Kinetic and thermodynamic studies for adsorptive removal of Sr2+ using waste iron oxide

• An iron oxide recovered from fluidized-bed Fenton reactor is used as adsorbent.
• BT1 adsorbent composes of poorly crystallized Goethite.
• High removal of Sr is achieved by BT1 with an adsorption capacity of near 40 mg/g.
• Kinetics and thermodynamics of Sr adsorption have been elucidated.

An iron oxide, BT1, recovered from a real fluidized-bed Fenton reactor, was studied to determine its effectiveness in the adsorptive removal of strontium ions (Sr2+) from water. Millimeter-scale BT1 (0.2–0.5 mm) mostly consisted of a poorly crystallized goethite phase (α-FeOOH), with a specific surface area of 185 m2/g. Batch jar-testing experiments were conducted at an initial Sr2+ level of 10 ppm to determine the effect of pH, the adsorption isotherms, the desorption process, and the kinetics of adsorption. The effectiveness of BT1 as an adsorbent for the removal of Sr2+ depended strongly on pH; at an equilibrium pH of 10.5, 5 g BT1 removed almost 100% of Sr2+. Sr2+ was desorbed by a solution of nitric acid at pH 3 with a relatively low rate, and the recycled BT1 maintained its high adsorption efficiency after at least three adsorption–desorption tests. The isotherms were accurately described using both Langmuir and Freundlich models, and the maximum adsorption capacity was found to be 38.46 mg/g. The thermodynamic parameters revealed the endothermic and spontaneous nature of the adsorption process at 20–45 °C. Kinetic studies revealed that the adsorption of Sr2+ ions on BT1 was a second-order reaction.