Integrated Process for Recovery of Rare-Earth Elements from Lamp Phosphor Waste Using Methanesulfonic Acid
2021
Rodriguez, Nerea Rodriguez | Grymonprez, Brent | Binnemans, K. (Koen)
End-of-life fluorescent lamps, collected in most countries for their mercury content, are also an interesting source of rare-earth elements. Methanesulfonic acid (MSA) is a cheap and environmentally friendly acid, which is produced in bulk. In this work, an integrated process for the recovery of valuable rare-earth elements via selective separation of three phosphor fractions using MSA as a lixiviant was developed. First, the halophosphate phosphor was selectively leached with pure MSA at room temperature (L/S = 10 L/kg, T = 25 °C, t = 2 h). Second, the valuable YOX phosphor was selectively leached with diluted MSA (5 vol %; L/S = 10 L/kg; t = 2 h, T = 80 °C). Finally, the remaining LAP phosphor was leached with pure MSA (T = 180 °C, L/S = 15 L/kg, t = 6 h). This highly selective sequential leaching process is based on the combination of hydro- and solvometallurgy. The calcium-rich pregnant leach solution was purified via vacuum distillation. The yttrium-rich and the lanthanum-rich pregnant leach solutions were purified via solvent extraction with bis(2-ethylhexyl)phosphoric acid, followed by stripping with oxalic acid. A conceptual flowsheet for the developed closed-loop recycling process is presented.
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