Microwave and Ultrasound Assisted Extraction of Heavy Metals from Sewage Sludge by HEDTA and Oxalic Acid

Ultrasound and microwave were applied to enhance extraction of heavy metals in sewage sludge with oxalic acid and hydroxyethyl ethylenediamine triacetic acids (HEDTA), and the effects of radiation time, power and energy of ultrasound and microwave on the extraction of heavy metals from sewage sludge were investigated. Besides, species of heavy metals fractions in sewage sludge before and after extraction were analyzed by the application of Tessier's sequential extraction procedure. In general, the extracted fractions of Cu, Ni and Cr in sludge were improved with the increase of time, power and energy, the extracted fraction of Zn had not been obviously improved. After the ultrasonic-assisted and microwave chemical extraction, the contents of organic compounds and residue forms of Cu, Cr and Ni were decreased. However, the contents of exchangeable and carbonate compounds forms were slightly increased, the speciation of Zn in sludge was hardly changed.