Effect of arsenate on adsorption of Cd(II) by two variable charge soils

doi:10.1016/j.chemosphere.2006.11.057

Chemosphere

Volume 67, Issue 10, May 2007, Pages 1949-1955

https://doi.org/10.1016/j.chemosphere.2006.11.057 Get rights and content

Abstract

The effect of arsenate on Cd(II) adsorption in two variable charge soils and the desorption of Cd(II) pre-adsorbed in the presence of arsenate were studied. The batch type experiments showed, the presence of arsenate led to increase in Cd(II) adsorption and the desorption of pre-adsorbed Cd(II). Further it was observed that the extent of adsorption and desorption of Cd(II) was greatly influenced by the initial concentrations of arsenate and Cd(II), the solution pH, and the nature of the soils. In general the increase in arsenate concentration and pH favored the uptake of Cd(II). Moreover, the arsenate concentration influenced more in Hyper-Rhodic Ferralsol than Rhodic Ferralsol at least for the Cd(II) adsorption/desorption. This may be due to the content of Fe/Al oxides in these soils. The larger the content of Fe/Al oxides, the more the adsorption of arsenate by the soil, hence greater the uptake of Cd(II). It can be assumed that the enhanced Cd(II) adsorption was mainly due to the increase in net negative surface charge of the soil induced by the adsorption of arsenate, because the presence of arsenate led to the decrease in zeta potential of these soil suspensions. The increase of electrostatically adsorbed Cd(II) was responsible for the increase in the desorption of Cd(II) pre-adsorbed in the presence of arsenate.

Introduction

The concentration of heavy metal in soil solution is of great importance for all ecological consideration because the plants are likely to take up the available metals from soil solution. The transport of metals within the soil or even to groundwater also depends on the metal concentration of the solution phase (Brummer et al., 1986). Chemical processes strongly affect the fate and availability of Cd in soils. It was suggested that sorption and desorption reactions on the surface of soil and oxides are two important processes controlling the concentration of heavy metals in solution (Brummer et al., 1988, Ainsworth et al., 1994, Backes et al., 1995, McLaren et al., 1998). Studies on Cd(II) adsorption was performed on soils and oxides (Forbes et al., 1976, Boekhold et al., 1993, Brummer et al., 1986, Naidu et al., 1994, Naidu et al., 1998) and mostly these studies were conducted in a single metal system and some of them were involved in competitive adsorption between Cd(II) and other heavy metal cations in soils and clay minerals (Echeverría et al., 1998, Gomes et al., 2001, Fontes and Gomes, 2003, Serrano et al., 2005, Srivastava et al., 2005). However, heavy metals exist as multiple pollutants, including different metals and different forms of the same metals, in wastes (Zagury et al., 2003). Arsenic and cadmium contamination are a common co-occurrence in many contaminated environments including mining areas, soils and sediments (Lee, 2006, Liu et al., 2005, Mirlean and Roisenberg, 2006). Hence, the investigation of interactions between multiple metal pollutants in soil samples would have greater practical importance to understand the fate of these pollutants in soils.

In recent years, co-adsorption of Cd(II) and other heavy metals with oxyanions has been investigated on soil and oxides (Benjamin and Leckie, 1982, Hoins et al., 1993, Davis and Bhatnagar, 1995, Venema et al., 1997, Collins et al., 1999, Lee and Doolittle, 2002). Wang and Xing, 2002, Wang and Xing, 2004 found that phosphate not only enhanced the Cd(II) adsorption on goethite, but also accelerated the adsorption process. The results of Hoins et al. (1993) suggested that there were two possible mechanisms for simultaneous adsorption of sulfate and Cd(II) on goethite: sulfate adsorption reduced the surface potential so that the surface became more attractive for Cd(II); ternary surface complexation took place on the reactive surface sites of goethite. Investigation with extended X-ray absorption fine structure (EXAFS) spectroscopy, Collins et al. (1999) concluded that the enhancement of Cd adsorption on goethite in the presence of phosphate and sulfate was solely by electrostatic interaction, no ternary complexes were observed in the presence of these inorganic ligands. However, while studying the co-sorption of Zn and arsenate at the goethite–water interface, Gräfe et al. (2004) found an adamite-like surface precipitation on goethite as revealed by the EXAFS spectroscopic studies. Further it was suggested, the surface adsorption reactions of Zn and arsenate with goethite were the part of initial reaction processes and precipitates formed while aging (Gräfe and Sparks, 2005).

