Speciation of toxic pollutants in Pb/Zn smelter slags by X-ray Absorption Spectroscopy in the context of the literature
Danting Chen, Amitava Roy, Yu Qian Li, Anna Bogush, Wing Yin Au, Julia A. Stegemann
Abstract
Pb/Zn smelter slag is a hazardous industrial waste from the Imperial Smelting Process (ISP). The speciation of zinc, lead, copper and arsenic in the slag controls their recovery or fate in the environment but has been little investigated. X-ray Absorption Spectroscopy (XAS) was applied to this complex poorly crystalline material for the first time to gain new insights about speciation of elements at low concentration. Zn, Cu, As K-edge and Pb L3-edge XAS was carried out for a Pb/Zn slag from a closed ISP facility in England, supported by Fe, S and P K-edge XAS. Results are presented in the context of a full review of the literature. X-ray fluorescence showed that concentrations of Zn, Pb, Cu and As were 8.4, 1.6, 0.48 and 0.45 wt.%, respectively. Wüstite (FeO) was the only crystalline phase identified by X-ray diffraction, but XAS provided a more complete understanding of the matrix. Zn was found to be mainly present in glass, ZnS, and possibly solid solutions with Fe oxides; Pb was mainly present in glass and apatite minerals (e.g., Pb5(PO4)3OH); Cu was mainly speciated as Cu2S, with some metallic Cu and a weathering product, Cu(OH)2; As speciation was likely dominated by arsenic (III) and (V) oxides and sulfides. Current production of Pb/Zn smelter slags is about 1Mt/y, and past disposal of more than 25 Mt of these slags has already deposited nearly 2 Mt of zinc, 0.2Mt of lead, 0.1 Mt of copper and 0.05 Mt of arsenic in the environment. These elements could potentially be recovered, or will gradually leach out, depending on their speciation and the disposal conditions. This work has used X-ray absorption spectroscopy to determined the speciation of these elements, which will help to understand the risks these slags pose and develop better disposal, utilisation or element recovery techniques.