Diferentes estratégias de flotação (reagentes, pH e rota) têm sido utilizadas na separação entre apatita e carbonatos em todo o mundo. Há evidências na literatura de que a cristalinidade afeta a flotação de apatitas e calcitas com oleato de sódio. Além disso, a dissolução dos sais semi-solúveis pode influenciar a interação entre a superfície dos minerais e os reagentes de flotação, uma vez que o mecanismo de adsorção mais importante é a precipitação de oleato de cálcio na interface sólido/líquido. Portanto, o objetivo deste trabalho é investigar a relação entre cristalinidade, cinética de dissolução e resposta à flotação de apatitas e calcitas de diferentes gêneses (ígnea, metamórfica e sedimentar) e origens. Quatro tipos de minerais foram utilizados: purificados a partir de minérios, previamente purificados, naturalmente puros e amostras de coleção. As amostras foram caracterizadas por fluorescência de raios-X e microanálise (WDS/EDS). Características físicas como densidade (d), área superficial (S) e porosidade (P) também foram determinadas. O método de Rietveld aplicado à difração de raios-X foi usado tanto para comprovar a pureza das amostras como para estudar a cristalinidade dos minerais por meio da determinação dos parâmetros de rede (distâncias a e c, e volume da cela unitária- VCU), além do grau de cristalinidade (GC), tamanho de cristalito (TC) e microdeformação (MD). Ensaios de dissolução, conduzidos na ausência de CO2, forneceram a quantidade (mol) de íons Ca2+ (nCa2+) dissolvidos em função do tempo (t) e normalizada em relação à área superficial. Os resultados se ajustam a um modelo de primeira ordem: nCa2+ = Ca2+MAX(1- e-kt). Este procedimento permitiu calcular os valores da quantidade máxima de íons Ca2+ dissolvidos (Ca2+MAX), bem como da constante cinética (k). Além disso, a velocidade de dissolução foi determinada para a etapa rápida (VR), que caracteriza o início da reação, e para a etapa lenta (VL), que ocorre nas proximidades do estado estacionário. A resposta à flotação com oleato de sódio foi determinada por meio de experimentos de microflotação. Várias relações de causa e efeito são encontradas: flotabilidade (F) versus VR, e VR versus características intrínsecas (parâmetros de rede, de cristalinidade e físicos). VR foi selecionado para participar de tais modelos, pois, caracteriza o intervalo de tempo em que o condicionamento (1 minuto) e a microflotação (1 minuto) ocorrem. Observa-se que a flotabilidade dos minerais aumenta com o aumento de VR, sugerindo que apatitas e calcitas que disponibilizam mais íons Ca2+ em solução para interagir com o oleato, exibem mais elevada flotabilidade. Equações lineares de F em função de VR em pH 8 (R = 0,97 para apatitas e R = 0,66 para calcitas) e pH 10 (R = 0,95 para apatitas e R = 0,63 para calcitas) foram encontradas. Correlações lineares múltiplas foram utilizadas para relacionar VR (em pH 8 e 10) com as características intrínsecas que exercem maior influência sobre este parâmetro. Para as apatitas, VR foi equacionado em função de GC, TC e c, enquanto para as calcitas, os parâmetros GC, TC, d e P foram selecionados para compor o modelo. Os valores de VR calculados se ajustam aos observados dentro de um intervalo de confiança de 95%. As equações lineares propostas para as apatitas foram usadas para se estimar F das amostras de Anitápolis-SC e Tapira-MG, que não foram submetidas aos ensaios de dissolução. Os valores de F calculados estão em concordância com aqueles experimentalmente determinados. / Different flotation strategies (reagents, pH and route) have been adopted to separate apatite from carbonates around the world. Literature provides evidences that crystallinity affects flotation response of apatite and calcite with sodium oleate. Furthermore, dissolution of salt-type minerals influences the interaction between mineral surface and flotation reagents, because the most important adsorption mechanism is the surface precipitation of calcium oleate onto mineral/water interface. Therefore, the objective of this research is to investigate the relationship between crystallinity, dissolution kinetics and flotation response of apatites and calcites from different genesis (igneous, metamorphic and sedimentary) and origins. Four sorts of minerals were utilized: minerals purified from ores, minerals previously purified, naturally pure minerals and collection samples. They were characterized by X-ray fluorescence and X-ray microanalysis (WDS/EDS). Physical characteristics, as specific gravity (d), surface area (S) and porosity (P), were also determined. The Rietveld method applied to X-ray diffraction data was used either to probe the purity of samples or to study the crystallinity of the minerals by means of determining their lattice parameters (a and c dimensions plus lattice volume-VCU), in addition to crystallinity degree (GC), crystallite size (TC) and microstrain (MD). Dissolution experiments, conducted in the absence of CO2, yielded curves which relate the amount (mol) of dissolved Ca2+ ions (nCa2+) versus time (t), normalized by the surface area. They fit a first order model: nCa2+ = Ca2+MAX(1- e-kt). Curve fitting via exponential adjustment was accomplished to calculate values of the maximum amount of dissolved Ca2+ ions (Ca2+MAX) and the kinetic constant (k). In addition, the dissolution rate was determined for the fast step (VR), which characterizes the beginning of the reaction, and for the slow step (VL), as it tends to the steady state. Flotation response with sodium oleate was determined by microflotation experiments. Several cause-effect relationships are found: floatability (F) versus VR, and VR versus intrinsic characteristics of minerals (lattice, crystallinity and physical parameters). VR was selected to participate in the model because it characterizes the length of time along which reagent conditioning (1 minute) plus microflotation (1 minute) take place. It is observed that F increases as VR becomes greater, suggesting that samples of apatites and calcites which place more Ca2+ ions in solution to interact with oleate exhibit higher flotation performance. Linear equations of F versus VR at pH 8 (R = 0,97 for apatites and R = 0,66 for calcites) and pH 10 (R = 0,95 for apatites and R = 0,63 for calcites) were found. Likewise, multiple linear correlations were used to relate VR (at pH 8 and 10) with the intrinsic characteristics of apatites and calcites that affect VR to a greater extent. For apatites, VR was modeled as a function of GC, TC and c, while for calcites, the parameters GC, TC d and P were selected to compose the model. The calculated VR values fit the experimental ones within 95% of confidence. The linear equations developed for apatites were used to estimate floatability of the samples from Anitápolis-SC and Tapira-MG, which were not submitted to dissolution experiments. The values of calculated floatability are in agreement with the experimental ones.

Introdução Análise da qualidade da água do reservatório Billings, situado na região Metropolitana de São Paulo, em decorrência do bombeamento de água proveniente de duas estações de Flotação experimentais, situadas no rio Pinheiros. Objetivo Analisar parâmetros de qualidade da água revertida para o reservatório Billings, sob o aspecto de poluição e toxicidade, objetivando a utilização deste reservatório para reúso recreacional e também para geração de energia na Usina Henry Borden em Cubatão. Metodologia Para a pesquisa quantitativa foram utilizados dados secundários, coletados ao longo de 22 de agosto de 2007 a 31 de maio de 2008, sendo este o período de funcionamento do sistema de flotação, nos pontos de amostragem convencionais e também nos pontos com monitoramento contínuo, em locais previamente estabelecidos. Resultados A análise indicou que o primeiro ponto de monitoramento dentro da represa sofre os efeitos diretos do bombeamento, o que não se constata nos pontos mais distantes do corpo central do reservatório. Apontou também a presença de alguns contaminantes importantes como chumbo e clorofórmio na água, em quantidade acima do permitido na legislação. Conclusão - A utilização do reservatório para reúso recreacional com contato primário está contra indicada e o bombeamento das águas para geração de energia pode ser mantido, uma vez que a qualidade de água para esta aplicação deverá ter baixa quantidade de sólidos, que são removidos pela flotação. Recomendações - Realização de estudos que contemplem a análise conjunta da influência dos benefícios oriundos do Programa de Despoluição do Tietê, em implantação pela Companhia de Saneamento Básico de São Paulo, e também do sistema de tratamento por flotação. Ajustes operacionais e adequações no sistema de flotação. Mapeamento e identificação de fontes de lançamento de esgotos diretamente no corpo da represa, e eliminação destas emissões clandestinas. Controle rigoroso da ocupação de áreas no entorno da Billings. / Introduction - A quality assessment of the water pumped from two experimental floating plants on the Pinheiros River into the Billings Reservoir, located in the Sao Paulo Metropolitan Region. Objective: To analyze quality parameters of the water pumped into the Billings Reservoir, scrutinizing both pollution and toxicity; with focus on the recreational use of the reservoir as well as generating energy at the Henry Borden Plant in the city of Cubatão. Methodology For the quantitative research, secondary data was collected from August 22, 2007 to May 31, 2008 the functioning period of the flotation systems. The data was gathered in conventional sampling points as well as pre-established continuous monitoring sampling points. Results - The assessment has indicated that the