A series of experiments were performed to study the sorption of humic acid and Eu3+ ion (at trace concentrations) on the minerals: montmorillonite, bentonite, diatomite and kaolinite in ternary systems. Humic acid and europium sorption were investigated as a function of humic acid concentration, ionic strength and pH. There was a strong uptake of humic acid on to the minerals with sorption increasing as humic acid concentration decreases. For montmorillonite, the uptake of discrete size fractions was also studied. It was found that the larger fractions were more strongly sorbing and were better able to retain Eu in solution.The ionic strength has an impact on Eu behaviour: in the absence of humic acid, sorption strength decreases, whilst in the presence of high concentrations of humic it increases. The sorption of Eu3+ increases from pH 2 to 5 in both the presence and absence of humic acid. Above pH 5, the Eu3+ showed different behaviour with and without humic acid, and as humic concentration became high (100 ppm), the Eu behaves in the same way as the humic. Bentonite is able to sorb humic acid and Eu3+ at any concentration expected in the environment, and shows the strongest sorption of any of the materials tested. Experiments confirmed that Eu is an excellent analogue for Am in these systems.The sorption of selected divalent and trivalent metal ions: Ni2+, Co2+, Zn2+, Cd2+, Eu3+ and Cr3+ on montmorillonite has been investigated in the micro-molar concentration range. In all cases, sorption strength increased with pH, and was consistently stronger for the tri-valent ions. In the presence of humic acid, there was some evidence for the enhancement of sorption. Uptake of metal ions (Co2+, Ni2+, Cd2+, Cr3+, Eu3+ and La3+) by natural and modified kaolinite was studied, and for all except Cr3+, it was found that kaolinite modified by manganese hydrothermal treatment gave the strongest sorption.A simple kinetic model was developed to simulate the experimental data for the sorption of humic acid and Eu3+ on the minerals. The model allows two humic binding sites on the mineral surface and two types of humic in solution, which can have different Eu3+ binding strengths. Metal ion surface complexation is modelled with a single kinetic equation. Ternary complexes are included in the model. The interaction of humic acid on the minerals can be fitted reasonably well. However, for the Eu3+ ion behaviour, although the model was able to give a reasonable fit to data for montmorillonite and bentonite, it could not reproduce the behaviour for kaolinite and diatomite.
|Date of Award
|1 Aug 2013
- The University of Manchester
|Nicholas Bryan (Supervisor)
- Humic acid, Montmorillonite, Adsorption, surface comlexation, Europium tracer