Highlights • This article will show that the quick leach model, also called the water-starved system, limits silica solubilisation and its subsequent polymerisation during manganese extraction from ferromanganese slags. • It will further illustrate that the silica content in the residue is dependent on the acid concentration used during acid digestion. It will also show that dissolved silica in the pregnant leach solution is dependent on the quantity of water used. • Furthermore, a method for silica gel recovery from ferromanganese slag will be presented, as well as the silica gel analysis, in order to confirm the theory presented in this article. • The silica and calcium sulphate-rich residue can be used as an addition to Portland cement or as a gypsum replacement.