Competitive Sorption of Metal Ions From Aqueous Solution Onto Sand
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Competitive Sorption of Metal Ions From Aqueous Solution Onto Sand Sonia Morandi, Francesca Giacobbo, Mario Mariani and Mirko Da Ros Dipartimento di Energia, Politecnico di Milano, Via Ponzio 34/3, 20133 Milano, Italy
ABSTRACT
The major part of groundwater contaminants strongly interact with soils and aquifer rocks. Therefore sorption processes on porous matrix are of utmost importance in the frame of the nuclear waste disposal. The objectives of this study were to evaluate sorption uptake by silica sand of some safety-relevant metal ions such as Cs+, Sr2+, Cu2+, Ni2+ and to investigate the existence of competitive sorption processes between these ions. To this aim, kinetic and equilibrium, mono-component and multi-component, batch experiments were carried out in order to study: i) the influence of metal concentration, pH and contact time, on sorption onto silica sand of the above ions in aqueous solution, and ii) the presence of competition phenomena. Sorption data were well fitted by Langmuir and Freundlich models. Multi-component tests show that the uptake of each ion is reduced in presence of other ions in solution with respect to monocomponent batch tests results and that competition between species appears influenced by the equilibrium times of the single species in solution and by pH.
INTRODUCTION
The necessity of an eco-sustainable development requires addressing the problem of disposal of industrial and civil wastes and, for the countries where nuclear plants are present, it is also necessary to define the proper procedures for the disposal of the radioactive wastes. In this contest, it is of great importance the study of the phenomena that govern the transport of contaminants, such as the exchanging processes between phases, and the successive development of models for the description of the migration processes through artificial and natural porous media. For what concerns exchanging processes between phases, since groundwater pollution involves in general more than one species in solution, it is of utmost importance to take into account competition between species for binding sites. The objectives of this study were to evaluate sorption uptake of silica sand for Cs+, Sr2+, Cu2+ and Ni2+ and to investigate the presence of competition between these ions. The above mentioned metal ions have been chosen for their safety-relevance: Cs and Sr are present in the spent fuel nuclear waste while Cu and Ni, extensively generated from industrial activities, are representative of transition metals. Equilibrium and kinetic batch experiments were performed in order to study the influence on the sorption onto sand of (i) metal ion concentration in aqueous solution (ii) contact time (iii) pH of solution and (iv) presence in solution of more than one species. The paper is organized as follows. The next Section reports the characteristics of the selected matrix and of the analyzed metal ions and briefly describes the general experimental methods
and the procedures adopted for equilibrium and kinetic batch experiments.
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