Zinc adsorption in highly weathered soils

Abstract

-The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L -1 ), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L -1 Ca(NO 3 ) 2 solutions containing 5 mg L -1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H-and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg ). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.Index terms: pH, adsorption envelope, adsorption isotherm, ionic strength, trace element. Adsorção de zinco em solos altamente intemperizadosResumo -O objetivo deste trabalho foi avaliar o efeito do pH e da força iônica sobre a adsorção de zinco, em três solos altamente intemperizados, com predomínio de cargas variáveis. A partir de experimentos tipo "batch", foram elaboradas isotermas de adsorção, com quantidades crescentes de Zn (0-80 mg L ).A adsorção de Zn foi favorável e espontânea, e mostrou nítido aumento (20-90%) no intervalo de pH entre 4 e 6. Não houve efeito da força iônica nos valores de pH abaixo de 5, o que indica o predomínio de mecanismos de adsorção específica na faixa de pH 3-5. Acima de pH 5 e no subsolo, o Zn foi adsorvido por mecanismos eletrostáticos, já que foi observado efeito da força iônica. Apesar dos efeitos da profundidade e da força iônica, a adsorção de Zn depende principalmente do pH.Termos para indexação: pH, envelope de adsorção, isoterma de adsorção, força iônica, elemento-traço.

Zinc, copper and manganese availability in soils treated with alkaline sewage sludge from Paraná state (Brazil)

“…The specific adsorption is one of the most important mechanisms for controlling Zn and Cu availability in soil. The Zn and Cu adsorption capacity varies depending on the texture, mineralogy, organic matter and pH (Arias et al, 2006;Casagrande;Soares;Mouta, 2008;Smolders et al, 2012), thus, the availability of these nutrients may vary from soil to soil. On the other hand, under natural acid soil condition the Mn usually has high availability, which may promote plants toxicity (Millaleo et al, 2010).…”

Nickel adsorption by variable charge soils: effect of pH and ionic strength

“…In these systems, dependence of adsorption in relation to the variations in the soil solution parameters, such as pH and ionic strength, is determinant for understanding the chemical performance of metals in the soil, from the agricultural, environmental and public health points of view (Uren, 1992). The pH is the primary factor that controls heavy metal adsorption and their availability (Harter, 1983;Casagrande et al, 2008). However, residues and effluents applied to the soil may contain a series of specific chemicals in solution (Tamanini et al, 2008) and the electrolytic concentration is frequently higher than that found in the soil solution (Bowman et al, 1981).…”

“…The Langmuir isotherm, fitted by nonlinear models, was successfully applied in the study of metals in Oxisols, including Ni (Camargo et al, 1989;Pombo et al, 1989). However, metal adsorption modeling in tropical soils is rarely accompanied by a more detailed description, based on thermodynamics concepts (Silveira et al, 1999;Dias et al, 2003;Soares et al, 2005;Iglesias et al, 2007;Casagrande et al, 2008;Mouta et al, 2008;. Some information has been obtained on thermodynamic modeling for the adsorption reaction of some metallic ions by homogeneous surfaces, such as kaolinite and oxidic interfaces (James and Healy, 1972;Angove et al, 1999;Trivedi and Axe, 2000), but there are few data on the thermodynamics of the Ni adsorption reaction in the soils (Sen Gupta and Bhattacharyya, 2006).…”

“…Some information has been obtained on thermodynamic modeling for the adsorption reaction of some metallic ions by homogeneous surfaces, such as kaolinite and oxidic interfaces (James and Healy, 1972;Angove et al, 1999;Trivedi and Axe, 2000), but there are few data on the thermodynamics of the Ni adsorption reaction in the soils (Sen Gupta and Bhattacharyya, 2006). As metal distribution among the liquid and solid phases is a measure of the position of equilibrium in the adsorption process, the state of this system can be defined by a set of thermodynamic properties that can serve as measures of the extension and spontaneity of the adsorption reaction (Soares et al, 2005;Casagrande et al, 2008). The objectives of this study were to investigate the parameters of the Ni adsorption reaction by the soils with predominantly Fe and Al (oxy)hydroxides in their mineralogy and to assess the directional force of this reaction by studying the thermodynamic parameters in function of the variation in soil solution pH and ionic strength.…”

Nickel adsorption and desorption in an acric oxisol as a function of pH, ionic strength and incubation time

“…In addition, the difference between the PZSE values of the soil samples studied by Moreira et al (2008) was similar to that observed in this study, supporting the above hypothesis. According to the results of Silveira and Alleoni (2003), Casagrande, Soares and Mouta (2008), Mouta, Soares and Casagrande (2008), and Soares, Casagrande and Mouta (2009), the higher amounts of metals adsorbed in topsoil horizons are correlated to the organic matter content. Soil organic matter may be responsible for 50 to 95% of the cation exchange capacity (CEC) in Brazilian Oxisols, whose inorganic fraction is predominantly composed by low reactive minerals Alleoni, 2008).…”