Metallide leostamine graptoliitargilliidist lämmastikhappe lahustega [Bakalaureusetöö. Juhendajad: S. Pajusaar, R. Hints]

Graptolite argillite, occurring in most of North Estonia, is a metalliferous Tremadocian black shale that contains number of technologically important metals and is thus a potential future resource. Previous attempts to find efficient methods for the mineral processing of these black shales have been mostly concentrated on the extraction of uranium. The aim of the bachelor thesis was to test leaching of enriched metals from graptolite argillite using nitric acid extraction, which is considerably less studied compared to sulfuric acid treatment. The research experiments were carried out with unprocessed and roasted (at 500°C and 950°C) graptolite argillite using concentrated and diluted nitric acids. The efficiency and time dependence of leaching were analyzed. The duration of the full leaching experiment was 168h. X-ray fluorescence spectrometry and inductively coupled mass spectrometry were implemented to analyze the chemical composition of the yields and residues of the leaching experiments. Leaching with nitric acids proved to be the most effective for REEs cerium and lanthanum, arsenic, copper, nickel and lead with the yield more than 80%. With these elements, the effectiveness of leaching varied noticeably in unprocessed and roasted material. The maximum yields of uranium and molybdenum were around 65%. As in previous studies, vanadium was most difficult to leach, reaching the maximum yield less than 40%. In conclusion, leaching of graptolite argillite with nitric acid gave similar outcomes for the targeted metals (except vanadium) as previous leaching experiments with sulfuric acid, so this extraction method should be further analyzed in the future studies.