Estudo da oxidação dos sulfetos sintéticos molibdenita (MoS2) e covelita (CuS) por Acidithiobacillus ferrooxidans via respirometria celular

This paper analyses the oxidation of covellite and molybdenite by Acidithiobacillus ferrooxidans strain LR using respirometric experiments. The results showed that both sulfides were oxidized by A. ferrooxidans, however, the covellite oxidation was much higher than molybdenite. Regarding the kinetic oxidation, the findings revealed that just molybdenite oxidation followed the classical Michaelis-Menten kinetic. It is probably associated with the pathway which these sulfides react to chemistry-bacterial attack, what is influenced by its electronic structures. Besides, experiments conducted in the presence of Fe3+ did not indicate alterations in molybdenite oxidation. Thus, ferric ions seem not to be essential to the sulfide oxidations.

Development of a flotation method for preconcentration-separation of trace amounts of some metal ions in plant tissues prior to their FAAS determinations

An efficient flotation method based on the combination of flame atomic absorption spectrometry (FAAS) and separation and preconcentration step for determination of Cr3+, Cu 2+, Co2+, Ni2+, Zn2+, Cd 2+, Fe3+ and Pb2+ ions in various real samples by the possibility of applying bis(2-hydroxyacetophenone)-1,4-butanediimine (BHABDI) as a new collector was studied. The influence of pH, amount of BHABDI as collector, sample matrix, type and amount of eluting agent, type and amount of surfactant as floating agent, ionic strength and air flow rates i.e. variables affecting the efficiency of the extraction system was evaluated. It is ascertained that metal ions such as iron can be separated simultaneously from matrix in the presence of 0.012 mM ligand, 0.025% (w/v) of CTAB to a test sample of 750 mL at pH 6.5. These ions can be eluted quantitatively with 6 mL of 1.0 mol L-1 HNO3 in methanol which lead to the enrichment factor of 125. The detection limits for analyte ions were in the range of 1.3-2.4 ng mL-1. The method has been successfully applied for determination of trace amounts of ions in various real samples.

Adsorption of glyphosate in a forest soil: a study using Mössbauer and FT-IR spectroscopy

We studied the adsorption of glyphosate (GPS) onto soil mineral particles, using FT-IR and Mössbauer spectroscopy. From IR measurements for samples collected under native vegetation of a forest reserve, bands at 1632 and 1407 cm-1 could be attributed to the interaction between the carboxylic group of GPS and structural Al3+ and Fe3+ on the surface of mineral particles; bands at 1075 and 1000 cm-1 were observed only for cultivated soil. Mössbauer spectra for these soils were definitely fitted using a broad central doublet in addition to the magnetic component. This multiple quadrupolar component may be attributed to all non-magnetic Fe3+ contributions, including that of the GPS/Fe3+ complex.

Análise cristalográfica da solução sólida com estrutura tipo Tungstênio Bronze de niobato de potássio e estrôncio dopado com ferro

Solid solution of iron doped potassium strontium niobate with KSr2(FeNb4)O15-Δ stoichiometry was prepared by high efficiency ball milling method. Structural characterization was carried out by X-ray diffraction. Crystalline structure was analyzed by the Rietveld refinements using the FullProf software. The results showed a tetragonal system with the tetragonal tungsten bronze structure - TTB (a = 12.4631 (2) Ã… and c = 3.9322 (6) Ã…, V = 610.78 (2) ų). In this work, the sites occupancy by the K+, Sr2+ and Fe3+ cations on the TTB structure were determined. NbO6 polihedra distortion and its correlation with the theoretical polarization are discussed.

