There are many production methods of ferrous sulfate, which can be produced by waste acid from steel plant and by-product of titanium dioxide plant. In addition, ferrous sulfate can be prepared by reaction of iron and dilute sulfuric acid.

The chemical equation of reaction between iron and dilute sulfuric acid is: Fe + H2SO4 = FeSO4 + H2. In this process, the reaction is a complex decomposition. Because H2SO4 contains hydrogen acid, it has oxidizability, so the iron pass peroxide reaction produces new divalent iron ion compound. It is concluded that the new ferro-ferrous compound ferrous sulfate is gradually dissolved to form gas, and the colorless solution becomes light green.

Iron can react with concentrated sulfuric acid. Although the oxidation of concentrated sulfuric acid is stronger than that of dilute sulfuric acid, different products such as iron sulfate will be reacted on the surface. However, because the oxidation of concentrated sulfuric acid mainly occurs on sulfur ions, passivation will occur, ferrous sulfate will be reacted at normal temperature, and 3 valent iron will be generated under high temperature: Fe + 2h2so4 = FeSO4 (3 valent iron) +so2 ↑ +2h20.

So why don't iron sulfate react with dilute sulfuric acid? In fact, the oxidation of dilute sulfuric acid h+ belongs to weak oxidation, because it is not strong enough, which leads to the oxidation of iron into 2 valent iron ions. If a certain amount of oxidant is added to the reaction between iron and dilute sulfuric acid, the oxidation property of iron will be enhanced, such as oxygen and bleaching water, which will lead to the oxidation of iron sulfate into 3 valent iron ions. The results show that the 3-valent iron ions are brown yellow or yellowish brown in the solution, while the 2-valent iron ions are light green. The determination of whether the iron ions are 2 or 3 can be measured by adding sodium hydroxide.