As a hazardous waste, pickling waste liquor must be properly treated. An alternative consists in promoting the formation of ferrous salts from this residue, due to its higher ferrous content. Since FeCl2·4H2O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl2·4H2O crystals have been obtained from pickling waste liquors. Their structural and morphological characteristics have been investigated by X-ray diffraction, scanning electron microscopy as well as Mössbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals change in colour from green to more yellowish. So, the aged sample has also been evaluated, and their structural characteristics are compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl2·4H2O structure, which is not modified with the aging of the sample.