Ethylenediaminetriacetic Acid-Functionalized Activated Carbon for the Adsorption of Rare Earths from Aqueous Solutions

A novel and low-cost ethylenediaminetriacetic acid-functionalized activated carbon (EDTA-AC) was synthesized by anchoring N-[(3-trimethoxysilyl)propyl]-ethylenediaminetriacetic acid (TMS-EDTA) to oxidized activated carbon (AC). Material characterization was done by FTIR and Raman spectroscopy, TGA, N2 physisorption, SEM and the Boehm titration method, the latter being used to determine the amount and type of oxygen functional groups present in carbon samples. EDTA-AC was tested for the adsorption and separation of rare-earth ions from aqueous solutions, in order to evaluate the feasibility of using this material for the recovery of rare earths from industrial wastewater, tailings and electronic waste, like batteries, magnets and lamp phosphors. The maximum adsorption capacity of EDTA-AC was derived for Nd(III) by constructing an adsorption isotherm and fitting the data to the Langmuir adsorption model. A kinetic and thermodynamic study were performed by varying the contact time and the temperature and plotting the corresponding adsorption data to the pseudo-second-order kinetic model and the Van’t Hoff equation, respectively. The affinity of EDTA-AC for each of the lanthanide ions was determined and from binary mixtures of La/Ni, Sm/Co, Eu/Y and Dy/Nd, the highest selectivity was observed for the (heavy) rare earths. The adsorbed metal ions could be recovered and the adsorbent regenerated by treatment with a dilute solution of HCl, thus showing the (large-scale) potential of EDTA-functionalized AC for the recovery of rare earths from aqueous waste streams.