Selective uranium extraction
The nickel producing mining company, Talvivaara in Finland, began investigations into the production of uranium as a byproduct after results revealed uranium content of 10 to15mg/l in nickel. The open pit black ore typically contains 15 to 20ppm uranium. However on commissioning the uranium content to the solution process this significantly increased.
The technique is based on bio-assisted heap leaching of nickel, zinc, cobalt and copper, where uranium is leached from the ore simultaneously giving the opportunity to recover uranium in the form of a yellow cake. The extraction is carried out in two stages and uses a strong organic phosphorous reagent which has good selectivity to iron, magnesium and aluminium, according to the company. ‘Typically tertiary amines are used to extract uranium but test work revealed a more robust organophosphoric compound was better suited due to the nature of the process solution which is practically free from ferric iron,’ adds Leif Rosenback, Chief Technology Officer.
The solvent extraction is followed by various washing stages and is stripped in mixer settlers, using soda ash. The uranium will be precipitated as a uranium peroxide using hydrogen peroxide. As yet, no ion exchange steps have been incorporated into the process and, although permitting requests are in progress, the project is still in basic engineering phase.
Further information: Talvivaara Materials World Magazine, 01 Apr 2010