Dynamic response in pH and the transient behavior of some chemical elements in pulp-water suspensions

The dynamic response in pH and the transient behavior of some chemical elem ents (Na, K, Mg, Ca, Ba, Mn, Si, and S) in an agitated pulp-water suspensio n at a consistency of 1.5% were measured for mill-produced oxygen-alkali de lignified Scandinavian softwood and hardwood kraft pulps. The results revea led time scales and differences in the distribution of the elements studied during the mass transfer process taking place between the pulp fibers and the free Liquid in the suspension. The dynamic response in pH varied from s ome minutes up to a few hours. An accidental change in the process liquor p H was followed by a mass transfer step continuing for from some minutes to ten minutes for most metallic elements measured. For most elements a dynami c change of 80% of the concentrations was obtained within 30 seconds after the pH adjustment. Monovalent cations, Na+ and K+, transfered back and fort h between the fiber phase and the free liquor phase, depending on the mass transfer of other components present in the system. Silicon showed a differ ent transient behavior compared to other chemical elements measured.