to obtain an aqueous solution rich in ferric ions and sulfate. Next, modifications were proceeded to establish an anaerobic condition in the reactor, converting the ferric to ferrous ions. Ethanol was added to the leaching solution to provide the precipitation of the Fe2+ and sulfate as ferrous sulfate heptahydrate. The ferrous sulfate precipitate was recrystallized, allowing producing melanterite crystals of higher purity. The crystals were characterized in terms of chemical and mineralogical composition. The process allowed producing crystals with a high purity attending chemical and pharmaceutical purposes. Thus, it was developed a process to produce ferrous sulfate from coal wastes (usually, ferrous sulfate crystals are produced as a co product from titanium dioxide and steel production). The technology presents a high conversion factor of soluble Fe2+ to melanterite and the necessary incomes are pyrite, water, and ethylic alcohol. The hydrometallurgical technique applied in this study allowed production of a commercial grade product from coal mining waste material.

A mineração de carvão gera grandes volumes de rejeitos que podem ser responsáveis por graves danos ambientais. A oxidação da pirita (FeS2), na presença de ar e água, promove a formação da drenagem ácida de mina (DAM), uma solução aquosa fortemente ácida e rica em sulfato e ferro (nas formas Fe²+ e Fe³+), além de outros metais associados. Atualmente, poucos estudos têm considerado a possibilidade da produção de materiais de valor econômico agregado a partir da água de percolação em rejeitos de carvão. Neste trabalho, o objetivo foi o desenvolvimento de uma rota hidrometalúrgica para a produção de sulfato ferroso (FeSO4). O trabalho experimental consistiu inicialmente na coleta de amostra de rejeitos de carvão rico em pirita e a sua caracterização. Realizou-se, em laboratório, a lixiviação do material em colunas de percolação em ambiente oxidante, adequado para proporcionar a oxidação da pirita em meio aquoso. A recirculação da lixívia permitiu a obtenção de um extrato rico em ferro. A seguir, procedeu-se a conversão do Fe³+ em Fe²+ para obtenção do sulfato ferroso, utilizandose radiação ultravioleta. O lixiviado, rico em Fe+², foi evaporado para cristalização do sulfato ferroso e purificado com álcool etílico. Os cristais foram caracterizados por análise química elementar, difração de raios X e microscopia eletrônica de varredura. A recuperação de Fe na forma melanterita (FeSO4.7H2O) em relação ao Fe pirítico existente na coluna (0,30 kg de Fe pirítico por kg de rejeito de carvão) variou de 7,5 a 9,0 %. Os resultados demonstraram que é possível produzir sulfato ferroso n-hidratado tendo como matéria-prima o rejeito rico em pirita resultante da mineração de carvão mineral. / The coal mining generates large volumes of tailings that may be responsible for serious environmental damages. The oxidation of pyrite (FeS2), in the presence of air and water, promotes the formation of acid mine drainage (AMD), an aqueous and highly acid solution rich in sulfate and iron (in the form Fe³+ and Fe²+), along with other associated metals. Currently, few studies have considered the possibility of production of materials with agregated economic value from the percolation of water in coal mining tailings. In this study, the objective was the development of a hydrometallurgical route for its production. The experimental work consisted initially in the collection of samples of coal waste rich in pyrite and its characterization. In the laboratory was performed the leaching of the material in percolation collums in an oxidizing environment, appropriate to provide the pyrite oxidation in aqueous medium. The recirculation of liquor allowed to obtain an extract rich in the iron. Then, the conversion of Fe³+ to Fe²+ for obtaining ferrous sulfate was performed using ultraviolet irradiation. The leached liquor, rich in Fe+², was evaporated for ferrous sulphate crystallization and purified with ethanol. The ferrous sulphate crystals were characterized by x ray diffraction and scanning electron microscopy. The recovery of Fe in the form melanterite (FeSO4.7H2O ) on pyrite Fe existing in the column (0,30 kg of Fe per kg of pyrite tailings and coal) ranged from 7,5 to 9,0 %. The results demonstrated that it is possible to produce nhydrated iron sulfate having as a raw material the waste rich in pyrite produced from the coal mining.