Acetatos homo e heterotrinucleares de ferro: um experimento para o laboratório de química de coordenação

Homo and heterotrinuclear acetates are unique compounds having μ3-oxo bridge and many interesting properties of such compounds are derived from this structure. Some undergraduate inorganic textbooks discuss several aspects of these compounds and we present here an undergraduate experiment for the high-yield synthesis of [Fe2MO(CH3CO2)6(H 2O)3], with M = Fe3+, Co2+ and Ni2+, as well as their characterization using infrared spectroscopy and cyclic voltametry. The proposed experiment gives the opportunity to discuss several concepts of coordination chemistry that follow the characterization techniques, such as: types of acetate coordination, reversibility of electrochemical processes, quelate and trans effects and lability.

Alvejamento químico de caulins Brasileiros: efeito do potencial eletroquímico da polpa e do ajuste do pH

Samples of Kaolin from different regions in Brazil were characterized by XRD, SEM and chemical analysis. A chemical bleaching study with pH adjustment was accomplished with the fractions below 37 μm, after classification by screening. The main objective was to evaluate the conditions of chemical bleaching that most increase the brightness of these kaolin's samples. Increases between 2.63 and 2.98% in the brightness (ISO) were observed after the chemical bleaching. We could say that the reduction of Fe3+ to Fe2+ during the chemical bleaching promoted an increase in the brightness, based on the Pourbaix Diagrams.

Determinação simultânea de ácido kójico e hidroquinona por espectrofotometria visível e calibração multivariada

A multivariate spectrophotometric method was developed for analysis of kojic acid/hydroquinone associations in skin whitening cosmetics. The method is based on the reaction between kojic acid and Fe3+ and on the reduction of Fe3+ by hydroquinone and further complexation of Fe2+ with 1,10-phenanthroline. The multivariate model was developed by Partial Least Squares Regression (PLSR), using 25 synthetic mixtures and mean-centered spectral data (350-380 nm). The use of 3 (kojic acid) and 2 (hydroquinone) latent variables permits the observation of mean errors of about 5% in the external validation phase.

Montagem de uma disciplina experimental: contribuição para a química geral

The purpose of this paper is to present a classification criterion for general chemistry experiments departing from a survey of 35 years of the experimental general chemistry discipline at the Chemistry Institute - UNICAMP. It is shown that by considering the most remarkable characteristics of an experiment and classifying it under Conceptual, Fundamental, Methodological or Quantitative criterion, teachers could better develop the discipline plan and prevent a subject superposition. Taking into account the system Fe3+/SCN- , the article also exemplify how is possible to modify an experimental approach and to conceive other procedures with different didactic purposes.

Preconcentration, determination and speciation of iron by solid-phase extraction using dimethyl (E)-2-[(Z)-1-acetyl)-2-hydroxy-1-propenyl]-2-butenedioate

A new sensitive and selective procedure for speciation of trace dissolved Fe(III) and Fe(II), using modified octadecyl silica membrane disks and determination by flame atomic absorption spectrometry was developed. A ML3 complex is formed between the ligand and Fe(III) responsible for extraction of metal ion on the disk. Various factors influencing the separation of iron were investigated and the optimized operation conditions were established. Under optimum conditions, an enrichment factor of 166 was obtained for Fe3+ ions. The calibration graph using the preconcentration system for Fe3+ was linear between 40.0 and 1000.0 μg L-1.

Actividad catalítica de metales de transición en la descomposición de peróxido de hidrógeno

This paper compares the catalytic activities of some transition metal ions (Fe3+, Co2+, Cu2+, Ni2+, Zn2+) in the H2O2 decomposition in homogenous and heterogeneous processes, including solid mixed systems (Fe-Cu-Co/Al2O3, Fe-Cu/Al2O3, Fe-Co/Al2O3 and Co-Cu/Al2O3). The solids were characterised by X-ray diffraction to explore evolution of phases or possible changes. Different trends of the catalytic activity were observed: in homogeneous medium the most active species was Fe3+, whereas in heterogeneous one the higher activities were shown for Co/Al2O3 and Co-Cu/Al2O3. A strong cooperative effect for the Co-Cu/Al2O3 system was observed, which can be considered as a new catalyst of interest for this type of reactions.

