Adsorption behavior of rare earth elements on silica gel modified with diglycol amic acid

For the recovery of rare earth elements, we previously synthesized an adsorbent consisting of silica gel particles modified with diglycol amic acid groups. In the present study, we optimized the amount of diglycolic anhydride used for the synthesis of the adsorbent and evaluated the utility of the adsorbent in terms of its selectivity for rare earth metal ions, the rate of metal ion adsorption, and the desorption behavior of the ions. We also analyzed the adsorption isotherms of the metal ions. The optimum amount of diglycolic anhydride was 4.0 mmol/gram of amino silica gel, and this amount resulted in the introduction of 1.04 mmol of diglycol amic acid groups per gram of adsorbent. The introduction of the diglycol amic acid groups had little effect on the specific surface area and average pore size of the silica gel particles, and we attributed the high adsorption rate to the large pore size. Acid concentration strongly influenced the adsorbability of rare earth metal ions, which were readily desorbed by 1 mol/L mineral acid. The adsorption isotherms for the lanthanoids at an initial pH of 1.0 were determined with the Langmuir equation. The adsorption capacities of the adsorbent for the heavy rare earth metal ions were higher than those for the light ones.