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Avaliação da estabilidade dos fármacos furosemida e aminofilina em soluções parenterais de grande volume. Utilização da proteína verde fluorescente (GFP) como biossensor da estabilidade de fármacos em soluções parenterais; Evaluation of furosemide and aminophilline stability in parenteral solutions. Utilization of Green Fluorescent Protein (GFP) as biosensor for drugs stability in parenteral solutions

Santos, Carolina Alves dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/02/2007 PT
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A avaliação da estabilidade dos medicamentos e sua correta utilização em diferentes veículos de infusão são fundamentais para garantir a manutenção das características terapêuticas do fármaco e para promover minimização de eventos adversos. Incompatibilidades entre as estruturas dos fármacos, em diferentes veículos de administração, podem gerar possíveis associações antagônicas ou sinérgicas, resultando em alterações das propriedades físico-químicas e, consequentemente, dos efeitos farmacológicos e das respostas clínicas esperadas. A proteína verde fluorescente (GFP) por apresentar propriedades de sensibilidade e especificidade, mostra-se promissora como potencial biossensor da estabilidade de fármacos em soluções parenterais de grande volume (SPGV), por apresentar sensibilidade a alterações das propriedades físico-químicas do meio. GFP é uma proteína compacta, globular e ácida, composta de um monômero de 27kDa, que vem sendo extensivamente utilizada como indicador biológico em processos de esterilização e desinfecção devido a sua estabilidade a altas temperaturas. O surgimento de métodos analíticos modernos e de alta precisão como a espectrofotometria de UV e a cromatografia líquida de alta eficiência (HPLC)...

Leaching of Ni and Cu from mine wastes (tailings and slags) using acid solutions and A. ferrooxidans

Muñoz, A.; Bevilaqua, D.; Garcia, O.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 425-428
ENG
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The objective of this work is to evaluate the acidic and biological leaching of tailings containing Ni/Cu from a flotation and smelting plant. Acidithiobacillus ferrooxidans, strain LR, was used for bioleaching at pH 1.8 and chemical controls were run parallel to that. The acidic leaching was done within 48 hours at pH 0.5 and 1.0. In the slag inoculated flasks the redox potential was high (600 mV), thus indicating oxidative bacterial activity, however, the obtained results after 15 days showed only around 13% Ni and 8% Cu extractions, which were not different to those of the controls. For the flotation tailings bioleaching extractions were approximately 45% for Ni and 16% for Cu while differing figures were obtained for the chemical controls. These were 30% and 12% respectively. Here we could observe that the presence of bacterial activity led to a higher solubility of Ni. Acid leaching of slag showed higher nickel and copper extractions: 56% and 24% respectively at pH 0.5 and 21% and 11% at pH 1.0. However, the acid consumption was 320 and 150 Kg/ton of slag, respectively, both much higher than in bacterial assays. These results indicated that Ni and Cu solubilization from the slag is acid dependent no matter the redox potential or ferric iron concentration of the leaching solution. For flotation tailings...

Carbon nanotube-reinforced siloxane-PMMA hybrid coatings with high corrosion resistance

Hammer, P.; Dos Santos, F. C.; Cerrutti, B. M.; Pulcinelli, S. H.; Santilli, C. V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 601-608
ENG
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35.92%
Siloxane-polymethyl methacrylate hybrid films containing functionalized multiwall carbon nanotubes (CNTs) were deposited by dip-coating on carbon steel substrates from a sol prepared by radical polymerization of methyl methacrylate and 3-methacryloxy propyl-trimethoxysilane, followed by hydrolytic co-polycondensation of tetraethoxysilane. The correlation between the structural properties and corrosion protection efficiency was studied as a function of the molar ratio of nanotubes carbon to silicon, varied in the range between 0.1% and 5%. 29Si nuclear magnetic resonance and thermogravimetric measurements have shown that hybrids containing carbon nanotubes have a similar degree of polycondensation and thermal stability as the undoped matrix and exhibit and excellent adhesion to the substrate. Microscopy and X-ray photoelectron spectroscopy results revealed a very good dispersion of carbon nanotubes in the hybrid matrix and the presence of carboxylic groups allowing covalent bonding with the end-siloxane nodes. Potentiodynamic polarization curves and electrochemical impedance spectroscopy results demonstrate that CNTs containing coatings maintain the excellent corrosion protection efficiency of the hybrids, showing even a superior performance in acidic solution. The nanocomposite structure acts as efficient corrosion barrier...

