3 Emerging Technologies for LBP Removal Paint From Nonsteel Substrates (Task 3)
CERL has evaluated environmentally acceptable chemical strippers and alternative blast media technologies for the removal of lead-based paint from DoD buildings and structures. The technologies evaluated include cryogenic blasting, laser paint removal, chemical stabilizers, alternative chemical strippers, and confined hydraulic blasting. A sponge media blasting technique appeared to be particularly promising for LBP removal from surfaces of buildings. Soft sponge media abrasive products have been developed to address issues of worker and public safety, hazardous waste minimization, and pollution prevention. The sponge medium consists of a matrix of water-based urethane foam within which abrasive particles are dispersed. The medium can be wet with water or chemical solutions to increase productivity. The aggressiveness of sponge media can be tailored for the specific application by changing the characteristics of the abrasive particles inside the urethane foam. However, during field testing, it was determined that sponge blasting caused unacceptable damage to historical wooden structures.
Granulated carbon dioxide (CO2 ) blasting and pelletized CO2 blasting have been evaluated for removing LBP from interior architectural wood components (Kominsky, Hock, and Daniels 1997). The CO2 blast medium is a soft abrasive that removes the LBP by mechanical impact and thermal expansion mechanisms. The spent media evaporates directly to a gaseous state and dissipates, leaving only paint solids as waste. However, it was found that both the granulated and pelletized CO2 proved ineffective in removal of the LBP from interior wooden components without severe damage to the underlying substrate. Also, residual lead levels of 6 mg/cm2, as determined by an XRF spectrum analyzer, exceeded the HUD guideline of 1 mg/cm2 (U.S. Public Law 102-550, 1992).
The TorboÒ wet abrasive blasting system, manufactured by Keizer Technologies America, Inc., uses conventional blast abrasives (such as coal slag or silica sand) mixed with water (80 percent abrasive to 20 percent water). The abrasive-water slurry mixture is fed through a blast nozzle system designed, in principle, to encase every particle of the abrasive in a thin layer of water. Water pressure forces the slurry into a compressor-generated airstream where it is accelerated to the blast nozzle. The LBP is removed by the kinetic energy and mechanical abrasion of the blast media striking the paint. BlastoxÒ, a chemical stabilizer, was added to the slurry mixture prior to blasting in order to create an “engineered abrasive,” that would react with the lead in the paint chemically in order to stabilize the leachable lead as lead silicate, with stabilization mechanisms similar to those of portland cement. The wet abrasive blasting technology used with the engineered abrasive efficiently removed LBP from exterior architectural wood components to bare substrate with no apparent damage, and yielded a substrate ready for repainting (Kominsky, Hock, and Daniels 1997). Overall, the residual lead levels as determined by XRF were 0.93 mg/cm2, which is below the HUD guideline.
Encapsulant paint removal technology effectively employs a two-part liquid system consisting of potassium hydroxide and a proprietary polymer, which are sprayed with an applicator gun that uses an external mixing technique. The dwell time is dependent on time and number of layers of paint, temperature, and other environmental factors. After the paint is absorbed into the remover matrix, the resulting residue is removed as a semi-solid material using a putty knife. Encapsulant paint removal technology has been used to remove LBP from interior architectural wood components to bare substrate with no apparent damage. The residual lead levels as determined by XRF were found to be 0.8 mg/cm2 (Kominsky, Hock, and Daniels 1997).
Reduced-toxicity chemical strippers are sometimes referred to as "environmentally acceptable (EA)" strippers. These chemicals are of interest because of their low volatility and low toxicity. They are noncorrosive and not caustic to humans. Typical EA strippers are based on ingredients that have low environmental impact, such as citric acid and N-methyl pyrrolidone (NMP). Where they can be used effectively, these products eliminate the need for sodium hydroxide and methylene chloride strippers. However, these new formulations require long dwell periods; consequently, in exterior applications, their performance is vulnerable to degradation by rain, wind, and low temperatures. Of the six EA strippers investigated in the laboratory, only NMP-based strippers performed comparably to conventional solvents and caustic strippers (Drozdz and Engelage 1996).
Laser paint removal systems have been designed and built for use on fragile historic wood structures. These systems contain a CO2 pulse laser and beam delivery system. Evaluation of the paint removal system by CERL showed potential as a paint removal technology for use on historic wood structures. Advantages include no containment costs, no requirements for worker protection, and reduction of hazardous waste compared to chemical paint strippers. However, further engineering enhancement will be necessary to make the process cost-effective.
Emerging technologies evaluated under this project have been documented in the following publications:
Boy, J., and A. Kumar, “Lead-Based Paint Hazard Mitigation” in The Encyclopedia of Environmental Analysis and Remediation, Robert A. Meyers, ed. (John Wiley and Sons, Inc., 1998) pp 2501-2516.
Drozdz, Susan A., and Jennifer D. Engelage, Evaluation of Reduced-Toxicity Chemical Paint Strippers, UR 96/111 (CERL, September 1996).
Kominsky, J., V. Hock, and A. Daniels, Field Demonstration of Clean Technologies for the Removal of Lead-Based Paint from Residential Housing in Buffalo, New York, draft report (U.S. Environmental Protection Agency, March 1997).
Hock, V.F., C.M. Gustafson, D.M. Cropek, and S.A. Drozdz, Demonstration of Lead-Based Paint Removal and Stabilization Using Blastox, FEAP TR 96/20 (CERL, October 1996).
