Dissolution reactivity of NiO obtained by calcination of pure and contaminated Ni-hydroxides

Samples of pure and contaminated NiO were prepared by air-calcination of hy droxides precipitated from NiSO4 solutions containing admixtures of Al, Cr, Cu, Fe, Mn and/or Zn with solution of NaOH at pH = 8-8.5. The samples were calcined for 2 to 3 h at temperatures ranging from 600 to 900 degrees C, T he resulting oxide mixtures contained substituted NiO and several other pha ses, such as MnO2 after calcination at 600 degrees C and corundum and spine l oxides of trivalent metals at 700-900 degrees C. These oxides were dissol ved in 0.5 or 1 M H2SO4 at 40, 60 or 80 degrees C to investigate the possib ility of recovering Ni from this oxide mixture. The dissolution curves were fitted to the modified Sestak-Berggren kinetic equation (MSB). The overall rate of dissolution of Ni from NiO contaminated by a single metal ion was found to decrease in the following order Zn similar to Mn > Cu > Al > Fe much greater than Cr The effect of a combination of the substituents cannot be directly predicte d. For example, the inhibiting effect of the trivalent metals on NiO dissol ution reactivity was less pronounced in the presence of Mn. The prospect of applying this approach of dissolution kinetics to the recovery of Ni from industrial wastes warrants further investigation. (C) 1999 Elsevier Science B.V. All rights reserved.