first monitoring point inside the reservoir is affected by the pumping, however, this fact does not occur in distant points located in the reservoirs central body. Some important pollutants such as lead and chloroform showed levels above allowed by law. Conclusion Primary contact for Recreational reuse is not indicated for this reservoir; however, the water pumping for energy generation can be kept, since the water for this application must have low quantities of solids. Recommendation Development of studies that assess both the resulting benefits of the Tiete River Clean-Up Project, implemented by The Sanitation Company of The State of Sao Paulo (SABESP), as well as Flotation Treatment System; Operational adjustments on Flotation System; Identify and eliminate underhand sewage discharged into the reservoir; Strict control of the occupied areas surrounding the Billings reservoir.

Trithiocarbonates (TTCs) with less than six carbon atoms per molecule historically have proved to be better bulk sulphide mineral collectors than conventional dithiocarbonates (DTCs). However, high vapor pressures of the short-chain mercaptan decomposition products prevented them from general industrial use. Impala’s commitment in TTC development changed in 2002 when the nC12-trithiocarbonate indicated strong synergism when added to their existing flotation suite. A concerted research effort at the University of Utah followed, and in particular on their surface chemistry. To compliment current research and development at Impala, fundamental work regarding the surface hydrophobicity of pyrrhotite under electrochemically controlled conditions was undertaken at Utah University. Controlled contact angle measurements showed that the surface hydrophobicity of pyrrhotite can be increased by small additions of nC12-trithiocarbonate to SIBX. It was also found that this improvement in the surface hydrophobicity with the SIBX-TTC mixture was more significant at lower oxidation potentials. Work at Utah University further showed that a C12 decomposition product may or may not be present with an adsorbed TTC molecule. External reflectance infrared spectroscopy in the mid infrared region suggested a “crowding” of the collectors at the surface when SIBX and TTC are combined. This was based on an increase in the absorbance of the -CH2- peaks in the mixed collector system. In bench scale flotation tests on PGM bearing samples from the Merensky reef, it was found that a 5 molar percent replacement of SIBX with nC12-trithiocarbonate improved the flotation activity relative to the standard SIBX-DTP mixture. Improvements were in the recoveries of PGMs, copper and nickel. The addition of TTC also increased the flotation rates of both slow and fast floating valuables as is predicted by the Kelsall equation. The optimum mixture for the pilot plant trials was thus a 5 molar percent replacement of the current collector suite with nC12-TTC. Based on the bench flotation results, research was extended to a pilot plant trial. At a depressant dosage of 100g/ton, the PGM concentrate grades from the first rougher cell improved from 120g/ton to 175g/ton when the TTC was introduced. This was achieved without any effect on the recovery from the first cell. This increase in concentrate grade is believed to arise from the nature of both: <ul> <li>The mineral-collector surface state, and</li> <li>The bubble surface interaction.</li> </ul> Overall, the standard SIBX-DTP collector combination and the new SIBX-DTP-TTC collector combination (both at 100g/ton depressant) was also compared to pilot plant tests with SIBX-DTP at high (350g/ton) depressant dosages. The latter suite forms the currents reagent suite at Impala Platinum. When comparing the first two trials, at 100g/ton depressant, the addition of TTC as a ternary collector resulted in a recovery improvement of approximately 2.2% with a simultaneous increase in final concentrate grade from 57g/ton to 73g/ton. The result was a reduction in solids recovery from 5.3% to 4.1%. When comparing the TTC trial to the standard collector suite at high depressant dosages, only a small reduction (3.6% vs. 4.1%) in solids recovery was achieved with a final concentrate grade of 85g/ton. The PGM recoveries were very similar. Based on current Merensky milling rates, depressant and TTC costs, and calculated replacements based on the pilot plant tests, a projected cost saving on chemicals is R9.6 million per annum. Financial impacts on processing, grade and kinetics have not been made. It was also concluded that the detrimental effect of mild steel milling on the flotation activity of SIBX-DTP was diminished with the addition of the long-chain TTC with SIBX and DTP. As part to this research, a preliminary plant trial on UG-2 underground material showed a reduced primary rougher chromite grade as well as a significant increase in PGM concentrate grade for the first two primary rougher cells. This is an important finding, especially for the melting process. In this final study a partial (5 molar percent) replacement of the standard collector used was also made. What was further realised was a significant increase in the final concentrate grade when compared to the standard conditions. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / MEng / unrestricted

