Role of carbonate for Pb sorption in some bentonites
2007
Nakano, A.(Kyushu Univ., Fukuoka (Japan)) | Ohtsubo, M. | Li, L. | Higashi, T. | Kanayama, M.
Bentonite is widely used for clay liner materials because of high swelling, low hydraulic conductivity, and the high sorption capacity of contaminants such as heavy metals. In this paper, batch sorption tests and selective sequential extraction tests were conducted to evaluate sorption capacity and forms for lead using three types of bentonites from Japan and US with different physical, chemical, and mineralogical properties. Cation exchange and carbonate phase were predominant for the sorption of lead by bentonites; the carbonate phase was dominant at high equilibrium pH, while the cation exchange phase became dominant as equilibrium pH decreases. The ratio of carbonate phase was greater for the bentonite with higher amount of carbonate, so was the maximum Pb retained. The Japanese bentonites sorbed greater amount of Pb than the US bentonite as they contained more carbonate. The formation of cerussite (PbCO3) primarily contributes to Pb sorption by carbonate, so does partially the formation of Pb hydroxycarbonate complexes.
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