Reprocessing rare earth phosphor mixtures from used fluorescent lamps

摘要

- Reprocessing rare earth phosphor mixtures from the decomposition of burnt-out or no longer functional tubular fluorescent lamps, containing mercury (Hg) and phosphate, especially halophosphate, comprises: (i) dissolving Hg and most of the phosphate phosphor by treating the mixture with dilute hydrochloric acid (HCl) and oxidant; (ii) removing completely residual halophosphate phosphor and phosphate phosphor, e.g. lanthanum phosphate doped with cerium and terbium (LaPO4:Ce,Tb) from the insoluble residue, by treating it with a chelating organic acid; (iii) washing the remaining insoluble fractions of europium-doped yttrium oxide (Y2O3:Eu), europium-doped barium-magnesium aluminate and terbium-doped cerium-magnesium aluminate with deionised water, separation from the aqueous phase, drying, calcining above 1200 deg C and re-using the resultant mixture of red-, green- and blue-phosphors, optionally mixed with fresh phosphor mixture, for the production of fluorescent lamps; (iv) separating Hg and antimony (Sb) from the solutions as metals, by electrolysis or as hardly soluble sulphides by adding sodium or ammonium sulphide; (v) neutralising the remaining solutions with aqueous sodium hydroxide (NaOH) solution to precipitate calcium phosphates, separating the precipitate containing di- and tri-calcium phosphate and also the manganese (Mn) present and traces of Sb by filtration and dumping this; and (vi) working up the resultant sodium chloride (NaCl) solution to salt.