An improved description of the interactions between rare earth elements and humic acids by modeling: PHREEQC-Model VI coupling

Abstract

The Humic Ion Binding Model VI (Model VI) -previously used to model the equilibrium binding of rare earth elements (REE) by humic acid (HA) -was modified to account for differences in the REE constant patterns of the HA carboxylic and phenolic groups, and introduced into PHREEQC to calculate the REE speciation on the HA binding sites. The modifications were shown to greatly improve the modeling. They allow for the first time to both satisfactorily and simultaneously model a large set of multi-REE experimental data with the same set of equations and parameters. The use of PHREEQC shows that the light rare earth elements (LREE) and heavy rare earth elements (HREE) do not bind to HA by the same functional groups. The LREE are preferentially bound to carboxylic groups, whereas the HREE are preferentially bound to carboxy-phenolic and phenolic groups. This binding differentiation might lead to a fractionation of REE-HA patterns when competition between REE and other metals occur during complexation. A survey of the available data shows that competition with Al 3+ could lead to the development of HREE-depleted HA patterns. This new model should improve the hydrochemical modeling of the REE since PHREEQC takes into account chemical reactions such as mineral dissolution/ precipitation equilibrium and redox reactions, but also models kinetically controlled reactions and one-dimensional transport.

Rare earths, zirconium and hafnium distribution in coastal areas: The example of Sabella spallanzanii (Gmelin, 1791)

“…MREE enrichment onto biological surfaces is also consistent with previous studies that demonstrate a large MREE affinity of bacterial colonies and/or humate and fulvate natural polymers to biological surfaces (Takahashi et al, 2005(Takahashi et al, , 2007. This affinity is apparently driven by the capability of some binding tags to extract REE from the aqueous phase (Marsac et al, 2011;Martinez et al, 2014;Park et al, 2016 and references therein).…”

Biogeochemical Factors Affecting Rare Earth Element Distribution in Shallow Wetland Groundwater

“…Same results were obtained by Stolpe et al (2013) using FFF separation for Alaskan rivers water samples. This strong binding of REE by organic matter was confirmed by several field, experimental and modeling studies (Tang and Johannesson 2003;Johannesson et al 2004;Sonke and Salters 2006;Pourret et al 2007a, b;Stern et al 2007;Pédrot et al 2008;Kerr et al 2008;Marsac et al 2011). Moreover, Davranche et al (2011) demonstrated that Fe occurs mainly in wetland soils as amorphous Fe(III)-nanoparticles embedded within the organic matter which are poor in REE and trace elements.…”

“…or the precipitation of LREE and HREE with phosphates (e.g., Johannesson and Lyons 1995;Byrne et al 1996;Taunton et al 2000). However, more recent studies have demonstrated that in organic-rich waters in which REE speciation is dominated by their binding with organic molecules, the REE pattern is controlled by the surface properties of the organic matter itself (e.g., Pourret et al 2007b;Kautenburger 2009;Marsac et al 2010Marsac et al , 2011Kautenburger et al 2014).…”

“…3.1 REE Loading and HA Surface Heterogeneity Marsac et al (2010Marsac et al ( , 2011 demonstrate that the discrepancy between these two types of REE patterns is explained by the combined effect of metal loading and the surface heterogeneity of HA. At low loading, REE are complexed to strong but less abundant HA sites, namely phenolic and/or multidendate/chelating sites.…”

“…This results in a wide range of diverse REE patterns, which can be characterized by a depletion or enrichment degree relative to heavy REE (La/Yb or Sm/Yb ratios) or by whether or not anomalies occur. More specifically, REE fractionation patterns and abundances have been used to investigate processes occurring in wetlands, such as the hydrological regime of the system, mineral phases activated during water saturation, trace element sources as well as fine sorption processes occurring onto wetland colloidal organic matter (Dia et al 2000;Grybos et al 2007Grybos et al , 2009Pourret et al 2007aPourret et al , b, 2010Marsac et al 2011;Davranche et al 2011). In turn, these studies have produced information that can be used to identify and discriminate the biogeochemical parameters that control their distribution in this type of surface environment.…”