3-phenyl-4-acyl-5-isoxazolones as reagents for liquid-liquid extraction of tetravalent zirconium and hafnium from acidic chloride solutions

Reddy,B. Ramachandra; Kumar,J. Rajesh; Reddy,A. Varada
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2006 EN
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Liquid liquid extraction of tetravalent zirconium and hafnium from acidic chloride solutions has been investigated using 3-phenyl-4-acyl-5-isoxazolones in xylene such as 3-phenyl-4-benzoyl-5-isoxazolones (HPBI), 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI). The extraction of zirconium(IV) / hafnium(IV) shows a ion exchange mechanism: MO2+ (aq) + 2 HA (org) « MOA2 (org) + 2 H+(aq), where M = Zr(IV) / Hf(IV) and HA = HPBI or HFBPI or HTPI. The variation of the D ([MOA2] (org) / [MO2+](aq); ratio of the possible extraction equilibrium species) values with an increase of the acid / extractant concentration showed a linear plot with a slope of 2. The effect of the nature of the diluents like carbon tetrachloride, cyclohexane, n-hexane, benzene, nitrobenzene, xylene, toluene and chloroform on the extraction of zirconium(IV) / hafnium(IV) has been studied. The extraction behavior of zirconium(IV) / hafnium(IV) was also compared with that of other metal ions like titanium(IV), aluminium(III) and iron(III), which can be generally associated with the metal ions studied.

Mechanisms for the solvolytic decompositions of nucleoside analogues. X. Acidic hydrolysis of 6-substituted 9-(beta-D-ribofuranosyl)purines.

Lönnberg, H; Lehikoinen, P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 24/07/1982 EN
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The pH-rate profiles were determined for the acidic hydrolysis of some 6-substituted 9-(beta-D-ribofuranosyl) purines. The product analyses indicated that the reactions generally proceed with formation of purine bases as initial products. However, at low oxonium ion concentrations the hydrolysis of the unsubstituted compound yields 4-amino-5-formamidopyrimidine, instead of purine formed in highly acidic solutions. The rate constants for the spontaneous and oxonium ion catalyzed heterolysis of the protonated substrates were calculated from the acidity constants and the observed rate constants. The dependence of the partial rate constants on the polar nature of the 6-substituents are consistent with rate-limiting formation of free purine bases and glycosyl oxocarbenium ions. No anomerization of the substrates was observed during the course of the hydrolysis.

Monomer concentrations and dimerization constants in crystallizing lysozyme solutions by dialysis kinetics.

Wilson, L J; Adcock-Downey, L; Pusey, M L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1996 EN
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35.96%
Dialysis kinetics measurements have been made to study the effect of ionic strength on the dimerization of lysozyme in acidic solutions that lead to the growth of tetragonal lysozyme crystals. Using glutaraldehyde cross-linked dimers of lysozyme, we have determined that both monomers and dimers can escape from 25,000 molecular weight cutoff dialysis membranes with velocity constants of 5.1 x 10(-7) and 1.0 x 10(-7) s(-1) for the monomer and dimer species, respectively. The flux from 25K MWCO membranes has been measured for lysozyme in pH 4.0 buffered solutions of 1, 3, 4, 5, and 7% NaCl over a wide range of protein concentrations. Assuming that dimerization is the first step in crystallization, a simple monomer to dimer equilibrium was used to model the flux rates. Dimerization constants calculated at low protein concentrations were 265, 750, 1212, and 7879 M(-1) for 3, 4, 5, and 7% NaCl, respectively. These values indicate that dimerization increases with the ionic strength of the solution suggesting that aggregation is moderated by electrostatic interactions. At high protein concentrations and high supersaturation, the dimerization model does not describe the data well. However, the Li model that uses a pathway of monomer <-> dimer <-> tetramer <-> octamer <-> 16-mer fits the measured flux data remarkably well suggesting the presence of higher order aggregates in crystallizing solutions.

