The Flotation of Niobium Oxide Minerals from Carbonatite Ores

Global niobium production is presently dominated by three operations, Araxá and Catalão (Brazil), and Niobec (Canada). Although Brazil accounts for over 90% of the world’s niobium production, a number of high grade niobium deposits exist worldwide. The advancement of these deposits depends largely on the development of operable beneficiation flowsheets. Pyrochlore, as the primary niobium mineral, is typically upgraded by flotation with amine collectors at acidic pH following a complicated flowsheet with significant losses of niobium. This research compares the typical two stage flotation flowsheet to a direct flotation process (i.e. elimination of gangue pre-flotation) with the objective of circuit simplification. In addition, the use of a chelating reagent (benzohydroxamic acid, BHA) was studied as an alternative collector for fine grained, highly disseminated pyrochlore. For the amine based reagent system, results showed that while comparable at the laboratory scale, when scaled up to the pilot level the direct flotation process suffered from circuit instability because of high quantities of dissolved calcium in the process water due to stream recirculation and fine calcite dissolution, which ultimately depressed pyrochlore. This scale up issue was not observed in pilot plant operation of the two stage flotation process as a portion of the highly reactive carbonate minerals was removed prior to acid addition. A statistical model was developed for batch flotation using BHA on carbonatite ore (0.25% Nb2O5) that could not be effectively upgraded using the conventional amine reagent scheme. Results showed that it was possible to produce a concentrate containing 1.54% Nb2O5 with 93% Nb recovery in ~15% of the original mass. Fundamental studies undertaken included FT-IR and XPS, which showed the adsorption of both the protonized amine and the neutral amine onto the surface of the pyrochlore (possibly at niobium sites as indicated by detected shifts in the Nb3d binding energy). The results suggest that the preferential flotation of pyrochlore over quartz with amines at low pH levels can be attributed to a difference in critical hemimicelle concentration (CHC) values for the two minerals. BHA was found to be absorbed on pyrochlore surfaces by a similar mechanism to alkyl hydroxamic acid. It is hoped that this work will assist in improving operability of existing pyrochlore flotation circuits and help promote the development of niobium deposits globally. Future studies should focus on investigation into specific gangue mineral depressants and inadvertent activation phenomenon related to BHA flotation of gangue minerals.

HPLC Determination of Angiotensin-Converting Enzyme Activity on Toyopearl HW-40S Column

Angiotensin-converting enzyme (EC3.4.15. I; ACE), isa membrane-bounddipeptidyl carboxypeptidase that mediates the cleavage of the C-terminal dipeptide His-Leu of the decapeptide angiotensin, generating the most powerful endogenous vaso-constricting angiotensin.
Some ACE inhibitors, such as Captopril, have been used as anti-hypertensive drugs. Moreover in recent years, large quantities of ACE inhibitors have been identijied and isolated from peptides derivedfrom food material such as casein, soy protein, jish protein and so on. Functional food with hypotensive effect has been developed on the basis of these works.
Typicalprocedures for screening hypotensive peptides offood origins are separationof products of peptic and tryptic digestion of proteins followed by inhibitory activitydetermination of each fraction. A method developed by Cushman has been the mostwidely used, in which ACE activity is determined by the amount of hippuric acid
generated as a product of enzymatic reaction of ACE with tripeptide of hippuryl-Lhistidyl-L-leucine. Hippuric acid is determined spectrophotometrically at 228 nm after its isolation from the reaction system by ethylacetate extraction, which not only requires alarge quantity of reagent but also results in large error.
An improved method based on Cushman ’s method is proposed in this paper. In this method, an enzymatic reaction system is based on Cushman’s method, while isolation and determination of hippuric acid is performed by medium perjormance gel chromatography on a Toyopearl HW-40s column. Due to the size exclusion nature of the column with somewhat hydrophobic properties, complete separation of four existing fractions in the reaction system is obtained within a smallfraction of the time necessary in Cushman’s method, with ideal reproducibility.

