Limestone: A Natural, Low-Priced Adsorbent for U(VI)

Limestone obtained from Kirari, Akaltara, Chhattisgarh was applied to adsorb uranium(VI) from an aqueous solution of uranyl nitrate. Batch tests were performed with varying pH (2-9), U(VI) concentration (10-100 mg/L), stirring time (10-80 min), and limestone dosage (0.1-0.6 g/50 mL). At ambient temperature, 60.5% removal efficiency was recorded at pH 6, U(VI) concentration of 25 mg/L, stirring time of 40 min, and limestone dosage of 0.4 g/50 mL. The adsorption kinetics, thermodynamics, and isotherm were studied. The U(VI) adsorption onto limestone was endothermic and obeyed the Langmuir model with pseudo-first-order kinetics. The U(VI) adsorption onto limestone is due to electrostatic affinity.