The adsorption of palladium(II), rhodium(III), and platinum(IV) from diluted hydrochloric acid solutions onto Fe3O4 nanoparticles has been investigated. The parameters studied include the contact time and the concentrations of metals and other solutes such as H+ and chloride. The equilibrium time was reached in less than 20 min for all metals. The maximum loading capacity of Fe3O4 nanoparticles for Pd(II), Rh(III), and Pt(IV) was determined to be 0.103, 0.149, and 0.068 mmol g(-1), respectively. A sorption mechanism for Pd(II), Rh(III), and Pt(IV) has been proposed and their conditional adsorption equilibrium constants have been determined to be log K = 1.72, 1.69, and 1.84, respectively. Different compositions of eluting solution were tested for the recovery of Pt(IV), Pd(II), and Rh(III) from Fe3O4 nanoparticles. It was found that 0.5 mol L-1 HNO3 can elute all of the metal ions simultaneously, while 1 mol L-1 NaHSO3 was an effective eluting solution for Rh(III), and 0.5 mol L-1 NaClO4 for Pt(IV). In competitive adsorption, the nanoparticles showed stronger affinity for Rh(III) than for Pd(II) and Pt(IV). (c) 2006 Elsevier Inc. All rights reserved.