Leaching Characteristics of Heavy Metals from Solidified Sludge Under Seawater Conditions

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Abstract
It was attempted to investigate the leaching characteristics of solidified materials under sea-water condition. In leaching test, three different leachants, namely, sea water, acidic water, and distilled water were used. Final pH and metal concentration of leachate after 24-hr extraction were strongly affected by the nature of leachant. Addition of fly ash resulted in the decrease of leachate pH and the increase of leachate metal concentration. During 60-day leaching test periods, cumulative cadmium released under sea water was linearly increased, but other metals leached in decreasing rate with increasing number of leachant renewal. After 60 days of leaching periods, sample weights were decreased as lime and heavy metal components dissolved, and particle size of leached sample having no fly ash was especially decreased under the sea water leachant. Dissolved heavy metals were considerably reprecipitated under alkaline sea water condition. Microscopic study on surface change of solidified materials made with Scanning Electron Microscopy (SEM) and X-ray diffraction analysis (XRD) showed that lime dissolved out while C-S-H, ettringite, and gypsum crystals were formed.