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.

Emprego de catalisadores à base de níquel para homo- e copolimerização de estireno

This review deals with the homo- and copolymerization of styrene with nickel catalysts. The catalytic activity, polymer stereoregularity, polymer molecular weight and polydispersity are dependent upon nickel ligands and reaction parameters. Catalysts supported on silica, treated with methylaluminoxane (MAO), have shown higher stereospecificity and activity compared to homogeneous ones. The influence of these parameters is discussed focusing on the elucidation of some aspects of the polymerization mechanism.

Aplicação e modificação química da sílica gel obtida de areia

The silica gel was obtained from sand and its surface was modified with POCl3 to produce Si-Cl bonds on the silica surface. Ethylenediamine was covalently bonded onto the chlorinated silica surface. The adsorption of the chlorides of divalent cobalt, nickel and copper was qualitatively studied to show that the bonding of ethylenediamine onto the silica gel surface produces a solid base capable of chelating metal ions from solution. The experiments illustrate the extraction of silica gel, its reactivity, the development of modified surfaces and its application in removing metal ions from water and are deigned for undergraduate inorganic chemistry laboratories.

O modelamento estatístico de misturas: experimento tutorial usando voltametria de redissolução anódica

This work illustrates the modeling procedure for a solvent mixture using the simplex- centroid approach. The selected experiment was the optimization of the peak current observed in the direct determination of nickel by anodic stripping voltammetry (ASV) in a solvent mixture composed of N,N-dimethylformamide, ethanol and water. The text is presented in a tutorial way, showing in detail the several steps which must be followed in such a process. Since not all possible mixtures lead to a measurable instrumental response, pseudocomponents had to be used to rescale the experimental design. This also allows to show how to apply this tool, usually troublesome for non-specialists in mixture modeling procedures.

Recuperação de metais de catalisadores de hidrorrefino usados via fusão com KHSO4

This work describes a process for metal recovery from spent NiMo and CoMo/Al2O3 commercial hydrorefining catalysts. The samples were treated by fusion with potassium hydrogen sulfate (5 h, 600 ºC) with a KHSO4/catalyst mass ratio of 10:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon compounds as residue. Losses of nickel and cobalt may reach 16 wt% of the amount present in the sample, depending on the silicon content. Soluble metals were isolated by selective precipitation techniques (nickel, cobalt, aluminum) or by solvent extraction with methyl-isobutyl ketone (molybdenum) in a hydrochloric acid medium. All metals were recovered in very good yields except for nickel and cobalt in the presence of considerable amounts of silicon. Soluble wastes consist of potassium/sodium sulfates/chlorides. Solid wastes correspond to about 4 wt% of the catalyst and can be discarded in industrial dumps.

Metil coenzima M redutase (MCR) e o fator 430 (F430)

This review presents studies on methyl coenzyme M reductase, the biological system Factor 430 (F430) and the use of nickel(II) complexes as structural and functional models. The ability of F430 and nickel(II) macrocycle complexes to mediate the reductive dehalogenation of cyclohexyl halogens and the CH3-S bond cleavage of methyl CoM (by sodium borohydride and some intermediate species) proposed for the catalytic cycle of the biological system F430 was reviewed. The importance of the structure of the nickel complexes and the condition of the catalytic reduction reaction are also discussed.

Síntese e caracterização de perovskitas LaNi(1-x)Co xO3 como precursores de catalisadores para a conversão do metano a gás de síntese pela reforma com CO2

LaNiO3 perovskite was modified by partial substitution of nickel by cobalt in order to increase the stability and resistance to carbon deposition during the methane CO2 reforming. The results showed that a suitable combination of precipitation and calcination steps resulted in oxides with the desired structure and with important properties for application in heterogeneous catalysis. The partial substitution of Ni by Co resulted in lower rates of conversion of both the reactants, but the catalyst stability was highly increased. The LaNi0.3Co0.7O3 catalyst, calcined at 800 ºC, was the most active under the reaction conditions.

Produção de hidrogênio a partir da reforma a vapor de etanol utilizando catalisadores Cu/Ni/gama-Al2o3

Cu/Ni/gamma-Al2O3 catalysts were prepared by an impregnation method with 2.5 or 5% wt of copper and 5 or 15% wt of nickel and applied in ethanol steam reforming. The catalysts were characterized by atomic absorption spectrophotometry, X-ray diffraction, temperature programmed reduction with hydrogen and nitrogen adsorption. The samples showed low crystallinity, with the presence of CuO and NiO, both as crystallites and in dispersed phase, as well as of NiO-Al2O3. The catalytic tests carried out at 400 ºC, with a 3:1 water/ethanol molar ratio, indicated the 5Cu/5Ni/Al2O3 catalyst as the most active for hydrogen production, with a hydrogen yield of 77% and ethanol conversion of 98%.

