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.

Uso de membranas de Nafion para a construção de sensores ópticos para medidas de pH

The behaviour of Nafion® polymeric membranes containing acid-base dyes, bromothymol blue (BB) and methyl violet (MV), were studied aiming at constructing an optical sensor for pH measurement. BB revealed to be inadequate for developing sensing phases due to the electrostatic repulsion between negative groups of their molecules and the negative charge of the sulfonate group of the Nafion®, which causes leaching of the dye from the membrane. On the other hand, MV showed to be suitable due to the presence of positive groups in its structure. The membrane prepared from a methanolic solution whose Nafion®/dye molar ratio was 20 presented the best analytical properties, changing its color from green to violet in the pH range from 0.6 to 3.0. The membrane can be prepared with good reproducibility, presenting durability of ca. 6 months and response time of 22 s, making possible its use for pH determination in flow analysis systems.

Influência do pH sobre a estabilidade de suspensões de alumina estabilizadas eletroestericamente

In this work, aqueous suspensions of aluminas with different particle sizes were evaluated. The effect of pH on the electrosteric stabilization using PMAA-NH4 (ammonium polymethacrylate) as deflocculant was studied. The amount of deflocculant was optimized and rheologic properties were determined at four different pH values. Sedimentation was also evaluated. For suspensions with pH 4, an electrostatic mechanism of stabilization was observed, probably due to a flat adsorption of PMMA- on the alumina surface, leading to a small efficiency in relation to steric stabilization. For a suspension with pH 12, the steric mechanism of stabilization prevails. Suspensions with pH 7 and 9 present a higher flocculation degree. In relation to particle size, A-1000 samples present a smaller particle size, leading to a smaller interparticle distance (IPS), making stabilization more difficult.

Quimissorção de cátions divalentes em sílica gel modificada com ácido tioglicólico: a influência do pH e força iônica

A novel type of heavy metal adsorbent was prepared by the covalent grafting of thioglycolic acid molecules on a silica gel surface previsiouly modified with 3-aminopropyltrimethoxysilane. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This material displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting from aqueous solutions cations such as Cu(II), Ni(II), Co(II), influenced by pH and ionic strength. This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. A modified Langmuir equation describes the experimental data.

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

1792/10-12 (T4).

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

1793/01-07 (T5).

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

1792/01-04 (T2).

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

1791/11-12 (T1).

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

Variante(s) de titre : La Chronique du mois ou les Cahiers patriotiques des Amis de la vérité

La Chronique du mois ou les Cahiers patriotiques de E. Clavière, C. Condorcet, L. Mercier, A. Auger, J. Oswald, N. Bonneville, J. Bidermann, A. Broussonet, A. Guy-Kersaint, J. P. Brissot, J. Ph. Garran de Coulon, J. Dussaulx, F. Lanthenas et Collot-d'Herbois

1792/05-09 (T3).

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.

Fitodisponibilidad de Cd en suelo de diferente pH tratado con lodo albañal estimada por método isotópico y extracción química

The Cd phytoavailability in sewage sludge-amended soils of different pHs using the 109Cd L-value isotopic method and Cd extracted by DTPA has been determined. Maize plants (Zea mais L.) were grown under greenhouse conditions in a xanthic ferralsol at different pHs amended with five sewage sludge (SS) rates, and labeled with 74 kBq kg-1 of 109Cd. The SS rates altered the properties of the soil chemicals and these influenced the isotopic parameter (L-value) and percent of Cd uptake by plants from soil (%Cdpdfs) and SS (%CdpdfSS). L-values and Cd extracted by DTPA correlate significantly with SS rates and Cd uptake by plants and are efficient for predicting the Cd phytoavailability in the sewage sludge-amended soil.

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.

pH effect on the synthesis of magnetite nanoparticles by the chemical reduction-precipitation method

This work aimed at putting in evidence the influence of the pH on the chemical nature and properties of the synthesized magnetic nanocomposites. Saturation magnetization measurements evidenced a marked difference of the magnetic behavior of samples, depending on the final pH of the solution after reaction. Magnetite and maghemite in different proportions were the main magnetic iron oxides actually identified. Synthesis with final pH between 9.7-10.6 produced nearly pure magnetite with little or no other associated iron oxide. Under other synthetic conditions, goethite also appears in proportions that depended upon the pH of the synthesis medium.

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.