Recycling of fluorescent light phosphors
Student name: Ms Parul Johar
Guide: Dr Lakshmi Raghupathy
Year of completion: 2017
Host Organisation: IIT Bombay
Supervisor (Host Organisation): Prof. Sudhanshu Mallick
Abstract: The re-use of end of life phosphor material is limited to the particular bulb type
and is of low quality and efficiency. This approach of recycling is cheap yet not
effective. Therefore, another route for recycling is the recovery of various
constituent rare earth metals from the phosphor. The phosphor mixture can be
separated into its individual components by various fluid extractions followed by
precipitation and also by electrodeposition using cyclic voltammetry. In this
paper, the dissolution of phosphor mixture was performed using citric acid, aqua
regia and sulfuric acid to extract the metals into solution for further analysis. The
recovery efficiency for Y recovery ( major rare earth present ) was found to be
93.6 %, 88.64% , 63.32% and 53.66 % using Sulfuric acid , citric acid ( 1h) ,
citric acid ( 2h) and aqua regia respectively. Further, the mechanism adopted was
2 –step leaching using dil. and conc. Sulfuric acid. This lead to the separation of
red phosphor constituents i.e. Y and Eu into the dil acid filterate and the
remaining rare earth metals were extracted into the conc. acid. Then after pH
adjustment and addition of oxalic acid into the individual leached solutions, the
rare earth oxalates were formed ,that was then further calcined to get the
recovered rare earth oxides separately. This extraction followed by calcination
led to the separation of red phosphor from the other phosphor components, that
can be effectively reused. The cyclic voltammetry was perfomed using the
original leached solutions to separate Y and Eu, that were the major elements
present in the sample. Y was separated and recovered from the rest of the
elements using cyclic voltammetry at pH 2.2 at its reduction potential i.e.-2.4 V
successfully.
Key Words : citric acid leaching , fluorescent light , phosphors, rare earth
metals , metal recovery , cyclic voltammetry, calcination.
