A Rapid and Selective Isolation of Rhodium from Aqueous Solution Using Nano-Al₂O₃

Nano-Al 2 O 3 was applied for the separation of Rh(III) ions from water solution. When pH value was within 5.0 to 9.0 and the concentration of Rh(III) was less than 50 mg·L –1, more than 90 % of Rh(III) ions were adsorbed by nano-Al 2 O 3 . Then the adsorbed Rh(III) ions were rapidly eluted when 2.0 mL of 0.3 mol·L –1 H 2 SO 4 was added. The adsorption data corrected well with the Langmuir equation, and the saturated adsorption capacity was 5.52 mg·g –1 (25 ± 0.1 °C). The dynamics data indicate that the equilibrium time was about 2.5 min. The rate constant k 2 = 2.714 g·mg –1 ·min –1 (25 °C) was gained according to the second-order-kinetic model. The overall rate process seemed to be affected by both film diffusion and interparticle diffusion, but it was mainly governed by interparticle diffusion. The average energy of sorption at ambient temperature was obtained to be 1.08 kJ·mol –1 through the Dubinin–Radushkevich (D-R) model. Moreover, the values of Δ H 0 and Δ G 0 for Rh(III) adsorption disclosed the spontaneous and endothermic nature of the process. The research of adsorption selectivity showed that 98 % of the Rh(III) ions could be adsorbed by nano-Al 2 O 3 in the presence of Zn 2+, Cu 2+, Cd 2+, Ni 2+, Co 2+, Fe 3+, and Pb 2+ .