Dept. of Chemical & Bio-Resource Engineering and Pulp and Paper Centre, The University of British Columbia, 2385 East Mall, Vancouver, BC, V6T 1W5, Canada.
* Institute for Chemical Process and Environmental Technology, National Research Council Canada, ON, Canada.
The effect on phosphate on the inihibiton of the dissolution of ground calcium carbonate filler was studied. Addition of small amount of phosphate signifcantly reduced the equilibrium dissolved calcium concentration (@24 hrs). The degree of inhibition was found to depend on the phosphate dosage in which an optimal dosage level was observed. Surface analysis confirmed the precipitation of Ca-P solid phase on the surface of treated GCC particles. The mechanism of the inhibition treatment was discussed.
INTRODUCTION
Application of CaCO3 in acidic papermaking system such as newsprint production has been limited by the extensive decomposition of filler under acidic condition. A change of pH from alkaline to acidic condition causes a dramatic increase in the filler solubility by several orders of magnitude. Not only does the dissolution increase the furnishes cost, it also buffers the wet end pH to 7.2-8.5 which can cause darkening of the mechanical pulp. In addition, dissolved calcium has been shown to have a detrimental effect on the efficiency of chemical additives such as retention aids.
Inhibition of the dissolution of CaCO3 has been studied extensively in the field of geochemistry. Various inorganic and organic compounds, which are termed inhibitors have been shown to have an inhibitory effect on the rate of CaCO3 dissolution(1-11). It is generally believed that this inhibitory effect is due to adsorption of the inhibitor on the reactive regions of the CaCO3 surface such as kinks which retards the rate of dissolution and precipitation of CaCO3.
We have previously examine the inhibiting capability of phosphate, oxalate, magnesium ions and anions of maleic acid, succinic acid, on the dissolution of PCC fillers in water(12). Phosphate was found to be the most effective inhibitor and was able to lower the solubility of PCC by 80%. It is proposed that the inhibition could be due to the precipitation of an insoluble Ca-P containing solid phase on the GCC surface and thus blocking the dissolution sites.
The objectives of this work are: