Elsevier

Journal of Hazardous Materials

Volume 330, 15 May 2017, Pages 142-148
Journal of Hazardous Materials

Competitive adsorption of As(III), As(V), Sb(III) and Sb(V) onto ferrihydrite in multi-component systems: Implications for mobility and distribution

https://doi.org/10.1016/j.jhazmat.2017.02.016Get rights and content

Highlights

  • Sb(III) had a stronger inhibitory influence on As(III) adsorption than Sb(V) did.

  • Sb(V) adsorption was more negatively affected by As(V) than As(III).

  • The affinity order of As(III), As(V), Sb(III) and Sb(V) in quaternary systems was dependent on pH.

  • Competitive adsorption mainly occur between As(III) and Sb(III), or take place between As(V) and Sb(V).

Abstract

The simultaneous adsorption behavior and competitive interactions between As(III), As(V), Sb(III) and Sb(V) by ferrihydrite were evaluated in multi-component (binary, ternary, quaternary) systems. In binary systems, Sb(III) had a stronger inhibitory influence on As(III) adsorption than Sb(V) did, and As(V) had a stronger inhibitory effect on Sb(V) adsorption than As(III) did. In ternary systems, NO3, PO43− and SO42− did not compete with the adsorption of As(III) and Sb(III). NO3 and SO42− also had no distinct effect on the adsorption of As(V) and Sb(V), while PO43− competed with As(V) and Sb(V) for surface sites. In quaternary systems, the simultaneous adsorption behavior of the four redox species was pH dependent. Sb(III) always showed the strongest adsorption affinity regardless of pH. At pH 3.5 As(III) showed the lowest affinity could be due to the presence and negative effect of Sb(III) and As(V). The Freundlich model provided a good fit for the simultaneous adsorption data under quaternary conditions. The study of competitive/simultaneous adsorption of the four possible redox species onto ferrihydrite contributed to a better understanding of their distribution, mobility and fate in the environment.

Introduction

Environmental contamination by coexisting toxic elements, such as arsenic (As) and antimony (Sb), has received substantial attention because of a higher risk to human health and ecological safety. High levels of co-occurring As and Sb in waters and soils around old mining and smelting areas have been reported in many areas [1], [2], [3], [4]. Arsenic and Sb are metalloids of the fifth main group of the periodic table sharing the same electron configuration in their outer shell (s2p3). They both occur in the same range of oxidation states (−3 to +5), which are mostly found in inorganic forms either as trivalent (As(III)) and (Sb(III)) species under anoxic conditions or as pentavalent (As(V) and Sb(V)) species under oxic conditions in aquatic environment. Since As and Sb are expected to share numerous similarities in chemical properties and toxicity, it is more difficult to assess and remediate the contamination of coexisting As and Sb species.

Both As and Sb can be adsorbed strongly onto hydrous ferric oxide (HFO), such as goethite, ferrihydrite and akaganeite [5], [6], [7], [8]. They appear to exhibit a similar adsorption behavior. For example, both the adsorption of As(V) and Sb(V) was found to be dependent on pH with increased adsorption under acidic pH conditions [9], [10], while the adsorption of As(III) and Sb(III) was reported as being less pH dependent [11], [12]. The coexistence of other potential adsorbates could have similar influences on adsorption behavior of As and Sb. For example, sulfate (SO42−), carbonate (HCO3) and nitrate (NO3) have minor influence on the individual adsorption of As and Sb, while phosphate (PO4) is a well-known competitor for the adsorption of both As(V) and Sb(V) [13], [14], [15], [16]. Moreover, As and Sb could share a similar adsorption mechanism through the formation of inner-sphere complexes [17], [18], [19]. Thus it is crucial to evaluate the simultaneous adsorption behavior of As and Sb, particularly when both compete for the surface sites. So far, few studies have been reported concerning the simultaneous removal of As and Sb. It was observed that Sb(V) adsorption was disturbed by As(V) onto akaganeite, while conversely, the addition of Sb(V) did not have any influence on the adsorption of As(V) [7]. Xu et al. [20] reported that the presence of As(III) affected Sb(V) adsorption on activated alumina slightly, while the coexistence of As(V) substantially suppressed Sb(V) adsorption. Unfortunately there has been no study focusing on the competitive adsorption of As(III,V) and Sb(III,V) in quaternary aqueous solutions, i.e., when all four possible species are present at the same time. However, around Sb mining areas the four possible redox species could occur together in waters and soils. Among the different types of hydrous ferric oxides (HFO), ferrihydrite is one of the predominant adsorbents for potentially toxic contaminants because of its large surface area and reactivity. It can be a low-cost adsorbent material for water treatment [21] and is commonly found in aquatic systems, soils and sediments. Due to its known affinity to both As and Sb, ferrihydrite should play an important role for the immobilization if both elements are present at the same time, thus it is worthy to explore the competitive/simultaneous adsorption behavior of As and Sb species.

