Removal of lead based coating by vitrification

Abstract

Lead in coatings on structures can be removed, without creating hazardous waste, by a flame spray process which utilizes a glass composition having high lead solubility, resistance to devitrification, and an expansion coefficient which is substantially different from that of the metal structure. The process comprises flame spraying particles of a glass powder composition onto the lead based coating to form a layer of glass material, permitting the glass layer to cool sufficiently so that it spalls, thereby forming fragments of the glass layer which readily separate from the structure, collecting the glass fragments, and repeating these steps until any organic material in the coating has been pyrolized and removed as part of the fragments, substantially all red lead present in the coating has been reduced to yellow lead, and all of the lead which was in the lead based coating has been removed from the structure by being incorporated into the glass layers. The preferred glass composition comprises at least one glass forming oxide selected from the group consisting of SiO.sub.2 and B.sub.2 O.sub.3 ; at least one intermediate oxide selected from the group consisting of Al.sub.2 O.sub.3, TiO.sub.2, ZnO, PbO, and ZrO.sub.2 ; and at least one glass modifier oxide selected from the group consisting of Na.sub.2 O, K.sub.2 O, CaO, BaO, and NiO.

Dependencies are inferred from the claim text.