Effects of inorganic and organic additives on the adsorption of nonionic polyacrylamide on hematite

The effects of inorganic anions such as chloride, sulfate, and phosphate on the adsorption of nonionic polyacrylamide on hematite are studied. Adsorption of the polymer is reduced in all cases, with complete depression by phosphate. The relative effectiveness of these anions in reducing polymer adsorption increases in the order chloride < sulfate < phosphate, a trend which corresponds to the relative stabilities of the anion-Fe3+ complex formation. The effectiveness of sulfate and phosphate in competing with the polymer for surface sites is explained in terms of the strong interaction of these anions with FeOH2+ and FeOH by ligand exchange, replacing the surface hydroxyl groups. Since at lower pH there is higher interaction of these anions with the surface, the effect of pH on polymer adsorption is reversed. Urea is also found to decrease polymer adsorption. In this case, the phenomenon is due to H-bonding of the urea with the surface hydroxyls, depleting adsorption sites for the polymer.