Flocculation of precipitated calcium carbonate (PCC) by cationic tapioca starch with different charge densities. I: Experimental

The dynamics of the flocculation of precipitated calcium carbonate (PCC) with two commercial cationic tapioca starches (S858 and S880) with different charge densities were studied by small angle static light scattering. The effects of temperature, polymer dosage, ionic strength, and shear rate on the floc size and structure were investigated by employing a response surface methodology involving the central composite statistical design and analysis of variance (ANOVA). The evolution of floc size and structure was observed and it was found that larger and more compact flocs were produced by the high charge density starch S880. The floc's mass fractal dimension indicates the floc's compactness and it was found that the compactness increases as the flocculation proceeds. The ionic strength plays a significant role on the floc size with S880. Finally, the negative effect of shear rate on floc size was more pronounced for the low charge density starch S858.

High charge density starch S880 resulted in larger flocs compared to those produced by low charge density starch S858.Figure optionsDownload as PowerPoint slideHighlights
► The PCC floc size went through a maximum before reaching steady state.
► Larger and more compact flocs were produced by higher charge density starch.
► The mass fractal dimension of the flocs continued increasing as flocculation proceeds.
► The high charge starch was negatively affected more by background electrolyte.
► PCC surface charge decay for S858 and S880 system was observed.