A thermodynamics-based model and data for Ca, Mg, and Na ion partitioning in kraft pulp fibre suspensions

Ions of Ca, Mg and Na are among the metal ions which originate from wood, w ater, and make up chemicals and are found in kraft pulp fibre suspensions. In closed-cycle mill operation, which is motivated by environmental concern s, such metal ions accumulate and create various operational and product qu ality problems. Partitioning data and a model that will predict the distrib ution of metal ions between the fibres and the surrounding liquor in a pulp suspension are needed for effective design of closed-cycle mill configurat ions. In this work, partitioning data for the ions of sodium, calcium and m agnesium in a post brown stock washer pulp are presented. Such data above a pH of 11 were previously not available. A model based on nonideal Donnan e quilibrium is also presented. The model was able to calculate the partition ing of Ca and Na ions. The magnesium data showed considerable scatter that prevented an effective comparison with the model-calculated values.