Mechanochemical Synthesis of Pharmaceutical Cocrystal Suspensions via Hot Melt Extrusion: Feasibility Studies and Physicochemical Characterisation

Engineered cocrystals offer an alternative solid drug form with tailored physicochemical properties. Interestingly, although cocrystals provide many new possibilities, they also present new challenges, particularly in regard to their design and large-scale manufacture. Current literature has primarily focused on the preparation and characterization of novel cocrystals typically containing only the drug and coformer, leaving the subsequent formulation less explored. In this paper we propose, for the first time, the use of hot melt extrusion for the mechanochemical synthesis of pharmaceutical cocrystals in the presence of a meltable binder. In this approach, we examine excipients that are amenable to hot melt extrusion, forming a suspension of cocrystal particulates embedded in a pharmaceutical matrix. Using ibuprofen and isonicotinamide as a model cocrystal reagent pair, formulations extruded with a small molecular matrix carrier (xylitol) were examined to be intimate mixtures wherein the newly formed cocrystal particulates were physically suspended in a matrix. With respect to formulations extruded using polymeric carriers (Soluplus and Eudragit EPO, respectively), however, there was no evidence within PXRD patterns of either crystalline ibuprofen or the cocrystal. Importantly, it was established in this study that an appropriate carrier for a cocrystal reagent pair during HME processing should satisfy certain criteria including limited interaction with parent reagents and cocrystal product, processing temperature sufficiently lower than the onset of cocrystal Tm, low melt viscosity, and rapid solidification upon cooling.

Reactions of atomic and molecular ions with acetone, 1,1,1- trifluoroacetone, and hexafluoroacetone: An investigation of the effects of molecular structure on the dynamics and kinetics of ion-molecule reactions

A selected ion flow tube study of the reactions of a series of gas-phase atomic cations (S⁺, Xe⁺, O⁺, Kr⁺, N⁺, Ar⁺ and Ne⁺) and molecular ions (SF _n⁺ (n = 1-5), CF_n⁺ (n = 1-3), CF₂Cl⁺, H₃O⁺, NO⁺, N ₂O⁺, CO₂⁺, CO⁺, and N₂⁺) spanning a large range of recombination energies (6.3-21.6 eV), with acetone, 1,1,1-trifluoroacetone, and hexafluoroacetone has been undertaken with the objective of exploring the nature of the reaction ion chemistry as the methyl groups in acetone are substituted for CF₃. The reaction rate coefficients and product ion branching ratios for all 66 reactions, measured at 298 K, are reported. The experimental reaction rate coefficients are compared to theoretically calculated collisional values. Several distinct reaction processes were observed among the large number of reactions studied, including charge transfer (non-dissociative and dissociative), abstraction, ion-molecule associations and, in the case of the reactions involving the reagent ion H₃O⁺, proton transfer. 

Synthèse de sulfilimines et de sulfoximines catalysée par les métaux de transition

