A method and system for measuring the adsorption potential of fly ash. A sample of the fly ash is mixed with an optically active reagent. The mixture is irradiated with light at a given wavelength and an optical parameter of the irradiated sample, such as intensity of optical absorbance or fluorescence emission is measured by an optical measuring apparatus. The adsorption capacity of the sample is determined as a function of the optical measurement. A controller is provided that communicates with the optical absorption measuring apparatus and controls flow of fly ash and sacrificial agent to a reaction zone or housing wherein the fly ash is contacted by the sacrificial agent.