| Mercury is a hazardous air pollutant emitted to the atmosphere in large amounts. Mercury emissions from electric power generation sources were estimated to be 48 metric tons/year, constituting the single largest anthropogenic source of mercury in the U.S. Settled mercury species are highly toxic contaminants of the environment. The newly issued Federal Clean Air Mercury Rule requires that the electric power plants firing coal meet the new Maximum Achievable Mercury Control Technology limit by 2018. This signifies that all of the air-phase mercury will be concentrated in solid phase which, based on the current state of the Air Pollution Control Technology, will be fly ash. Fly ash is utilized by different industries including construction industry in concrete, its products, road bases, structural fills, monifills, for solidification, stabilization, etc. Since the increase in coal combustion in the U.S. (1.6 percent/year) is much higher than the fly ash demand, large amounts of fly ash containing mercury and other trace elements are expected to accumulate in the next decades. The amount of mercury transferred from one phase to another is not a linear function of coal combustion or ash production, depends on the future states of technology, and is unknown. The amount of aqueous mercury as a function of the future removal, mercury speciation, and coal and aquifer characteristics is also unknown.; This paper makes a first attempt to relate mercury concentrations in coal, flue gas, fly ash, and fly ash leachate using a single algorithm. Mercury concentrations in all phases were examined and phase transformation algorithms were derived in a form suitable for probabilistic analyses. Such important parameters used in the transformation algorithms as Soil Cation Exchange Capacity for mercury, soil mercury selectivity sequence, mercury activity coefficient, mercury retardation factor, mercury species soil adsorption ratio, and mercury Freundlich soil adsorption isotherm coefficients were derived. Mercury air-phase removal efficiency was studied as a function of dominant mercury species vapor pressures, the amount of chlorine, sorbent injection rate and adsorption capacities, and process temperature and modifications. A mercury air phase removal algorithm was derived which defines the future removal efficiencies as a function of activated carbon injection rate. Mercury adsorption on soil was studied as a function of Mercury Mass Law incorporating the dominant aquatic mercury species, pH, chlorine and sulfur concentrations, and the amount of complexed hydroxyl groups. Aquatic mercury longitudinal plume delineation was studied using the Domenico and Robbins function. A Monte Carlo simulation was performed using random number series (5000) for all of the variables in the Domenico and Robbins and mercury retardation functions. The probability that the Maximum Contaminant Level for mercury will be exceeded was found to be equal approximately 1 percent of all soil-related fly ash applications. |
