INHIBITION OF THE DISSOLUTION OF PAPERMAKING GRADE PRECIPITATED CALCIUM-CARBONATE FILLER

The inhibition of the dissolution of papermaking grade precipitated ca lcium carbonate filler with sodium oxalate and phosphoric acid at pH 7 .5 increased with inhibitor concentration. The saturation points for s odium oxalate and phosphoric acid were 1.0 x 10(-2) mol/L and 0.5 x 10 (-3) mol/L. Oxalate ions inhibited the calcium carbonate dissolution i n the entire range of pH studied. The inhibition was greater at lower pH. At an inhibitor concentration of 0.0014 mol/L and pH 7.5, the most effective chemical was phosphoric acid. The solubility of calcium ion was 80% lower than that in a solution without inhibitor. The authors also studied the inhibition of calcium carbonate dissolution by phosph oric acid in a CTMP suspension. For each level of precipitated calcium carbonate lading, a saturation point occurred, and the amount of phos phoric acid required to achieve the saturation point increased with th e filler loading.