Extraction of Yttrium from Light-Emitting Diode Waste by Alkali Fusion Followed by Acid Leaching

Literature regarding metals recovery from LED waste mainly focuses on semiconductor materials and precious metals, lacking data about rare earth elements. This paper explores this gap presenting an experimental study of yttrium extraction from LED waste by alkali fusion/acid leaching method. For this purpose, LED samples were obtained from tubular lamp. Chemical and thermal analyses were performed. Alkali fusion preprocessing was adopted followed by nitric acid leaching to solve difficult yttrium extraction from aluminate structure of LED phosphor. A chemical reaction mechanism in the alkali fusion involving degradation of the silicone polymer and destruction of the aluminate phosphor has been proposed as a novel approach to the subsequent easy leaching of rare earths from LED waste. Fusion conditions were 700 °C, for 3 h, NaOH/LED relation 1:1. Leaching solutions and solid residue were analyzed by energy dispersive X-ray fluorescence spectrometry, induced coupled plasma optical emission spectrometry, X-ray diffractometry and Fourier transform infrared spectroscopy. It was observed the undesirable formation of silica gel in the leaching liquor processed in temperatures below 70 °C. In that way, it is recommended the leaching at 90 °C, with formation of insoluble SiO₂. Optimal leaching conditions found were leaching time of 20 min, 1/20 solid/liquid ratio, with 91% yttrium extraction in HNO₃ 2.5 mol/L at 90 °C.