The main objectives of this study were to compare the competitive interactions and simultaneous adsorption behavior of As(III, V) and Sb(III, V) onto ferrihydrite (1) in binary systems by varying the solution pH, (2) in ternary systems under the presence of interfering ions of NO3, PO43− and SO42− and (3) in quaternary systems at varying pH.

Section snippets

Materials

All reagents used were of analytical grade. Stock Sb(III, V) and As(V) solutions were prepared by dissolving potassium antimonyl tartrate trihydrate (C8H4K2O12Sb2⋅3H2O, Sigma-Aldrich), potassium hexahydroxoantimonate (H6KO6Sb, Fluka) and sodium arsenate Na2HAsO4·7H2O (Sigma-Aldrich) in deionized distilled (DDI) water, respectively. Another stock solution of As(III) was prepared by dissolving As2O3 (Sigma-Aldrich) in a 4% NaOH solution. All working As and Sb solutions were freshly prepared each

Competitive adsorption in binary systems

In Fig. 1 the simultaneous adsorption behavior of As and Sb as a function of pH is shown in the binary systems of As(III)/Sb(III) and As(V)/Sb(III). The adsorption envelopes of Sb(III) in the presence of As(III) and As(V) were similar indicating that the two As species had the same (little) effect on Sb(III) adsorption, although it seemed that at low pH, As(V) somewhat interfered with the adsorption of Sb(III). At a pH of 3.5 approximately 5% more Sb(III) were adsorbed in the presence of

Competitive interactions between As and Sb

In the binary and ternary systems Sb(III) was more strongly adsorbed by ferrihydrite than As(III) (Fig. 1a and Fig. 5), as well as in the quaternary systems (Fig. 3). The removal of Sb(III) being preferred to As(III) was reported previously [26], [27]. The relatively stronger adsorption of Sb(III) compared to As(III) could be attributed that Sb(III) is a stronger Lewis base than As(III) [28], having a higher pKa value (pKa1 (H3AsO3) = 9.22; pKa (Sb(OH)3) = 11.9). The iron hydroxides are frequently

Conclusions

Our study demonstrated that ferrihydrite is a potential effective adsorbent for the simultaneous removal of As(III), As(V), Sb(III) and Sb(V) in multi-component systems. The four possible redox species did compete for the available surface sites. Both the adsorption of As(III) and Sb(V) onto ferrihydrite was obviously reduced as a result of the addition of Sb(III) and As(V), but on the other hand the presence of As(III) and Sb(V) did not play any significant role in the adsorption of Sb(III)

Acknowledgements

We acknowledge Laura Knigge for her help on measuring the samples by ICP-OES. We also thank Debo Wu for his help measuring the samples by ICP-MS, and Britta Hinz for English editing. PQ thanks the China Scholarship Council (CSC) and University of Bremen for financial support. TP acknowledges support by the German Research Foundation (DFG) INST 144/288-1.

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