Les sulfilimines et les sulfoximines sont des motifs structuraux dont l’intérêt synthétique est grandissant, notamment du fait de leurs applications en chimie médicinale et en agrochimie. Les travaux rapportés dans cet ouvrage décrivent le développement de nouvelles méthodes de synthèse efficaces pour la production de ces unités atypiques. Ces méthodes sont basées sur la réactivité d’une source d’azote électrophile, vis-à-vis de thioéthers et de sulfoxydes. L’utilisation d’un complexe métallique introduit en quantité catalytique a permis de favoriser le processus réactionnel. En tirant bénéfice de l’expertise de notre groupe de recherche sur le développement de réactions d’amination stéréosélectives de liaisons C-H et d’aziridination de styrènes, nous avons d’abord étudié la réactivité des N-mésyloxycarbamates comme source d’azote électrophile. Après avoir optimisé sa synthèse sur grande échelle, ce réactif chiral a été utilisé dans des réactions d’amination de thioéthers et de sulfoxydes, catalysées par un dimère de rhodium (II) chiral. Un processus diastéréosélectif efficace a été mis au point, permettant de produire des sulfilimines et des sulfoximines chirales avec d’excellents rendements et sélectivités. Au cours de l’optimisation de cette méthode de synthèse, nous avons pu constater l’effet déterminant de certains additifs sur la réactivité et la sélectivité de la réaction. Une étude mécanistique a été entreprise afin de comprendre leur mode d’action. Il a été observé qu’une base de Lewis telle que le 4-diméthylaminopyridine (DMAP) pouvait se coordiner au dimère de rhodium(II) et modifier ses propriétés structurales et redox. Les résultats que nous avons obtenus suggèrent que l’espèce catalytique active est un dimère de rhodium de valence mixte Rh(II)/Rh(III). Nous avons également découvert que l’incorporation de sels de bispyridinium avait une influence cruciale sur la diastéréosélectivité de la réaction. D’autres expériences sur la nature du groupe partant du réactif N-sulfonyloxycarbamate nous ont permis de postuler qu’une espèce nitrénoïde de rhodium était l’intermédiaire clé du processus d’amination. De plus, l’exploitation des techniques de chimie en débit continu nous a permis de développer une méthode d’amination de thioéthers et de sulfoxydes très performante, en utilisant les azotures comme source d’azote électrophile. Basée sur la décompositon photochimique d’azotures en présence d’un complexe de fer (III) simple et commercialement disponible, nous avons été en mesure de produire des sulfilimines et des sulfoximines avec d’excellents rendements. Le temps de résidence du procédé d’amination a pu être sensiblement réduit par la conception d’un nouveau type de réacteur photochimique capillaire. Ces améliorations techniques ont permis de rendre la synthèse plus productive, ce qui constitue un élément important d’un point de vue industriel.

Production of Gaseous Radiotracers Ch3i and I2 Through Na123i Salt

The objective of the present work was to develop, separately, methodology for production of two gaseous tracers through the sodium iodide NaI marked with 123I. Found in the nature in form different, the iodine has been used in diverse works in the area of the industry and health. These two forms of the gaseous iodine, the methyl iodide, CH3I, and molecular iodine, I2, are very unstable and volatile in the ambient temperature and presents different problems in clean-up and monitoring systems. The syntheses were processed with sodium iodide (NaI) 1M aqueous solution marked with 123I. The production of gas I2 was realized with in chlorine acid (HCl) and sodium iodate salt (NaIO3) and the CH3I was used, the salt of NaI and the reagent (CH3)2SO4. The production of gases was initially realized through in unit in glass with an inert material and the purpose was to study the kinetic of reaction and to determine the efficiency of production. The two synthesis occurs in the reaction bottle and after of produced, the gas is stored in the collect bottle that contains a starch solution for fixed the I2, and in syntheses of CH3I contains a silver nitrate solution for your fixation. To determine the efficiency of production of gases, analytic tests were realized, where the consumption of iodide ions of the bottle of reaction are measured. The optimization of production of the each gaseous tracer was studied varying parameter as: concentration of iodide, concentration of acid and temperature. After, the syntheses of the radiotracers were realized in the compact unit, having been used as main reagent the salt radiated of sodium iodide, Na123I. The transportation of elementary iodine and methyl iodine was studied by a scintillation detector NaI (2 x 2)” positioned in the reaction bottle.

Production of Gaseous Tracer I2 from the Sodiumiodide Salt

Found in the nature in form different, the iodine has been used in diverse works in the area of the industry and health. The iodine is very unstable and volatile in the ambient temperature and the I2 is one of the diverse gaseous forms found. In this work was developed methodology for production of gaseous tracer from the sodium iodide (NaI) 0,1 M marked with 123I. The synthesis was processed with in chlorine acid (HCl) 1M and sodium iodate salt (NaIO3). The production of gas I2 initially was carried through in unit of glass with the inert material and the purpose was to study the kinetic of reaction. The synthesis occurs in the reaction bottle and the produced gas is stored in the collect bottle that contains a starch solution (5 g/100 mL water). To determine the efficiency of production of gas I2, analytic tests had been carried through, where the consumption of iodide ions of the bottle of reaction is measured. The optimization of production of the gaseous tracer was studied varying parameters as: concentration of iodide and iodate, concentration of acid and temperature. Then, the synthesis of the radiotracer was realized in the compact unit, being utilized as main reagent the salt radiated of sodium iodide, Na123I. The transportation of elementary iodine was studied by a scintillation detector NaI (2 x 2)” placed in the reaction bottle. To acquire the data, the detector use a set of electronic modules for the acquisition of signals generated.

