Association of individual soil mineral constituents and heavy metals as studied by sorption experiments and analytical electron microscopy analyses

doi:10.1016/j.jhazmat.2009.03.033

Journal of Hazardous Materials

Volume 168, Issues 2–3, 15 September 2009, Pages 1512-1520

https://doi.org/10.1016/j.jhazmat.2009.03.033 Get rights and content

Abstract

Sorption characteristics of bulk soil samples and discrete soil mineral constituents were studied by Cu, Zn and Pb batch sorption experiments and analytical electron microscopy analyses. Copper and zinc sorbed mostly on soil mineral constituents, while lead was associated mainly to soil organic matter. Additionally, the competitive situation resulted in increase of the role of iron oxides in Pb sorption. Close association of iron oxides and silicates resulted in significant change in their sorption capacities for all the studied metals. The alkaline conditions due to the calcite content in one of the studied soil samples resulted in both increased role of precipitation for Pb and Cu and elevated sorption capacity for Cu by discrete mineral particles. Using the analytical electron microscopy analyses the sorption characteristics of metals were supported by particular data. When the methods used in this study are combined, they become an extremely powerful means of getting a deeper insight into the soil–metal interaction.

Introduction

The ability of soils to adsorb metal ions from aqueous solution is of special interest and has consequences both for agricultural issues and environmental questions. As adsorption is a major process for accumulation of potentially toxic metals in soils, its study is of utmost importance for the understanding of how metals are transferred from a liquid mobile phase to the surface of a solid phase [1]. The exact retention mechanism of metal ions at soil surfaces is often unknown, so the term sorption is preferred, which in general involves the loss of a metal ion from an aqueous to a contiguous solid phase and consist of three important processes: adsorption, surface precipitation and fixation [2]. These processes are dependent on soil properties which are strongly influenced by the soil constituents. The organic matter, clay minerals, as well as Fe and Mn oxides are the most important components determining the sorption of metals in soils [3]. The organic components form stable metal–organic complexes with a variety of metals, while clay minerals and oxides concentrate heavy metal ions through surface ion exchange and metal-complex surface adsorption.

Batch equilibrium techniques are widely used to study the retention of metals in soils and the sorption data are described by using isotherms. The analysis of isotherms may provide information about the retention capacity and the sorption strength by which the sorbate is held onto the soil. However, the information gained through adsorption isotherms is limited because the interaction of metals with solid phases cannot be determined and the actual partitioning of metals in various chemical phases cannot be identified [4]. Additionally, when extending the number of the studied soils, including soils of contrasting characteristics, it is difficult to draw clear conclusions on the soil phases responsible for the sorption of the target metals, since sorption is a process that depends on variety of factors [5]. Additionally, despite the intense study of metal sorption capacity of separated soil constituents, little is known about the metal retention capacity of discrete mineral constituents within the soil.

To overcome the limitations of sorption studies mentioned above, it is worth combining sorption isotherm analyses with direct instrumental analytical techniques to study the characteristics of metal sorption onto soil components. Besides the application of X-ray absorption spectroscopy methods [6], [7], this kind of approach was successfully used also by Sipos et al. [8] who studied the sorption properties of lead onto soil mineral constituents by analytical electron microscopy. However, metal sorption in soils is a competitive process among different ions [9], so the direct analysis of sorption of a given metal in the presence of others is of primary importance. In this study, the integrated use of analytical electron microscopy analyses and competitive sorption experiments were performed on soil samples with different composition. Samples for Cu, Zn and Pb sorption experiments were selected according to their significant organic matter, carbonate mineral and iron oxide content, as well as to their different clay mineralogy as these phases play an important role in metal immobilization in soils. The aim of this study was to investigate the metal sorption capacity of discrete soil mineral constituents (mainly clay minerals, iron oxides and carbonates). Special attention was directed to study the effect of presence of organic matter as well as carbonate and iron oxide phases on the sorption capacity of discrete soil clay mineral phases.

Section snippets

Studied soil samples

Four natural soil samples were used in the laboratory experiments. The samples were collected from a Calcic (P9) and a Haplic Luvisol (P13) profiles, with silt loam and clay loam textures, respectively [10]. The air-dried samples were passed through a 2 mm sieve. Some physico-chemical properties of the studied samples are presented in Table 1. The sample from the A horizon of the profile P9 (P9A) is characterized by relatively high total organic carbon content (67.4 g kg⁻¹) and intermediate cation

Sorption studies

Copper, Zn and Pb sorption experiments were carried out to study the immobilization of metals by the soil samples with different composition. As the affinity of metals to soil may be strongly influenced by the initial metal concentrations in solutions used (which is six times higher for Zn than for Cu in our case), therefore, the sorption intensity values will be used to compare the sorption capacity of the studied samples. According to Xiong et al. [15] sorption intensity is a useful measure

Conclusions

Higher sorption intensity for Cu and lower for Zn was observed by both the results of sorption experiments and analytical electron microscopy analyses. Despite its highest sorption intensity among the studied metals, the generally lowest Pb sorption capacity of discrete mineral particles was found suggesting indirectly the significant role of soil organic matter in Pb immobilization which was also supported by the sorption experiments. Additionally, the competitive situation resulted in

Acknowledgements

This study was financially supported by the Hungarian Scientific Research Fund (OTKA no. F 62760 and PF 63973).

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Association of individual soil mineral constituents and heavy metals as studied by sorption experiments and analytical electron microscopy analyses

Abstract

Introduction

Section snippets

Studied soil samples

Sorption studies

Conclusions

Acknowledgements

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Environ. Int.

Geochim. Cosmochim. Acta

Geoderma

J. Anal. Appl. Pyrolysis

Chem. Geol.

Environ. Pollut.

Appl. Clay Sci.

Appl. Geochem.

Chemosphere

Chem. Geol.

Colloid Surf.

Geochim. Cosmochim. Acta

J. Colloid Interface Sci.

Chemosphere

Geochim. Cosmochim. Acta

Adsorption of heavy metal ions on soil surfaces and similar substances: theoretical aspects

Nickel adsorption on MnO2, Fe(OH)3, montmorillonite, humic acid and calcite: a comparative study

Environ. Technol.

Effect of natural organic matter on arsenic release from soils and sediments into groundwater

Environ. Geochem. Health

Sorption of heavy metals in strongly weathered soils: an overview

Environ. Geochem. Health

Geologic and pedogenic effects on heavy metal distributions in forest soils from the Cserhát Mts and the Karancs area, NE Hungary

Acta Geol. Hung.

Characterization of clay minerals in brown forest soil profiles (Luvisols) in Cserhát mountains (North Hungary)

Agrokem. Talajtan

Nickel adsorption on MnO₂, Fe(OH)₃, montmorillonite, humic acid and calcite: a comparative study