Comparison of methods for stabilization of PCC against dissolution at acid papermaking conditions

Different methods presented in the literature for stabilizing precipitated calcium carbonate (PCC) against dissolution in weakly acidic media have been compared. The criteria for comparison are 1) stability in slurry form using pH and aluminium sulphate consumption measurements, 2) dissolution behaviour at papermaking conditions using calcium ion concentration measurements and 3) optical properties of paper using light scattering coefficient and brightness measurements. Initially five treatment methods were applied to prepare the PCC samples. All of them significantly improved the stability. Three of these methods which showed the best results were chosen for further experiments. These three methods represent different approaches: polymer adsorption on the surfaces of PCC particles, weak acid/base buffering system and silicate precipitation on the surfaces of PCC particles. The silicate precipitation met hod showed smoothening of the coarse surface structure of the scalenohedral PCC in the Scanning Electron Microscopy (SEM) images. The handsheet experiments showed that the optical properties when using stabilised PCC exceeded those of the kaolin filled sheets. Significant differences in the optical properties between the different treatment methods of PCC were not observed. Calcium ions can cause runnability problems in a paper machine. The lowest calcium ion concentration in the process waters was achieved with the silicate precipitation method. The possible runnability issues regarding silicate ions were not investigated in this study.