Estudo do equilíbrio e cinética da biossorção do pb2+ por saccharomyces cerevisiae

The biosorption, based on the use of biomass for removal of ions is distinguished as an innovative and promising technology when compared with the traditional methods. In this context, the aim of the present work is to use Saccharomyces cerevisiae as biosorbent for the retention of Pb2+ metal ions. Factorial design was used for evaluation of the process. The observed equilibrium data were well described by Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity was 1486.88 mg/g. The results indicated that Saccharomyces cerevisiae is suitable for biosorption of Pb2+ metal ions.

Simulação do equilíbrio: o método de Monte Carlo

We make several simulations using the Monte Carlo method in order to obtain the chemical equilibrium for several first-order reactions and one second-order reaction. We study several direct, reverse and consecutive reactions. These simulations show the fluctuations and relaxation time and help to understand the solution of the corresponding differential equations of chemical kinetics. This work was done in an undergraduate physical chemistry course at UNIFIEO.

Aplicação de Zr/Ti-PILC no processo de adsorção de Cu(II), Co(II) e Ni(II) utilizando modelos físico-químicos de adsorção e termodinâmica do processo

The aim of this investigation is to study how Zr/Ti-PILC adsorbs metals. The physico-chemical proprieties of Zr/Ti-PILC have been optimized with pillarization processes and Cu(II), Ni(II) and Co(II) adsorption from aqueous solution has been carried out, with maximum adsorption values of 8.85, 8.30 and 7.78 x10-1 mmol g-1, respectively. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data with a linear regression process. The energetic effect caused by metal interaction was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

A primeira lei da termodinâmica dos processos homogêneos

Thermodynamics of homogeneous processes, which corresponds to the very special situation in thermodynamics of continuous media, is used to discuss the first law. An important part of this work is the exposition of some typical mathematical errors, frequently found in the traditional presentation of thermodynamics. The concepts of state and process functions are discussed, as well as reverse and reversible processes, temporality and its implications on thermodynamics, energy reservoirs and symmetry. Our proposal is to present the first law by using a time dependent viewpoint coherent with mechanics and the foundations of that viewpoint.

Condições de equilíbrio termodinâmico: a função disponibilidade

The thermodynamic equilibrium is a state defined by conditions which depend upon some characteristics of the system. It requires thermal, mechanical, chemical and phase equilibrium. Continuum thermodynamics, its radical restriction usually called homogeneous processes thermodynamics, as well as the classical thermodynamic science of reversible processes, each of them defines equilibrium in a differing way. But these definitions lead to the same physical contents.

A Equação-Mestra: atingindo o equilíbrio

In the last years, a great interest in nonequilibrium systems has been witnessed. Although the Master Equations are one of the most common methods used to describe these systems, the literature about these equations is not straightforward due to the mathematical framework used in their derivations. The goals of this work are to present the physical concepts behind the Master Equations development and to discuss their basic proprieties via a matrix approach. It is also shown how the Master Equations can be used to model typical nonequilibrium processes like multi-wells chemical reactions and radiation absorption processes.

Modelagem termodinâmica por extração por solvente de metais divalentes em meio sulfato usando D2EHPA

The extraction of divalent metals (Mn2+, Ni2+, Co2+ and Cu2+) in the system MSO4 - H2SO4 - H2O - D2EHPA in isoparaffin (17/21) was studied by a thermodynamic model based on chemical equilibria with mass and charge balance equations. The activity coefficients of all solutes in the aqueous phase were calculated by Davies equation. By applying this model, the equilibrium concentrations of solutes were calculated from de concentration of divalent metals and pH. The predicted distribution coefficients for the divalents metals were in good agreement with experimental results.

A segunda lei da termodinâmica

Considering intrinsic characteristics of the system exclusively, both statistical and information theory interpretations of the second law are used to provide more comprehensive meanings for the concepts of entropy, temperature, and Helmholtz and Gibbs energies. The coherence of Clausius inequality to these concepts is emphasized. The aim of this work is to re-discuss the second law of thermodynamics in accordance to homogeneous processes thermodynamics, a temporal science which is the very special oversimplification of continuum mechanics for spatially constant intensive properties.

Remoção de cromo (VI) de soluções aquosas utilizando o compósito magnético calcinado hidrotalcita-óxido de ferro: estudo cinético e de equilíbrio termodinâmico

In this work, hydrotalcite, a layered double hydroxide, had its ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe 500. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. Removal of chromium (VI) from aqueous solutions using HT-Fe 500 was achieved using batch adsorption experiments. The adsorption capacity, calculated with the Langmuir-Freundlich model showed to be dependent on temperature, reaching values of 25.93 and 48.31 mg g-1, respectively, for temperatures of 25 and 30 ºC.