O objetivo deste trabalho é de avaliar o desempenho do concentrador Falcon® no beneficiamento de finos de carvão. Para tal foi usada uma amostra de carvão ROM da mina LEÃO II. Nos ensaios foi usado o concentrador Falcon® modelo L40. As variáveis operacionais estudadas foram: a aceleração da centrífuga, a granulometria da alimentação e a pressão da água de fluidização. Para todos os ensaios realizados na faixa granulométrica -0,25mm as taxas de rejeição de enxofre variaram entre 42,55% e 69,51%, e a recuperação da matéria orgânica variou entre 65,79% e 95,85%. Na faixa granulométrica de -0,5+0,25mm o valor mínimo da rejeição de enxofre total foi de 53,63% e o máximo de 75,22%. A recuperação de matéria orgânica variou entre 57,77% e 90,86%. Já a rejeição de cinzas mostra as taxas mais baixas para a faixa granulométrica-0,25mm, que varia entre 11,78% a 46,87%, comparada à faixa granulométrica de -0,5+0,25mm que apresenta valores entre 29,98% e 60,42%. Em geral o processo mostrou-se mais eficiente quando operado com valores baixos de aceleração (78G), e pressão de água relativamente baixa (entre 4 e 8Psi). / This study aims to evaluate the performance of the Falcon® concentrator in beneficiation of fine coal. A sample from LEAO II ROM and a L40 Falcon® concentrator was used for all tests. Operating variables studied were: G forces, the feed particle size and the water backpressure. For the tests performed with samples of -0.25mm particle size, sulfur rejection rates ranged from 42.55% to 69.51%, and the coal recovery ranged from 65.79% to 95.85%. In the -0.5+0.25mm size fraction the minimum value of total sulfur rejection was 53.63% and a maximum of 75.22%. The recovery of organic matter ranged from 57.77% to 90.86%. The ash rejection shows the lowest rates for the -0.25mm particle size, ranging from 11.78% to 46.87%, compared to -0.5+0.25mm size fraction which has values between 29.98 % and 60.42%. In general the process was more efficient when operated at low values of G-Force (78G), and low water pressure (4 and 8Psi).

Aquifer storage and recovery (ASR) is a strategy in which water is injected into an aquifer when it is plentiful and pumped from the aquifer when water is scarce. An impediment to ASR in Florida is leaching of naturally-occurring arsenic from limestone of the Upper Floridan Aquifer System (UFAS) into stored water. The concentration of arsenic in surface water, which serves as the recharge water for many ASR systems, and native groundwater is usually much less than 3.0 µ/L. However, data from ASR wells in Florida show that arsenic in recovered water frequently exceeded the 10 µg/L maximum contaminant level (MCL) established by the Environmental Protection Agency and were as high as 130.0 µg/L. The cause of elevated arsenic concentrations is displacement of reduced native groundwater with oxygenated surface water that dissolves arsenic-bearing pyrite in limestone. Although arsenic can be removed from recovered water during final treatment, mobilization of arsenic in the aquifer at levels that exceed the MCL is problematic under federal regulations. This dissertation investigated a number of aspects of the ASR/arsenic problem to provide additional insights into the mechanisms of arsenic mobilization and measures that could be taken to avoid or reduce the release of arsenic during ASR operations. Chapter 2, involved development of a geochemical model to simulate an ASR system’s injection of oxygenated surface water into reduced groundwater to determine whether aquifer redox conditions could be altered to the degree of pyrite instability. Increasing amounts of injection water were added to the storage-zone in a series of steps and resulting reaction paths were plotted on pyrite stability diagrams. Unmixed storage-zone water in wells plotted within the pyrite stability field indicating that redox conditions were sufficiently reducing to allow for pyrite stability. Thus arsenic is immobilized in pyrite and its concentration in groundwater should be low. During simulation, as the injection/storage-zone water ratio increased, redox conditions became less reducing and pyrite became unstable. The result would be release of arsenic from limestone into storage-zone water. Chapter 3 examined the importance of maintaining a substantial volume of stored water around an ASR well to prevent recovery of reduced native groundwater to the vicinity of the well. Depleting the stored water and recovering reduced native groundwater would result in dissolution of arsenic-bearing hydrous ferric oxide (HFO) and release of arsenic into water recovered from the ASR well. Injection/recovery volumes for each cycle for each well were tracked to determine if a substantial volume