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Titrating for Iron content in pickling acid and flux tanks ?

June 30, 2009

hi all,
I just wanted to ask about a way find the amount of iron in accurate way I use chemical kits but I want a titration way ,
thanx a lot

Doaa Arafa
galvanization - Egypt

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July 8, 2009

This method for determining iron is taken from Atotech, I use this for acid zinc solutions, acid pickling solutions and flux;
The result give total iron (Fe II and Fe III)

Reagents required:
ammonia ⇦this on eBay or Amazon [affil links] conc., density 0.91
ammonia 2 N (150 ml/l NH3)
Hydrogen peroxide 30%
Hydrochloric acid 6 N (HCl conc., diluted 1 : 1 with water)
sodium hydroxide solution 2 N (80 g/l NAOH)
Glycine solution 2 M (150 g/l glycine)
Sulphosalicylic acid 0.4 M (10 g sulphosalicylic acid dissolved in 100 ml water)
EDTA volumetric solution 0.01 M (EDTA = disodium salt of ethylene diamine tetraacetic acid ⇦this on eBay or Amazon [affil links] )
Procedure:
50.0 ml**test solution are mixed in a 400 ml glass beaker [beakers on eBay or Amazon [affil links] with
1 - 2 ml hydrogen peroxide and so much concentrated ammonia until the solution shows an alkaline reaction (for flux pH 6). The solution is now heated for about 5 mins. to boiling point and the still hot solution filtered over a black band filter (Schleicher & Schüll, No. 595). The glass precipitation beaker and the precipitate of the filter must be washed out well with 2 N ammonia. The precipitate is dissolved with about 10 ml warm 6 N hydrochloric acid in a 300 ml Erlenmeyer flask and the filter washed out well with a little amount water so that a volume of about 100 ml is obtained.
After the addition of10 ml 2 N glycine solution and
2 ml 0.04 M sulphosalycilic acid
2 N sodium hydroxide solution is added in drops until the solution turns deep red but no iron is precipitated. Titration is then performed with 0.01 M EDTA volumetric solution until the colour of the solution changes from red to light yellow. The volumetric solution should be added slowly towards the end of titration.


Multiplying the number of ml 0.01 M EDTA volumetric solution** used by 11.17 produces the content of iron in the solution in mg/l.

Franz R Wagner
- Blumenau SC Brazil

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July 10, 2009

Sir:
Iron (+2; ferrous) is normally directly titrated using standard hexavalent chrome with a reducing acid buffer and suitable redox indicator. This can be done using a buret or calibrated dropper bottle and takes about 5 minutes. In pickling acid there is normally little iron +3 and in flux the iron +3 is on the bottom of the tank as iron (+3) hydroxide. The end point is light green to purple/blue.
Regards,

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