Application of surface complexation modeling on adsorption of uranium at water-solid interface: A review

Highlights

• The rationale of various surface complexation modeling (SCM) was briefly summarized.

• Application of SCM on uranium sorption on various adsorbents was detailed reviewed.

• Understanding the sorption mechanism of uranium at water-mineral interface.

• Beneficial guidelines for the actual treatment of radionuclides in environment.

Abstract

Precise prediction of uranium adsorption at water-mineral interface is of great significance for the safe disposal of radionuclides in geologic environments. Surface complexation modeling (SCM) as a very useful tool has been extensively investigated for simulating adsorption behavior of metals/metalloids at water-mineral interface. Numerous studies concerning the fitting of uranium adsorption on various adsorbents using SCM are well documented, but the systematic and comprehensive review of uranium adsorption using various SCM is not available. In this review, we briefly summarized the rationale of SCM, including constant-capacitance-model (CCM), diffuse-layer-model (DLM), triple-layer-model (TLM); The recent progress in the application of SCM on the fitting of uranium adsorption towards metal (hydr)oxides, clay minerals and soil/sediments was reviewed in details. This review hopefully provides the beneficial guidelines for predicting the transport and fate of uranium in geologic environments beyond laboratory timescales.

Introduction

The pollution of uranium into subsurface environments is an increasingly concern associated with the natural activities and anthropogenic sources (e.g., the milling of uranium mine, post-processing of spent fuel and nuclear test), which exhibits the potential threats to eco-environmental diversity and human health (Burns et al., 2012; Hiess et al., 2012; Rosa et al., 2010). A understanding the transport and fate of uranium in subsurface environments, including hexavalent U (e.g., highly soluble and mobile U^(VI)O₂²⁺ species) and tetravalent U (e.g., sparingly soluble U^(IV)O₂ species), is crucial for the remediation of uranium-contaminated sites (Fletcher et al., 2010). The effect of environmental factors (e.g., pH, Eh, Ca²⁺, CO₃²⁻, organic matter and microbes) on the transport and fate of uranium had been widely elucidated in recent years (Cumberland et al., 2016; Geckeis et al., 2013; Gorman-Lewis et al., 2008; Ishag et al., 2020). The transport and fate of uranium are strongly influenced by geochemical processes such as adsorption/desorption, precipitation/dissolution, accumulation/diffusion, mobilization/migration, oxidation/reduction. However, The prediction of transport and fate of uranium under the actual complicated environments remains unclear due to the geographical and temporal limitations (Hu et al., 2019; Langmuir, 1978; Mitchell et al., 2013). To solve these uncertainties and difficulties, the precise prediction of uranium adsorption at water-mineral interface beyond laboratory timescales is of great significance for the safe disposal of radionuclides in geologic environments.

Modeling refers to the simulation process of the real system using fundamental knowledge to achieve certain aims (Stumm et al., 1970). These empirical adsorption modeling (e.g., Langmuir (1918), Freundlich (1906), distribution coefficient (Kaplan et al., 1996)) can only describe the adsorption process under the simple experimental conditions, whereas the effect of various environmental factors (e.g., pH, ionic strength, competing ions, surface area, surface charge and potential of sorbent properties) on adsorption behavior can not explicitly simulated by these models (Stumm et al., 1970; Villalobos and Leckie, 2001). Surface complexation modeling (SCM) described the equilibrium of ion binding to complex reactive components of surface environments (Nano and Strathmann, 2008; Sposito, 1984), which is based on surface complexation (ion-binding) of adsorbed ion adjacent to the surface of adsorbent through the electrical double layer (EDL, specific electrostatic planes). SCM as a powerful tool has been widely used to simulate adsorption processes of various organics (Hwang and Lenhart, 2009; Ravat et al., 2000; Ruyter-Hooley et al., 2015), heavy metals (cadmium (Huang et al., 2015; Kantar et al., 2009; Kaulbach et al., 2005; Schaller et al., 2009), chromium(Han et al., 2006; Huang et al., 2016; Reich and Koretsky, 2011; Xie et al., 2015), copper (Gu and Evans, 2008; Gu et al., 2010; Peacock and Sherman, 2004; Swedlund et al., 2009; Xue et al., 2009), cobalt (Berka and Banyai, 2001; Bradbury and Baeyens, 2005b, 2011), mercury (Daughney et al., 2002; Lv et al., 2012; Mangold et al., 2014), nickel (Yang et al., 2015), lead (Ding et al., 2016; Dyer et al., 2003; Gu and Evans, 2007; Gu et al., 2010; Xue et al., 2009), zinc (Balistrieri et al., 2008; Dyer et al., 2004; Gu and Evans, 2007; Ha et al., 2010; Sitko et al., 2013; Swedlund et al., 2009)) and radionuclides (thorium (Bradbury and Baeyens, 2005a; Hu et al., 2017b; Pan et al., 2011; Xie and Powell, 2018), europium (Bradbury et al., 2005; Chen et al., 2014; Jin et al., 2014; Sun et al., 2012), strontium (Borrok and Fein, 2005; Chen et al., 2008; Gu and Fein, 2015; Hu et al., 2017a; Naveau et al., 2006; Nie et al., 2017), cesium (Fang et al., 2016)). Although the explosive growth in surface complexation modeling describing the adsorption behavior of uranium at water-solid interface has been widely investigated in the last several decades (Arai et al., 2006; Barnett et al., 2002; Ding et al., 2014; Guo et al., 2009b; Loganathan et al., 2009; Lu et al., 2017; Nair et al., 2014; Ordonez-Regil et al., 2003; Rotter et al., 2008; Sun et al., 2020; Guo et al., 2009b; Xie et al., 2016), the review concerning the application of SCM on uranium adsorption is not available (Cumberland et al., 2016; Wang and Giammar, 2013).

In this review, the fundamental rationale of SCM, including constant-capacitance- model (CCM), diffuse-layer-model (DLM), triple-layer-model (TLM), was firstly summarized; Then adsorption behaviors of uranium on various adsorbents (i.e., metal hydr/oxides, clay minerals and soil/sediments) using SCM was reviewed in details, which is of great importance for the precise prediction of transformation and fate uranium in actual aquifers. This review provides the guideline for designing cost-effective remediation technology and developing suitable materials for encapsulation and disposal of nuclear waste (Schindler et al., 1976).