Characterization of a catalytically efficient acidic RNA-cleaving deoxyribozyme

Kandadai, Srinivas A.; Li, Yingfu
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
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We previously demonstrated—through the isolation of RNA-cleaving deoxyribozymes by in vitro selection that are catalytically active in highly acidic solutions—that DNA, despite its chemical simplicity, could perform catalysis under challenging chemical conditions [Liu,Z., Mei,S.H., Brennan,J.D. and Li,Y. (2003) J. Am. Chem. Soc. 125, 7539–7545]. One remarkable DNA molecule therefrom is pH4DZ1, a self-cleaving deoxyribozyme that exhibits a kobs of ∼1 min−1 at pH 3.8. In this study, we carried out a series of experiments to examine the sequence and catalytic properties of this acidic deoxyribozyme. Extensive nucleotide truncation experiments indicated that pH4DZ1 was a considerably large deoxyribozyme, requiring ∼80 out of the original 123 nt for the optimal catalytic activity. A reselection experiment identified ten absolutely conserved nucleotides that are distributed in three catalytically crucial sequence elements. In addition, a trans deoxyribozyme was successfully designed. Comparison of the observed rate constant of pH4DZ1 with experimentally determined rate constant for the uncatalyzed reaction revealed that pH4DZ1 achieved a rate enhancement of ∼106-fold. This study provides valuable information about this low-pH-functional deoxyribozyme and paves way for further structural and mechanistic characterization of this unique catalytic DNA.

Helicobacter pylori is killed by nitrite under acidic conditions

Dykhuizen, R; Fraser, A; McKenzie, H; Golden, M; Leifert, C; Benjamin, N
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1998 EN
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Background—Due to the expression of urease, Helicobacter pylori is able to establish itself in the human stomach under acidic conditions. A novel host defence mechanism was recently proposed, suggesting that the formation of salivary nitrite in symbiosis with facultative anaerobic bacteria in the oropharynx, is aimed at enhancing the antimicrobial activity of gastric juice. 
Aims—To investigate whether the addition of nitrite in physiological concentrations influences the resistance of H pylori to acid.
Methods—H pylori cultured from fresh gastric biopsy specimens was exposed for 30 minutes to normal saline and to HCl/KCl buffer (0.2M) at pH 2 with urea (5 mM) added. The influence of potassium nitrite (50-1000 µmol/l) on bacterial survival was determined.
Results—Addition of nitrite (1 mM) to acidic solutions (pH 2) resulted in complete kill of H pylori within 30 minutes exposure time whereas acid alone allowed the organism to survive (p<0.001). The antimicrobial effect of nitrite at pH 2 against H pylori was dose dependent and complete kill of organisms occurred at concentrations ⩾500 µmol/l.
Conclusion—Acidified nitrite has antibacterial activity against H pylori. This should prompt further research into the effect of salivary nitrite on the survival of H pylori in the human stomach. 



Acidic Hydrolysis of N-ethoxybenzylimidazoles (NEBIs): Potential Applications as pH-Sensitive Linkers for Drug Delivery

Kong, Seong Deok; Luong, Alice; Manorek, Gerald; Howell, Stephen B.; Yang, Jerry
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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This paper describes the development of a new class of N-linked imidazoles as potential pH-sensitive, cleavable linkers for use in cancer drug delivery systems. Kinetic analysis of 8 derivatives of N-ethoxybenzylimidazoles (NEBIs) showed that their rates of hydrolysis are accelerated in mild aqueous acidic solutions compared to in solutions at normal, physiological pH. Incorporation of electron donating or electron withdrawing substituents on the phenyl ring of the NEBI resulted in the ability to tune the rates of hydrolysis under mild acidic conditions with half-lives ranging from minutes to months. A derivative of NEBI carrying doxorubicin, a widely used anticancer agent, also showed an increased rate of hydrolysis under mild acid compared to at normal, physiological pH. The doxorubicin analog resulting from hydrolysis from the NEBI exhibited good cytotoxic activity when exposed to human ovarian cancer cells. These results demonstrate a potentially useful, general strategy for conjugating a wide range of drugs to imidazole-containing delivery vessels via NEBI functionalities for controlled release of therapeutics for drug delivery applications.