Platinum-group elements (pGEs) are recovered from UG2 chromitite by milling and flotation. The mechanisms involved during beneficiation of this type of ore are still poorly understood, partly because of its complex nature. Image-analysis techniques were used to characterise the mineralogy ofUG2 chromitite from diverse geological environments, as well as the milling and flotation products derived from each of these ores. Postmagmatic alteration ofUG2 chromitite has a profound effect on the mineralogy, chemistry and recovery characteristics of the UG2 chromitite. Relatively unaltered UG2 chromitite consists predominantly of chromite and primary silicates, mostly bronzite and plagioclase with minor phlogopite, and small amounts of secondary silicates such as talc and chlorite. Trace quantities of base-metal sulphides, predominantly pentlandite, pyrrhotite and chalcopyrite ± pyrite, generally occur at chromite-silicate grain boundaries. PGEs are present both as discrete PGE minerals, and, to a lesser extent, sub-microscopically in other phases, mostly palladium and rhodium in pentlandite. The PGE mineral assemblage is characterised by sulphide minerals, mostly braggite, cooperite, nickeloan malanite and laurite, and is closely associated with the base¬metal sulphides. Recovery of PGE minerals is strongly dependent on the degree of liberation, with liberated PGE minerals and PGE minerals associated with liberated base-metal sulphides, the fastest-floating particles. PGE minerals report to flotation tailings predominantly as fine-grained inclusions in coarse silicate particles. In places, the footwall rocks have been replaced by iron-rich ultrabasic pegmatoid. As a result of interaction with Fe- and Ti-rich fluids, the chromite grains in the UG2 chromitite have been enlarged due to sintering, and the PGE mineral assemblage replaced by one consisting predominantly of laurite, Pt-Fe alloy and other non¬sulphide PGE minerals. The non-sulphide PGE mineral grains appear to be slower ¬floating than sulphide PGE minerals. Low temperature hydrothermal alteration appears to have caused relatively widespread alteration of the UG2 chromitite in some areas, resulting in corrosion and redistribution of sulphide minerals, as well as the replacement of primary magmatic silicates by secondary silicates such as pumpellyite, epidote, prehnite, albite, talc, chlorite and quartz. Ore from such areas are characterised by a base-metal sulphide assemblage consisting predominantly of millerite, chalcopyrite, and pyrite. Base¬metal sulphide and PGE minerals occur in fine-grained intergrowths with silicates, resulting in poor liberation. In the samples investigated, composite particles were often faster-floating than expected, at least partly due to the presence of naturally floatable talc. The effect of faulting on the mineralogy of the UG2 chromitite probably depends on distance from the fault zone, and possibly also timing of faulting, and can cause cataclasis of the ore. Where cataclasis occurred, broken mineral grains are cemented by secondary, hydrous silicates. Liberation of base-metal sulphides and PGE minerals are poor, and recoveries consequently very low. It was demonstrated that reasonable estimates of total PGE+Au recovery can be made from the mineralogical characteristics ofUG2 chromitite ore. Based on the mineralogy of ore from a specific area, provision can be made for appropriate adjustments to metallurgical flowsheets. / Thesis (PhD)--University of Pretoria, 2006. / Geology / Unrestricted

This study investigated the development potentials in the mineral processing plant of Björkdal. The flotation processes were explored with the purpose of finding out how to achieve a higher and a more uniform gold recovery with adapted choices of parameters. A material balance was carried out to describe in what flows the gold was distributed the current day of sampling. The material was sampled, prepared, and analysed according to gold grade. The sampling method of grab sampling was used and samples from seven occasions during the day were added and created the sample of the day. The sizes of the samples were based on experience but were checked by the Gy´s sampling formula. The sampling was performed during three days and the results were compiled in three material balances, one of which was a fraction balance. The pulp flow, the solid flow and the gold flow were documented as