Recovery of rare earth elements from CRT phosphors. Part I: Processing fractions characterization, leaching kinetics and modelling

Rare earth elements (REEs) are critical raw materials with unique physical-chemical properties, being widely used in phosphors for lighting devices, including CRT screens. These are now being stockpiled, and greener recovery routes are needed to reintroduce REEs into the market for proper valorisation. This work (part one of a two-paper set) evaluates phosphor sieving and acid leaching to select optimal fractions and elucidate leaching kinetics. Phosphors were characterized by XRD, PIXE and SEM-EDS. Sieving effectively removed contaminants (Al, Si, Sr, Ba, Pb). The <38 μm fraction is enriched in ZnS and Y 2 O 2 S; XRD, PIXE, XRF, ICP-OES and SEM-EDS showed Zn, S and Y as main elements. ZnS and (Y 0.9597 Eu 0.0403 ) 2 O 2 S appear as angular or modular particles without clear phase distinction. For this fraction, mass density was 2.41 g/cm 3 and humidity 0.1912%. Acid leaching with 3 M HNO 3 plus 6 g H 2 O 2 /g sulphur was tested at 25, 40 and 55 °C to track Y, Eu and Zn leaching profiles. Higher temperatures enhanced Y, Eu and Zn leaching recoveries and rates, while 25 °C improved REE selectivity from Zn. Recoveries were fit into shrinking-core and shrinking-particle models. At lower temperature, leaching rates are reaction-controlled; at higher temperatures, diffusion becomes significant, particularly for Zn. SEM-EDS revealed alpha-sulphur deposition on unreacted cores, introducing diffusion limitations at higher temperature. The apparent activation energy for Zn leaching was much higher than for REEs, explaining slower Zn release. Differences likely stem from transition state enthalpy and crystal structure rather than lattice energy. • Y and Eu are mainly found in sieving fraction under 38 μm. • CRT phosphor mixture was fully digested. • The rate controlling step varies with temperature, according to shrinking core models best fit. • Alpha-sulphur deposits around the unleached particles, introducing diffusion limitations. • ZnS leaching is less favoured due to a higher transition state enthalpy.