A Study on the Potential Release of Hazardous Elements from Municipal Solid Waste
--An Evaluation of Leaching Test Results using Sequential Extraction--

Tong Ouyang*, Makoto Torigai*, Ruriko Sakai*, Ning Wang*, Sun-ja Yun*, Kiyoshi Iwashima* and Masahiro Osako**

* The Institute of Basic Environmental Research, Environmental Control Center Co., Ltd.,
** Department of Waste Management Engineering The Institute of Public Health

+ Correspondence should be addressed to Tong Ouyang:
(323-1 Shimo-ongata-machi, Hachioji city, Tokyo 192-0154 Japan)

Abstract

To assess the effectiveness of a leaching test that aims at estimating the release potential of elements, it is necessary to have an understanding of how the major chemical species of objective elements change during leaching. In this study, a sequential extraction (SQE) procedure was employed to evaluate leacheability in a modified availability test (A-test) on As, Cd, Cu, Fe, Mn, Mo, Ni, Pb, Sb and Zn in selected municipal solid waste materials. The degree to which that A-test was effective with respect to the practical potential release limit indicated by the SQE results, and to which that certain chemical speciation form contributed to the released amounts, was quantitatively evaluated by comparing the distribution of different forms of the elements before and after the A-test. In most samples, the amounts released by the A-test were smaller than the sum of the geochemically extractable fractions obtained by SQE. The A-test under a nitrogenous atmosphere resulted in an increase in the release of As, Sb and Mo, together with Fe and Mn, and a decrease in the release of Cd, Ni, Cu, Pb and Zn. A comparison with the changes in chemical speciation forms subjected to the A-test under different atmospheric conditions, revealed that the difference in release behaviors between the elements was primarily caused by the changes in the moderately reducible fraction, which was regarded as the mixture of Fe and Mn oxides. It is likely that, at least, under the acidic medium (pH4), both the adsorption of cationic elements and the rejection of anionic elements on Fe/Mn-rich oxides are factors controlling mobilization of these elements in municipal solid waste materials when the redox potential changes.

Key words: potential release, leaching test, redox potential, chemical speciation form, sequential extraction procedure