Recuperação de cádmio de baterias níquel-cádmio via extração seletiva com tributilfosfato (TBP)

This work describes a recovery process of cadmium from spent nickel-cadmium batteries by a new hydrometallurgical route based on the selective extraction in hydrochloric acid medium with tributylphosphate (TBP), alone or dissolved in kerosene. The best results were obtained when TBP concentration was at least 75 vol%. Nickel extraction was negligible under these conditions. It was isolated after processing the rafinate through an anionic ion-exchange column. Final wastes generated are basically sodium chloride solutions, with no turbidity, color or heavy metals present in significant amounts.

Electrooxidación de glifosato sobre electrodos de níquel y cobre

The electrochemical oxidation of glyphosate on an electrode of nickel and on one of copper was studied. With both electrodes electrochemical signals related to the glyphosate concentration were observed. However, the behaviour of the copper electrode was much better than that of the nickel electrode. A calibration curve was obtained of the electrical signal of this electrode as a function of the glyphosate concentration. The detection limit was 30 µM. In the case of nickel, an increase in the oxidation signal, which is related to the glyphosate concentration, was obtained. However, the results were less reproducible and additional information is necessary to propose an interaction mechanism between glyphosate and the electrode.

Rota hidrometalúrgica de recuperação de molibdênio, cobalto, níquel e alumínio de catalisadores gastos de hidrotratamento em meio ácido

This work describes a hydrometallurgical route for processing spent commercial catalysts (CoMo and NiMo/Al2O3). Samples were preoxidized (500 ºC, 5 h) in order to eliminate coke and other volatile species present. The calcined solid was dissolved in concentrated H2SO4 and water (1:1 vol/vol) at 90 ºC; the insoluble matter was separated from the solution. Molybdenum was recovered by solvent extraction using tertiary amines at pH around 1.8. Cobalt (or nickel) was separated by addition of aqueous ammonium oxalate at the above pH. Phosphorus was removed by passing the liquid through a strong anion exchange column. Aluminum was recovered by neutralizing the solution with NaOH. The route presented in this work generates less final aqueous wastes because it is not necessary to use alkaline medium during the metal recovery steps.

Alteraciones químicas y fitodisponibilidad de níquel en suelo tratado con lodo albañal

The alteration of soil chemicals and its influence on availability (DTPA extractant method) and phytoavailability (63Ni L-value, isotopic method) of Ni was studied in sewage sludge-amended soil at different pHs. The soil pHs were 4.3, 5.3 and 5.9 and the rates of sewage sludge (SS) 0, 15, 30, 45 and 60 Mg ha-1. The chemical and physicochemical soil characteristics were altered by the SS rate and increased the Ni availability and phytoavailability. The isotopic method (63Ni L-value) was more efficient in predicting the Ni phytoavailability that the Ni-DTPA extractant in soil pHs 5.3 and 5.9.

Estudo da eletrocristalização de Ni e Ni-P sobre ultramicroeletrodo de platina

This work describes a comparative study of the electrocrystallization of Ni and Ni-P on Pt ultramicroelectrodes using chronoamperometric measurements. It was possible to confirm that in all cases a progressive nucleation was the predominant mechanism. Moreover, the application of the Atomistic Theory to the experimental rate of nuclei formation showed that the number of atoms in the critical nucleus was zero, except for Ni-P on Pt at low overpotentials were a value of one was observed. Furthermore, the physical characterisation of the different deposits on Pt by atomic force microscopy allowed observing the coalescence of the hemispherical nuclei of Ni and Ni-P at t max thus confirming the results obtained from the current-time analysis.

Avaliação da composição química de sedimentos do Rio Barigüi na região metropolitana de Curitiba

Sediment samples from the Barigui River in Curitiba, south of Brazil, were evaluated following granulometric composition, organic carbon content, nitrogen, phosphorus and metals such as zinc, lead, chrome, nickel and cadmium. The sediments shown high percentage of phosphorus and nitrogen. Also the elemental organic C:N:P exceed the Redfield ratios possible because the large amount of sewage input into river. The presence of metals is also high, however the metal cadmium has not been found. But the other metals are in greater concentrations and possibly the presence of these metals is given by industrial and domestic sewage.

Hidrogenação eletrocatalítica de substratos orgânicos utilizando eletrodos modificados poliméricos contendo partículas de Ni/Pd e Ni/Pt

Novel modified electrodes bearing dispersed Pd and Pt particles have been prepared from poly (allyl ether of the p-benzenesulfonic acid) films with incorporated nickel particles making use of galvanic displacement reactions. The SEM analysis of the new modified electrodes revealed efficient deposition of Pd but weak up-take of Pt. Electrocatalytic hydrogenation of several classes of organic substrates were carried out using the MEs Ni, Ni/Pd and Ni/Pt. The Ni/Pd ME showed to be the best of them for the hydrogenation of double, triple and carbonyl bonds. The complete hydrogenation of the aromatic rings for the well-adsorbed substrates acetophenone and benzophenone is noteworthy.