Sorption of Cs, Ba, Co, and Eu onto biotite: experiments and modelling

The sorption of 134Cs, 133Ba, 60Co and 152Eu, all at about [~10-8 M] onto biotite mineral was studied using the batch method with S: L = 1:50 at three different ionic strengths (0.001, 0.01 and 0.1M NaClO4) and five different pH (5,6,7,8,9) at 25\ub0C for up to two months in an inert atmosphere glovebox. The results revealed that the sorption of all metals was dependent on both pH and ionic strength. \ua0At 25\ub0C, the measured sorption distribution coefficients (Rd -values) for 0.001 M were (pH 5-9): (Cs) 0.6-1.2, (Ba) 0.3-8.3, (Co) 0.01-1.9 and (Eu) 2.7-18 m3/kg, respectively. For I = 0.01 M, the corresponding results were (Cs) 0.1-0.7, (Ba) 0.01-4.4, (Co) 0.01-7.5 and (Eu) 0.2-4.3 m3/kg, respectively. For I= 0.1M, the corresponding results were (Cs) 0.01-0.2, (Ba) 0.03-0.4, (Co) 0.01-4.7 and (Eu) 2.1-6.7 m3/kg.\ua0The surface acidity constants for the amphoteric surface site of biotite mineral were determined with the continuous potentiometric titration on a biotite suspension to pKa1= 0.30 and pKa2 = 0.20. These acidity constants were obtained by fitting titration data through the use of PHREEQC and PYTHON code optimization routines.\ua0The biotite size fraction of 0.25-0.5 mm was characterized for acidic site density (ASD), cation exchange capacity (CEC) and the specific surface area (SSA) and were determined to be 6.7mmol/m2, 1.01 \ua00.03 meq/100g and 0.47 m2/g by using tritium uptake, ammonium acetate (NH4Ac), and Kr-BET adsorption methods, respectively.\ua0\ua0To model the experimental sorption data, PHREEQC geochemical modelling software coupled with PYTHON code optimization routines was used. The results shows that a two-step protolysis (2-pKa) non-electrostatic model (NEM) representing edge site with one additional ion-exchange site representing basal plane site is sufficient to reproduce the data for all four metals

Redox, solubility and sorption chemistry of technetium in dilute to concentrated saline systems (KIT Scientific Report ; 7703)

This PhD work represents a comprehensive investigation of redox processes, solubility and sorption behaviour of technetium in the absence of complexing ligands extending from dilute to concentrated NaCl, MgCl2 and CaCl2 systems. The complete chemical, thermodynamic and activity models derived in this work provide key input for understanding the chemical behaviour of Tc in conditions relevant for nuclear waste disposal

Key Topics in Deep Geological Disposal : Conference Report (KIT Scientific Reports ; 7696)

The current state of knowledge of central aspects of radioactive waste repository research was presented in the course of the DAEF conference "Key topics in deep geological disposal". For the first time socio-economic and socio-technical issues played an important role within a conference focusing on the disposal of radioactive waste. Scientists from about 16 different countries presented their scientific work in 8 sessions and during a poster session