Synthetic polyacrylamide as a potential flocculent to remove commercial chromium(III) oxide from aqueous suspension

The effects of solution pH and cationic group contents in polyacrylamide (PAM) macromolecules on the polymer adsorption mechanism on chromium(III) oxide surface were studied. The structure of PAM adsorption layer was also characterized to explain the changes in solid suspension stability. The following methods were applied: turbidimetry, spectrophotometry, potentiometric titration and microelectrophoresis. Thanks to them, the stability of the Cr2O3-polymer systems, polymer-adsorbed amount, surface charge density and zeta potential of solid particles were determined. The experimental results indicate that adsorption of cationic PAM increases with the rising pH. The larger the content of cationic groups in PAM chains is, the higher the adsorption level is observed. The most effective chromium(III) oxide removal is achieved at pH 9 after addition of PAM with the largest content of cationic groups (i.e. 80 %). The neutralization of solid surface negative charge by positively charged polymer chains (assuming more coiled conformation) is responsible for this.