Estudo anatômico de trembleya phlogiformis dc.

v. 13, n. 2, p. 82-92, 2016.

Catalytic decomposition of formic acid using supported metal nanoparticles

Upgrade of hydrogen to valuable fuel is a central topic in modern research due to its high availability and low price. For the difficulties in hydrogen storage, different pathways are still under investigation. A promising way is in the liquid-phase chemical hydrogen storage materials, because they can lead to greener transformation processes with the on line development of hydrogen for fuel cells. The aim of my work was the optimization of catalysts for the decomposition of formic acid made by sol immobilisation method (a typical colloidal method). Formic acid was selected because of the following features: it is a versatile renewable reagent for green synthesis studies. The first aim of my research was the synthesis and optimisation of Pd nanoparticles by sol-immobilisation to achieve better catalytic performances and investigate the effect of particle size, oxidation state, role of stabiliser and nature of the support. Palladium was chosen because it is a well-known active metal for the catalytic decomposition of formic acid. Noble metal nanoparticles of palladium were immobilized on carbon charcoal and on titania. In the second part the catalytic performance of the “homemade” catalyst Pd/C to a commercial Pd/C and the effect of different monometallic and bimetallic systems (AuxPdy) in the catalytic formic acid decomposition was investigated. The training period for the production of this work was carried out at the University of Cardiff (Group of Dr. N. Dimitratos).

Finite volumes simulations in magnetohydrodynamics

Abstract not available

Computational solid mechanics using a vertex-based finite volume method

A number of research groups are now developing and using finite volume (FV) methods for computational solid mechanics (CSM). These methods are proving to be equivalent and in some cases superior to their finite element (FE) counterparts. In this paper we will describe a vertex-based FV method with arbitrarily structured meshes, for modelling the elasto-plastic deformation of solid materials undergoing small strains in complex geometries. Comparisons with rational FE methods will be given.

Finite volume methods for multiphysics problems

Abstract not available

Greener methodology for the synthesis of alpha-diazocarbonyl compounds and a novel approach to dioxinone derivatives

This thesis outlines a more environmentally benign approach to diazo transfer, and the investigation of the reactivity of -diazocarbonyl compounds when subjected to transition metal and lanthanide catalysis. Extensive studies were carried out to find the optimum conditions for a greener diazo transfer methodology, and this was also applied to a continuous process for the synthesis of -diazo--ketoesters. The first chapter includes a literature review of the synthesis and subsequent reactivity of -diazocarbonyl compounds. An overview of the applications of flow chemistry for the synthesis of hazardous intermediates is also included. The applications of lanthanide catalysts in organic synthesis is also discussed. The second chapter outlines the extensive studies undertaken to determine the optimum conditions for a greener diazo transfer methodology, including base and solvent studies. Use of water as a viable solvent for diazo transfer was successfully investigated. Diazo transfer to a range of -diazo--ketoesters was achieved using 5 mol% triethylamine or DMAP in water with high conversions. Polystyrene-supported benzenesulfonyl azide as an alternative diazo transfer reagent was also explored, as well as investigations into cheaper generation of this safer reagent. This polymer-supported benzenesulfonyl azide was used with 25 mol% of base in water to achieve successful diazo transfer to a range of -diazo--ketoesters. The third chapter describes the application of the new methodology developed in Chapter 2 to a continuous processing approach. Various excellent conditions were identified for both batch and flow reactions. A series of -diazo--ketoesters were synthesised with excellent conversions using 25 mol% triethylamine in 90:10 acetone water using flow chemistry. Successful diazo transfer was also achieved using a polymer-supported benzenesulfonyl azide in water under flow conditions. The fourth chapter discusses the reactivity of -diazo--ketoesters under transition metal and lanthanide catalysis. This chapter describes the synthesis of a range of -ketoesters via transesterification, which were used to synthesise a range of novel -diazo--ketoesters that were used in subsequent decomposition reactions. A novel route to dioxinones via rhodium(II) catalysis is reported. Attempted OH and SH insertion reactions in the presence of various lanthanide(II) catalysts are outlined, leading to some unexpected and interesting rearrangement products. The experimental details, including spectroscopic and analytical data for all compounds prepared, are reported at the end of each chapter.

