Influence of pH on the adsorption of dissolved and colloidal substances in a thermo-mechanical pulp filtrate onto talc

Talc is often used to control unwanted deposition of resins and wood processing derivatives in the wet end circuit of a paper mill. The effect of pH was studied on the adsorption of dissolved and colloidal substances originating from thermo-mechanical pulp (TMP) onto talc. In this study we investigate, for the first time, the influence of pH on the adsorption of wood resin on talc, dealing with the complex system of real pulp mill water without the presence of fibres, in the pH range of 4-9. It was found that with increasing pH the maximum loading of colloidal substances on the investigated talc grade decreased. The experimental evidence suggests that this was not simply an effect of the changing electrostatic stability of the colloids, but mainly the competition between soluble species and colloidal material. Analysis of the total organics by chemical oxygen demand allowed estimation of the competition of dissolved and colloidal substances for the adsorption onto talc. For the adsorption of the colloidal fraction, characterised by turbidity, a Langmuir adsorption isotherm provided a simplistic characterisation of the process.