Extraction, solubility and stability of metal complexes using stainless steel supercritical fluid extraction system

Abstract

Conventional supercritical fluid extraction (SFE) system are constructed using stainless steel due to its relative inertness, ready availability, tensile strength and low cost. Recently, metal complex solubilities and metal extraction using chelating agents have been investigated using a stainless steel SFE system. Metal complexes are usually soluble in supercritical carbon dioxide (SC-CO 2) and so this was the fluid of choice for the experiments. During the chelation step, temperature and pressure have great effect on the extraction efficiency. Using a metal salt as a sample, and hexafluoroacetylacetone (HFAcAc) as a ligand, the most efficient extraction conditions were found to be 60°C and 400 atm. However, when contaminated soil was used as a sample, extraction efficiency fell. This was thought to be related to the corrosion of the stainless steel SFE system by the ligand HFAcAc. During the 30 min extraction period, 1678 μg of iron was obtained. The corrosion of the SFE system was much greater during the soil extraction than during both the metal salt extraction and metal complex solubility experiments.