Liquid-liquid extraction of rare earth fluorescent powders for recycling

The paper describes a method for separation of ultra-fine particles prior to recycling. In other words, the authors are putting forward a two-step process for separating a mixture of rare earth fluorescent powders (i.e. red, green, blue). Each step of the process is a liquid-liquid extraction, which involves two organic solvents (i.e. non-polar and polar solvents, in order to create two phases), and a surfactant to manipulate the wettability of powders. In the first step, the green powder migrates toward a non-polar phase such as n-heptane, and remains at the interface of two solvents. The remaining two components precipitated in the polar phase. In the second step, the blue powder migrates toward a non-polar phase, and remains at the interface of two solvents; whereas the red powder precipitated, on the other hand, in the polar phase. After testing various types of non-polar solvent, a selection was made, and then the operational parameters (e.g. concentration of surfactant and solid concentration) were varied in order to maximize the efficiency of the process. The grade and recovery of each separated fluorescent powder were greater than 90%.