【Paper】
Influences of PH and Anions on Insolubility of Lead Ion by the 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 reduction of lead is dependent on the insolubility of the lead ion which was converted into basic lead carbonate（2PbCO3・Pb（OH）2）by precipitation reaction.
In this investigation, we examined the influences of pH and anions on the insolubility of the lead ion by utilizing slag leachates instead of slags. The pH value of the slag leachate was adjusted across a range of pH values from 9.2 to 11.4 under solid liquid ratio（S/L）. Regarding anions, we examined with chloride, sulfate, acetate and nitrate which were ionized to Cl ion, SO4 ion, CH3COO ion and NO3 ion, which might be leachated in the incineration ash and organic matter. Consequently, it was confirmed that basic lead carbonate（2PbCO3・Pb（OH）2）was best formed with S/L（2w/v％）and a pH value of about 10.5. When chloride concentration was about the same as that of the lead compound's, a kind of lead oxychloride, laurionite（PbCl（OH））was predominantly formed and basic lead carbonate（2PbCO3・Pb（OH）2）was not formed. However, lead sulfate（PbSO4）was predominantly formed when the SO4 ion and the Cl ion coexisted. Basic lead carbonate（2PbCO3・Pb（OH）2）was formed when CH3COO ion and NO3 ion existed. As a result, it was confirmed that coexistent salts with slag leachate effected the reduction of lead.


Key words: molten slag, insolubility of lead, pH, anion, chemical speciation form