Moving Towards a Circular Economy
Recovery of Nutrients & Other Valuable Compounds
The recovery of valuable compounds and nutrients from food and agricultural waste is a proven opportunity for supercritical fluids. Extraction using Supercritical Carbon Dioxide is seen as an attractive alternative to mechanical press or conventional solvent extraction for the recovery of valuable compounds. Supercritical Fluid Extraction offers a higher quality product at a lower environmental impact and with lower GHGs. De Melo et al. (2014) reviewed Supercritical Fluid Extraction of vegetable matrices (300+ species), identifying nearly 600 publications over the time-period from 2000 to 2013. Some examples are:
- Extraction of carotenoids from tomato residues (Aniceto et al., 2022): Tomatoes and tomato residues are known to contain carotenoids (e.g., lycopene and β-carotene). Lycopene has application in the nutraceutical industry, in addition to being widely used as a food coloring. β-carotene is an antioxidant agent, in addition to playing a key role in human nutrition as provitamin A.
- Spent coffee grounds contain valuable compounds such as phenolics, which are human health related compounds with demonstrated antioxidant, antibacterial, antiviral, anti inflammatory and anti carcinogenic benefits. A review of Supercritical Fluid Extraction and Fractionation of valuable compounds from spent coffee grounds is provided by Bitencourt et al. (2022).
Moving Towards a Circular Economy
Recovery of Metals
The recovery of metals from a wide range of waste streams is a growing opportunity for supercritical fluids. Broadly, a ligand complexes with the metals in the waste. The metal-ligand complex dissolves into the supercritical phase for recovery. The metal–ligand complex is recovered from the Supercritical Fluid and the Supercritical Fluid is recirculated. Ideally, the ligand is then recovered from the complex so that the ligand can be recirculated. Just a few examples include:
- Gold recovery from secondary mine tailings waste using Supercritical Fluids and various ligands (demonstrated by van Dyk et al. 2022).
- Rare Earths (Yttrium and Europium) recovered from luminescent bulb waste using Supercritical Carbon Dioxide (at 313 K & 15 MPa) and tri-n-butyl phosphate (demonstrated by Shimizu et al., 2005).
- Indium recovery from cell phone LCDs using Supercritical Carbon Dioxide (at 308 K & 8 MPa) with citric acid and hydrogen peroxide (demonstrated by Argenta et al. 2017).
