Ferrous sulphate refers to the crystal formed by dehydration, while ferrous sulphate heptahydrate is the hydrate product with the highest water content in ferrous sulphate products. The chemical properties of these two substances are not quite the same. In short, ferrous sulphate heptahydrate contains seven crystal water, while ferrous sulphate heptahydrate is a crystal formed by dehydration. Ferrous sulphate heptahydrate can gradually lose water and become anhydrous ferrous sulphate. Ferrous sulphate monohydrate is the product of partial dehydration of ferrous sulphate heptahydrate. Generally speaking, ferrous sulphate is anhydrous ferrous sulphate.

The difference between ferrous sulphate heptahydrate and ferrous sulphate monohydrate can be summarized as follows: ferrous sulphate heptahydrate is just made, with high moisture content; ferrous sulphate monohydrate is ferrous sulphate heptahydrate, with low moisture content in secondary processing; ferrous sulphate monohydrate has high moisture content after secondary processing, and can be used for feeding.

Ferrous sulphate heptahydrate is commonly used in industry as water purifier, gas water purifier, mordant, catalyst, disinfectant, magnetic material, ink and pigment.

Ferrous sulphate heptahydrate can be used as fertilizer in agriculture. It is a catalyst for plants to produce chlorophyll. It plays an important role in the absorption of plants. It can also be used as fertilizer, herbicide and pesticide. It can cure the head smut of wheat and cure the moss and lichen of trunk.