Natural sediment at a dam and its inorganic materials as adsorbents of praseodymium (Pr(III))

The sediment deposited behind a dam (DS) and its inorganic materials (IM-DS) were characterized and used for the removal of praseodymium (Pr) from aqueous solutions. Quartz, albite, and kaolinite were found in the sediment by X-ray diffraction. Kinetic data fit well to a pseudo second-order model, the equilibrium time for DS and IM-DS was 2 h and 3 min, respectively, and the adsorption capacity was higher for Pr/DS (q_e = 4.91 mg/g) than for Pr/IM-DS (q_e = 3.01 mg/g) in these conditions. Pr/DS and Pr/IM-DS data isotherms were in agreement with the Langmuir–Freundlich model and the maximum adsorption capacities were 4.95 and 4.01 mg/g, respectively. Both processes are exothermic (enthalpy change, ΔH⁰ = −22.8 and −21.8 kJ/mol for DS and IM-DS, respectively), the increase of the randomness is small, and the feasibility and spontaneity are low. Praseodymium was desorbed by ethylenediaminetetraacetic acid disodium (EDTA-Na₂), sodium chloride, nitric, citric, and humic acids solutions, and one hundred percent of praseodymium was desorbed by the EDTA-Na₂ solution. The Pr₂(EDTA)₃ (praseodymium ethylenediaminetetraacetate) complex was completely desorbed from both materials (DS and IM-DS). Distribution coefficients (K_D) depend upon praseodymium concentration, temperature, pH, and the kind of adsorbent. Chemical reactions of praseodymium with kaolinite and iron minerals could explain the adsorption.