Polyaluminum Chloride (PAC), abbreviated as polyaluminum, is a water-soluble inorganic polymer compound that lies between AlCl3 and Al(OH)3. Its general chemical formula is [Al2(OH)nCl6-n]m, where m represents the degree of polymerization, and n indicates the neutralization level of the polyaluminum chloride product. When n=1~5, it forms a highly charged polymeric ring chain with a Keggin structure, which exhibits strong electrical neutralization and bridging effects on colloids and particles in water. It effectively removes toxic substances and heavy metal ions, maintains stable properties, and is commonly used as an emerging water purification material and coagulant. It is widely applied in the purification of drinking water, industrial wastewater, and urban sewage.