Translocation of single stranded DNA through the α-hemolysin protein nanopore in acidic solutions

de Zoysa, Ranulu Samanthi S.; Krishantha, D.M. Milan; Zhao, Qitao; Gupta, Jyoti; Guan, Xiyun
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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35.92%
The effect of acidic pH on the translocation of single-stranded DNA through the α-hemolysin pore is investigated. Two significantly different types of events, i.e., deep blockades and shallow blockades, are observed at low pH. The residence times of the shallow blockades are not significantly different from those of the DNA translocation events obtained at or near physiological pH, while the deep blockades have much larger residence times and blockage amplitudes. With a decrease in the pH of the electrolyte solution, the percentage of the deep blockades in the total events increases. Furthermore, the mean residence time of these long-lived events is dependent on the length of DNA, and also varies with the nucleotide base, suggesting that they are appropriate for use in DNA analysis. In addition to be used as an effective approach to affect DNA translocation in the nanopore, manipulation of the pH of the electrolyte solution provides a potential means to greatly enhance the sensitivity of nanopore stochastic sensing.

Valence stabilization of polyvalent ions during gamma irradiation of their aqueous solutions by sacrificial protection. III-Valence stabilization of Fe(II) ions by organic additives

Barakat, M. F.; Abdel Hamid, M. M.
Fonte: Springer Netherlands Publicador: Springer Netherlands
Tipo: Artigo de Revista Científica
EN
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Valence stabilization of polyvalent ions in gamma irradiated aqueous solutions is sometimes necessary in some chemical operations. In previous publications, valence stabilization of some polyvalent ions in solution upon gamma irradiation was achieved by using inorganic additives capable of interacting with the oxidizing or reducing species formed during water radiolysis. The results showed that the nature and duration of valence stabilization of Fe(II) depend on the concentration of the inorganic additives used. In the present work, a series of some organic additives has been used to investigate their capability in inducing valence stabilization of polyvalent iron ions, taken as an indicator, in aqueous acidic solutions when subjected to extended gamma irradiation. The results showed that the efficiency of valence stabilization depends on the amount and chemical structure of the organic additive used.

Hydrolysis of Plutonium(IV) in Acidic Solutions - No Effect of Hydrolysis on Absorption-spectra of Mononuclear Hydroxide Complexes

WALTHER C.; CHO H. R.; MARQUARDT C. M.; NECK V.; SEIBERT Alice; YUN J.-I.; FANGHAENEL THOMAS
Fonte: OLDENBOURG VERLAG Publicador: OLDENBOURG VERLAG
Tipo: Articles in Journals Formato: Printed
ENG
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Tetravalent plutonium readily undergoes hydrolysis even in highly acidic aqueous solutions. In the past, many attempts were made to quantify hydrolysis species by means of optical absorption spectroscopy. In the present work solutions ranging from 10-5 M to 10-2 M (total Pu) concentration in 0.5M HCl/NaCl (0.3 < pHc < 2.1) are carefully investigated by combining absorption-spectroscopy (UV-Vis, liquid core waveguide capillary) and laser-induced breakdown detection, with special emphasis on the limited solubility of Pu(IV). The results clearly indicate that all changes in the absorption spectra originate from the formation of Pu-polyspecies and colloids. The molar absorptivity of mononuclear Pu(IV) hydroxide complexes does not vary with increasing pHc and ongoing hydrolysis. The normalized absorption spectra of at least the first and the second hydroxide complex (Pu(OH)n 4-n n = 1, 2) do not differ from those of the hydrated Pu4+ ion.; JRC.E.5-Nuclear chemistry

Influência de bebidas ácidas e alcoólicas sobre as propriedades físicas e mecânicas de resinas compostas; Influence of acidic and alcoholic beverages on the physical and mechanical properties of composite resins

