BONDING BETWEEN POLYACRYLAMIDE AND CLAY MINERAL SURFACES

Abstract

The objectives of this research were to determine the effects of clay mineralogy on the efficacy of cationic and anionic polyacrylamides (PAM) as flocculents for dispersed clays and to evaluate bonding mechanisms between clay mineral surfaces and both cationic and anionic PAM. A relative flocculation index was used to quantify the interaction between PAM and the Ca- and Na-forms of kaolinite, illite, and quartz. The cationic PAM was highly effective for flocculating all three minerals regardless of the electrolyte concentration or saturating cation. Under basic (pH = 10.9) conditions, the cationic PAM was slightly less effective than under neutral (pH = 5.9-8.2) or acidic (pH = 3.4) conditions. Positive charge functional groups on the cationic PAM are believed to bond directly with negative charge sites on the mineral surfaces. The efficacy of anionic PAM as a flocculent varied with saturating cation (Ca ≫ Na), mineralogy (kaolinite > illite ≫ quartz), and treatment (acid > salt > H2O > base). The results suggest that cation bridging (PAM-Ca-clay) is the major bonding mechanisms between anionic PAM and clay mineral surfaces. However, hydrogen bonding between electronegative moieties on the PAM and protonated nonbridging aluminol groups on lateral edges of kaolinite and illite and hydrophobic bonding between the carbon chain of the anionic PAM and basal surfaces of kaolinite were also suggested by the flocculation data.