Main use: It is used as water purifying agent, gas purifying agent, mordant, herbicide, and used in making ink, pigment, etc., and is used as a blood supplement in medicine. Industrially used in the manufacture of iron salts, inks, iron oxide red and indigo, used as mordants, tanning agents, water purifying agents, wood preservatives and disinfectants; agricultural fertilizers, herbicides and pesticides. Decomposition products: (high temperature) SO2 (g), SO3 (g)