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How much iron exhausts a pickling solution and how to measure it?

2003

Dear Sir,

Sub: Measurement of Iron content in sulfuric Acid H2so4 pickling

In our pickling bath meant for steel rods, we use sulfuric acid solution. Due to rust steel rods, iron content in the bath increases. I want to drain out the piclling solution once it goes beyond a certain limit of iron content. What should be that iron content and please tell me how to measure the iron content in a pickling bath containing sulfuric acid.

C.Lakshmanan
Lab Technician - Chennai, Tamilnadu, India

The concentration of iron that you can live with is affected by the temperature and the acidity in your tank. It is what you can live with, not someone else's number. Analyze for iron on a daily basis and keep a log of how long it took to achieve the results that you need. When you reach a point that you can not live with, that is your maximum number. So you will need to subtract a percentage of that number which will give you a value where you will go into a bleed & feed.

James Watts
- Navarre, Florida
2003

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There is a theoretical limit. The iron is going to either valance +2 or +3. If it is plus 2 then it takes 2 moles of sulfuric acid to complex or put into solution one mole of iron. For +3 it takes 3 moles. Since the amount of whichever species is related to the oxygen in the atmosphere when the iron was processed at the elevated temperature, this number is not a constant. The practical limit is far less than the theoretical limit. The standard method in the US for analytical chemists is Flame AA or ICP-AAS.

Dave Fairbourn
- Sandy, Utah
2003