of stored water was maintained for each cycle or if it was depleted so that reduced native groundwater was brought back to the well. Each well was assigned to either the “storage zone maintained group” where a zone of stored water was established in early cycles and largely maintained through the period of investigation, or the “storage-zone depleted group” where a zone of stored water was either established in later cycles and/or was depleted during the period of investigation. Graphical and statistical analyses verified that maximum arsenic concentrations for storage-zone maintained wells were nearly always lower in each cycle and declined below the MCL after fewer cycles than those of storage-zone depleted wells. Chapter 4 was a mineralogical investigation of cores located at 20 m (ASR core 1), 152 m (ASR core 2), and 452 m (ASR core 3) from operating ASR wells to determine where mobilized arsenic in limestone is precipitated during ASR. If arsenic is precipitated distally, reduced concentrations of elements in pyrite, (iron, sulfur, arsenic, etc.) would be expected in ASR core 1 relative to more distant cores and there would be noticeable changes in appearance of pyrite crystals due to enhanced oxidation. The results showed that mean concentrations of the elements were lowest in ASR core 2, which did not support distal precipitation. However, scanning electron microscopy identified well-defined pyrite framboids only in core 3 while framboids in ASR cores 1 and 2 were less clear and distinct, indicating pyrite oxidation in cores closest to ASR wells. Statistical comparison of concentrations of iron, sulfur, and arsenic between the three ASR cores and 19 control cores not subject to ASR, showed that mean concentrations in ASR cores 1 and 2 were statistically similar to concentrations in control cores. This indicated that concentrations in ASR cores 1 and 2 had not been significantly reduced by ASR. The concentrations of elements were higher in ASR core 3 than in ASR cores 1 and 2 and control cores and statistically dissimilar to all but one control core. This indicated natural heterogeneity in core 3 rather than diminution of elements in ASR cores 1 and 2 due to ASR. The statistical analysis supported local precipitation. Once arsenic is mobilized from dissolved pyrite, it is rapidly complexed with precipitated HFO near the well. As long as all of the stored water is not removed during recovery so that reduced native groundwater is brought back to the well, HFO remains stable and complexed with arsenic. The concentration of elements would not have been lowest in ASR core 1 for this reason and because calculations showed that the mass of arsenic removed during recovery events prior to coring was minor compared to the total in limestone surrounding the well. The implications of this are that while large quantities of arsenic are present near the ASR well, only a small percentage may be available for dissolution. Most arsenic occurs with pyrite in limestone, which may insulate it from exposure to oxidized injection water. Water recovered from ASR wells may continue to have low concentrations of arsenic indefinitely because as limestone is dissolved, more pyrite becomes exposed and available for dissolution. The primary contribution of this dissertation to understanding and overcoming the arsenic problem in ASR systems is the empirical data developed to support or challenge important ASR/arsenic hypotheses. These data were used to 1) establish that background concentrations of arsenic in groundwater of the Suwannee Limestone were less than 1µg/L, 2) demonstrate that redox conditions necessary for pyrite in limestone to become unstable and dissolve occur when oxygenated surface water is injected into the aquifer, 3) demonstrate that the concentration of pyrite in the Suwannee Limestone is spatially variable to a high degree, 4) support the hypothesis that following injection of oxygenated surface water, pyrite in limestone dissolves and releases arsenic into solution and HFO forms and complexes with the arsenic near the ASR well, 5) propose that only a small percentage of pyrite near an ASR well may be available for dissolution during each cycle because most occurs in the limestone matrix and is isolated from injection water, 6) propose that as a result of the previous conclusion, water recovered from ASR systems may continue to have low concentrations of arsenic indefinitely because as limestone that contains pyrite is dissolved with each cycle, additional pyrite is exposed and is available for dissolution, and 7) support the effectiveness of maintaining a zone of stored water in an ASR well as an effective means of minimizing arsenic in recovered water during ASR.

