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Type: Artigo de periódico
Title: Natural vermiculite as an exchanger support for heavy cations in aqueous solution
Author: da Fonseca, MG
de Oliveira, MM
Arakaki, LNH
Espinola, JGP
Airoldi, C
Abstract: The natural highly charged lamellar silicate vermiculite was investigated as an exchanger matrix in doubly distilled water solution to exchange magnesium inside the lamella with the heavy cations copper, nickel, cobalt, and lead at the solid/liquid interface. The extension of each exchange reaction was dependent on time of reaction, pH, and cation concentration. The maximum time presented the following order Pb2+ < Ni2+ < Cu2+ < CO2+, which corresponds to 12, 24, 48, and 72 h, respectively. The best performance was observed for nickel, as represented by the exchange capacity N-f, which gave values 0.59, 0.76, 0.84, and 0.93 mmol g(-1) for Pb2+ < CO2+ < Cu2+ < Ni2+, respectively. This capacity is dependent on pH interval variation from I to 9, being significantly increased in alkaline condition. The isotherm data were adjusted to a modified Langmuir equation and from the data the spontaneous Gibbs free energy was calculated. Linear correlations were obtained through Gibbs free energy or the maximum capacity against the cationic radius plot, with the lowest values for the largest cation lead. An exponential con-elation was also observed for the maximum capacity versus enthalpy of hydration plot, indicating a difficulty of the less hydrated cation, lead, in exchanging with magnesium inside the lamellar space, as suggested by the proposed mechanism. The saturated matrices with cations presented a decrease in interlayer distance in comparison with the original vermiculite, which can be related to the hydrated phases, characteristic for each cation, with a lowest value for lead. (c) 2004 Elsevier Inc. All rights reserved.
Subject: ionic exchanger
heavy ions
Country: EUA
Editor: Academic Press Inc Elsevier Science
Citation: Journal Of Colloid And Interface Science. Academic Press Inc Elsevier Science, v. 285, n. 1, n. 50, n. 55, 2005.
Rights: fechado
Identifier DOI: 10.1016/j.jcis.2004.11.031
Date Issue: 2005
Appears in Collections:Unicamp - Artigos e Outros Documentos

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