Adsorption of hybrid polyacrylamides on anisotropic kaolinite surfaces: Effect of polymer characteristics and solution properties

• Increasing the molecular weight resulted in an increase of the mass uptake of the polymer on silica and alumina basal planes.
• The amount of the polymer adsorbed on silica increased by increasing Al content in contrast to the adsorption on alumina.
• Fitting of the adsorption data to the Langmuir adsorption isotherm revealed spontaneous adsorption of Al-PAM on silica.
• The adsorption of Al-PAM on silica was shown to decrease in plant recycle water compared to deionized water at pH ∼8.
• Maximum coverage of Al-PAM on silica basal planes is lower at higher temperatures.

Adsorption kinetics of organic-inorganic (hybrid) Al(OH)3-polyacrylamide (Al-PAM) with different molecular weights (for organic characteristics) and contents of aluminum hydroxide nanoparticles (for inorganic characteristics) on kaolinite basal planes was studied using a versatile quartz crystal microbalance with dissipation (QCM-D). The flocculation dynamics of kaolinite by Al-PAMs was assessed by measuring the initial settling rate of flocculated kaolinite particles and the turbidity of the supernatant after settling of flocculated solids. The areal mass (mg/m2) of Al-PAMs adsorbed on tetrahedral silica and octahedral alumina basal planes of kaolinite increased with increasing molecular weight of the polymer. Increasing the content of Aluminum hydroxide nanoparticle in Al-PAM has resulted in an increase of the amount of the polymer adsorbed on silica basal planes while opposite trend was found on alumina basal planes. Results obtained from the adsorption kinetics study of Al-PAM6R (Mw = 2.2 million Dalton, 0.11 wt% Aluminum) on silica basal planes revealed that the early stage of adsorption is diffusion-controlled. Thus, initially the adsorption rate increased with increasing temperature while the maximum coverage decreased. Moreover, the adsorption of Al-PAMs on silica basal planes was shown to decrease significantly in plant recycle (process) water compared to deionized water. Al-PAMs of higher molecular weight and/or high content of inorganic Al (OH)3 nanoparticles were found to be more effective in flocculating kaolinite as indicated by the faster settling rates and clearer supernatant.

(A) Comparison of the total amount of adsorbed mass of different Al-PAMs on silica and alumina basal planes of kaolinite measured by QCM-D and; (B) Comparison of settling rates of 5 wt% kaolinite suspensions after flocculation by Al-PAMs. Settling rates (1/s) was obtained by plotting the normalized mudline height (h/H, where “h” is the mudline height at settling time “t” and “H” is the initial suspension or mudline height) versus the settling time.Molecular weight: Al-PAM6R = Al-PAM6H > Al-PAM4R; Aluminum content: Al-PAM6R = Al-PAM4R <  Al-PAM6H.Figure optionsDownload as PowerPoint slide