This research evaluates two different Biological Nitrogen Removal (BNR) systems for enhanced nitrogen removal in decentralized wastewater treatment. The first study evaluated the performance of Hybrid Adsorption and Biological Treatment Systems (HABiTS) at the pilot scale with and without stage 1 effluent recirculation. HABiTS is a system developed at the bench scale in our laboratory and was designed for enhanced BNR under transient loading conditions. It consists of two stages; an ion exchange (IX) onto clinoptilolite media coupled with biological nitrification in the aerobic nitrification stage 1 and a Tire-Sulfur Adsorption Denitrification (T-SHAD) system in the anoxic denitrification stage 2. The T-SHAD process incorporates NO3- adsorption onto tire chips and Sulfur Oxidizing Denitrification (SOD) using elemental sulfur as the electron donor for NO3- reduction. Previous bench scale studies evaluated HABiTS performance under transient loadings and found significantly higher removal of nitrogen with the incorporation of adsorptive media in stage 1 and 2 compared with controls (80% compared to 73%) under transient loading conditions. In this study, we hypothesize that a HABiTS system with effluent recirculation in nitrification stage 1 may enhance nitrogen removal performance compared to that without recirculation. The following were the expected advantages of Stage 1 effluent recirculation for enhanced nitrogen removal: 1) Pre-denitrification driven by the mixture of nitrified effluent from stage 1 with high concentrations of biochemical oxygen demand (BOD) septic tank effluent. 2) Moisture maintenance in stage 1 for enhanced biofilm growth. 3) Increased mass transfer of substrates to the biofilm in stage 1. 4) Decreased ratio of BOD to Total Kjeldahl Nitrogen (TKN) in the influent of stage 1. Two side-by-side systems were run with the same media composition and fed by the same septic tank. One had a nitrification stage 1 effluent recirculation component (R-system), which operated at a 7:1 stage 1 effluent recirculation ratio for the first 49 days of the study and at 3:1 beginning on day 50 and one was operated under forward flow only conditions (FF-system). The R system removed a higher percentage of TIN (35.4%) in nitrification stage 1 compared to FF (28.8%) and had an overall TIN removal efficiency of 88.8% compared to 54.6% in FF system. As complete denitrification was observed in stage 2 throughout the study, overall removal was dependent on nitrification efficiency, and R-1 had a significantly higher NH4+ removal (87%) compared to FF-1 (70%). Alkalinity concentrations remained constant from stage 1 to stage 2, indicating that some heterotrophic denitrification was occurring along with SOD, as high amounts of sCOD leached from the tire chips in the beginning of the study, reaching sCOD concentrations of 120-160 mg L-1 then decreasing after day 10 of operation of stage 2. Sulfate concentrations from stage 2 for each side were low until the last 10 days of the study, with an average of 16.43 ± 11.36 mg L-1 SO42--S from R-2 and an average of 16.80 ± 7.98 SO42--S for FF-2 for the duration of the study, however at the end of the study when forward flow rates increased, SO42--S concentrations increased to 32 mg L-1 for R-2 and 40 mg L-1 for FF-2. Similar performance was observed in the FF system as the bench scale reactor tests. The second part of the research focused on the findings from a study of a Particulate Pyrite Autotrophic Denitrification (PPAD) process that uses pyrite as the electron donor and nitrate as the terminal electron acceptor in upflow packed bed bioreactors. The advantages of using pyrite as an electron donor for denitrification include less sulfate production and lower alkalinity requirements compared with SOD. The low alkalinity consumption of the PPAD process led to comparison of PPAD performance with and without oyster shell addition. Two columns were operated side-by-side, one packed with pyrite and sand only (P+S), while another one was packed with pyrite, sand and oyster shell (P+S+OS). Sand was used as a nonreactive biofilm carrier in the columns. My contribution to this research was to carry out Scanning Electron Microscopy-Energy-Dispersive X-Ray Spectroscopy (SEM-EDS) analysis to support the hypothesis that oyster shell contributes to nitrogen removal because it has a high capacity for biofilm attachment. SEM analysis showed that oyster shell has a rough surface, supported by its high specific surface area, and that there was more biofilm attached to oyster shell than pyrite or sand in the influent to the column. EDS results showed a decrease in atomic percentages for pyrite sulfur in the effluent of both columns (59.91% ± 0.10% to 53.94% ± 0.37% in P+S+OS column and to 57.61% ± 4.21% in P+S column). This finding indicated that sulfur was oxidized more than iron and/or the accumulation of iron species on the pyrite surface and supports the coupling of NO3- reduction with pyrite oxidation.