Preparation and evaluation of magnetic chitosan particles modified with ethylenediamine and Fe(III) for the removal of Cr(VI) from aqueous solutions

The adsorption of Cr(VI) in aqueous solution by magnetic particles of crosslinked chitosan-ethylenediamine-Fe(III) (MPCh-EDA-FeCL) was studied in a batch system. Fe3+ in the MPCh-EDA-FeCL permitted that adsorption of Cr(VI) occurred with maximum efficiency between pH 3 and 11. The maximum adsorption capacity at pH 7.0 was 81.04 mg g-1 at 25 ºC. The adsorption kinetic process was described by the pseudo-second-order model. Thermodynamic parameters indicated spontaneous, exothermic and chemical adsorption nature. The adsorbent was successively regenerated using a 0.1 mol L-1 NaOH solution. Results were satisfactory for treatment of wastewater from the electroplating industry.

Ascorbic acid determination using a carbon paste electrode modified with iron(III) ions adsorbed on humic acid

An amperometric sensor was constructed, by using humic acids to immobilize Fe3+ ions on a carbon paste electrode (CPE-HA-Fe), and used for ascorbic acid (H2A) determination. The cyclic voltammogram of the electrode showed electrochemical response due to the Fe3+/Fe2+ couple at E1/2=+0.78 V vs SCE, using 0.5 mol L-1 KCl and 0.2 mol L-1 acetate/0.020 mol L-1 phosphate buffer, at pH = 5.4, as supporting electrolyte. When H2A is added to the electrolyte solution it is observed an oxidation process. The oxidation current, obtained by chronoamperommetry at +0.87 V vs SCE, is proportional to the concentration, represented by the equation I(µA) = 7.6286 [H2A] (mmol L-1) + 1.9583, r = 0.9996, for concentrations between 0.0 and 1.4 mmol L-1. The electrode showed high stability and was used for H2A determination in a natural orange juice.

Assessment of hydrochemical quality of ground water under some urban areas within sana'a secreteriat

Groundwater from nine wells of three different districts, located at Sana'a secretariat was analyzed for hydrochemical quality assessment. Measurements of water quality parameters including pH, EC, CO3(2-), HCO3-, Cl-, NO3-, SO4(2-), Ca2+, Mg2+, Fe3+, K+, and Na+ were carried out . Classification of the groundwater samples according to Cl, SO4(2-), CO3(2-) and HCO3-, hardness (H), total dissolved solids (TDS), base-exchange, and meteoric genesis was demonstrated. Suitability of ground water samples for irrigation and industrial uses according to sodium adsorption ration (SAR), ratio of dissolved sodium (RDS), residual sodium carbonate (RSC) and saturation index (SI) was also investigated. The results of this study showed that almost all ground water samples were of good quality that makes them suitable for drinking and domestic uses. Results also indicated that even though some of the ground water samples were suitable for irrigation purposes, almost all of them were found not be good for industrial uses. Despite all drawbacks of the sewerage system built around Sana'a secretariat at the beginning of the first decade of the third millennium, the results of this study indicate that there is scope of significant improvement in Sana'a secretariat ground water quality.

Análise quantitativa da ecogenicidade testicular pela técnica do histograma de ovinos da baixada ocidental maranhense

