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.