【Paper】
Influence of Carbon Dioxide on Removal and Capture of Lead Ions by Molten Slag
Yukio Fujita*, Takayuki Shimaoka* and Seizou Kenmoku**
* Institute of Environmental Systems, Graduate School of Engineering, Kyushu University
** Tochigi Prefectural Ceramic Steering Office
† Correspondence should be addressed to Yukio Fujita: Institute of Environmental Systems, Graduate School of Engineering, Kyushu University
（6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581 Japan）
Abstract
It has already been confirmed that the removal and capture of lead ions by molten slag and coexistent anions is dependent on the insolubility of the lead which was converted into basic lead carbonate, a kind of lead oxychloride, laurionite and lead sulfate.
In this investigation, we studied the contribution of carbon dioxide toward the formation of basic lead carbonate（2PbCO3・Pb（OH）2）and the effect of coexistent molten slag under the influence of carbon dioxide to reduce further lead concentration. Consequently, carbon dioxide in the atmosphere was converted into carbonic acid ions in water and it was contributed to the formation of basic lead carbonate with molten slag. Basic lead carbonate, laurionite and lead oxide were converted into lead carbonate in distilled water, and lead sulfate was converted into lead carbonate in a 1％ sodium hydroxide solution. However, after carbonation, when the pH value of the solution was reduced, the lead concentration of the solution was higher than that of the solution before carbonation. However, when carbonation was carried out with the coexistent crystallized molten slags, the pH value of the solution was not much reduced. It was confirmed that coexistent crystallized molten slag effected the reducing of lead. The reason for this was that the pH value of the solution was not much reduced from the neutralization of hydroxide ions and the buffer action of calcium ion by the molten slag and the slag's adsorption.
Key words: molten slag, carbon dioxide, carbonation, lead carbonate