Adsorption of hexavalent uranium on dunite

Pollution of the environment with uranium and associated health effects to human have
recently become of major concern, particularly due to the use of depleted uranium in armourbreaking
bullets. Indeed, uranium in environmentally significant concentrations is found near to
uranium mining and processing facilities and usually involves large volumes of wastewater.
Removal of uranium from such large volumes of wastewaters will require a cost effective
remediation technology. Conventional wastewater treatment technologies usually rely on
mineral adsorbents and chemical flocculating agents. On the other hand chemical behaviour
and migration of uranium species in the geosphere is strongly governed by
adsorption/desorption phenomena on the underlying rock formations. Hence, studies
regarding uranium adsorption on natural minerals and the evaluation of the corresponding
thermodynamic data is of fundamental importance with respect to the treatment of
contaminated waters and uranium migration in the geosphere.
The present paper reports about the adsorption of hexavalent uranium on dunite at various
experimental conditions (e.g. uranium concentration, amount of adsorbent, ionic strength, pH,
temperature and contact time) and discusses the effect of these parameters on uranium
adsorption. Evaluation of the experimental data shows that the optimum pH regarding uranium
adsorption on dunite is about 6.5. The experimental adsorption data are well fitted by the
langmuir isotherm and there is a linear correlation between adsorbent mass and amount of
uranium, indicating on the formation of inner-sphere complexes. Moreover, adsorption
experiments at various temperatures indicate on a spontaneous, entropy-driven processes
and kinetic measurements show that the adsorption process follows a first order rate
expression.