Substance description/characteristics
The substance Zinc, dross is a UVCB (origin: inorganic)
Public name: Zinc dross
| EC number: | 273-694-8 |
| EC name: | Zinc, dross |
| CAS number (EC inventory): | 69011-50-3 |
| IUPAC name: | Scum formed on the surface of molten zinc and zinc alloys |
| Description: | During the melting and alloying phase(s) of Zinc metal ingots-, one produces: - On the surface of the bath a lighter Zinc/Zinc oxide-rich Intermediate phase, - In the bag-house filter –cleaning the process gasses-, a similar Zinc/Zinc oxide-rich Intermediate phase. Due to the addition of especially chosen fluxes, the separation of the drosses from the bath-surface is eased and occurs, at regular intervals. The process gasses are de-dusted in appropriate equipment, including a final bag-house filter. The filter-dust has a composition similar to the surface dross. |
| Molecular formula: | n.a. |
| Molecular weight range: | n.a. |
| Physical state: | solid (massive) at 20°C, 1013 hPa |
| Source | Zinc cathodes |
| Process | When melting and casting zinc and zinc alloys, a scum is formed on the surface of the melt, consisting of zinc, zinc oxide and small amounts of the alloying elements, their oxides and possibly fluxing agents. The scum is extracted/isolated from the surface of the metallic bath by mechanical separation. The separated material is poured into small containers near the furnace or the casting line and allowed to cool down. The melting, holding furnace(s) and casting unit are placed under negative pressure and the exhaust gasses are filtered before release to the stack; the dust collected in the bag-house filters has a very similar composition as the Intermediate EC 273-694-8. So, the basic reaction to form the intermediate is the atmospheric oxidation of metallic zinc to zinc oxide. The molten metallic zinc phase or alloyed zinc (EC 273-175-3) are cast and delivered to downstream users. Zinc dross is further transferred to enclosed storage zones or silos through especially designed transfer units: forklift, containers and/or conveyors, pneumatic transport. Zinc dross is optionally blended with other zinc containing primary or secondary materials and fed to the treatment unit if not temporarily stored. - The mixture can be fed to: => Pyro-process: rotary furnace, induction furnace, Fluid Bed roasters, ISF, Waelz kiln, etc. for production of zinc => Hydro-process: chemical hydrometallurgical reactors for further synthesis reactions of another zinc compound, i.e. zinc sulphate EC 231-793-3; optionally, the zinc sulphate solution is fed to electrolytic cells for production of zinc metal, EC 231-175-3 Zinc dross is typically used in the production of zinc or zinc compounds. |
| Conclusion | Zinc dross is scum formed on the surface of molten zinc and zinc alloys which is isolated and further used for the production of zinc and zinc compounds. |
3. Composition of the substance
The Zinc, dross boundary composition is detailed here below.
Elemental composition - boundary:
| Core | min (% w/w) | max (% w/w) | Typical (% w/w) |
| Zn | 50 | 99 | 97.35 |
| Cu | 0 | 1 | 0.23 |
| Fe | 0 | 2 | 0.07 |
| Al | 0 | 3.75 | 0.06 |
| Cl | 0 | 1 | 0 |
| Pb | 0 | 0.3 | 0 |
Mineralogical composition - boundary:
| Core | min (% w/w) | max (% w/w) | Typical (% w/w) |
| Zn | 45.65 | 90.38 | 88.88 |
| ZnO | 5.39 | 10.67 | 10.49 |
| Al2O3 | 0 | 15 | 0.24 |
| Cu | 0 | 1 | 0.23 |
| ZnFe2O4 | 0 | 4.32 | 0.15 |
| PbCl2 | 0 | 0.4 | 0.01 |
4. Classification revised in 2024
| The classification is always based on the worst case. For the generic grade Zinc, dross, this corresponds to: | |
| Hazards to the aquatic environment (acute/short-term): | |
| Hazards to the aquatic environment (long-term): | Aquatic Chronic 4 |