Comparison of methods for stabilization of PCC against dissolution at acidpapermaking conditions

Different methods presented in the literature for stabilizing precipitated calcium carbonate (PCC) against dissolution in weakly acidic media have bee n compared. The criteria for comparison are 1) stability in slurry form usi ng pH and aluminium sulphate consumption measurements, 2) dissolution behav iour 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. A ll of them significantly improved the stability. Three of these methods whi ch 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 precipitati on on the surfaces of PCC particles. The silicate precipitation met hod sho wed smoothening of the coarse surface structure of the scalenohedral PCC in the Scanning Electron Microscopy (SEM) images. The handsheet experiments s howed that the optical properties when using stabilised PCC exceeded those of the kaolin filled sheets. Significant differences in the optical propert ies 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 silic ate precipitation method. The possible runnability issues regarding silicat e ions were not investigated in this study.