Design and Development of a Continuous-Flow Countercurrent Metal ExtractionSystem to Remove Heavy Metals from Contaminated Soils

摘要

The purpose of the research was to design a pilot scale soil washing system andto determine its optimal operating conditions to effectively remediate soils contaminated with heavy metals. The research focused on eight contaminated soils from Army installations and the metal extraction capabilities of eight extracting agents including HNO3, HCI, fluorosilicic acid, citric acid, EDTA, DTPA, NTA, and NaOH. These extracting agents were tested at concentrations of 0.01 M, 0.05 M, and 0.1 M. Among the solid to liquid ratios of 0.005, 0.01, 0.05, 0.2, and 0.5, the most efficient and effective ratio for the removal of heavy metals was a solid to liquid ratio of 0.05. In evaluating the extracting agents for removal of heavy metals from soil, citric acid, HC1, HNO3, and DTPA were the most effective reagents for the removal of lead (Pb). HNO3, HC1, EDTA, and citric acid were the most effective for the removal of cadmium (Cd). Citric acid was most effective for the removal of chromium (Cr). The reaction times to reach chemical equilibrium between the metal contaminated soils and extracting agents varied from 30 min to 30 hr depending on the soil type, the heavy metal contaminant, and the type and concentration of extracting agent.