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

    Year: 2022

    Journal: Sci. Total Environ., Volume 816, APR 10

    Authors: Xu, Ruijing; Zou, Wenjie; Wang, Ting; Huang, Jun; Zhang, Zhijun; Xu, Chengyan

    Organizations: National Natural Science Foundation of China [51604019]; Fundamental Research Funds for the Central Universities [FRF-IP-20-03]; National Key Research and Development Program of China [2020YFC1807804]; Foundation of State Key Laboratory of Mineral Processing of China [BGRIMMKJSKL-2020-11]

    Keywords: Chi-g-P(AM-DMDAAC); Two-step flocculation; Adsorption; QCM-D; AFM

    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.
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