In situ kinetics and flocs conformation studies of kaolinite flocculated by Chi-g-CPAM

This study presents a comparative study of the flocculation behavior of kaolinite induced by chitosan-graft-poly(acrylamide-dimethyl diallyl ammonium chloride)(Chi-g-CPAM) and a commercial cationic polyacrylamide(CPAM).The flocculation behaviour was characterised in terms of both flocculation kinetics and the corresponding morphology changes during flocculation.Both Chi-g-CPAM and CPAM were grafted from silica wafers by means of atom transfer radical polymerization(ATRP).The quartz crystal microbalance with dissipation(QCM-D) tests were conducted.The equilibrium time flocculated by Chi-g-CPAM was found to be 0.46 times as that of CPAM,together with a larger total mass of kaolinite layer.The flocculation behaviour by Chi-g-CPAM can be well captured by a pseudo-first-order model.In contrast,the presence of CPAM leads to a more complex kinetics.A relatively larger fitting slope(0.4663) was obtained at the initial stage but the fitting slope droped to 0.2026 after 800 min,indicating a densification process caused by CPAM.The flocculation kinetics of CPAM can be captured by the Elovich model for the inital stage but the combination of pseudo-first-order and pseudo-second-order models for the latter stages,which can be attributed to the long chain of CPAM.With a dosage of 75 g/t,the settling test with Chi-g-CPAM exhibits the same turbidity in the supernatant but a smaller layer thickness of the settlement compared to CPAM.The study enables a better understanding of the flocculation behavior and contributes to the development of efficient flocculants in mineral processing and tailings treatment.