Nickel retention by goethite and hematite.
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The association of nickel with goethite and hematite is of importance for various processes concerned with nickel extraction. The adsorption of Ni2+(aq) by goethite and hematite in aqueous solutions were investigated over the pH range of 3 to 9. Similar tendencies were exhibited by both minerals. Firstly, an increase in nickel adsorption as the pH increased from 3 to 8 was observed. This can probably be attributed to the fact that the positively charged nickel cations are repulsed less by the oxide surfaces at higher pH values. Secondly, a sharp decrease in adsorption at pH > 8, due to a strong increase in nickel precipitation, was observed. Experimentally, it was found that goethite and hematite samples from different sources differed in terms of their ability to adsorb nickel over a 24 hour period. Examination of the physical characteristics of the samples used suggested that the ability to adsorb nickel is determined by their surface areas. In order to asses the importance of nickel inclusion, relative to nickel adsorption, into the mineral lattice of the iron oxide minerals under consideration, synthetic goethite and hematite were synthesised in the presence Ni2+(aq). These experiments were, however, less successful, and further work needs to be done in this area.