Zinc slag is primarily the product of the reaction between zinc and iron. Its main composition is the ζ-phase of the iron-zinc alloy layer formed after the combination of zinc and iron. Therefore, the iron content in zinc slag is generally around 3-6%, and the zinc content is around 94-97%. In some hot-dip galvanizing processes, lead is added to protect the galvanizing pot bottom. In such cases, the zinc slag contains 1.5-2% lead. Sometimes, aluminum is also added to improve the surface finish and structural properties of the galvanized layer, resulting in some aluminum content in the zinc slag.
The iron in zinc slag mainly originates from iron salts adhering to the surface of steel pipes during pretreatment, the steel pipes themselves, and the formation of the iron-zinc alloy layer after the dissolution of the galvanizing pot and galvanizing equipment by zinc liquid and the mutual diffusion of iron and zinc atoms. The crystalline ζ-phase layer (drifting layer) detaches from the steel substrate and accumulates at the bottom of the galvanizing pot, gradually forming a zinc slag layer.
The reactions during the formation of zinc slag are:
Reactions caused by iron salts:
FeCl₂ + 8Zn → ZnCl₂ + FeZn₇
FeCl₂ + 14Zn → ZnCl₂ + FeZn₁₃
Reactions caused by steel:
Fe₃C + 21Zn → 3FeZn₁₃ + C
(Note: The second reaction Fe₃C + 39Zn → 3FeZn₁₃ + C provided in the original text seems to be an error or redundancy, as it yields the same products as the first reaction with Fe₃C and a higher amount of Zn, which is chemically implausible. Therefore, it has been omitted here.)
Properties of zinc slag:
The melting point of zinc slag is higher than that of pure zinc.
The density of zinc slag is greater than that of pure zinc. According to measurements by Schulmann, the densities of zinc slag with iron contents of 6.2%, 7.0%, 9.0%, and 22% are 7.15, 7.24, 7.24, and 7.36 kg/dm³, respectively.
The crystalline shape of zinc slag belongs to the symmetric monoclinic system and hexagon, with unique angular characteristics.
The color of zinc slag is grayish white with a silvery光泽.
Zinc slag contains impurities such as lead, aluminum, antimony, cadmium, copper, and insoluble compounds of acids.
The zinc content in zinc slag is approximately 94-97%.
The iron content in zinc slag is approximately 3-6%.
Zinc slag is brittle compared to pure zinc and lacks flexibility.
Essentially, zinc slag is an alloy formed by the ζ-phase drifting layer, δ₁栅状 layer, and other impurities interspersed in zinc.
