EXTRACTION OF LANTHANIDES FROM SPENT POLISHING AGENT

The polishing of glass substrates or wafers requires fine-grained particles, frequently based on oxides of the lanthanides cerium and lanthanum. During processing the slurries become enriched with different elements depending on the specific production program and the chemical composition of the work piece. Concentrations of these impurities can reach critical values and may negatively influence the surface quality of the substrates. Therefore, the polishing agents have to be removed from the system and are sent to a landfill or recycled. This chapter describes options for processing such secondary rare earth resources using different hydrometallurgical methods including mineral acids for extraction. In some cases, the focus is also on the evaluating precipitation methods by carbonate or oxalate carriers to produce a rare earth concentrate that meets requirements for reuse in fabricating new polishing powders.