Metal finishing Q&As since 1989

-----

How much chrome passivation goes on the strip and how much to waste?

I want to know, how much hexavalent chrome solution is getting used up by the metal strip while passivation after galvanising (Hot dip Zn bath). For example if I use 1000 M3 of chromate solution for 1 ton of a cold rolled steel coil (width = 1300 mm and thickness = 0.4 mm), then how much (VOL) will be left over in the chrome bath & how much will be used up by the metal for passivation and how much (Vol) can be rinsed out by water to the effluent.

Koushik Chakravarty
Researcher - Jamshedpur, Jharkhand, India
February 17, 2010

---

First of two simultaneous responses --

Your vendor could give you a very rough estimate, but your actual line operation will seriously affect that. Take bath samples at appropriate times (metes of product) and analyze.
pH, concentration, temperature, drag out and time in the tank all have huge inputs on chemical use. Then, do the calculations.

James Watts
- Navarre, Florida
February 18, 2010

---

Second of two simultaneous responses -- February 19, 2010

Sir:

I spent two weeks in Jamshedpur on two pipe lines so I expect you work for the same company.

You do not mention the concentration of the hex chrome solution? It is my understanding that hex chrome is not allowed in Europe and your question seems to relate to the environmental side of hex chrome especially in the effluent hex chrome rinse. There is now available a reverse osmosis machine that I believe is capable of stripping out the hex chrome from the hex chrome rinse water for reuse. In addition the proper parameters (e.g. pH, conc., etc.) are known so as to keep hex chrome functioning for very, very long periods. Thus your environmental problem can likely be largely solved by proper technical knowledge and operation.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA