Effect of DTPA on europium sorption onto quartz - Batch sorption experiments and surface complexation modeling.

Sorption of radionuclides on mineral surfaces retards their migration in the environment of a repository. Presence of organic ligands, however, affects sorption and consequently influences their transport behavior. In this study, we quantify the sorption of Eu(III) onto quartz surfaces as a function of pH in the absence and presence of diethylenetriaminepentaacetic acid (DTPA). Batch sorption experiments show a pH-dependent sorption of Eu(III) on quartz. The presence of DTPA results in slightly higher sorption of Eu(III) at neutral to slightly acidic pH and considerably lower sorption at alkaline conditions. Sorption experiments were simulated using the Diffuse Double Layer Model (DDLM) with single sorption sites (≡QOH) and monodentate surface complexation. The reactions were established based on the aqueous speciation calculation under the experimental conditions, and the thermodynamic constants of surface reactions were obtained and refined by numerical optimization. Results of surface complexation modeling show the formation of a surface species ≡QOHEuDTPA2-, explaining the elevated sorption of Eu(III) at neutral to slightly acidic pH. In contrast, dissolved EuDTPA2- complex species are present at alkaline pH, resulting in an enhanced mobility of Eu(III).

Effect of glutamic acid on copper sorption onto kaolinite - Batch experiments and surface complexation modeling.

High carbonate content of the European Kupferschiefer ore deposits is a challenge for acid copper leaching (pH ≤ 2). Therefore investigating the mobility behavior of Cu(II) under conditions related to an alternative, neutrophil biohydrometallurgical Cu(II) leaching approach is of interest. As glutamic acid (Glu) might be present as a component in the growth media, we studied its effects on the adsorption of Cu(II) onto kaolinite. The binary and ternary batch sorption measurements of Cu(II) and Glu onto kaolinite were performed in the presence of 10 mM NaClO4 as background electrolyte and at a pH range from 4 to 9. Sorption experiments were modeled by the charge-distribution multi-site ion complexation (CD-MUSIC) model by using single sorption site (≡SOH) and monodentate surface complexation reactions. Glu sorption on kaolinite is weak (<10%) and independent of pH. Furthermore, Glu slightly enhances the Cu(II) sorption at low pH but strongly hinders (up to 50%) the sorption at higher pH and therewith enhances copper mobility. The results of isotherms show that Cu(II)-Glu sorption onto kaolinite mimics the Freundlich model. The proposed CD-MUSIC model provides a close fit to the experimental data and predicts the sorption of Cu(II), Cu(II)-Glu and Glu onto kaolinite as well as the effect of Glu on Cu(II) mobility.

Mobility and transport of copper(II) influenced by the microbial siderophore DFOB: Column experiment and modelling.

Acid Cu leaching from the European Kupferschiefer ore deposits is a challenge e.g. due to its high carbonate content. In this study, we investigated the transport behaviour of Cu under conditions related to a biohydrometallurgical leaching approach using neutrophil microorganisms in neutral to slightly alkaline solutions. We studied the effect of the microbial siderophore desferrioxamineB (DFOB) as a model leaching organic ligand on Cu mobility in column experiments with kaolinite. The results revealed that DFOB strongly enhances Cu mobility. The breakthrough of Cu occurs considerably earlier in the presence of DFOB than in the absence of the organic ligand. Furthermore, complete elution of Cu was observed at 5 pore volume exchanges faster compared to elution with deionized water. The established geochemical transport model shows good agreement with the experimental data and suggests a maximum efficiency at a Cu to DFOB molar ratio of 1:1. In addition, results of modelling revealed that in the absence of the ligand, a pH increase from 6.5 to 8.5 significantly retarded Cu breakthrough, whereas in the presence of DFOB, Cu breakthrough curves were nearly insensitive to pH changes and close to the breakthrough curve of a non-reactive tracer.

Effect of microbial siderophore DFO-B on Cd accumulation by Thlaspi caerulescens hyperaccumulator in the presence of zeolite.

Hyperaccumulators are grown in contaminated soil and water in order that contaminants are taken up and accumulated. Transport of metals from soil to plant is initially dependent on the solubility and mobility of metals in soil solution which is controlled by soil and metal properties and plant physiology. Complexation with organic and inorganic ligands may increase mobility and availability of metals for plants. In this work the influence of desferrioxamine-B (DFO-B), which naturally is produced in the rhizosphere, and zeolite on Cd accumulation in root and shoot of Thlaspi caerulescens (Cd hyperaccumulator) was investigated. Plants were grown in pots with clean quartz sand, amended with 1% zeolite; treatment solutions included 0, 10, and 100 µM Cd and 70 µM DFO-B. Addition of zeolite to the quartz sand significantly reduced Cd concentration in plant tissues and translocation from root to shoot. On contrary, DFO-B considerably enhanced Cd sorption by roots and translocation to aerial part of plants. Treating the plants with zeolite and DFO-B together at 10 µM Cd resulted in reduction of the bioaccumulation factor but enhancement of Cd translocation from root to shoot at the rate of 13%. In contrast, at 100 µM Cd in the solution both bioaccumulation and translocation factors decreased. Total metal accumulation as a key factor for evaluating the efficiency of phytoremediation was highly influenced by treatments. Presence of zeolite in pots significantly decreased total Cd accumulation by plants, whereas, DFO-B clearly enhanced it.