From: Sandy King (sanking@clemson.edu)
Date: 12/15/02-03:26:20 PM Z
Richard wrote:
>
>I did some investigation and ran some tests this weekend. The
>iron is forming iron hydroxide. The formation
>of the hydroxide is a strong function of pH. It takes
>tens of seconds at pH = 8, minutes at pH = 7, and hours at
>pH = 6. Once formed, the hydroxide appears to be difficult
>to remove.
>
>For my tests I coated some paper with straight ferric ammonium
>citrate. I then exposed this to full sun for a few minutes.
>This should ensure a good mix of ferric and ferrous states.
>I then tried clearing the paper is plain water, 1% citric,
>2% citric and 3% citric.
>
>My conclusions were:
>1) The FAC reacts with some papers, resulting in iron hydroxide
>formation even in a 3% citric wash. This is the yellow-brown
>stain which some papers produce when using cyano, VDB etc.
>
>2) A plain water wash (tap water filtered through mechanical and carbon
>filters) does allow a small amount of iron hydroxide to form. With
>a citric acid wash, there is no difference between 1%, 2% and 3%
>acid concentration, on both staining and non-staining papers.
>
>Thus only a small amount of acidity is required to ensure that
>no iron hydroxide is formed. A non-staining paper should be used.
>
>Richard
Richard,
How are you verifying the presence of iron hydroxide?
Sandy King
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