Stabilize Ash Using Clemson's Sintering Process at Clemson University, Clemson, South Carolina

Site Name:

Clemson University


Clemson, SC

Period of



Bench-scale treatability study

Stabilization using Clemson's Sintering Process
- Used a high iron/high potassium aluminosilicate clay material - Red Roan Formation (RRF)
- A preliminary study and three statistically designed experiments performed to evaluate and optimize processing parameters
- Preliminary study - 67 vol% to 50 wt% equivalent fly ash/RRF mixture and a high moisture content (18.1 wt%), pressed at 5,000 psi, then fired at 1,000C to produce waste form pellets
- Experiment I - to evaluate the effects of different physical properties on the waste form included 16 batches to test varying formulations; batch size - 270 grams; material pressed at 1,000 psi then fired between 1,025 and 1,075C
- Experiment II - to optimize factors from experiment I included 15 batches (500 grams each); fired between 1,025 and 1,075C; TCLP leach testing performed on waste forms
- Experiment III - to further evaluate effects of four physical properties (moisture content, waste loading, mixing time, auger speed) involved 27 batches, prepared using varying formulation based on the results of the second experiment

Cleanup Authority:
Not identified

Principal Investigator:
H. David Leigh, III
Department of Ceramic
and Materials Engineering
Clemson University
P.O. Box 340907
Clemson, SC 29634
Telephone: 864-656-5349
MWFA Product Line Manager:
Vince Maio
Advisory Engineer
Mixed Waste Focus Area
Lockheed Martin
Idaho Technologies Company
Idaho National Engineering
and Environmental Laboratory
P.O. Box 1625
Idaho Falls, ID 83415
Telephone: 208-526-3696
Fax: 208-526-1061

- Fly ash contained heavy metals - cadmium (5,000 mg/kg), chromium (1,000 mg/kg), and lead (35,000 mg/kg)

Waste Source:
Fly ash from the WERF incinerator at INEEL

Type/Quantity of Media Treated:
Incinerator fly ash

Purpose/Significance of Application:
Treatability study of stabilization of mixed waste fly ash using a sintering process

Regulatory Requirements/Cleanup Goals:
RCRA Land Disposal Restriction criteria
- TCLP concentrations in mg/L - cadmium (0.19), chromium (0.86), lead (0.37), and zinc (5.3)

- Preliminary study - TCLP results were above the limits for cadmium, lead, and zinc
- Experiment I - significant factors affecting the waste form included firing temperature, the RRF particle size distribution, and waste loading
- Experiment II - TCLP results showed that leach values for metals increased with increased waste loadings and decreased as the temperature increased; TCLP limits were met when waste loadings were below 20% vol
- Experiment III - TCLP results showed that leach values for metals increased as the waste loading increased, decreased as moisture content decreased; mixing time and auger speed were not significant factors

Cost Factors:
No methodology has been selected to date to evaluate costs associated with full-scale deployment of the Clemson stabilization process

A bench-scale treatability study was conducted at Clemson University in 1995 to determine whether stabilization using a sintering process could be used to immobilize DOE waste. The study was funded by DOE through a cooperative agreement with University Programs at the Savannah River Site. The process involves mixing a high iron/high potassium aluminosilicate clay material with the waste, pressing the material, then firing the material to produce a ceramic waste form. For this study, Red Roan Formation (RRF) was used as the clay material and fly ash from the WERF incinerator at INEEL (containing high levels of metals) was used as the waste. A preliminary study and three statistically designed experiments were performed to evaluate the process and to obtain operating data for use in future pilot-scale testing.

The results of the treatability study showed that the process can produce stable, low porosity waste forms that meet the RCRA TCLP limits for metals at waste loadings of 20% vol or lower. This waste loading was lower than originally anticipated. Other significant factors affecting the waste form included firing temperature and the particle size distribution of the RRF. The process is applicable to most inorganic homogeneous solids and sludges such as ash, soils, and particulates, but is not well siuted for aqueous and organic liquids or heterogeneous debris. Based on the results of the treatability study, a pilot-scale demonstration of the process is planned for FY 1999.