The Department of Defense (DoD) spends millions of dollars each year to dispose of hazardous liquid wastes from military facilities and needs better and cheaper disposal options. Recognizing that industry uses sorbent materials to absorb chemical and oil spills, the National Defense Center for Environmental Excellence investigated sorbents for their ability to render hazardous liquid wastes non-hazardous and in compliance with Land Disposal Restrictions. This project sought to identify, demonstrate, and validate a simple, efficient, and cost-effective technology based on sorbents. The following three representative DoD wastes were chosen for investigation: acidic electroplating waste, paint wastes, and degreasing solvents.

Demonstration Results

Bench-scale investigations on surrogate wastes showed: (1) waste acids containing heavy metals (nickel, cadmium, chromium, lead and zinc) up to 100 ppm could be rendered non-hazardous using treated clay sorbents; (2) no sorbent acceptably treated ignitable paint-related waste; and (3) no sorbent acceptably treated chlorinated solvent degreasing waste. Although these tests showed that sorbents are a not a universal cost-effective solution, the most successful sorbent, a treated attapulgite clay, was used subsequently in on-site demonstrations during August and September of 1997 for stabilization of the acidic metal-finishing waste generated by three DoD facilities. These facilities were the Naval Aviation Depot, Jacksonville, FL, Tobyhanna Army Depot, PA, and Tinker AFB, OK. The treated attapulgite clay successfully solidified and stabilized acidic waste containing up to 100 ppm heavy metals.

Implementation Issues

A cost analysis of this application to heavy-metal-contaminated spent electroplating bath contents showed that the savings realized by using the treated attapulgite clay mixture depends on the cost of conventional off-site hazardous waste disposal, which varies from site to site. Cost savings might only be marginal. Clay treatment costs were estimated at $0.78 per pound of waste acid treated compared to the conventional hazardous waste disposal cost of $0.45 to $1.25 per pound.

As a general solution, sorbents are not recommended for treating hazardous waste streams generated by the DoD, although they have considerable value for spill control purposes. At heavy metal concentrations above 100 ppm, an appropriate use of the treated attapulgite clay may be in spill neutralization and containment through solidification, but the sorbed material would have to be managed as hazardous waste unless further treatment could be applied to reduce the toxicity of the heavy metals. However, use of sorbent clays to eliminate hazardous waste generation completely may be an attractive option for very small volume generators of acidic heavy-metal contaminated streams. Also, due to favorable performance with lead contaminants, another possible niche is in treating waste battery acid.