material balances. Deficiencies in the form of imbalances between inflows and outflows were corrected by a method of data reconciliation. The balanced measured values were used for analysis and documentation.In the mine of Björkdal the pH values were measured in the flotation processes. The residence times of the flows through the flotation plant was calculated from the material balance. The additions of reagents were noted and scaled down to the conditions of the laboratory. The conditioning was not included in the Björkdal process.In the flotation experiments at the Mineral processing laboratory, Luleå University of Technology, the influence of the adaptable parameters on the gold recovery was investigated. The following parameters were included in the experiments: pH, flotation time, particle sizes, conditioning time, and reagents additions. The conditions in the Björkdal plant were scaled down to correspond to those of the flotation cells of RÅ0 and RÅ1-3. For the experiments the material was sampled from the RÅ0 entry flow and from the Flotation entry flow. The material samples from the Flotation entry flow replaced the RÅ1-3 entry flow to imitate the conditions of the RÅ1-3 cell. This simplification was motivated by the practical sampling conditions.The results showed that it was possible to achieve a higher gold recovery by adapting pH, residence time and particle sizes. The gold recovery appeared to be independent of conditioning time. The experiment with reagent additions as parameter indicated that higher reagent additions resulted in faster flotation in the introduction part of the process. The report summarized graphically the measurements from the material balance and the flotation experiments in order to give best possible survey of the dependences between parameters and gold recovery. The experiments made it obvious that higher gold recovery resulted in lower gold grade. Therefore a compromise of adjustment between gold recovery and gold grade is important to consider. Variations of the gold recovery could be connected to the geological conditions. In the report significant results were documented. / <p>Validerat; 20130618 (global_studentproject_submitter)</p>

The growth and removal of inclusions in stirred ladles hasbeen studied. First, the importance of different growthmechanisms suggested in the literature were studied. Simulationresults from a fundamental model of an induction-stirred ladlehave been used as input in the calculations. Based on thegrowth calculations it was concluded that four of the growthmechanisms need not to be considered since they contribute solittle: i) diffusion of oxygen and aluminum to the inclusionsurface, ii) diffusion coalescence, iii) Brown motioncollision, and iv) laminar shear collision. The majorcontributor to inclusion growth is turbulent collision. Growthdue to Stoke's collisions is also somewhat important if largedifferences among inclusion sizes exist. Growth of inclusions in gas stirred ladles was studied usinga similar approach as the one for induction stirred ladles, butwith use of simulation results from a fundamental mathematicalmodel of a gas-stirred ladle. Similarly to what was found inthe case of induction stirring, it was found that turbulentcollisions and Stokes collisions appeared to be the majormechanisms for inclusion growth. The contribution of laminarshear collisions to growth was deemed negligible compared tothat of turbulent collisions. For the gas stirred ladle different removal mechanisms werealso studied, based on input data from a mathematical model ofa gas-stirred ladle. It was found that different modelssuggested to predict the inclusion removal due to bubbleflotation gave very different results. Also, all models assumeda spherical shape of the gas bubbles, which was found to beless realistic. Therefore, a new model for inclusion removal byspherical cap bubble flotation was developed. In the newcalculations, the most important mechanisms of inclusionremoval were found to be removal to the top slag and removal bybubble flotation, assuming spherical-cap bubbles and planecontact. When the bubbles were assumed to be spherical,resulting removal rates were lower than when they were assumedto be spherical caps. Based on these results it is concludedthat more research is needed to obtain a better understandingof the importance of bubble flotation on inclusion removal.Experiments are clearly needed to determine which modelconcepts produce predictions in best agreement withcorresponding data from actual steelmaking processes. / NR 20140805