Melhoria do processo de lavação das rolhas de cortiça

O presente trabalho, realizado na empresa Amorim & Irmãos, S.A. teve como principal objetivo a avaliação e otimização da lavação de rolhas de cortiça técnicas, designadas por Twin Top®, em termos do perfil de consumo de reagentes químicos e do desenvolvimento da sua brancura. Para tal foi desenvolvida uma metodologia de análise de brancura de rolhas Twin Top® que serviu de base para a determinação de uma gama de brancuras aceitável. Para além disto, efetuou-se a avaliação do processo de lavação atualmente praticado e apartir do qual se realizaram os ensaios de otimização a nível laboratorial e piloto. Foram aplicados diferentes métodos de análise tais como, UV-Vis, FTIR-ATR, RMN e brancura ISO. Tendo como base de análise os espetros de refletância difusa de espetroscopia de UV-Vis foi proposta uma metodologia de determinação da brancura de rolhas Twin Top® a 457nm, adoptando as condições da Norma ISO 3688, aplicada na indústria da pasta e papel. De seguida, aplicando o método anteriormente definido, analisaram-se 1000 rolhas Twin Top® de lavação branca. Sendo que os resultados demonstraram que para rolhas dentro de especificação a brancura ISO deve estar entre os 30 e 35%. Foram ainda analisadas rolhas de diferentes classes visuais e provenientes de várias máquinas de lavação da fábrica para determinar possíveis diferenças. Para proceder à avaliação da lavação existente analisaram-se as colas usadas na produção das rolhas, um grânulo de cortiça e a matéria seca do efluente de lavação por FTIR-ATR e RMN. Desta avaliação resultou a presença de compostos de cortiça e cola degradada no efluente de lavação. Determinou-se a concentração dos reagentes intervenientes no processo que se mostraram de acordo com as especificações indicadas pelos fornecedores. Para a otimização da lavação combinou-se o peróxido de hidrogénio e hidróxido de sódio em diferentes quantidades, concentrações e diferentes tempos de reação o que permitiu identificar a melhor alternativa à lavação convencional. Assim existem duas propostas que devem ser tidas em consideração: uma em que a lavação mantém a mesma sequência da convencional e em que se altera o local de adição dos reagentes, que deve ser o mais próxima e direta possível das rolhas, e a outra em que se reduz o tempo do processo em 29,3 min, que compreende apenas uma oxidação e em que a quantidade de reagentes aplicada corresponde à soma dos volumes de reagentes das três oxidações do processo convencional.

Towars a chemical reagents and residues management at the teaching laboratories of the Chemistry School of the Universidad Nacional

The academic activities carried out at the School of Chemistry make indispensable to develop actions oriented toward the consolidation of a reagent and residue management system, especially in the teaching laboratories. The project “Management of reagents and residues in the teaching laboratories of the School of Chemistry” works under the Green Chemistry values which designs products and chemical processes that reduce or eliminate the use and production of dangerous substances, to benefit the environment. With a preventive vision, a change from the  laboratory practices is looked to select those with less environmental impact. Additionally, residue quantification is made and its management protocols are developed for each practice. The project has several stages: diagnose, action implementation, student, teacher and administration personnel training and evaluation during the process and at the end of it. The article describes methodological aspects of the project operation emphasizing on reagent and residue quantification through flow diagrams.