Modified sulfur cement encapsulation of mixed waste contaminated incinerator fly ash

Abstract

As part of an effort to develop new and innovative materials for solidification/stabilization of mixed wastes generated at Department of Energy facilities, work is currently being performed at Brookhaven National Laboratory to encapsulate incinerator fly ash waste. A process using modified sulfur cement, a thermoplastic material with a melting point of 119°C, is described. Monolithic waste forms containing as much as 55 wt% incinerator fly ash have been formulated with modified sulfur cement, whereas maximum waste loading for this waste in hydraulic cement is 16 wt%. Compressive strength of these waste forms exceeded 27.6 MPa (4,000 psi). Wet chemical and solid phase waste characterization analyses performed on the fly ash revealed high concentrations of soluble metal salts including lead (Pb) and cadmium (Cd), identified by the Environmental Protection Agency (EPA) as toxic metals. Leach testing of the fly ash waste according to the EPA Toxicity Characteristic Leaching Procedure (TCLP) resulted in concentrations of Pb and Cd above allowable limits that define a characteristic hazardous waste. Encapsulation of fly ash (at waste loadings up to 43 wt%) in modified sulfur cement, with a small quantity of sodium sulfide added to enhance retention of soluble metal salts, reduced TCLP leachate concentrations of Pb and Cd well below EPA toxicity characteristic concentration criteria.