Extraction of yttrium from fluorescent lamps employing multivariate optimization in aqueous two-phase systems.

Abstract

This paper presents for the first time the application of aqueous two-phase systems for yttrium recovery from fluorescent lamp residues, a rare earth element with high added value and widely used in the technology in dustry. A multivariate study was carried out, using experimental design, for yttrium extraction employing ATPS using alizarin red as extracting agent, in order to expand the possibilities of the ATPS application in industrial scales. The optimized variables, employing 26–1 fractional design, were pH (3.00–9.00), extracting agent con centration (2.3–23.0 mmol kg−1), tie-line length (TLL), ATPS-forming copolymers (L35 and L64) and electro lytes (Na2SO4 and C6H5Na3O7·2H2O), and mass ratio between top and bottom phases (mTP/mBP = 0.5–2.0). It was observed for the first time, that the metal ions partition in ATPS is mainly influenced by the salt-forming anion species distribution as a function of pH at high TLL values. The extraction of yttrium was optimized in a 23 factorial design with no lack of adjustment and it was able to predict the extraction response with accuracy close to 96%. The optimized conditions of yttrium extraction were applied using a leach liquor from real sample of fluorescent powder. After five extraction steps, 90% of yttrium was selectively recovered.