Two-phase equilibria of metal ions in pulping process from impregnation to oxygen delignification. Part I. Metal ion concentrations

Two-phase equilibria of metal ions at different stages of the pulping process have been studied. Pulp samples were taken from two modern kraft pulp mills using modified batch cooking process. One of these produces modified kraft pulp from a mixture of coniferous trees and the other also from birch. The concentrations of Na, K, Ca, Mg, Zn, Fe, Mn, Cu, Al, Ba and Si both in the liquid and the fibre phases were determined by using DCP-AES, ICP-MS and AAS analysis techniques. Also wood chips were analysed for metal ions. Conditional distribution coefficients were determined between the liquid and pulp for several metal ions in different pulp samples. The metal ions can on the basis of conditional distribution coefficients be arranged in an affinity order at the different stages of the pulping process.