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Leaching Behavior of Various Trace Metals in Aqueous Medium from Two Fly Ash Samples

Regional Research Lab., Bhubaneswar-751 013, Orissa, India.

^* Corresponding author (root{at}csrrlbhu.ren.nic.in).

ABSTRACT

By using the batch, continuous, and column leaching methods, an attempt has been made to study the behavior of various metal ions release in water from two fly ash samples collected from two thermal power plants in Orissa, India. The USEPA extraction procedure has been followed to determine the early release of several hazardous elements, and it has been observed that their concentrations are within the prescribed limits for both the fly ash samples. Batch leaching at different pH values shows that trace metal ions release decreases sharply with increase of pH from 3.0 to 8.0. Continuous leaching at the liquid/solid ratio of 20:1 shows that both the samples are mildly acidic in nature with pH value stabilizing at 5.4 to 5.9. This is because of the high Fe and low Ca contents in the samples, where the pH value is controlled by the cyclic release and Fe and Al hydrolysis. An attempt has been made to correlate percentage of decrease in metal ions concentration with those of constants of the formation of different hydrolytic species, namely MeOH⁺ and Me(OH)₂ with increase in pH of the medium. A comparison between repeated leaching in columns using a low liquid/solid ratio and continuous leaching at a high liquid/solid ratio indicates that the general trend of dissolution of metals is essentially similar for both the methods.