Preparation of Double Carboxylic Corn Stalk Gels and Their Adsorption Properties Towards Rare Earths (III)

A novel biosorbent, corn stalk gels with double carboxylic groups synthesized by two oxidation steps (the double carboxylic groups modified adsorbent is abbreviated as DCCS-2), was prepared, characterized, and applied for the recovery of rare earths (III) from the nitric media. For the whole lanthanides, it exhibits a distinct “tetrad effect” with the increase of atomic numbers. Taking Nd(III) as a representative element, the adsorption capacity, kinetics, selectivity and mechanism were investigated. Thermodynamics and kinetic fittings were found to abide by Langmuir and pseudo-second-order rate equations and the corresponding parameters were calculated. The maximum adsorption capacity was calculated to be 2.44 mol/kg at 298 K for DCCS-2. Results showed that the double carboxylic groups played an important role for improving the adsorption capacity, e.g. the adsorption capacity of Nd(III) by DCCS-2 increased to 53.5 times compared to the raw corn stalk. Furthermore, DCCS-2 also shows a good selectivity between Nd(III) and many non-rare earth metal ions. The cation exchange is proposed to be the possible adsorption mechanism.