Adsorção de íons Cu2+ em latossolo vermelho-amarelo húmico

Abstract

Recebido em 1/6/98; aceito em 1/7/99 ADSORPTION OF Cu2+ IONS BY A HUMIC YELLOW RED OXISOL. In environmental studies it is necessary to know the adsorption behavior of metals by soils, since the unfavorable effects of heavy metals and even the micronutrients at high concentrations in the environment are related to these adsorbents' ability to immobilize them. A sample of a humic yellow red oxisol from Araponga region in the State of Minas Gerais, Brazil, was used to verify the adsorption behavior of Cu 2+ ions in this substrate. The mathematical model described by Langmuir's adsorption equation in its linearized form was applied and the values of the maximum capacity b and those of the constant related to the bonding energy a were obtained. Aliquots of copper nitrate solutions containing several concentrations of this metal were added to soil samples, the pH being predetermined for developing the adsorption experiments. The chemical and physical characterization of soil sample were performed by determining the organic carbon, nitrogen and phosphorus concentrations, cation exchange capacity (CEC), pH, concentration of metals (Al, Fe, K, Mg, Ca, Zn, Cu, Ni, Cr, Co, Pb, and Cd), granulometric analysis and X-ray diffraction. Langmuir isotherms presented two distinct adsorption regions at both pH 4 and pH 5, showing that the adsorptive phenomenon occurs in two distinct stages. The adsorption sites for the lower part presented greater bonding energy and low adsorption capacity compared with the adsorption sites of the part of the curve corresponding to higher Cu concentrations in the equilibrating solution.Keywords: copper; adsorption; oxisol. ARTIGO INTRODUÇÃOEm estudos ambientais, há a necessidade de se conhecer o comportamento adsortivo de metais por solos, pois os efeitos desfavoráveis em função de altas concentrações no meio ambiente, estão relacionados à habilidade desses substratos em adsorver tais substâncias. Altas concentrações de cobre na camada superficial do solo indicam a adição ao mesmo de restos de fundição, fertilizantes, fungicidas, bactericidas, lodo de esgoto ou outros rejeitos 1 . Por definição, metais pesados são elementos que têm peso específico maior que 5 g cm -3 . A expressão metal pesado também é usada para designar os metais classificados como poluentes do ar, água, solo, plantas e alimentos, ou seja, do meio ambiente 2 . Alguns deles são benéficos em pequenas quantidades para microorganismos, plantas e animais; porém, em concentrações elevadas, tornam-se perigosos, pois são introduzidos na cadeia alimentar, podendo contaminar as plantas e os animais consumíveis pelo homem 3 . Nutrientes, tais como cálcio, potássio e magnésio, são geralmente requeridos por plantas ou microorganismos em altas concentrações, sendo chamados de macronutrientes; enquanto que cobre, ferro, zinco, manganês, molibdênio e outros elementos são apenas necessários em pequenas quantidades e são chamados de micronutrientes. Esses micro e macronutrientes atendem aos critérios de essencialidade, pois na sua ausência as plan...

Influência do tempo de agitação na adsorção de Cd, Cu, Ni e Zn em latossolo tratado com lodo de esgoto

“…Esse fato demonstra a alta afinidade dos constituintes do solo, principalmente a matéria orgânica com este elemento. Conforme JORDÃO et al (2000), o tempo de agitação para completar o equilíbrio de adsorção do Cu varia entre 1 e 24 horas para diferentes tipos de solo. SOARES et al (2004) verificaram que para vermicomposto de esterco bovino o equilíbrio é alcançado em torno de 20 horas, o que condiz com os resultados constantes deste trabalho.…”

“…Segundo JORDÃO et al (2000), o tempo de agitação para completar o equilíbrio de adsorção dos metais varia para diferentes tipos de solo e com o pH.…”

Copper adsorption in tropical oxisols

“…The adsorption reactions which occur at the solid-liquid interface are an important mechanism for controlling the activity of heavy metals, not only in the soil solution, but also in natural water bodies (McLaren and Crawford, 1973;McBride et al, 1997;Salam and Helmke, 1998). The forms of adsorbed Cu control its concentration in the soil solution (Jordão et al, 2000). In this context, an understanding of the behavior of copper in the soil is fundamental for the prediction of the environmental consequences of its incorporation in the agroecosystem.…”

“…When applied to minerals, sediments and soils, it is used in the form: x/m= KbC/1 + KC, in which K = parameter related to the affinity of the adsorvent by the adsorvate b = maximum adsorption. Despite their limitations, the Freundlich and the Langmuir models have been used in various studies of Cu adsorption (Petruzzelli et al, 1985;Temminghoff et al, 1994;Yuan and Lavkulich, 1997;Jordão et al, 2000) and may be useful to predict the behavior of metals in the soil. The correlation coefficients obtained in these studies varied between 0.83 and 0.99, indicating that these models are well adjusted to diverse soil conditions and metal concentrations.…”

“…The correlation coefficients obtained in these studies varied between 0.83 and 0.99, indicating that these models are well adjusted to diverse soil conditions and metal concentrations. One of the advantages of modeling is the possibility to express mathematically some of the soil properties, such as the nature of the adsorption processes (Jordão et al, 2000). Furthermore, the maximum adsorption parameter (Langmuir) may be used as an indicator to compare soil with different characteristics, as well as the effects of pH and organic material in the adsorption of the metal.…”