Remoção de metais pesados de efluentes aquosos pela zeólita natural escolecita - influência da temperatura e do pH na adsorção em sistemas monoelementares

Cation exchange capabilities of a Brazilian natural zeolite, identified as scolecite, were evaluated for application in wastewater control. We investigated the process of sorption of chromium(III), nickel(II), cadmium(II) and manganese(II) in synthetic aqueous effluents, including adsorption isotherms of single-metal solutions. The natural zeolite showed the ability to take up the tested heavy metals in the order Cr(III) > Cd(II) > Ni(II) > Mn(II), and this could be related to the valence and the hydration radius of the metal cations. The influence of temperature (25, 40 and 60 ºC) and initial pH value (from 4 to 6) was also evaluated. It was found that the adsorption increased substantially when the temperature was raised to 60 ºC and that maximum adsorption capacity was observed at pH 6. These results demonstrate that scolecite can be used for removal of heavy metals from aqueous effluents, under optimized conditions.

Influência da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de Lippia alba (Mill) N. E. Brown

Leaves of Lippia alba were submitted to six different drying treatments, using air at ambient temperature and heated up to 80 °C. The essential oil was extracted by steam distillation and analyzed by GC-MS. For the dried leaves, the oil content was reduced by 12 to 17% when compared with the fresh plant (0.66%). The major oil component was citral, representing 76% for the fresh plant, and varying from 82 to 84% for the dried material. These results showed that L. alba can be submitted to a drying process of up to 80 ºC without degradation and/or loss of the major, [LC1] active component.

Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário

Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 ºC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 ºC in air atmosphere and at 894 ºC in nitrogen atmosphere.

Otimização e validação da técnica de extração líquido-líquido com partição em baixa temperatura (ELL-PBT) para piretróides em água e análise por CG

The liquid-liquid extraction with the low temperature partition technique was developed for the analysis of four pyrethroids in water by CG. Using a factorial design the extraction technique was optimised evaluating the effect of the variables ionic strength, contact time and proportion between sample and solvent volumes. The validation parameters sensitivity, precision, accuracy and detection and quantification limits were evaluated. The LOD and LOQ of the method varied from 1.1 to 3.2 µg L-1 and 2.7 to 9.5 µg L-1, respectively.

Nióbia magnética como adsorvente de contaminantes orgânicos em meio aquoso: efeito da temperatura e do pH

This work describes novel materials based on pure iron oxide and iron oxide/niobia composite to produce a magnetic adsorbent. These materials were prepared with synthetic iron oxide and characterized by powder XRD, SEM, FTIR, TPR and Mössbauer spectroscopy. Results showed that the main iron oxides formed were goethite (aFeOOH) and maghemite (gFe2O3) with small particle size. The iron oxide and iron oxide/niobia composite showed high adsorption ability for organic compounds. The positive enthalpy indicated an endothermic adsorption process suggesting physical adsorption.

Influência da temperatura de secagem sobre o rendimento e a composição química do óleo essencial de Tanaecium nocturnum (barb. Rodr.) bur. & K. Shum

The yields and chemical compositions of the essential oils obtained by steam distillation of the fresh and dried (30 and 40 ºC) leaves, stems and roots of Tanaecium nocturnum are reported. The identification and quantification of the volatile constituents were accomplished by GC/MS and GC/FID, respectively. The essential oils obtained from the various parts of the plant were constituted mainly of benzaldehyde. Large losses and variations in the quantities of the components during the drying process were observed. The presence of mandelonitrile in higher concentration in the stem and roots indicates that this species produces cyanogenic glycosides.

Influência da luz e da temperatura sobre a oxidação do óleo essencial de capim-limão (Cymbopogon citratus (D.C.) Stapf)

The identification of the chemical compounds of the essential oil was performed with a gas chromatograph coupled to a mass spectrometer. The oil was left in the presence and absence of light and submitted to different temperatures to evaluate its stability. The yields of the major compounds were evaluated every fifteen days. Citral and myrcene, the major compounds of the essential oil, were degraded over time in both the presence and absence of light, but temperature only influenced the degradation of myrcene.

Estudo da degradação fotocatalítica de dimetil dissulfeto: avaliação estatistica do efeito do pH da temperatura e concentração do contaminante orgânico

This work aimed to assess the photocatalytic degradation of a model odor compound (dimethyl disulfide, DMDS), found in liquid and gaseous wastes of plants for processing poultry byproducts. The effect of pH and temperature on adsorption and photocatalytic degradation was evaluated through factorial experimental designs. The results suggest the presence of an optimum region for adsorption, at 45.0 ºC and pH 4.0. In the photocatalytic runs an optimum for temperature and pH was also observed. At 45 ºC and pH 4.0 the removal of DMDS was 99% after 60 min of irradiation.

