Extraction of heavy metals from a contaminated soil using citrate-enhancing extraction by pH control and ultrasound...

A novel extraction method has been developed for remediation of a heavy-metal contaminated soil. Citrate was used as environmentally-friendly extractant to remove Pb, Zn, Cd, and Cu. Heavy metals were extracted effectively at two different pH regions around 2 and 4-5. Kinetic study showed that heavy metal extraction by washing at pH around 2 reached equilibrium within 4h, while extraction by washing at pH 4-5 increased gradually by the end of 24 h washing. Washing extraction at pH 2 for 6 h which was followed by washing at pH 5 for 16 h increased the percentage extraction of Pb and Cu from 67.6 to 85.9% and from 77.5 to 83.4%, respectively. Ultrasound application has been also investigated to enhance extraction of heavy metals by using citrate. Only 30 min ultrasound application at 19.5 KHz attained higher extraction of heavy metals than those by washing for 24h, showing the enhancement of heavy-metal removal. Thus, the performance of citrate for removing heavy metals was improved.