| Abstract: | SUMMARIES. • The higher the concentration of EDTA, the easier and more complete will be the complexing of metal ions. A concentration of 3.0% can be accepted as sufficient to remove iron stains in a short time at pH 4.6. Making the EDTA solution alkaline by adding NaOH or KOH results in a lengthening of time re¬quired for stain removal, but also in better stain removal. • Paper strength measured as folding endurance is affected by a high concentra¬tion of EDTA and also by making the EDTA solution alkaline. Using alkaline EDTA solutions the higher concentration is of less influence. • EDTA treatment alone, though able to remove iron stains, cannot be suggested for this purpose because of its acidid nature. It is advisable to use it together with alkalies to protect the physical strength properties of the treated paper. • Sodium dithionite, being a reducing agent, helps to remove the stains already in a minimum concentration in a short period but it is reported that the effect is not stable. The reduced ferrous iron can re-oxide and the iron stain can re¬appear. This is why a chelating agent like EDTA used together with SDT can be very helpful in removing the reduced iron ions from paper. • SDT in the minimum concentration of 2% along with EDTA has been found to be the most effective of the tested procedures to remove iron stains from paper in a comparatively short time.
CONCLUSION. Paper samples (pure cellulose: Whatman chromatography paper) were stained with iron and then submitted to a treatment with the chelating agent EDTA in different concentrations in order to remove the stains during a stipulated time period (24 hours). As EDTA is acidic, which means that it can harm the paper, the solutions were modified with alkali (NaOH and KOH, 2%). Another variant was to add a reducing agent, i.e. sodium dithionite, to the chelating solution. This last variant gave the best results together with the least reduced fold number and highest brightness. Elimination des taches de rouille des documents en papier à l'aide de l'agent chélateur EDTA Des échantillons de papier en cellulose pure (papier de Whatman) ont été tachés avec de la rouille et soumis à un traitement comportant l'agent chélateur EDTA à des concentrations diffé¬rentes afin d'éliminer les taches dans une période donnée (24 h). Etant donné que l'EDTA a un pH acide, ce qui signifie qu'il peut causer un dommage au papier, les solutions d'EDTA ont été modifiées avec des alcalins (NaOH et KOH, 2%). Une autre variante consistait à ajouter un agent réducteur, le dithionite de sodium, dans la solution. Cette dernière variante a fourni le meilleur résultat en ce qui concerne la résistance au pliage et le degré de blancheur du papier. |
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