The use of porous high surface area calcium carbonate for the adsorption of dissolved and colloidal substances from thermo mechanical pulp filtrates

Talc is often used to control unwanted deposition of resins when the colloidal concentration is high, but when the colloidal concentration is low, adsorbs substantial amounts of dissolved carbohydrates. Natural calcium carbonate and surface hydrophobised calcium carbonate largely avoid this problem, adsorbing limited amounts of solid species at neutral to alkaline pH. Modified calcium carbonate (mcc), displaying an internally porous structure, high specific surface area and both anionic and cationic surface sites, has even greater specificity for particulate pitch adsorption. The mixed charges on the surface of mcc also give rise to selective adsorption of soluble species at high doses, at adsorption sites inaccessible to pitch.