Marcos Aurelio Bomfim da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/01/2013 PT
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36.18%
Os objetivos nesta tese, composta por 2 capítulos, foram: (1) avaliar a rugosidade de superfície, microdureza e microinfiltração marginal de uma resina composta nanopartículada quando submetida à degradação em soluções ácidas e (2) avaliar a influência de soluções alcoólicas sobre a rugosidade e dureza de superfície de resinas compostas microparticulada, microhíbrida e nanoparticulada. No capítulo 1, foram preparadas 60 cavidades na face vestibular de incisivos bovinos, restauradas com resina de nanopartículas Filtek Z350 XT (3M/ESPE). Os dentes foram separados em três grupos de tratamento (n = 20): A (controle) - imersão em saliva artificial durante 30 dias; B - Imersão em café por 15 min (3x/dia), durante 30 dias, e C - imersão em Coca-cola® por 15 min (3x/dia), durante 30 dias. Após os períodos de imersão, os espécimes foram analisados quanto à microdureza em microdurômetro com edentador tipo Knoop, rugosidade de superfície em microscópio de força atômica e microinfiltração marginal com penetração de corantes quando submetidos à ciclagem térmica e mecânica. A rugosidade de superfície e microdureza foram submetidas à análise de variância (ANOVA) seguida pelo teste- t com nível de significância de 5% e a microinfiltração marginal ao teste de Mann-Whitney...

Thermal denaturation in acidic solutions of double-helical ribonucleic acid from virus-like particles found in Penicillium chrysogenum. A spectrophotometric study

Cox, R. A.; Kanagalingam, K.; Sutherland, Elisabeth
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1971 EN
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1. Two species of double-helical RNA isolated from mycelium of Penicillium chrysogenum were titrated with acid at 25°C and 95°C (solvent 0.1m-sodium phosphate buffer). At 25°C denaturation occurred at about pH3. At 95°C in the denatured form cytosine residues titrated as a simple monobasic acid of pK3.9 compared with pK≃2.5 for the native form at 25°C. 2. On thermal denaturation in neutral and acidic solutions one species of RNA (38% rG·rC) `melted' in three distinct stages, equivalent to a mixture of three species, namely one of about 25% rG·rC, another of about 33% rG·rC and a third of about 46% rG·rC: the relative proportions were 0.25:0.35:0.40. 3. On thermal denaturation in acidic solutions the increase in the fraction of ionized cytosine residues concomitant with the `melting' of rG·rC base pair also affects the spectrum especially at 280nm and serves to enhance the contribution of rG·rC base pairs at this wavelength. The increment in ε(P) at 280nm on `melting' an rG·rC base pair approaches 53501·mol−1·cm−1 depending on pH, compared with 33501·mol−1·cm−1 at pH7. In contrast ε(P) at 280nm is scarcely affected by `melting' rA·rU base pairs or by the protonization of adenine residues. 4. Changes in the spectrum of Escherichia coli rRNA on denaturation in acidic solutions were studied to yield the mole fractions of rA·rU and rG·rC base pairs `melting' at particular pH values.

Effect of Acidic Solutions on the Surface Degradation of a Micro-Hybrid Composite Resin

Münchow,Eliseu A.; Ferreira,Ana Cláudia A.; Machado,Raissa M. M.; Ramos,Tatiana S.; Rodrigues-Junior,Sinval A.; Zanchi,Cesar H.
Fonte: Fundação Odontológica de Ribeirão Preto Publicador: Fundação Odontológica de Ribeirão Preto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
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36.28%
Composite resins may undergo wear by the action of chemical substances (e.g., saliva, alcohol, bacterial acids) of the oral environment, which may affect the material's structure and surface properties. This study evaluated the effect of acidic substances on the surface properties of a micro-hybrid composite resin (Filtek Z-250). Eighty specimens were prepared, and baseline hardness and surface roughness (KMN0 and Ra0, respectively) were measured. The specimens were subjected to sorption (SO) and solubility (SL) tests according to ISO 4049:2009, but using different storage solutions: deionized water; 75/25 vol% ethanol/water solution; lactic acid; propionic acid; and acetic acid. The acids were used in two concentrations: PA and 0.02 N. pH was measured for all solutions and final hardness (KMN1) and surface roughness (Ra1) were measured. Data were analyzed with paired t-tests and one-way ANOVA and Tukey's test (a=5%). All solutions decreased hardness and increased the Ra values, except for the specimens stored in water and 0.02 N lactic acid, which maintained the hardness. All solutions produced similar SO and SL phenomena, except for the 0.02 N lactic acid, which caused lower solubility than the other solutions. Ethanol showed the highest pH (6.6) and the 0.02 N lactic acid the lowest one (2.5). The solutions affected negatively the surface properties of the composite resin; in addition...

