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Investigation of Optimum Firing Degree of Calcined Dolomite Used for Insolubilization Treatment of Heavy Metals and Analysis on Crystal Structure Change of Dolomite by Firing

Calcined dolomite shows excellent adsorption ability for heavy metals, metalloids and halogens (hereafter collectively referred to as “heavy metals”) in soil, compared with raw dolomite. It is well known that dolomite is thermally decomposed into MgO and CaO in two stages. To study the relation between the heavy metal adsorption ability and crystal structure of calcined dolomite, 1) adsorption test using a solution containing heavy metals 2) specific surface area measurement 3) quantitative determination of the crystal phase by Rietveld analysis, and 4) K-edge XANES (X-ray Absorption Near-Edge Structure) analysis of Mg and Ca, were performed. The results of measurement of specific surface area after calcination and Rietveld analysis showed that there is a relation between the dolomite phase reduced by thermal decomposition and the specific surface area value and adsorption ability for heavy metals. The measured XANES spectra revealed that the local structure around Ca atoms did not change during calcination but that the local structure of Mg atoms changed gradually during calcination. Furthermore, the Mg K-XANES spectra measured in Partial Fluorescence Yield (PFY) mode and in Total Electron Yield (TEY) mode showed different spectra variations. These results suggest that MgO derived from calcined dolomite has structural differences between the outermost layer and the inside.