PREDICTING THE ION-EXCHANGE OF KRAFT PULPS USING DONNAN THEORY

When pulp fibres are placed in a solution of electrolytes, the anionic acid groups within the fibre wall cause an unequal distribution of ev ery ionic species between the solution within the fibre wall and the s olution external to the fibres. Using the Donnan Equilibrium Theory to characterize the distribution, a mathematical model has been develope d to describe the partitioning of cations between fibre walls and surr ounding liquor. The model was tested using two unbleached kraft pulps and trace metals naturally occurring in such pulps. Excellent agreemen t was found between predicted and measured distributions of sodium, ca lcium, magnesium and manganese over a pH range of 2 to 10.