Title: An immobilisation mechanism for lead in fly ash subjected to mechanochemical treatment

Authors: Nomura Yugo; Fujiwara Kazuo; Akihiko Terada; Nakai Satoshi; Hosomi Masaaki

Addresses: Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan ' Engineering Department Fuji Oil Co., Ltd., 1 Sumiyoshi-cho, Izumisano, Osaka 598-8540, Japan ' Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan ' Graduate School of Technology, Hiroshima University, 1-4-1, Kagamiyama, Higashi-hiroshima, Hiroshima 739-8527, Japan ' Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan

Abstract: Mechanochemical (MC) processes immobilise heavy metals in fly ash, a desirable outcome because recycled fly ash is commonly used in the synthesis of inorganic materials. We investigate the extent of immobilisation and the mechanism of lead (Pb) leaching during MC treatment of fly ash, using lead oxide (PbO) and lead dichloride (PbCl₂) as model compounds. MC treatment of the fly ash inhibited Pb leaching by about 97% after a 12 h treatment. PbO was reduced to elemental Pb in a redox reaction by abraded iron (Fe) produced from the stainless steel ball mill used for MC treatment, and a phase transition of the PbO crystal structure from orthorhombic to tetragonal was confirmed. Production of Pb species with sparing solubility in water resulted in immobilisation of the Pb within the fly ash. Other insoluble intermediates detected in the milled samples, such as Pb₂O₃, potentially contribute to the inhibition of Pb leaching.

Keywords: mechanochemical treatment; fly ash; heavy metals; lead leaching; inhibition; reduction; lead oxide; lead dichloride; phase transition; solubility; water; iron; immobilisation; environmental pollution; Pb leaching.

DOI: 10.1504/IJEWM.2013.056199

International Journal of Environment and Waste Management, 2013 Vol.12 No.3, pp.340 - 353

Published online: 20 Sep 2014 *

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