【Paper】
Characteristics of Alkali Elution on Incinerator Ash of Sewage Sludge
Yasuhiro Takahashi
Iriezaki Sogo Sludge Center, Kawasaki City Sewerage Public Corporation
（3-24-12 Shiohama, Kawasaki-ku, Kawasaki, 210-0826 Japan）

Abstract
In order to recover a useful resource from the incinerator ash of sewage sludge, an examination of elution was conducted by soaking in sodium hydroxide solution. Using 4 samples of incinerator ash with different phosphorus contents, the elution property of phosphorus and useful elements was clarified. For phosphorus, the role of temperature and time in elution was verified. The concentration of the incinerator ash and its temperature were studied in order to determine effective elution conditions for aluminum and zinc. The elution content of aluminum was not related to aluminum concentration in the ash, but rose in relation to the phosphorus content in the ash. Because phosphorus and aluminum were the same characteristics of elution despite aluminum content ratio, it is assumed that aluminum phosphate is eluted in ash. This showed that the elution ratio of aluminum is related to temperature and ash concentration. The maximum elution rate of zinc was 16％, when elution was performed at 80℃ using 10％ Sodium Hydroxide solution.

Key words: incinerator ash of sewage sludge, phosphorus, aluminum, alkali elution, phosphorus recovery