... cryastal cargo. 3.mainly used in industry water treatment,agriculture fertilizer, Name of Specification/Index IndexFeSO4. ... red and indigo-blue, as mordant, tanning, water purification, preservative of wood and disinfectant etc. In ... agriculture, it is for fertilizer, weedicide, pesticide treating wheat smut etc. ... . ferrous sulphate (heptahydrate used for water treatment)