A ultrassonografia é um método de diagnóstico por imagem que permite a avaliação de diferentes órgãos e estruturas corpóreas de maneira não invasiva. No entanto, a avaliação subjetiva das imagens caracteriza um dos grandes entraves na utilização desta técnica de diagnóstico, havendo necessidade de mecanismos que minimizem a subjetividade do exame e a divergência na interpretação dos achados ultrassonográficos. Desta forma este trabalho objetivou caracterizar a ecogenicidade do parênquima e mediastino testicular de ovinos utilizando a técnica do histograma escala-cinza. Foram utilizados 30 animais divididos em três grupos de acordo com a faixa etária (FE): de três a seis meses (FE1), sete a 12 meses (FE2), 13 a 18 meses (FE3) e realizadas varreduras testiculares nos planos frontal, sagital e transversal, elaborando ao final um histograma a partir das imagens ultrassonográficas. Observou-se que tanto a ecogenicidade do parênquima quanto a do mediastino testicular aumentaram gradativamente com a progressão das idades dos animais, com média e desvio-padrão de 95,00±19,05 e 94,35±18,82 para a ecogenicidade do parênquima do antímero direito e esquerdo, respectivamente, e 127,95±12,97 para o mediastino direito e 126,59±11,78 para o esquerdo. A técnica do histograma escala-cinza demonstrou ser um método eficiente na determinação da ecogenicidade testicular, possibilitando o estabelecimento de padrões de normalidade que venham a auxiliar pesquisas futuras no monitoramento do desenvolvimento testicular bem como na detecção de patologias. Para a regimes exclusivos de criação extensiva, como na baixada maranhense, representa ferramenta valiosa para sua utilização em projetos sociais do Estado que atendem a agricultura familiar.

Wet oxidation of biomass for chemical production

Tämän kandidaatintyön tarkoituksena oli tutkia märkähapetusprosessia jätevesien käsittely-menetelmänä ja mahdollisena menetelmänä kemikaalien tuottamiseksi jätevesistä. Erityishuomio on kiinnitetty paperiteollisuudessa syntyviin jätevesiin. Teoriaosassa käsitellään vesikiertoja paperitehtaassa, paperitehtaalla syntyvän jäteveden ominaisuuksia sekä itse märkähapetusprosessia. Märkähapetusprosessissa perehdytään tavalliseen happea käyttävään märkähapetukseen sekä vetyperoksidia käyttävään menetelmään sekä näissä prosesseissa syntyviin väli- ja lopputuotteisiin. Märkähapetus (WO) on terminen hapetusmenetelmä, jolla voidaan käsitellä jätevesiä, jotka ovat liian konsentroituja biologisiin käsittelyihin tai jotka ovat huonosti biohajoavia. Märkähapetuksen tarkoituksena on parantaa molekulaarisen hapen ja orgaanisen aineen välistä kontaktia, jolloin orgaaninen aines pilkkoutuu muodostaen pääasiassa karboksyylihappoja, aldehydejä, hiilidioksidia ja vettä. Märkähapetuksessa hapettavana kaasuna voidaan käyttää joko puhdasta happea tai ilmaa. Vetyperoksidia käyttävässä märkähapetuksessa (WPO) hapettava kaasu on korvattu nestemäisellä vetyperoksidilla. Kokeellisessa osassa tutkittiin orgaanisen aineksen hapetusta käyttäen Fentonin reagenssia, jolloin katalyyttina reaktiossa toimii rautaionit (Fe2+ ja Fe3+) ja hapettimena vetyperoksidi. Hapetettavana jätevetenä käytettiin paperitehtaan hiomolta saatua kiertovettä, TMP-vettä. Hapetuskokeita tehtiin eri vetyperoksidin annoksilla ja katalyytin määrillä eri lämpötiloissa. Hapetuksen jälkeen näytteistä mitattiin kemiallinen hapenkulutus (COD), orgaanisen hiilen kokonaismäärä (TOC) sekä pH. Lisäksi näytteistä määritettiin nestekromatografilla (HPLC) tyypillisten välituotteiden, kuten oksaalihapon, muurahaishapon ja etikkahapon, määrät. Tehdyissä kokeissa COD-arvoja saatiin pienennettyä 50-88 % siten, että suodatetuissa näytteissä muutos oli suurempi kuin suodattamattomissa näytteissä. Lisäksi TOC-arvot laskivat 28-58 %. Tehdyissä kokeissa saatiin myös tuotettua välituotteina karboksyylihappoja, joista etikkahappoa ja oksaalihappoa tuotettiin suurimmat määrät. Myös muurahaishappoa ja meripihkahappoa saatiin tuotettua.