The approximately 2.9 Ga old Witwatersrand Basin of South Africa hosts different types of pyrite grains. The pyrite grains are hosted in different quartz pebble conglomerate reefs including the Ventersdorp Contact Reef (VCR). The various reefs are accessible from numerous goldfields. Regardless of years of studying the various types of pyrite grains from the VCR, there is still a disagreement as to their origins. Numerous pyrite grains of different types, shapes, and textures have been identified in the VCR of the Kloof Gold Mine. The origin of the different types of pyrite grains have been attributed to various mechanisms. Consequently, different depositional models were suggested for the mineralisation of the pyrite grains. Nevertheless, the style of mineralisation and origin of the different types of pyrite grains require further work especially for the VCR. This study determined whether a single or multiple processes were responsible for the formation of the different pyrite grains. The different types of pyrite grains including the rounded porous, rounded massive and angular massive grains were identified using a reflected light microscopy, scanning electron microscopy, and Röntec energy-dispersive x-ray spectroscopy. The above techniques were used to describe the shapes, sizes, and textures of the different types of pyrite grains in order to classify and group the pyrite grains for further investigation by chemical analysis. Identification and description of minerals associated with pyrite were conducted to determine the environment and conditions under which pyrite grains were formed. Genetic structures were identified in order to resolve whether the pyrite grains were transported or crystallised in situ. Different types of inclusions hosted in pyrite grains were identified and described to determine the nature of pyrite grains. Rounded zircon grains were identified in rounded massive pyrite grains, and the appearance the rounded zircon grains might suggest that the rounded massive pyrite grains formed later after the deposition of the Witwatersrand basin sediments. A particle induced x-ray emission, an electron microprobe, and a laser ablation inductively coupled plasma mass spectrometry were used to carry out chemical analysis of the major, minor and trace elements of the different pyrite grains. The chemical analyses were conducted to investigate and determine the chemical signatures and the composition of the different types of the pyrite grains to determine their processes of formation. Compositional zonation patterns and overgrowths of the pyrite grains were identified in order to determine whether the pyrite grains were formed through multiple mechanisms. The compositional zonation patterns were observed in the rounded porous pyrite grains. The zonations suggest multiple stages of growth processes resulting in most porous parts of the pyrite being enclosed by nearly pure pyrite. The rounded pyrite grains are generally containing high concentrations of Ni and Co as opposed to angular pyrite grains. The Ni/Co ration is low in the angular pyrite grains, but high in the rounded grains. The high Ni/Co ratio in rounded grains may be related to low-temperature sedimentary processes, whereas the low Ni/Co ratio in angular pyrite grains may indicate hydrothermal source. The differences between rounded and angular pyrite grains can be interpreted as a result of different genetic history, and origin from different sources. Thus the different pyrite grains formed under different chemical and atmospheric conditions, and by different depositional mechanisms. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Geology / unrestricted