Leaching process for terbium recovery from linear tube fluorescent lamps: optimization by response surface methodology.

Until now, rare earth elements (REEs) recycled from the green phosphor of waste fluorescent lamps (FLs), essentially terbium, remain a major challenge. The sulfuric acid effect on leaching efficiency of REEs from phosphor powder (PP) is investigated in this paper. According to a composite central design, experimental leaching study is performed under various parameters (acid concentration, leaching temperature, and time as well as liquid-to-solid ratio (L/S)). A statistical model of experiments and an analysis of variance are studied in order to predict leaching process. The results showed that by decreasing concentration and L/S ratio while increasing leaching time at optimal temperature value permits profitable terbium extraction. Afterwards, the developed statistical model is explored for an optimized response surface methodology. The obtained results were tested experimentally and showed best terbium extraction with 75%. Moreover, 0.01% for the major contaminant, that is calcium, is reached. This low calcium yield may have a further advantage during REE recovery in the downstream. Therefore, resulting solution under optimal conditions is treated with oxalic acid followed by a calcination of the solid precipitate. Finally, 43.57% and 49.38% are produced for terbium and yttrium oxides, respectively.