Supercritical Fluid Extraction of Metal Ions from a Solid Matrix with 8‐Hydroxyquinoline and Carbon Dioxide

Abstract

8‐Hydroquinoline (8‐HQ) was first used as a chelating agent for supercritical fluid extraction (SFE) of mixed metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Cd²⁺, Cr³⁺, Ni²⁺, Co²⁺) from solid samples in this study. The experimental variables such as pressure, temperature, extraction time, and flow rate of supercritical CO₂ were optimized, in order to maximize the recovery of the metal ions in a relatively short time. The collected analytes were analyzed by an atomic adsorption method. The results showed that the recoveries of the metal chelates were less than 50%, just with pure supercritical CO₂. Using methanol as a modifier for supercritical CO₂ can greatly improve the extraction efficiencies, and the addition of a surfactant can further enhance the recoveries of the metal chelates to a large degree. Quantitative extractions were obtained at 50°C, 15 MPa, 15 min dynamic extraction with methanol, and surfactant modified supercritical CO₂. Cu²⁺, Pb²⁺, Zn²⁺, Co²⁺ ions can be extracted completely, and Cd²⁺, Cr³⁺, Ni²⁺ ions can be extracted efficiently (>80%). Also, extraction of metal ions from real solid environmental matrices, such as standard reference soil sample and river sludge, was investigated; the results were satisfactory.

Keywords:

• 8‐HQ
• SFE
• Chelating agent
• Supercritical CO₂
• Extraction efficiency