Tantalum, Niobium and Thorium Cake Production at the Sillamäe Oil Shale Processing Plant

The shale oil factory at Sillamäe, Estonia was founded in 1928 by the “Estonian Oil Consortium”, belonging to Swedish capital. Their original internally heated retorts were not successful, but after restarting in 1935 with the local tunnel ovens, good yields of shale oil from the brown kukersite shale were achieved. The factory was destroyed by the Soviet occupation forces and rebuilt after WWII for uranium production from the local black alum (dictyonema) shale. Uranium production was soon replaced by uranium processing, but the factory (P.O.B. P-6685) retained the old shale-related name. In 1970 tantalum, niobium and rare earths’ production from the Khibina (Kola Peninsula, Lovozero) loparite ore was added and operated until the demise of the Soviet Union in the end of 1991. The uppermost layer in the tailings dump consists of thorium-rich loparite waste while the lowermost represents the black dictyonema shale processing waste, rich in uranium. We compare these two sources of radioactive pollution.