Industrially, ferrous sulfate is mainly used as a precursor to other iron compounds. It is a reducing agent, mostly for the reduction of chromate in cement.

Nutritional supplement
Together with other iron compounds, ferrous sulfate is used to fortify foods and to treat iron-deficiency anemia. Copperas was given indiscriminately by untrained persons to slaves in the 18th and 19th centuries for various ailments.

Colorant
Ferrous sulfate was used in the manufacture of inks, most notably iron gall ink, which was used from the middle ages until the end of the eighteenth century. It also finds use in wool dyeing as a mordant.

Two different methods for the direct application of indigo dye were developed in England in the eighteenth century and remained in use well into the nineteenth century. One of these, known as china blue, involved iron(II) sulfate. After printing an insoluble form of indigo onto the fabric, the indigo was reduced to leuco-indigo in a sequence of baths of ferrous sulfate (with reoxidation to indigo in air between immersions). The china blue process could make sharp designs, but it could not produce the dark hues of other methods.

Ferrous sulfate can also be used to stain concrete a yellowish rust color.[3]

Woodworkers use ferrous sulfate solutions to color maple wood a silvery hue.

Other uses
In horticulture it is used as a lawn conditioner and moss killer.

In the second half of the 19th century, ferrous sulfate was also used as a photographic developer for Collodion process images.

Ferrous sulfate is sometimes added to the cooling water flowing through the brass tubes of a turbine condenser. It forms an erosion-resistant, protective coating on the inside of the tube.

It has been applied for the purification of water by flocculation and for phosphate removal in municipal and industrial sewage treatment plants to prevent eutrophication of surface water bodies.