Ultrasound-assisted extraction of matrix elements and heavy metal fractions associated with Fe, Al and Mn oxyhydroxides from soil

Abstract

Single agent extractions of major and trace metals from soil samples were conducted by means of a rotary mixer and an ultrasonic bath with sonication times of 10, 20, 30, 40 and 50 min. The sequential extraction was undertaken according to the European Community Bureau of Reference. The obtained soil extracts were analyzed by inductively coupled plasma-optical emission spectrometry and according to the results, the rotary mixer-assisted extraction was more efficient in the case of alkaline earth elements. However, by use of ultrasound, several times higher amounts of matrix elements (Fe, Al and Mn) and heavy metals predominantly associated with Fe, Al and Mn oxyhydroxides were extracted. The increase of the sonication time failed to improve the extraction yields. The changes in the conductivity, pH, redox potential, particle size diameter and zeta potential of colloid particles with increasing sonication time were measured. The extraction mechanism and expressed selectivity of ultrasound is discussed and an explanation is suggested.