Adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) assisted settling of kaolinite in a two-step flocculation process

Flocculation has been widely employed in treatment of mineral tailings and water management. In this study, a chitosan-graft-poly(acrylamide-dimethyl diallyl ammonium chloride) (Chi-g-P(AM-DMDAAC)) was synthesized in-house. The adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) and an anionic polyacrylamide (APAM) in a two-step flocculation process of kaolinite were explored using settlement tests, zeta potential measurement, quartz crystal micro-balance with dissipation (QCM-D) and atomic force microscopy (AFM) technique. The type of primary flocculant was critical for the two-step flocculation process. The treatment of the kaolinite suspension using 1 mg/L of Chi-g-P(AM-DMDAAC) followed by adding 2 mg/L of APAM displayed more efficient flocculation performance. QCM-D results showed that three dissipative layers were assembled on model kaolinite surface after sequentially injecting 3.5 mg/L of Chi-g-P(AM-DMDAAC), 0.05 wt% kaolinite suspension and 2.5 mg/L of APAM. The above total adsorption amount (Delta f of -64.9 Hz) was much higher than that of using the two flocculants in reverse order (Delta f of -23.1 Hz). This result indicated that the adsorption layer of the positively charged Chi-g-P (AM-DMDAAC) on kaolinite surface provided active adsorption sites for APAM. Further AFM measurement confirmed that the average adhesion between the silicon tip adsorbed Chi-g-P(AM-DMDAAC) and model kaolinite surface in 2.5 mg/L APAM solution increased from 0.25 +/- 0.1 nN to 4.2 +/- 0.3 nN with the effective interaction range of 700 nm, which was stronger than that measured between a bare silicon tip and silica substrate in single-componentflocculant solutions. The highly efficient two-step flocculation process could be ascribed to the strong electrostatic attraction between the kaolinite and the oppositely charged Chi-g-P(AM-DMDAAC) and APAM. Findings in this study will benefit the development of environmentally friendly flocculant for mineral tailings and water treatment. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study explores the adsorption and interaction mechanisms of a chitosan-graft-poly(acrylamide-dimethyl diallyl ammonium chloride) and an anionic polyacrylamide in the flocculation process of kaolinite. The results show that the combination of these two flocculants exhibits efficient flocculation performance, which will benefit the development of environmentally friendly flocculants for mineral tailings and water treatment.