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Show to 94.4 percent as a function of temperature. At 1520°F, 94.4 percent of the arsenic did not volatilize but remained in the kiln ash while at 1700°F the percent volatilizing increased to 16 percent. Additional experiments by Waterland et. al. [25] document similar results with the incineration of arsenic contaminated soils in a pilot scale rotary kiln system. At kiln temperatures of 1520 - 1550°F (1105 - 1117°K) 66 - 76 percent of the arsenic remained in the kiln ash and was not volatilized. At kiln temperatures of 1822°F (1267°K) 36 - 56 percent of the arsenic remained in the kiln ash and was not volatilized. The temperature phenomena is readily apparent. Waterland et. ale [25] document an additional phenomena: the impact of calcium to depress the volatility of arsenic. Waterland et. ale [25] conclude: "Adding lime to the site soil significantly decreases both the volatility of arsenic in the soil, as well as the fractional leachability of the arsenic remaining in the soil ash." Like other observers, Waterland and co-workers have found that the presence of calcium suppresses the volatility of arsenic, and its subsequent reactivity. Numerous others have observed similar phenomena. In all of the research by Thurneau [21], S tumbar et ale [20], and Waterland [25] there is significant evidence that the arsenic was reactive, and probably did react due to the temperatures of the environment; however the arsenic remained with the solid products of combustion in stable form. The more recent data are consistant with fmdings by other researchers on various heavy metals such as lead, cadmium, and copper (see, for example, [9], [10], [26]). They lead to additional empirical and theoretical investigations into speciation, and metal behavior mechanisms. The recent experiments indicate that much of the arsenic may not enter the vapor phase or may be in the vapor phase only briefly; consequently the only oxidation processes applicable to the bulk of the arsenic (that which remains in the solid phase) would be heterogeneous gas-solids reactions. Further, the use of lime to suppress arsenic volatilization suggests that more complex reactions may be occurring. Consequently there is significant evidence to require additional analysis of the arsenic speciation in the solid products of combustion at Tacoma Steam Plant #2. The Tacoma Steam Plant #2 is a fluidized bed, designed to carry all solid products of combustion out as flyash. Consequently particles bearing arsenic will not report as bottom ash, but will always be transported from the combustor as flyash. The flyash will contain arsenic which has not become vapor, which has become vapor and rapidly recondensed, and which has gone through the entire cycle that is predicted by equilibrium calculations. Analysis of arsenic speciation, then, must be carried out only on the flyash. 3.0. EXPERIMENTAL AND RESULTS The experience of other incinerator installations provides strong evidence that the arsenic in the fly ash may well be in products other than arsenic trioxide, given the partitioning and potential reactions available. In order to directly address the potential speciation of arsenic in the flyash, Tacoma Public Utilities commissioned a short study of Flyash Sample #142, containing 114 |