It is well known, tropical and subtropical regions are distributed with large areas of variable charge soils. These soils usually carry both positive and negative charges on their surfaces, therefore can adsorb both anions and cations (Yu, 1997). Similar to goethite system, co-adsorption of heavy metals with oxyanions possibly exists in this type of soil (Xu et al., 2005). The objective of this study is to evaluate the effect of arsenate on Cd(II) adsorption by two variable charge soils and to discuss the mechanisms involved at solid/solution interface.

Section snippets

Soils

Two variable charge subsoils, a Hyper-Rhodic Ferralsol (located at 102°43′E, 25°3′N) and a Rhodic Ferralsol (located at 110°10′E, 20° 20′N), were collected respectively, from Kunming, Yunnan Province and Xuwen, Guangdong Province, China. The soil samples were air-dried and ground to pass a 60-mesh sieve. Selected properties of the soils were given in Table 1.

Adsorption/desorption experiments

A stock solution containing 0.01 or 0.1 M Cd(NO₃)₂ was prepared using reagent-grade Cd (NO₃)₂ · 3H₂O. 0.01 mol l⁻¹ KH₂AsO₄ solution was

Effect of arsenate on Cd(II)adsorption and the desorption of pre-adsorbed Cd(II)

The effect of arsenate on the adsorption in two variable charge soils and the desorption of Cd(II) pre-adsorbed in the presence of arsenate were studied and the results obtained were presented graphically in Fig. 1, Fig. 2. These figures clearly indicated, the presence of arsenate induced an apparent increase in Cd(II) adsorption onto these two soils and this increase in Cd(II) adsorption was further enhanced with an increase of adsorption equilibrium concentration of Cd(II). Comparatively, the

Discussion

The present study deals to find out the possible effect of arsenate on Cd(II) adsorption by the variable charge soils. Moreover, the mechanistic aspects can perhaps be explained on the basis of following three mechanisms:

1.
Enhancement by electrostatic interaction (e.g., Diaz-Barrentos et al., 1990);
2.
Formation of a ternary cation–anion-surface complex (e.g., Lamy et al., 1991);
3.
Formation of a surface precipitate (e.g., Hawke et al., 1989).

The results reported here suggested that Cd(II) adsorption in

Conclusions

The results presented in this study confirmed that the presence of arsenate led to an increase in Cd(II) adsorption by variable charge soils mainly through the change in surface charge and surface potential induced by specific adsorption of arsenate. The adsorption and desorption of Cd(II) onto these two soil surfaces i.e., Hyper-Rhodic Ferralsol and Rhodic Ferralsol in presence of arsenate largely depends on the solution pH, the initial concentrations of arsenate and Cd(II) and also the nature

Acknowledgements

The financial support from the National Natural Science Foundation of China (No. 20577054) and National Basic Research and Development Program of China (2002CB410808) is greatly acknowledged.

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Effect of arsenate on adsorption of Cd(II) by two variable charge soils

Abstract

Introduction

Section snippets

Soils

Adsorption/desorption experiments

Effect of arsenate on Cd(II)adsorption and the desorption of pre-adsorbed Cd(II)

Discussion

Conclusions

Acknowledgements

Geochim. Cosmochim. Acta

Chemosphere

Environ. Pollut.

Appl. Geochem.

Geochim. Cosmochim. Acta

Geoderma

Sci. Total Environ.

Environ. Pollut.

Geoderma

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Chemosphere

Environ. Pollut.

J. Colloid Interface Sci.

Cobalt, cadmium, and lead sorption to hydrous iron oxide: residence time effect

Soil Sci. Soc. Am. J.

Kinetics of cadmium and cobalt desorption from iron and manganese oxides

Soil Sci. Soc. Am. J.

Effects of complexation by Cl, SO4, and S2O3 on adsorption behaviour of Cd on oxide surfaces

Environ. Sci. Technol.

Influence of electrolyte composition and pH on cadmium sorption by an acid sandy soil

J. Soil Sci.

Effects of complexation by Cl, SO₄, and S₂O₃ on adsorption behaviour of Cd on oxide surfaces