To extremely improve the brightness of pulp, by adding an effective amount of a fluorescent whitening agent to an aqueous slurry of a lignin- containing pulp before a drying process in a pulp production or a paper-making process.
After an effective amount of a chelating agent such as ethylenediaminetetraacetic acid is added to an aqueous slurry of a pulp containing 5 wt.% or more lignin calculated as a dry weight before the final dehydration and drying process in a pulp production or a paper-making process or after the completion of the final bleaching process to reduce the contents of iron and other heavy metal salts to 100 ppm or lower than it based on a dried pulp weight, a fluorescent whitening agent such as 4,4'-bis-(triazinylamino)- stilbene-2,2'-disulfonic acid in an amount of 0.02-2 wt.%, preferably 1-1.5 wt.%, more preferably 0.2-0.8 wt.% based on the driven pulp weight is added to the aqueous slurry.
JOKINEN OLLI JUHANI
ROHRINGER PETER
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