Preparation of polyaluminum chloride by microwave hydrothermal and its composite coagulation system with chitosan for the removal of anionic dyes: Mechanism and application exploration

Polyaluminum chloride (PAC), as a typical inorganic flocculant for the treatment of anionic dye wastewater, was often constrained by drawbacks such as the long preparation period of the traditional alkali-addition method and the excessive residual Al concentration in the treated water. This study adopted microwave hydrothermal technology to efficiently prepare PAC with a high content of Al_b within 10 min, and deeply combined it with chitosan (CTS) to construct a PAC-CTS composite coagulation system, in order to simultaneously improve flocculation efficiency and reduce the risk of residual Al. Experiments demonstrated that the PAC-CTS composite flocculant demonstrated significant flocculation performance enhancement compared to PAC alone. Response surface experiments indicated that the PAC-CTS composite flocculant demonstrated particularly outstanding dye removal performance under acidic conditions, achieving a dye removal rate of up to 99.05 % under optimal flocculation process conditions. Additionally, a comprehensive analysis was conducted on the cost-effectiveness of the PAC-CTS composite coagulation system and on its coagulation efficiency under different scenarios. The results showed that it had good application prospects in practical wastewater treatment. Mechanistic analysis revealed that the main mechanism of action of the coagulation system for the removal of anionic dyes was charge neutralization-hydrogen bonding synergy. In summary, this study designed a new and efficient method for the synthesis of PAC, and provided a solution for the treatment of anionic dye wastewater with high efficiency and environmental friendliness.