Widely used as a coagulant in water and wastewater treatment to remove suspended solids, phosphates, and heavy metals. It helps clarify water by forming flocs that settle easily. Commonly applied in municipal sewage treatment and industrial effluent treatment. Used in etching copper-based materials in printed circuit board (PCB) manufacturing due to its ability to oxidize copper. Provides precise circuit patterning and is valued for its effectiveness and low cost. Acts as a catalyst in organic synthesis, particularly in chlorination and Friedel-Crafts reactions. Also employed in the production of other iron compounds and pigments. Applied in the oil industry for treating hydrogen sulfide gas and controlling odor in sewage systems by precipitating sulfides. Used in small amounts in medical and cosmetic formulations as an astringent or styptic to stop minor bleeding.