Treatment of powders coming from exhaust fluorescent lamps: an evaluation of the experimental parameters influencing the recovery of rare earth elements

The research described in this work focused on recovery of yttrium (Y) from powder coming from exhaust fluorescent lamps. different leaching procedures were explored. Sulphuric acid leaching showed the advantage of reduction of the solubilization of Ca, thus improving the quality of the final product. The influence of the experimental parameters has been evaluated observing that that the best conditions are the following: sulphuric acid 2M, room temperature (20°C), S/L ratio 0.2 g/mL (a typical experiment was carried out by treating 4 g of powder with 20 mL of acid) for 30h under stirring. Under these conditions the yield for Y extraction is higher than 90%. Precipitation tests have been carried out by using different O-chelating agents. The best results in term of yield and selectivity of yttrium precipitation have been obtained by using oxalic acid from the solution of diluted sulphuric acid. By thermal treatment (700°C, 1h) yttrium oxalate was converted into the corresponding oxide. The whole process was demonstrated to achieve a very good yield (more than 90%) of yttrium oxide recovered from exhaust fluorescent lamps.