Separation of rare earth fluorescent powders by two-liquid flotation using organic solvents

In this paper, we describe a method for separation of ultra-fine particles prior to recycling. The authors suggest a two-step process for separating a mixture of three different rare earth fluorescent powders (i.e., red, green, and blue). Each step of the process is a two-liquid flotation, which involves two organic solvents (i.e., a non-polar and a polar solvent, in order to create two different phases) and a surfactant to manipulate the wettability of the 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 precipitate 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, while the red powder precipitates in the polar phase. After testing various non-polar solvents, a selection was made, and the operational parameters (e.g., concentration of surfactant and solid) were varied in order to maximize the efficiency of the process. The grade and recovery of each separated fluorescent powder were both greater than 90%.