Metals 1: General & Steel Recycling Flashcards
Why do we recycle metals?
Constant increase in industrialisation => increasing use of metals. Recycling reduces the supply challenges, and can also save energy due to less air pollution. Some metals are easily recycled and are economically profitable to recycle, e.g. lead, copper, steel, aluminium, and zinc.
What are the metals sources for recycling?
Metallics (scrap):
- Metal discards from metal producers (home scrap) or metal fabricators (prompt, or manufacturing scrap)
- EoL industrial equipment, salvaged structures (bridges, railroad, etc.)
- Other sources
- UBCs
- Demolished buildings
- Municipal Solid Waste
Waste: residues, ashes, slags, sludge
What are the basic operation steps in metals recycling?
Collection -> Physical separation -> Metallurgical refining
Physical separation: Dismantling, compacting -> Size reduction: cutting, shredding -> Sorting and separation -> Pre-treatment: cleaning, de-coating
Compare the similarities and differences b/w primary metals production and metals recycling (recycling metallurgy)
The mined ores are prepared, and in some cases refined (e.g. aluminium), then molten and refined again (pig iron to steel), followed by alloying and casting. The pre-refining is not necessary for scrap as the metals are already metallic.
Primary metals production:
Mining -> Preparation -> Refining -> Melting -> Refining -> Alloying -> Casting
Metals recycling:
Scrap collection -> Preparation -> Melting -> Refining -> Alloying -> Casting
What are the main differences b/w recycling of steel and of non-ferrous metals?
Steel is magnetic which makes separation easy. Steel is 100 % recycled in primary steelmaking plants, using basic oxygen furnace (BOF) and electric arc furnace (EAF) smelters. Non-ferrous metals have more divers processes; primary smelters, secondary smelters. The temperature is also different.
Explain how carbon steel and stainless steel is recycled?
The metals are collected and shredded. Then the magnetic steel components, i.e. all carbon steel and ferritic SS, are removed using a magnet. The rest of the SS is collected using eddy current separators. Carbon steel is melted in electric arc furnaces (EAF), and SS in argon oxygen decarburisation (AOD) furnaces.
What are the limitations for increasing the recycling rates (EOL-RR, OSR) for carbon- and stainless steel?
The recycling rates of steel and SS are already very high, further increasing them is costly. The old scrap ratio is limited by the production, and the steel production is so large that the ratio doesn’t increase easily.
