Yukio Noma* and Akiko Kida*

* Hiroshima Prefectural Health and Environment Center

+ Correspondence should be addressed to Yukio Noma:
(1-6-29 Minami-machi, Minami-ku, Hiroshima 734-0007 Japan)

Abstract

The formation of calcium scales have been found in leachate treatment facilities at landfill sites. This problem has a result of the landfilling of incineration ash which contained a large amount of soluble salts. 15 municipal landfill sites were investigated with regard to scale formation and chemical analysis of leacheates. Contributing factors such as calcium concentration, alkalinity, water temperature and ion strength, in particular the former two contributed to calcium scale formation in landfill leachates and the saturation pH (pHs) levels calculated were important. In using two convention indices of scale formation namely the Langelier Saturation Index and the Ryzner Stability Index both were unsufficient in explaining real scale formation, the former overestimating the amounts and the latter underestimating the amounts. It is considered that if a leacheate is in a condition with pHs<7, calcium concentration>100mg/l and alkalinity>100mg/l, these levels are liable to form calcium scales. Calcite as the main mineral and aragonite were found in real scale, while geochemical calculations showed the possible precipitation of calcite and dolomite, and the possible existence of aragouite, magnesite and huntite in oversaturated solution.

Key words: calcium scale, calcium carbonate saturation pH, alkalinity, landfill leachate, geochemical thermodynamic calculation