The development of hydrophobised ground calcium carbonate particles for the effective adsorption of dissolved and colloidal substances (DCS) from thermo mechanical pulp (TMP) filtrates

Talc is often used to control unwanted deposition of resins and wood processing derivatives in the wet end circuit of a paper mill. It was the aim of this study to develop a calcium carbonate based mineral particle with improved pitch adsorption properties, and to compare these properties with those of talc. Partially treating the surface of the calcium carbonate with stearic acid led to improved adsorption of wood resin constituents and useful wetting properties. It was shown that the partially hydrophobised calcium carbonate had a higher capacity for the adsorption of the colloidal fraction of TMP than did the corresponding untreated calcium carbonate. Both calcium carbonates preferentially adsorb colloidal substances together with a minor amount of dissolved carbohydrates. In contrast, talc preferably adsorbs colloidal substances when the colloidal concentration is high but starts to adsorb substantial amounts of dissolved carbohydrates at lower concentration of colloidal wood resin droplets.