Hidrólise do óleo de Azadirachta indica em água subcrítica e determinação da composição dos triacilglicerídeos e ácidos graxos por cromatografia gasosa de alta resolução a alta temperatura e cromatografia gasosa de alta resolução acoplada à espectrometria de massas

The development of modern analytical tools plays an important role in quality control. The main purpose of this study was to explore the use of subcritical water as a versatile analytical tool, employed simultaneously as a reagent and solvent, as well as the application of high temperature-high resolution gas chromatography (HT-HRGC) to develop a procedure for the analysis of triacylglycerides and fatty acids in Azadirachta indica A. Juss. (Neem) oil without the need for solvents, chemical reagents, or catalytic agents. The developed method presented satisfactory results and is in agreement with the concepts of Green Analytical Chemistry (GAC).

Possibilidades e limitações no uso da temperatura em cromatografia líquida de fase reversa

High-temperature liquid chromatography (HTLC) is a technique that presents a series of advantages in liquid phase separations, such as: reduced analysis time, reduced pressure drop, reduced asymmetry factors, modified retentions, controlled selectivities, better efficiencies and improved detectivities, as well as permitting green chromatography. The practical limitations that relate to instrumentation and to stationary phase instability are being resolved and this technique is now ready to be applied for routine determinations.

Influência da temperatura, umidade e profundidade do solo na persistência do diurom e sulfato de endossulfam em um solo tropical

The influence of temperature (30 and 40 ºC) and soil humidity (20, 50 and 70% of water holding capacity) on the degradation of the herbicide diurom and the endosulfan metabolite, endosulfan sulfate was studied under laboratory conditions, in different soil layers (0-30, 30-38 and 38-83 cm) of an Oxisol (Yellow Latosol) collected in an agricultural area of Mato Grosso State, Brazil. Endosulfan sulfate was rapidly degraded under lower soil humidity, higher temperature and deeper soil layers. For diurom the opposite was observed as a consequence of its higher water solubility and lower soil sorption coefficient.

Um sistema microcontrolado para o monitoramento on-line, in situ e remoto de pH, condutividade e temperatura de águas

A portable microcontrolled system is proposed to monitor conductivity, temperature and pH in on-line, in situ and remote way from a water reservoir faraway 200 m. The system comprises two modules: one for data reception (located in laboratory) and another for data acquisition/transmission (located near water reservoir). It uses a microcontroller and a transceiver to remote data transmission/reception by radio frequency. Variations of water parameters were simultaneously monitored without interruption during a period of ten hours with a relative error about 4.0 %. The developed system showed simple, stable, accurate, robust and low-cost to determine parameters of water in field.

Variación del grado de avance de reacción en sistemas cerrados en equilibrio químico que modifican la temperatura a volumen constante

In this paper it is presented a thermodynamic analysis that aims to find the mathematical expression of the variation of extent of reaction with the infinitesimal variation in the temperature at constant volume of a chemical equilibrium mixture. The goal of this paper is to establish an alternative approach to avoid both the Le Chatelier's principle and the problems that emerge when trying to apply its qualitative statements. This attempt is based on the laws of thermodynamics.

Efeito da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de Pectis brevipedunculata

Leaves and flower heads of P. brevipedunculata were submitted to four drying-air temperatures (room temperature, 40, 50 and 60 ºC). Room temperature (approximately 30 ºC) and higher temperature drying (50 and 60 ºC) had a deleterious effect on the essential oil content. The recommended drying-air temperature for the species is 40 ºC for it results in the same amount of essential oil observed in fresh cut plants. Overall, 13 components accounting for more than 92% of the total composition were identified. Citral was the major component, followed by α-pinene and limonene. The essential oil showed high toxicity against Artemia salina larvae.

Dinâmica oscilatória em sistemas contendo bromato e 1,4-ciclo-hexanodiona em meio ácido: I. Efeito da temperatura

We present in this work the influence of temperature on the dynamics of homogeneous chemical systems containing bromate and 1,4-cyclohexanedione (1,4-CHD) in acidic media. In particular, the following systems were studied: bromate/1,4-CHD/acid, bromate/1,4-CHD/ferroin/acid and bromate/1,4-CHD/trisbipyridine ruthenium/acid. Investigations were carried out by means of an electrochemical probe, at five temperatures between 5 and 45 °C. Activation energies (Ea) were estimated in different ways for the pre-oscillatory and oscillatory regimes. In any case, the Ea was found to depend on the catalyst, composition and initial concentrations. In addition, it was observed that ferroin and trisbipyridine ruthenium act as catalysts only during the transition between the induction period and oscillatory regime.