Identifying key controls on the behaviour of an acidic-U(VI) plume in the Savannah River Site using reactive transport modeling

Bea, Sergio Andrés; Wainwright, Haruko; Spycher, Nicolas; Faybishenko, Boris; Hubbard, Susan S.; Denham, Miles E.
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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Acidic low-level waste radioactive waste solutions were discharged to three unlined seepage basins at the F-Area of the Department of Energy (DOE) Savannah River Site (SRS), South Carolina, USA, from 1955 through 1989. Despite of many years of active remediation, the groundwater remains acidic and contaminated with significant levels of U(VI) and other radionuclides. Monitored Natural Attenuation (MNA) is a desired closure strategy for the site, based on the premise that regional flow of clean background groundwater will eventually neutralize the groundwater acidity, immobilizing U(VI) through adsorption. An in situ treatment system is currently in place to accelerate this in the downgradient portion of the plume and similar measures could be taken upgradient if necessary. Understanding the long-term pH and U(VI) adsorption behavior at the site is critical to assess feasibility of MNA along with the in-situ remediation treatments. This paper presents a reactive transport (RT) model and uncertainty quantification (UQ) analyses to explore key controls on the U(VI)-plume evolution and long-term mobility at this site. Two-dimensional numerical RT simulations are run including the saturated and unsaturated (vadose) zones, U(VI) and H+ adsorption (surface complexation) onto sediments...

Extraction of cadmium from aqueous solutions by emulsion liquid membranes using a stirred transfer cell contactor

Marchese, José; Valenzuela, Fernando; Ochoa, Ariel; Sapag Hagar, Jaime; Acosta, Adolfo; Poblete, Maritza; Basualto Flores, Carlos Alfonso
Fonte: SOC BRASILEIRA QUIMICA Publicador: SOC BRASILEIRA QUIMICA
Tipo: Artículo de revista
EN
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It is studied the extraction of cadmium( II) ions from acidic aqueous solutions using a stirred transfer cell-type emulsion liquid membrane ( ELM) prepared by dissolving in kerosene, with D2EHPA ( an alkylphosphoric acid) as mobile carrier and Span-80 as surfactant. The ELM allowed efficient metal transport from the feed solution to the stripping liquor in experiments carried out at 25 C. The significant variables on cadmium transport through the membrane were extractant concentration and metal content in the feed metal-donor solution. Concentration of HCl as stripping agent affected only the initial metal extraction rate but not the extraction extent. The surfactant content used in this study stabilized the membrane adequately, but the use of a higher content produced a smaller initial extraction rate due to higher interfacial resistance. The experimental results suggest the possibility of recovering or removing valuable or toxic metals from dilute aqueous solution in an extractor based on emulsified liquid membranes.

On the kinetics of Cu, As and Sb transport through cation and anion exchange membranes in acidic electrolytes

