Study of hydrogen gas formation during leaching of weakly radioactive ores of the Tomtor deposit: Geo-radiochemical nature of the reducing properties of the ore

Direct alkaline leaching of weakly radioactive rare metal ores of the Tomtor deposit (Russia) was investigated. It was found that the process of leaching monazite with sodium hydroxide solutions in the presence of various associated mineral components is accompanied by the release of significant amounts of hydrogen and the formation of stable foam filling the reactor and preventing the elimination of hazardous gas. The discovered phenomenon is unique, since hydrogen release occurs at a high rate even at low temperatures (40–50 °C) and when leaching ores in both alkaline and acidic environments (hydrofluoric acid solutions). It is assumed that the high reduction potential of the ores is associated with the deaeration of mineral components (oxygen removal) during their long-term radiochemical irradiation. Preliminary studies using solid-state NMR confirmed this assumption. A significant amount of hydride ions, which are part of stable mixed cluster compounds of aluminum oxides and phosphates, were found in ore samples. It is assumed that the high stability of the foam formed in this process is due to the formation of a structural and mechanical barrier of hydrophobic pulp particles, including un-decomposed pyrite. Undesirable foaming is eliminated by adding an anionic surfactant (sodium stearate) to the pulp, which ensures the removal of hydrophobic particles from the surface of gas bubbles.