Abstract The sorption of cobalt species from nitrate solutions on cation and anion exchangers was studied in aqueous and non-aqueous solutions. The absorption spectra of the various cobalt species sorbed were recorded. From these spectra it is seen that the tetrahedral ions Co(NO 3 ) 4 2− and [Co( X )(NO 3 ) 3 ]- are sorbed on an anion exchanger. The i.r. spectra of the same species show that the nitrato ion (0-NO 2 − is coordinated to the cobalt ion. Molar extinction coefficinets and oscillator strengths were calculated. These measurements and calculations show some evidence of a weak mononitrate complex sorbed on a cation exchanger. The formation of the tetrahedral nitrato complex on the exchanger from aqueous solution is discussed.