Ibáñez, J. P.; Cifuentes, L.
Fonte: METALLURGICAL SOC-C I M, CANADIAN METALLURGICAL Q, QUEENS UNIV, GOODWIN HALL Publicador: METALLURGICAL SOC-C I M, CANADIAN METALLURGICAL Q, QUEENS UNIV, GOODWIN HALL
Tipo: Artículo de revista
EN
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35.92%
Experiments were conducted in a batch electrodialysis cell containing aqueous acidic solutions of copper, arsenic and antimony in order to evaluate their transport kinetics through commercial ion exchange membranes. A relatively high unwanted transport of bisulfate through the cation exchange membrane was observed with the transport rate being 0.39 mol/h/m2 at 225 A/m2. The bisulfate transport rate through the anion exchange membrane was found to be 1.05 mol/h/m2 at the same current density. The transport rate for the unwanted transfer of copper ions through the anion exchange membrane varied linearly with time and current density; the transport rates were 0.07 and 0.10 mol/h/m2 at 150 and 225 A/m2, respectively. These values were found to be lower than 1/7 of the transport rate of copper for both current densities, through the cation exchange membrane. Arsenic transport was found to be highly dependent on speciation. In a 1.5 mol/L H2SO4 solution, As(III) was transported as AsO+ with a rate of 0.02 mol/h/m2 at 225 A/m2 and As(V) was transported as H2AsO4 - with a rate of 0.01 mol/h/m2 in 0.5 mol/L of acid. At pH 2.8, the transport of As(V) increased tenfold to about 0.1 mol/h/m2. Antimony was transported through both anion and cation membranes at 2.7 and 3.4 mmol/h/m2...

Lead Chemical Dissolution in Acidic Medium in the Presence of Citrate; Dissolução Química do Chumbo em Meio Ácido na Presença de Citrato

Walysson G. Pereira; Universidade Estadual do Ceará; Gledson V. Lima; Universidade Estadual do Ceará; Felipe D. Abreu; Universidade Estadual do Ceará; Carlos Emanuel de C. Magalhães; Universidade Estadual do Ceará; Eduardo B. Barros; Universidade
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 25/12/2012 PT
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Lead is metal of great interest to scientific community due to the toxicity of its compounds against living beings. Otherwise, the citrate ion is a complexing agent with the ability to solubilize many metallic ions in solution. However, a few works are reported in the literature upon the dissolution of metallic lead in the presence of citrate ions in acidic solutions. The present work aims to study the lead dissolution into acidic solutions (pH 4) in the presence of citrate ions. It was observed the formation of insoluble lead citrate on the metal surface and its stoichiometric structure is Pb3(C6H5O7).4 H2O. The lead dissolution is affected to the concentration of citrate ions in the medium and to the buffering solution characteristics. When increasing citrate ions concentration in solution, the formation of insoluble lead citrate on the metal surface does not occur. Probably this compound is precipitated due to the pH increase nearby the metal surface. The lead dissolution kinetics and the lead citrate morphology are influenced by the stirring of the solution. However, the mechanism of dissolution is practically unchanged. DOI: 10.5935/1984-6835.20120049; O chumbo é um dos metais que mais desperta o interesse da comunidade científica devido à sua toxicidade e a de seus compostos frente aos seres vivos. Por outro lado...

Removal of uranium from aqueous solutions using ammonium-modified zeolite

Bakatula,Elisée N.; Mosai,Alseno K.; Tutu,Hlanganani
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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Batch experiments were conducted to study the effects of contact time, pH (3 to 8), initial concentration, presence of carbonate, sulphate, and competing ions (Fe³+,Ca²+,Sr²+,Mg²+) on the adsorption of U(VI) on ammonium-modified zeolite (AMZ). The structural features of the modified zeolite were assessed by Fourier Transform Infra Red Spectroscopy (FTIR) while the metal content was determined by Inductively Coupled Plasma Optical Emission Specroscopy (ICP-OES). The removal of uranium was effective and maximal under acidic conditions (pH 3 to 5). The kinetics of adsorption of U-nitrate and U-sulphate on AMZ were described by the pseudo-second-order model (R² ≥ 0.9820). In the presence of SO4²" and CO3(2-), a significant reduction of 67.88 % and 71.63 %, respectively, in uranium uptake was observed. The distribution coefficient, K D(L g-1), was in the order of: U-nitrate (1.116) > U-sulphate (0.029) > U-carbonate (0.019), suggesting that AMZ had a high affinity for U-nitrate. The presence of Fe³+ enhanced the removal of U(VI) from U-nitrate, U-sulphate and U-carbonate by 20.18 %, 72.48 % and 82.43 %, respectively, while the presence of Ca²+,Mg²+ and Sr²+ reduced the removal to 19.57 %, 31.60 % and 23.65 %, respectively. AMZ is an effective adsorbent for uranium removal from aqueous solutions dominated by nitrate...