Inhibition of the Dissolution of Calcium Carbonate Filler
EXPERIMENTAL
Papermaking grade GCC filler in 70 wt. % suspension was obtained from Columbia River Carbonates (Woodlands, WA). The average particle size was measured to be 0.92 mm (Malvern Mastersizer 2000, Malvern Instruments, Inc., WA). Phosphoric acid (Aldrich Chemical Company Co., Milwaukee, WI) was used as the source of phosphate inhibitor.
Dissolution of GCC:
In a 2.5 L beaker, a required amount of inhibitor was first added to 2 L of de-ionized water. The pH of the solution was then adjusted to 5.5 with 0.01 moles/L HCl or NaOH aqueous solution. Afterwards, the solution was stirred at 800 rpm for 20 mins prior to the start of the dissolution experiment. 20 g of 10 wt. % GCC stock suspension was then added to the solution to give an overall concentration of 0.1 wt. %. The suspension was stirred at 800 rpm for 24 hrs. At regular time intervals, the pH of the suspension was measured and 30 ml of sample was taken with a syringe and filtered through a 0.22 microns membrane filter. The filtrate was then analyzed for Ca content by atomic adsorption spectroscopy (GBC) using an air-acetylene flame. The filter cake was collected and dried in a vacuum dessicator prior to surface analysis.
Surface Analysis:
Various techniques were used to study and characterize the surface structure of the treated GCC. These analysis which were carried at Institute for Chemical Process and Environmental Technology, NRC Canada were: