Seminar Muqeet Iqbal

Abstract

Rare Earth Elements (REE) are not only considered as high-technology components but also as emerging contaminants when released into ecosystems. However, there is a lack of comprehensive investigations on their mobility, environmental fate and transport in geochemical settings. REE can bind to the surface of minerals such as goethite, which can alter their fate and transport. Here, we have thoroughly examined the adsorption of the entire REE group with goethite via batch experiments at environmentally relevant geochemical conditions, over a wide range of pH and varying REE concentrations. As typically encountered for cations, REE binding increased with increasing pH values. Results from the experiments showed that at low pH values there is a stronger adsorption for middle REE (MREE) as compared to light REE (LREE) or heavy REE (HREE). Conversely, at higher pH values HREE are preferentially complexed. These two distinct complexation processes likely arise due to two different types of binding sites: (i) a larger number of weak sites that prefer HREE occurring on the major faces of goethite particles, and (ii) a smaller number of strong sites that primarily complexed MREE and occur at the termination of the goethite particles. A Surface Complexation Model (SCM) based on CD-MUSIC approach has been developed for goethite, which successfully predicted both sorption edges and sorption isotherms. These results have strong implications for an accurate assessment of the transport behavior of REE in natural systems.