Recovery of rare earth oxides from waste fluorescent lamps, The

Abstract

Phosphor dust was characterized to quantify the various mineralogical phases. QEMSCAN determined that more than 70% of the rare earth minerals are less than 10µm in size and the main gangue material, quartz, was primarily larger than 74µm. Beginning with a europium and yttrium-rich pregnant leach solution, the optimized conditions for oxalic acid precipitation were determined. Grade and recovery curves were developed using the conditions optimized by Stat-Ease 9.0.5. The results demonstrate that using ambient temperature and native pH were ideal for creating 99% pure yttrium and europium mixed oxides with more than 99% stage recovery.The selective reduction and precipitation of europium from mixed yttrium and europium powders was completed with more than 95% pure europium (II) sulfate with more than 80% recovery at lab scale. The oxidation-reduction potential was demonstrated versus time for the selective reduction of europium (III) to europium (II). A novel SEM image was discovered and can be used as a signature for europium (II) sulfate. Gibbs minimization was used to model the preparation, reduction, and precipitation portion of the experiments.A scoping study was conducted to analyze the economics of building a phosphor dust recycling facility beginning with pre-sieved, freight-on-board (FOB) waste lamp phosphor powder and ending with a salable 99% pure mixed yttrium and europium oxide product to a customer willing to purchase it for a 30% discount from China FOB rare earth prices. The process was economic using a 6 year REO price average (NPV $17.7 million) and 2 year REO price average (NPV $2.4 million), but is uneconomic at current REO prices. The break-even price for europium oxide is $420 per kg and $15.50 per kg for yttrium oxide.