Analysis of hydrolysis reaction of aluminum polynuclear complex with Cl- and SO42- anions by quantitative multinuclear NMR and evaluation of coagulation behavior of model sludge water

The first establishment of the Cl-35 qNMR method was achieved in this study. The calibration curves showed that extremely high linearity was established over a wide chloride concentration range from 1.0 x 10 3 to 3.6 mol L (-1). The various Al hydrolysis products were detected nondestructively by 27Al qNMR, and their concentrations were determined. The K-Al-13 was not detected in the solutions containing a large amount of SO42- ions, and K-Al-13 was observed at pH 3-6. The K-Al-13 concentration reached a local maximum when the aging time was approximately one day to one week. The highly charged K-Al-13 (i.e., 7 +) and DLVO theory revealed an efficient coagulation mechanism for the model sludge. The aggregation rate of the PACS-0.15 model sludge containing SO42- ions with an SO42- /Al molar ratio of approximately 10% was high over a wide Al concentration range owing to the formation of large flocs. If the model sludge water contains excess SO42- ions, the SO42- ions contribute minimally to the growth of large flocs of model sludge, hence, the model sludge did not aggregate efficiently.

Automated summary

The Cl-35 qNMR method was successfully established, showing high linearity in calibration curves and detecting various Al hydrolysis products. The study revealed the concentration changes of K-Al-13 and the efficient coagulation mechanism for the model sludge with highly charged K-Al-13. The aggregation rate of the PACS-0.15 model sludge was influenced by the presence of SO42- ions, affecting the formation of large flocs.