Koagulant

Koagulant, sometimes spelled coagulant, is a term used across fields to denote a substance that promotes coagulation—the transformation of stable colloids into a solid or semi-solid mass. In water treatment and related industries, coagulants destabilize suspended particles so they can be removed as sludge. In medicine, coagulants or procoagulants promote blood clotting to control bleeding.

In water treatment, common inorganic coagulants include aluminum salts (such as alum) and ferric salts (such as ferric chloride). Organic and inorganic polymer coagulants, including polyacrylamide derivatives and polyaluminum chlorides, are also used. Natural or plant-based coagulants and synthetic coagulants designed for specific streams may be employed to reduce sludge volume or improve filtration. The choice of coagulant depends on water chemistry, pH, and the desired level of turbidity removal.

Mechanistically, coagulants work by neutralizing negative surface charges on colloidal particles, allowing them to come together, form larger aggregates, and be removed more easily. Some coagulants also act as bridges, linking particles into larger flocs. The efficiency of coagulation is influenced by pH, dosage, residence time, and the presence of natural organic matter.

Applications span potable water production, wastewater treatment, mining, pulp and paper processing, and various industrial clarification steps. In medicine, coagulants or hemostatic agents (such as topical thrombin or fibrin sealants) assist in stopping bleeding, while systemic agents (like vitamin K) address deficiencies that impair coagulation.

Safety and environmental considerations include managing residual metal concentrations, minimizing sludge production, and ensuring appropriate dosing to avoid excessive coagulation or downstream complications.