... blue-green cryastal cargo. 3.mainly used in industry water treatment,agriculture fertilizer, Name of Specification/Index ... 60ferrous sulphate 98heptahydrateUses: In industry,it is used to make ferric salt,ink iron oxide red ... and indigo-blue, as mordant, tanning, water purification, preservative of wood and disinfectant etc. In ... each. ferrous sulphate (heptahydrate used for water treatment)