Adsorption of Anionic Dissolved and Colloidal Substances on the Calcium Carbonate Fillers, 1999 Papermakers Conference Proceedings

Takanori Miyanishi, Yasuyuki Kamijo, Hiroshi Ono

The proliferation of on-site precipitated calcium carbonate (PCC filler) plants allows substitution of an inexpensive material for fibers and a reduction in raw material cost, while at the same time enables an increase in brightness and opacity. In neutral papermaking with wood containing pulp grades, anionic trash derived from mechanical pulp has a tendency to cause pitch problems. The purpose of this study is to evaluate the pitch controlling ability of PCC, which has not been well documented in the literature. The key to pitch adsorption on PCC was the surface area and charge of PCC. Oleic acid was adsorbed on PCC 10 times more than abietic acid was. This is ascribed to the different equilibrium constant to form calcium salt. The zeta potential of PCC changed from positive to negative with the adsorption of pitch model compounds. Anionic dissolved and colloidal substances in BTMP filtrate were adsorbed on PCC. Measurement of the total organic carbon (TOC) and colloid titration revealed that they were adsorbed on PCC until the anionic demand of PCC was neutralized. Colloidal substances were adsorbed on PCC more preferentially than dissolved substances were. PCC and talc adsorbed a similar amount of pitch. But when they adsorbed pitch, PCC agglomerated while talc dispersed. Particle size measurement indicated that hydrophilic tails of pitch molecules attach to the PCC surface by chemical adsorption, forming calcium salt. It is hypothesized that the surface charge of PCC is neutralized by direct contact of polar hydrophilic groups of pitch. Hydrophobic chains, which extrude in water, agglomerate PCC by the van der Waals forces. In the case of talc, hydrophobic tails of pitch molecules attach to the talc surface by physical adsorption and free carboxyl groups, which are dissociated under the alkaline pH, create the negative surface charge and screen the approach of other talc particles. Free carboxyl groups repel each other and disperse talc. It is concluded that the zeta potential is an important parameter and an increase of the first pass ash retention can reduce the pitch problems.