Físico-química experimental: uma proposta para abordar equilíbrio de fases em sistemas ternários

On undergraduate courses, practical classes represent periods in which students can verify the concepts presented in theoretical classes. Conversely, the teaching internship in graduate programs allows these students to incorporate pedagogical practices into their experience, predominantly involving observation and reproduction of methods adopted by supervisors. We propose internship teaching as a period for reflection on our pedagogical practice and present a methodology for an experimental physical chemistry classroom. The students can interact with the experiment and instructor, furthering the study of ternary systems while developing their skills for investigative work.

Remoção de compostos fenólicos de soluções aquosas utilizando carvão ativado preparado a partir do aguapé (Eichhornia crassipes): estudo cinético e de equilíbrio termodinâmico

Activated carbon was produced from the water hyacinth (CAA) by impregnation with ZnCl2 (1:2), followed by pyrolysis at 700 ºC, under N2. CAA was used for the adsorption of phenol, m-cresol and o-cresol from aqueous solutions, using batch adsorption. The effects of contact time, pH, temperature and concentration on sorption were investigated. Adsorption capacity, calculated using the Langmuir model proved to be dependent on temperature, reaching values of 163.7, 130.2 and 142.3 mg g-1 for phenol, m-cresol and o-cresol, respectively, at 45 ºC. Thermodynamic data at the solid-liquid interface suggests an endothermic, spontaneous and environmentally-friendly process.

Adsorção de alfa-lactalbumina do soro de leite em hidroxiapatita: efeito do pH e da temperatura e análise termodinâmica

The nutritional and functional benefits offered by whey protein α-lactalbumin justify the great interest in its manufacture in large quantities at a high purity level. Hydroxyapatite is a calcium phosphate material able to adsorb proteins and can be synthesized at low production cost. Therefore, this work evaluated the adsorption of α-lactalbumin on hydroxyapatite using solid-liquid phase equilibrium data reported as adsorption isotherms. Van't Hoff's thermodynamics analysis showed that the adsorption process is entropically driven.

Dinâmicas de inquiry no estudo de perturbações a um estado de equilíbrio químico

Educational institutions are not being effective, because they do not give individuals what they need to integrate into postmodern society, nor produce citizens that postmodern society needs. Shortcomings include the scientific literacy and cognitive domain levels attained, with an aggravating waning interest in science among pre-university students. We present an inquiry module, an inquiry dynamic, as an education resource for the study of perturbations of a chemical equilibrium state by pre-university or university students of basic chemistry, to contribute to the relevance and popularity of science, potentiation of science literacy and development of cognition. Here we describe an investigation with pre-university students.

Umidade de equilíbrio de painéis de madeira

Este estudo teve como objetivo a determinação da umidade de equilíbrio de painéis de madeira numa câmara de climatização e comparação dos seus valores com os obtidos através da equação de Nelson. O trabalho foi desenvolvido na Unidade Experimental de Produção de Painéis de Madeira da Universidade Federal de Lavras. Foram utilizadas amostras de aglomerado, compensado multilaminado e sarrafeado, chapa dura, OSB (Oriented Strand Board) , MDF (Medium Density Fiberboard), HDF (High Density Fiberboard), madeira-cimento e madeira-plástico, sendo esses produtos de escala industrial e experimental. As dimensões dos corpos-de-prova foram de 2,60 cm de largura por 2,60 cm de comprimento. As espessuras foram aquelas mais utilizadas comercialmente de cada produto, sendo utilizadas cinco repetições por painel. Os corpos-de-prova foram pesados e levados para uma câmara de climatização, onde foram submetidos a diferentes condições de umidade relativa (90, 80, 70, 60, 50 e 40%) e uma temperatura constante de 30 ºC. Determinaram-se a histerese e a umidade de equilíbrio, que variaram de 40 a 90%. Os resultados indicaram que a equação de Nelson se mostrou eficiente na estimativa da umidade de equilíbrio e que não existe em média diferença de histerese entre os produtos estudados, mostrando que todos apresentam a mesma estabilidade dimensional. Observou-se, também, que o revestimento dos painéis não afetou a umidade de equilíbrio.

Determinação do equilíbrio higroscópico e do calor isostérico do bagaço de cana-de-açúcar

Com o intuito de analisar a dinâmica de sorção e a energia necessária para a vaporização da água na desidratação do bagaço da cana-de-açúcar, o presente trabalho teve como objetivo a determinação de seu equilíbrio higroscópico e calor isostérico, a partir de diferentes condições controladas de temperatura (20; 40; 55 e 70 ºC) e umidade relativa do ar (10; 12; 17; 18; 30; 40; 45; 50; 60 e 85%), assim como avaliar, entre diversos modelos descritos na literatura, o que melhor represente o comportamento de sorção. Como resultado, foi verificado que o modelo que melhor se ajustou aos dados empíricos do processo de sorção do bagaço de cana-de-açúcar foi o Modelo de Henderson Modificado, com coeficiente de determinação de 0,972, enquanto o calor isostérico integral de dessorção variou de 2524,09 a 2951,95 kJ kg-1, para os teores de água de equilíbrio de 0,014 a 0,170 b.s., respectivamente.