Abstract

In this work, the synthesis and application of a promising magnetic adsorbent for the recovery of lanthanum, praseodymium, and samarium was studied. To obtain the magnetic adsorbent, magnetite nanoparticles were functionalized with a phosphonic acid group (PA-MNPs) by an efficient and reproducible method. Based on HR-TEM analysis, PA-MNPs present an average diameter of 6.8 nm, have a spherical shape, and a certain degree of agglomeration at approximately 20 to 40 nm. The nanoparticles' magnetic saturation was found to be approximately 55 emu/g, enough to provoke their complete separation from an aqueous raffinate using a common magnet. The XPS and FTIR analyses provided evidence for a phosphonic acid group on the surface of the magnetite nanoparticles. The effect of the pH and the initial concentration of lanthanide ions in the aqueous feed solution and the adsorbent dose on REE adsorption was studied. Maximum lanthanide ion loading capacities in the range of 20–24 mg lanthanide/g adsorbent were measured close to pH 4 (contact time: 5 min.; mass of adsorbent: 200 mg). The PA-MNPs adsorbent presented high mechanical and chemical stability in aqueous solutions with initial pH between 3 and 7. The more efficient desorption (75–100%) of lanthanide ions from the adsorbent was achieved using H2SO4 0.1 M solution. The feasibility of regenerating and reusing functionalized magnetic nanoparticles in five cycles of adsorption/desorption was verified. Freundlich and Langmuir adsorption isotherms fit the experimental equilibrium data well, which would be indicating that the adsorption process would be ruled by a hybrid model. The results of kinetic experiments were well explained by a pseudosecond-order kinetic model, and a very fast initial adsorption rate was observed.