Leaching behaviour of trace toxic metals from flyash, their seepage control to groundhater and utilisation of flyash

Abstract

The flyash of coal based thermal power plants is being dumped openly from the last several years in the form of wet slurry in a pond where leaching of trace toxic metals contaminate both surface and ground water. The leaching characteristics of chromium (III), chromium (VI), mercury (n) and arsenic from flyash were investigated at various pH levels. It was estimated at pH 7.0 that about 40% of these toxic elements present in flyash was leachatable and may leach out to groundwater. Twelve monitoring wells were selected surrounding the dumping site for studying these metals in groundwater. The ash transport water samples of the pond were also examined for these toxic metals. PH of both surface and groundwater were measured and found in the range of 6.5 to 7.8. The concentration of these toxic metals in groundwater around the dumping site as well as in ash transport water samples were determined by grafite AAS and Sp‐500 spectrophotometric methods and the results are incorporated in Table‐1. A control technology is suggested for seepage control of these trace toxic metals to groundwater with proper synthetic liners.

A method for flyash utilisation is developed for building materials/smooth road or airport runway construction. In this method the fLyash is mixed with bitumen (tarcoal) in the ratio of 70:30 at about 80–90 °C. The specimen of flyash‐bitumen was a very strong tensile material after cooling because of the flyash contains high percentage of oxides of silicon, aluminium etc. It is a good way for utilisation of flyash as compared to flyash brick manufacturing as a building material. The leaching behaviour of these toxic metals in flyash‐bitumen was studied at various pH values. It was found that the metals in the leachate solution in negligibly small.

Key words:

• Flyash
• leaching
• toxic metals
• pH effects
• control
• flyash utilisation