Adsorption of sodium polyacrylate in high solids loading slurries

The world demand for calcium carbonate has been increasing by 7% per year since 2002 reaching a world capacity of 71.7 megatons in 2007. The demand continues to increase due to the diverse applications of calcium carbonate such as building materials, medicines, additives to food, filler for plastics and paper, and more. Calcium carbonate is often stored and transported by dispersing it into an aqueous medium with a polyelectrolyte to achieve up to 75 wt% solids loading. One of the most frequently applied dispersants for calcium carbonate is sodium polyacrylate (NaPAA). Higher solids loading of the calcium carbonate slurries are desired to increase storage capacity and decrease transportation cost. In order to achieve higher solids loading slurries the science behind the adsorption of NaPAA onto the calcium carbonate within high solids loading slurries must be understood. Currently all research which has been performed on the adsorption of NaPAA onto calcium carbonate has been performed in dilute systems. The goal of this research is to understand the adsorption of NaPAA onto calcium carbonate in high solids loading slurries up to 75 wt% ground calcium carbonate (GCC).;The adsorption of NaPAA onto calcium carbonate was investigated utilizing several techniques including adsorption isotherms, turbidity measurements, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and probe molecule adsorption. The adsorption of the NaPAA was determined to be due to the chelating ability of the carboxylate groups with calcium carbonate. The carboxylate groups were determined to adsorb through unidentate, bidentate, and bridging modes. Also, the mode of adsorption of the carboxylate group was dependant on the solids loading and age of a slurry system. Further analysis revealed the CH groups of adsorbed NaPAA were interacting with the surface of the GCC.;Another novel discovery demonstrated that the water structure within a GCC slurry dispersed with NaPAA is dependant on solids loading and age. With increasing solids loading there is a decrease in the concentration of structured water. Also, with an increase in age there is an increase in the concentration of structured water. Chemicals with the ability to either make or break water structure were introduced into 75 wt% solids loading slurries. The water structure breakers demonstrated that their inclusion in the slurry decreased viscosity and prevented an increase in the structured water due to aging.