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Ethylenediaminetetraacetic acid (EDTA) functionalized silica spheres were used to remove metal ions from aqueous solutions. The adsorption kinetics of Cu 2+ , Zn 2+ , and Cd 2+ (60 mg•L −1 , pH 5.5) were fitted to the pseudosecond order model. Adsorption equilibria were reached within 20 min, indicating that chemisorption may be the limiting step in the adsorption process. Adsorption isotherms were analyzed with nonlinear models by considering the ERRSQ error function and the determination coefficient R 2 . The data with monoion solutions (10 mg•L −1 to 300 mg•L −1 ) were tested with Langmuir, Freundlich, and Redlich−Peterson isotherm models. The best fit was found with the Langmuir model, and maximum adsorption capacities followed the order: Cu 2+ > Zn 2+ > Cd 2+ . Breakthrough curves were obtained using filled columns. The adsorbed ions were quantitatively recovered on elution with hydrogen chloride (0.10 M). After three adsorption−recovery cycles, the metal ions could still be recovered almost quantitatively, which demonstrates the good performance of the EDTA-functionalized silica spheres.

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Coconut bagasse, an agricultural solid waste was used as biosorbent for the removal of cadmium after modification with thiourea. The adsorption of Cd 2+ was studied at pH 5.5. Langmuir, Freundlich, and Temkin isotherms were used to model the adsorption equilibrium data, and it was found that the system followed the Langmuir and Temkin isotherms. The adsorption capacity of the biosorbent was found to be 35.97 mg g -1 , which is higher or comparable to the adsorption capacity of various adsorbents reported in literature. Kinetic studies showed that the adsorption followed a pseudo-second-order rate model.

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Modelagem de Equilíbrio e Cinética de Adsorção: Avaliação do Desempenho do Adsorvente no Abrandamento da Água para Irrigação e o Consumo de Animais Resumo: O bagaço de coco, um desperdício sólido agrícola foi utilizado como biossorvente para remoção de dureza após tratamento alcalinizado. A adsorção de Ca (II) foi estudada a pH 6,8. A análise das isotermas pelo modelo não-linear mostrou que os dados experimentais foram melhor descritos pelo modelo de Temkin, com menor valor χ2 obtido. As capacidades máximas de adsorção pelo modelo de Langmuir foi de 30,20 mg.g-1. Os resultados utilizando o método não linear e linear mostraram baixa discrepância entre eles para o estudo de equilíbrio. Os resultados mostram que o adsorvente de CHA pode ser aplicado para a remoção da dureza das águas residuais.

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