Loop closure at the bleaching plant leads to increased concentrations of or
ganic and inorganic substances, and this may impair bleachability and cause
precipitation on fibres and process equipment. Analysing both pulp and fil
trates from each bleaching stage, gives a general picture of the situation
at tie mill. The objectives were to compare TCF bleaching of softwood pulp
on the mill scale under closed conditions,vith bleaching on the laboratory
scale using a totally open system.