Recycling of coated steel scrap: coating removal rates of different types of organic coated steel

摘要

The demand for organic and metallic coatedsteels has risen dramatically over the past twodecades. The future requirement to recycle largequantities of organic and metallic coated steels inan environmentally satisfactory manner through basicoxygen steelmaking (BOS) or electric arc furnace (EAF)routes has been examined. The coating removal retesof different types of organic coated steel have beeninvestigated over a range of different conditions.This research has been carried out with the aim ofdelaminatin organic coatings using wet chemicaltreatments with and without the use of ultrasonics.Results indicate that successful coating removalusing a caustic solution was due to a chemical attackof the coating. The acid reaction solution producedsuccessful coating removal via an undercutting of thezinc substrate layer. Use of ultrasonicsdisintegrated the thinner coatings for both thecaustic and acid reaction solutions. Ultrasonic usealso initiated undercutting of the zinc layer whenused with a caustic reaction solution. Plastisol wasnot chemically attacked by any reaction solution, nordisintegrated by the use of ultrasonics. The plastisolmaterial required a thermal pretreatment to producesuccessful coating removal with the use of a causticreaction solution. Base hydrolysis and the additionof metal ions were found to be unsuccessful inproducing degradation of the plastisol. The datapresented in this paper have led to the design andconstruction of a larger scale pilot plant. This workis currently in progress and is intended to be thesubject of a future paper. The project as a wholecontributes to environmental protection by providinga process route for removing coatings from coatedsteels, should this become necessary.