Carbon matrix composite (CMC) electrode and surface conducting (SC) electrode have been developed to study the copper-activation and the subsequent xanthate adsorption on insulating sphalerite. Fabricating CMC electrode involves embedding sphalerite particles in carbon to form a carbon matrix composite; and SC electrode is designed by contacting a platinum wire to the sphalerite surface. When these electrodes are activated by heavy metal ions such as copper, a conducting layer is formed on the mineral surfaces that allows dynamic electrochemical studies to be conducted. Voltammetric studies on the copper activated CMC:ZnS electrodes in inert electrolytes show that although the activation product and kinetics may differ with pH, copper-activation occurs at all pH ranges. At acidic pH, a Cu2S-like activation product was formed at open circuit. When activation was conducted at near neutral and alkaline pH at open circuit, the surface products formed were identified to be CuS-like. It was also established that the amount of copper uptaken by sphalerite is strongly dependent on the time of activation and on the electrochemical potential applied during activation. Activation at potentials positive of the rest potential decreases the amount of copper on the surface. Indeed, activation at potentials of 50 to 100 mV more positive of the rest potential in the activating solution completely inhibits copper activation. This result is consistent with the anodic stripping voltammetry that shows copper can be removed from the surface of sphalerite at oxidizing potentials. Activation at potentials mildly negative of the rest potential causes a progressive increase in the amount of copper on the surface, consistent with the diffusion controlled reduction process between ZnS and Cu2+ ions observed in the activating solution. At very low potentials, however, elemental copper is formed, which may worsen the selectivity of the sphalerite flotation. Controlled potential contact angle measurements showed that xanthate adsorption does occur on copper-activated sphalerite at all pH ranges. However, the contact angles and flotation recovery decrease at near neutral pH. This problem is caused by the adsorption of the copper-hydroxy species on the activated sphalerite surface. It was found that addition of small amount of complexing reagent can improve the flotation recovery at the near neutral pH. The results obtained in the present work show that potential control of the activation process can provide a means of controlling copper uptake and, hence, the selectivity and recovery of sphalerite flotation. The development of CMC:ZnS and SC:ZnS electrodes provides a practical and reliable way to quantitatively estimate the amount of copper uptake on sphalerite surface after activation. / Ph. D.

The extended DLVO theory was used to develop a flotation model by considering both hydrodynamic and surface forces involved in the process. A stream function was used to estimate the kinetic energies for thinning the water films between bubbles and particles, which were compared with the energy barriers, created by surface forces, to determine the probability of adhesion. A general expression for the probability of detachment was derived from similar mechanism for chemical reaction, and the kinetic energy for detachment was estimated with French and Wilson's model. The hydrophobic force parameter (K132) calculated from the rate constants of single bubble flotation tests showed that, K132 for bubble-particle interaction were close to the geometric means of K131 for particle-particle interactions and K232 for bubble-bubble interaction, indicating that the combining rules developed for dispersion forces may be useful for hydrophobic forces. The model was used to predict flotation results as functions of several important parameters such as contact angle, double-layer potentials, particle size, bubble size, etc. The predictions were consistent with experience, and could be explained in view of the various subprocesses considered in the model development. Furthermore, the model suggested optimum conditions for achieving the maximum separation efficiency. The extended DLVO theory was also used to determine the hydrophobic force between two oil/solution interfaces from the equilibrium film thicknesses of dodecylammonium chloride (RNH3Cl) solutions obtained using Thin Film Balance (TFB) technique. The results showed that, the oil droplets were inherently hydrophobic, and the hydrophobic force played an important role in the stability of emulsions. This force decreased with increasing surfactant concentration, and also changed with pH and the addition of electrolyte. The interfacial area occupied by molecules indicated that, the dodecane molecules might present between two surfactant ions at interface, thus the hydrophobicity of oil/solution interface was less sensitive to the addition of the surfactant than that of air/solution interface. Thermodynamic analysis suggested that, there might exist a relationship between the interfacial hydrophobicity and the interfacial tension. / Ph. D.

No description available.

M. S.