Extraction of Heavy Metals from Fly Ash and Sand with Ligands and Supercritical Carbon Dioxide

Abstract

This project further develops supercritical fluid extraction as an industrial remediation process for soil and other heavy-metal-contaminated solid materials. In this study, divalent metals such as Zn2+, Cu2+, Pb2+, Cd2+, and Cr3+ are removed from sand and fly ash using CO2. When the solvating power of supercritical CO2 is combined with the metal ion complexing power and selectivity of organic ligands, a clean alternative to conventional liquid−liquid and liquid−solid extraction is obtained. Extraction technologies are required, which not only remove the mobile or total fraction of metals but also maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the application of supercritical fluid technology. In a study with spiked sand samples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO2 on the extraction efficiency is investigated. Influences of the type of complexing ligands is studied with both fly ash and sand samples. It is shown that the use of methanol as the entrainer and the humidity have strong effects on the metal extraction.

Concentration of Natural Vitamin E Using a Continuous Countercurrent Supercritical CO2 Extraction‐Distillation Dual Column

“…When the solvent-tofeed ratio increased, the VE content and yield at the bottom of the distillation column increased, reaching around 55 and 95 wt-%, respectively. The optimum solvent-to-feed ratio was found to be 100 kg CO 2 …”

“…At an extraction column pressure of 24 MPa, a temperature of 50°C, a distillation column pressure of 16 MPa, a temperature gradient of 80-70-60-50-40°C, and a solvent-to-feed ratio of 100 kg CO 2 …”

“…The technique of supercritical fluid extraction (SFE) offers several competitive advantages over conventional distillation or solvent extraction processes for natural products [1,2]. The extraction process using supercritical CO 2 (SC-CO 2 ) is widely investigated as a promising separation process for natural products, due to the non-toxic, non-flammable, non-corrosive, and low-cost nature of CO 2 , as well as its low critical temperature (304.1 K), convenient critical pressure (7.38 MPa), and environmental friendliness [3,4].…”

Extractability of Metals in Municipal Solid Wastes Fly Ash Using Supercritical CO2 Containing Cyanex 302

“…The extract was collected in the collection vessel (10). The temperatures of the reaction vessels (7,8) and the mixing vessel (6) were kept at 323 K throughout the experiment using water bathes (5,9). Extraction under flowing conditions.…”

“…As for the SFE of fly ash, Kersch et al studied the removal of heavy metals from fly ash and simulated ash. 7,8 They found that Cyanex 302 (bis(2,4,4-trimethylpentyl)monophosphinic acid) was effective as a ligand to extract lead with SC-CO2. 8 We employed Cyanex 302 as a ligand, and compared the extractability of lead with Cyanex 302 and SC-CO2 with the leachability by the JLT13 process for 6 samples of fly ash.…”