Adsorptive Removal of Trace Elements from Coal Fly-Ash Wastewaters onto Iron Oxyhydroxide

Certain processes used for the handling of coal combustion residuals in electric generating plants have the potential for the mobilization and release of trace elements into the environment. This chapter summarizes some of the results of a research program investigating adsorption onto amorphous iron oxyhydroxide, am-Fe₂O₃·H2_O, as a treatment process for removing trace metals from coal fly-ash wastewater. It highlights typical adsorption phenomena observed in simple, well characterized clean systems. The clean system equilibrium adsorption experiments were conducted in a swamping electrolyte (0.1M NaNO₃) maintained at 25°C in a jacketed Pyrex reaction vessel. The development of the removal curve depends on the availability of empirical adsorption data developed for each trace element of interest in each wastestream of interest. The modeling work using a mathematical equilibrium model shows promising results in predicting the adsorptive removal of several trace elements of concern. Adsorption experiments were conducted in simple, well characterized "clean systems" and in fly-ash wastewaters from five power plants.