Classification of Reagents Used in Ultrapure Water Coagulation Process

Based on their role in the coagulation process, coagulants can be divided into two categories: coagulants and flocculants. They function as destabilizers and flocculants respectively, and are collectively referred to as coagulants. Traditional coagulants such as aluminum sulfate or ferric chloride belong to the category of coagulants. When using these coagulants, sufficiently large and easily settling flocs often automatically appear during the flocculation stage of coagulation, thus eliminating the need for additional flocculants. Sometimes, to form flocs, or for economic or other reasons, it is necessary to add additional flocculants; these flocculants generally refer to polyelectrolytes. Flocculants mainly work by bridging destabilized colloidal particles. In this case, the coagulant that performs the colloidal destabilization function is called the primary coagulant. The distinction between coagulants and flocculants here refers to their functional use. Some coagulants, especially high molecular weight polymers, can not only be used as coagulants but also often act alone, simultaneously serving as both coagulants and flocculants. The flocculant used with the primary coagulant is in a much smaller dosage than the primary coagulant, generally below 10 mg/L. For direct filtration, the dosage can be as low as 0.01 mg/L. Flocculants used for direct filtration are conventionally called filter aids.