Radioisotope tracer techniques were used to study the process of in-situ chelation/supercritical fluid extraction (SFE) of La3+ and Lu3+ from a solid matrix using mixed ligand hexafluoroacetylacetone (HFA) and tributylphosphate (TBP) as chelating agents. A lab-built SFE extractor was used in this study and the extractor design was optimized based on the experimental results. Quantitative recovery of La and Lit was achieved when the extractor design was optimized. Extraction of uranium from real world samples was also investigated to demonstrate the feasibility of this chelation/SFE technology for environmental remediation applications. A novel on-line back extraction technique for the recovery of metal ions and regeneration of ligands is also reported.