Enhanced Elution Efficiency of Scandium from Ion Exchange Resins

Abstract.

Atmospheric leaching of mineralized wastes, such as coal fly ash, with dilute H₂SO₄ is often able to extract a significant fraction of the contained Sc and rare-earth element (REE) components, producing low concentrations of the valuable metals and high concentration of nuisance metals into the pregnant leach solutions (PLSs). Recovery of parts per million (ppm) levels of valuable metals from a matrix containing several g/L nuisance metals requires a very selective separation technique, such as ion exchange (IX). This paper builds on previous work, in which two solvent-impregnated IX resins were identified with remarkable selectivity for adsorption of Sc from coal fly ash PLS while absorbing a minimum amount of REEs and the other nuisance elements. While 2 M H₂SO₄ was basically unable to recover Sc from these IX resins, addition of some water miscible organic additives (WMAs) substantially improved the elution efficiency of Sc to as high as 79%. In continuation of the previous work, elution of Sc from these resins was investigated in using columns. After nine bed volumes (BVs) of elution and under identical operating temperature and flow rates, nine times the mass of Sc was recovered with the blended eluent compared to 2 M H₂SO₄. Moreover, the maximum concentration of Sc in the eluted fractions was significantly increased to over 1800 ppm (with the blended eluent) compared to 167 ppm (with 2 M H₂SO₄).