Soil remediation potential of illite and Na-MMT for As and H3AsO3 adsorption: Insights of ab initio calculations

Abstract

Understanding the adsorption behavior of heavy metals and metalloids on clay minerals is essential for remediating heavy metal-contaminated soils. The adsorption of heavy metals and metalloids on illite(001) and sodium-montmorillonite (Na-MMT)(001) surfaces was investigated using first-principles calculations in this study, especially As atom and H3AsO3 molecule. The adsorption energies of the As atom were −1.94 eV on the illite(001) and −0.56 eV on the Na-MMT(001), whereas, the adsorption energies of the H3AsO3 molecule were −1.40 eV on illite(001) and −1.01 eV on Na-MMT(001). The above results indicate that the adsorption was more energetically favorable on illite(001). Additionally, compared to Na-MMT(001), there were more significant interactions between the atoms/molecules on the illite(001). After As atom and H3AsO3 molecule adsorption, the electrons were transferred from mineral surface atoms to the adsorbates on both illite(001) and Na-MMT(001) surfaces. Moreover, the adsorption of As atom on illite(001) and Na-MMT(001) surfaces were more energy favorable compared to Hg, Cd, and Cr atoms. Overall, this work provides new insights into the adsorption behavior of As atoms and As molecules on illite and Na-MMT. The results indicate that illite-rich soils are more prone to contamination by arsenic compared to soils primarily composed of Na-MMT minerals.

1. Introduction

Rapid human industrialization has increased the use of heavy metals and metalloids, both of which cause significant environmental damage [1−4]. Large quantities of heavy metals and metalloids can contaminate soil via processes such as wastewater irrigation, atmospheric deposition, and the application of fertilizers and pesticides [5, 6]. Soil is a vital natural resource for almost all life on land and is essential for human activities, especially for growing food and building houses [7, 8]. Long-term exposure to heavy metals and metalloids in soil can lead to permanent intellectual and developmental disabilities [9, 10]. Therefore, reducing soil heavy metal and metalloid pollution has become a critical environmental challenge for human civilization [11, 12].

Heavy metals and metalloids found in soil include arsenic (As), mercury (Hg), cadmium (Cd), and chromium (Cr) [13, 14]. Among them, As is the top-ranked hazardous substance listed by the Toxic Substances and Disease Registry Agency and the United States Environmental Protection Agency [15]. In natural soil environments, As exists in various complex forms, which can be categorized into two main types: organic and inorganic. In most environmental systems, the inorganic form of As is more dominant [16−19] and toxic [20] than the organic form. As(0) (As atom) and As(III) (H₃AsO₃ molecule) are the widely distributed forms of inorganic arsenic present in the natural environment [21], which significantly increase the risk of cancer, birth defects, cardiovascular disease, and other diseases in humans [22].

In recent decades, many methods have been proposed to remediate contaminated soils, including chemical, biological, and physical remediation methods [23, 24]. Chemical remediation methods, while known for their effectiveness, present the potential risk of introducing additional chemical contaminants into soils [25−27]. Biological remediation methods, although user-friendly, are less suitable for heavily contaminated soils due to their relatively slow remediation rates [28, 29]. Therefore, physical remediation approaches have been favored by numerous scholars in recent years as these methods are suitable for treating a wide range of contaminated soils [30]. Clay minerals are recognized as important adsorbent materials for physical remediation owing to their large specific surface area and low cost [31−33]. In particular, illite and montmorillonite, two of the main clay mineral species, are present abundantly in sedimentary soils, ...