Abstract
ABSTRACT
With chemical precipitation being the most widely used treatment process, the ultimate disposal of the sludges generated is a real concern to the environmental community. Relatively few studies have addressed the leaching/ dissolution phenomena of heavy metals from sludges. Such leaching behavior is addressed using both synthetic plating sludges [Zn(OH)2, ZnS, and Cd(OH)2] and an industrial plating sludge in columnar leaching experiments. Various pH conditions (3.85 ≤ pH ≤ 6.99) and applied flow rate conditions (0.372 mL/min ≤ applied flow rate ≤ 0.828 mL/min) were employed. The hydroxide sludges behaved as expected with the greatest degree of solubilization exhibited at the lowest pH condition. The metal sulfide system is extremely complex; the dissolution behavior is not governed solely by pH. Oxidation of sulfide to sulfate seems likely in this current study. This leaching process is controlled by diffusion.
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