Rapid and selective separation of iridium ions from aqueous solutions using nano-Al2O3

γ-nano-Al2O3 was used for the separation and enrichment of iridium (Ir(IV)) ions from an aqueous solution. A systematic study of the adsorption process was performed by varying pH, sorbent amount, sorption time and temperature. The adsorption efficiency could reach 99% at pH 3.0, suggesting that nano-Al2O3 is an excellent sorbent for iridium ions. The sorbed iridium ions can be desorbed with 2.0 mol·L− 1 HNO3. Iridium adsorption reaction was found to be fast, and equilibrium was attained within 3.0 min following the pseudo-second-order model with observed rate constants (k2) of 19.26–37.93 mg·mg− 1·min− 1 (at varied temperatures). The overall rate process appeared to be influenced by both intraparticle diffusion and boundary layer diffusion, but mainly governed by intraparticle diffusion. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 2.10 mg·g− 1 (293 K) of iridium on nano-Al2O3. The mean energy of adsorption was calculated to be 2.60 kJ·mol− 1 (293 K) from the Dubinin–Radushkevich (D–R) adsorption isotherm. Moreover, the thermodynamic parameters showed the endothermic and spontaneous nature of the adsorption process. The investigation of adsorption selectivity showed that nano-Al2O3 could adsorb 99% of Ir(IV) ions in the presence of Cu(II), Ni(II), Cd(II), Zn(II), Co(II), Fe(III) and Pb(II).