Gao, DC
1996
Temperature and the Fate of Heavy Metals During the Incineration of Solid Hazardous Waste in Rotary Kilns
Gao, D.-C.
Temperature and the Fate of Heavy Metals During the Incineration of Solid Hazardous Waste in Rotary Kilns, Ph.D./U of U, 1996. Advisor: Silcox
Field Investigation of the Temperature Distribution in a Commercial Hazardous Waste Slagging Rotary Kiln
Veranth, J.M.; Gao, D.-C. and Silcox, G.D.
ES&T, 30:3053-3060, 1996. Funded by ACERC and Gas Research Institute.
Gas and bed temperatures were studied in a 4.4 m by 12 m, co-current flow, slagging rotary kiln at a commercial hazardous waste incinerator. The visual observations used by the kiln operators to control the process are described. These observations were quantified using thermocouples, radiation pyrometers, and phase-change indicators. The objectives were to estimate the peak bed temperature and compare this to measurements at the kiln exit. The maximum bed temperature occurs toward the middle of this type of kiln and not at the discharge. The slag melting temperature and test pellets with known melting points indicate that the peak bed temperature can be 100-300 K higher than the kiln exit temperature reported by the permanent instruments at this facility. Both broadband radiation pyrometers and thermocouples give a qualitative temperature indication that can be used for process control, but the readings depend on the sensor locations relative to the incompletely mixed air and combustion products. Two-color radiation pyrometer measurements of surface temperature near the kiln exit are higher than the actual temperature due to reflected radiation.
1993
The Effect of Treatment Temperature of Metal Recovery from a Porous Silica Sorbent by EPA Method 3050 and by an HF-Based Method
Gao, D. and Silcox, G.D.
JAWMA 43:1004-1005, July 1993. Funded by Gas Research Institute and ACERC.
Determining the fate of metals during hazardous waste incineration is important because of environmental concerns. Such a determination requires an analysis of the waste ash. At high temperatures, metals are frequently immobilized by reactions with silicates or by encapsulation with silicates. In order to determine the metal retention levels in waste ash, a digestion method that insures total metal recovery is necessary. This study compares two digestion techniques and uses each to look at the effect of the incinerator's temperature on the apparent fraction of metal retained in the waste ash. Four metals on a diatomaceous earth matrix were studied: Cr, Cd, Pb, and Ni. An HF-based digestion yielded fractional metal retentions of about 1.0 while an HNO3-based digestion yielded apparent retention levels that decrease from 1 to 0.2 as the reactor temperature was increased from 25 to 870ºC.
A commonly used HNO3-based digestion procedures is EPA SW-846, Method 3050. It is successful at extracting those metal compounds that are soluble at conditions that characterize natural leaching and biological processes. However, Method 3050 was not designed to digest metals immobilized by silicates.
Gao, DC
1996
Temperature and the Fate of Heavy Metals During the Incineration of Solid Hazardous Waste in Rotary Kilns
Gao, D.-C.
Temperature and the Fate of Heavy Metals During the Incineration of Solid Hazardous Waste in Rotary Kilns, Ph.D./U of U, 1996. Advisor: Silcox
Field Investigation of the Temperature Distribution in a Commercial Hazardous Waste Slagging Rotary Kiln
Veranth, J.M.; Gao, D.-C. and Silcox, G.D.
ES&T, 30:3053-3060, 1996. Funded by ACERC and Gas Research Institute.
Gas and bed temperatures were studied in a 4.4 m by 12 m, co-current flow, slagging rotary kiln at a commercial hazardous waste incinerator. The visual observations used by the kiln operators to control the process are described. These observations were quantified using thermocouples, radiation pyrometers, and phase-change indicators. The objectives were to estimate the peak bed temperature and compare this to measurements at the kiln exit. The maximum bed temperature occurs toward the middle of this type of kiln and not at the discharge. The slag melting temperature and test pellets with known melting points indicate that the peak bed temperature can be 100-300 K higher than the kiln exit temperature reported by the permanent instruments at this facility. Both broadband radiation pyrometers and thermocouples give a qualitative temperature indication that can be used for process control, but the readings depend on the sensor locations relative to the incompletely mixed air and combustion products. Two-color radiation pyrometer measurements of surface temperature near the kiln exit are higher than the actual temperature due to reflected radiation.
1993
The Effect of Treatment Temperature of Metal Recovery from a Porous Silica Sorbent by EPA Method 3050 and by an HF-Based Method
Gao, D. and Silcox, G.D.
JAWMA 43:1004-1005, July 1993. Funded by Gas Research Institute and ACERC.
Determining the fate of metals during hazardous waste incineration is important because of environmental concerns. Such a determination requires an analysis of the waste ash. At high temperatures, metals are frequently immobilized by reactions with silicates or by encapsulation with silicates. In order to determine the metal retention levels in waste ash, a digestion method that insures total metal recovery is necessary. This study compares two digestion techniques and uses each to look at the effect of the incinerator's temperature on the apparent fraction of metal retained in the waste ash. Four metals on a diatomaceous earth matrix were studied: Cr, Cd, Pb, and Ni. An HF-based digestion yielded fractional metal retentions of about 1.0 while an HNO3-based digestion yielded apparent retention levels that decrease from 1 to 0.2 as the reactor temperature was increased from 25 to 870ºC.
A commonly used HNO3-based digestion procedures is EPA SW-846, Method 3050. It is successful at extracting those metal compounds that are soluble at conditions that characterize natural leaching and biological processes. However, Method 3050 was not designed to digest metals immobilized by silicates.