Effect of a low-molecular-weight polyacrylic acid on the coagulation of kaolinite particles

Kaolinite is of very fine particle size in nature and thus its dispersion plays a key role in the successful removal of kaolinite in iron ore flotation and selective flocculation processes. As the most widely used dispersant in the world, sodium silicate has been used as a standard dispersant in iron ore industry. However, in the author's previous work, the actual effect of sodium silicate on the colloid stability of kaolinite particles was found to be weak under the typical conditions of iron ore flotation and selective flocculation.In this work, the dispersive effect of a low molecular weight polyacrylic acid on kaolinite particles was systematically investigated through electrophoretic mobility and colloidal stability studies. The results demonstrate that interactions between polyacrylic acid and kaolinite take place over the entire pH range studied in this work, from pH 5 to 10.5, with stronger interactions observed at neutral and acidic pH. This indicates that polyacrylic acid adsorbs on both positively and negatively charged sites on kaolinite, although the presence of positively charged sites on the clay surfaces at low pH and in CaCl2 and MgCl2 solutions at high pH significantly enhances its interactions with kaolinite. The strong dispersive effect of polyacrylic acid on kaolinite in the presence of CaCl2 and MgCl2 shows that polyacrylic acid is a promising dispersant for kaolinite under the typical conditions of iron ore flotation and selective flocculation.

Research Highlights
► It was for the first time demonstrated that interactions between polyacrylic acid and kaolinite take place at high pH when the clay surfaces are free of positively charged sites.
► Fast coagulation of kaolinite particles takes place in CaCl2 and MgCl2 solutions at high pH, while polyacrylic acid can fully disperse kaolinite under such conditions.
► It was found that polyacrylic acid is a better dispersant of kaolinite than sodium silicate under typical conditions of iron ore flotation and selective flocculation.