Acid Digestion of Organic Waste at Savannah River Site, Aiken, South Carolina

Site Name:

Savannah River Site

Location:

Aiken, South Carolina

Period of
Operation:

1996 to 1997

Cleanup
Type:

Bench and pilot-scale testing

Technology:
Acid Digestion Process
- Process consists of an oxidation vessel, acid recycle and offgas treatment system, and acid stabilization and waste immobilization system
- Organic destruction takes place in oxidation vessel; waste is added to a bath of 14.8M phosphoric acid containing 0.5 to 1.0M nitric acid
- The vessel is heated to 150 to 200°C under pressure of 0 to 20 psig
- Bench-scale tests were conducted in units with 2-5 L capacity and pilot-scale tests in a 40 L glass reactor

Cleanup Authority:
Not identified

Principal Investigator:
Robert A. Pierce
Westinghouse Savannah River Co.
P.O. Box 616, Bldg. 773A, Rm. C-137
Aiken, SC 29802
Telephone: (803) 725-3099
E-mail: robert.pierce@srs.gov
DOE Contact:
William Owca
U.S. DOE Idaho Operations Office
850 Energy Drive
Idaho Falls, ID 83401-1563
Telephone: (208) 526-1983
Fax: (208) 526-5964
E-mail: owcawa@id.doe.gov

Contaminants:
Organic wastes and simulated radioactive wastes; no specific contaminants identified

Waste Source:
Nuclear processing operations

Type/Quantity of Media Treated:
Organic wastes
- Cellulose (240 gms of KimWipes™), neoprene, polyethylene, and PVC

Purpose/Significance of Application:
Demonstrate acid digestion of organic wastes as an alternative to incineration

Regulatory Requirements/Cleanup Goals:
- Determine applicable organic wastes for technology, and related operating conditions
- No specific cleanup goals were identified

Results:
- Tests were conducted on cellulose, neoprene, polyethylene, and PVC
- Tests on cellulose showed that 240 gms of KimWipes™ were oxidized to CO2 and H2O in 70 mL of acid and residual phosphoric acid was stabilized, providing for a volume reduction of 50 to 100 fold
- Tests showed that dissolution time for organic wastes depends on the type of waste, temperature, pressure, and acid concentration
- The dissolution rate for mixtures of waste types will be limited by the PVC dissolution rate, even when PVC is present in small quantities

Cost Factors:
- Actual costs for this demonstration were not identified
- Projected costs for full-scale acid digestion systems are under preparation, but were estimated to range from $2,000,000 to $8,000,000 for design, construction, and demonstration

Description:
Bench- and pilot-scale tests of an Acid Digestion system were conducted at DOE's Savannah River Site in 1996 and 1997. This technology was tested using job control wastes organic waste forms consisting of materials such as cellulose, neoprene, polyethylene, and PVC. Acid Digestion is one of several Alternative Oxidation Technologies (AOT) under consideration by SRS for treatment of their plutonium 238 contaminated job control wastes.

Acid Digestion consists of dissolution of organic materials in a solution of nitric acid in phosphoric acid, and is conducted at operating conditions of 150 to 200°C and 0 to 20 psig. Tests were conducted on cellulose, neoprene, polyethylene, and PVC, and showed that dissolution time for organic wastes depended on the type of waste, temperature, pressure, and acid concentration. Further, tests showed that the dissolution rate for mixtures of waste types will be limited by the PVC dissolution rate, even when PVC is present in small quantities. Because the process involves the use of nitric acid, controlling the reaction is an important safety consideration. Issues associated with monitoring the oxidation rate and water content need to be resolved for full-scale deployment of the technology.