The recycling and processing of galvanized coils mainly includes sorting, smelting and extraction, purification, and resource utilization. Depending on the different waste forms and industry needs, different technical paths are adopted, such as pyrometallurgical, hydrometallurgical, or physical sorting. Currently, mainstream recycling processes have achieved high efficiency and have significant advantages in environmental protection and resource recycling.
Main Recycling and Processing Process
Sorting Processing: The first step in recycling is to classify the waste galvanized coils, distinguishing them by material, coating thickness (e.g., Z100 to Z275 grades), and whether they contain restricted elements such as lead and chromium. Accurate identification can avoid value loss due to mixing. For example, if SPCC and SECC waste coils are not separated, the average loss rate per batch can reach 9.7%. It is recommended to confirm the material through original labels, furnace codes, or XRF spectrometer testing.
Zinc Removal or Whole-Smelting
For galvanized steel scrap with high zinc content (such as offcuts and scrap steel plates), it can be directly fed into the steel smelting system as raw material for recycling. The zinc volatilizes at high temperatures and enters the dust collector, which can then be further recycled.
If zinc needs to be recovered separately, mechanical stripping or chemical/thermal dezincification methods are used. For example, new galvanized waste recycling equipment can automatically scrape off the surface zinc layer using a scraper structure, improving recycling efficiency.
Smelting and Extraction
The sorted material is then smelted at high temperatures to separate zinc from other metals. Pyrometallurgical processes, such as the Waelz rotary kiln method, can volatilize and condense zinc oxide into ZnO powder at 1100–1200℃, achieving a recovery rate of 92%–96%.
Purification and Deep Processing: The extracted crude zinc requires further purification. Common methods include:
- Electrolysis: Suitable for high-purity raw materials, yielding zinc ingots with a purity of over 99.995% and a direct recovery rate as high as 97.24%, but it consumes significant amounts of electricity and acid.
- Distillation: Including atmospheric or vacuum distillation, suitable for treating hot-dip galvanizing slag, achieving efficient zinc recovery.
- Wet Leaching-Electrolytic Deposition: For low-grade zinc-containing solid waste, selective leaching with dilute sulfuric acid followed by electrolysis yields high-purity zinc.
- Resource Utilization: Recycled zinc can be used in smelting zinc alloys and preparing zinc salts, widely applied in electroplating, chemical, and battery industries. Simultaneously, the dezincified steel matrix can still be used as high-quality scrap steel in steelmaking, achieving dual resource recovery.
