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The effect of iron ion and hydrochloric acid in help bath on galvanizing

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Effect of iron ion: when galvanizing, even though trace amounts of iron ions go into the galvanizing zinc, it will obviously increase the production of zinc dross. When most FeCl2 reacts with zinc, there will produce Fe -Zinc alloy, which is a major cause of the generation of zinc dross, and the chemical formula is: FeCl2 + x Zn - > Fe. Zn (x - 1). The zinc dross must be periodically removed, otherwise there may cause the upturning of zinc dross, zinc leakage of zinc pot, and an increased cost.

Note 1: Each one kilogram of iron ions will combine with 20 to 50 kilograms of zinc and generate zinc dross. In addition, iron ions in FLUX will form very wispy zinc dross crystals on the galvanized layer surface, and cause a thick galvanized layer.

Note 2: If each liter of FLUX has 6 g/l of iron ions content, the thickness of galvanized layer will increase by 11.4%. In other words, if the surface area of the work piece is 80 m2/ton, zinc consumption will increase by 4.3 kg per one ton of work pieces.

Influence of hydrochloric acid: if there is hydrochloric acid in FLUX, it will lead to a phenomenon of overpickling and generate FeCl2.

Conclusion: In FLUX tank, the content of iron ions and hydrochloric acid should be controlled at the lowest level, and the highest content should be less than 1 gram per liter.

v Principle of help bath automatic iron-removal equipment

It pumps the help bath needing to be disposed from FLUX tank into the reaction groove of help bath automatic iron-removal equipment, automatically adds H2O2 (hydrogen peroxide) and NH4OH (ammonia water) into the reaction tank, provides air and fully mix, quickens the reaction speed, pumps the processed clean solution back into the FLUX tank, filter sludge from the produced precipitation through plate and frame filter, and then makes an outsourcing processing. The whole process is automatically controlled by PLC. The heart of help bath automatic iron-removal equipment is the reaction tank, HCl and NH4OH ammonia neutralization, FeCl2 + H2O2 = Fe (OH) 3.

Reaction equation is as follows:

• HCl + NH4OH -> NH4Cl + H2O

• 2FeCl2 + H2O2 -> 2Fe (OH)3 + 4NH4Cl

• Zn+ ustill keeps the status in ZnCl2

In the reaction tank, NH4Cl and ZnCl2 can regenerate. In general, the ratio of the regenerated NH4Cl / ZnCl2 can meet the demands on the concentration of help bath, and there is no need to add again, if not, it needs to add a small amount of ZnCl2 or ZnCl2-2NH4Cl.

v Technological process

Help bath→ hydrogen peroxide oxidation → adjust PH with ammonia water →precipitation reaction tank →diaphragm pump →plate and frame filter press→ sludge outward transport.

v Treatment efficiency

Ø After being processed by equipment, iron ion content in FLUX tank is less than 1.0 gram per liter.

Ø PH value of help bath is controlled between 4.0 to 5.0.

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