Saint Petersburg State Polytechnical University

L. V. Volkov, Professor

Gipronickel Institute Ltd

M. I. Kalashnikova, Head of Laboratory of Hydrometallurgy, e-mail: MIKal@nikel.spb.ru

Mechanism of nickel oxides dissolving by sulphuric acid has been proposed. The mechanism explains sharp acceleration of the process running at the solution redox potential of ~1.4 V created by the oxidants not participating in the reaction. In the above environment, reaction NiO dissolving takes place via formation and dissolution of NiO_x (1 < x < 2). Values of the both reactions’ equilibrium potentials have been calculated as x functions, and values of their over-voltage have been defined according to the model of the reactions speed control by the stage of charge’ transfer through the interphase’ surface. The calculations have revealed that the reaction maximum speed is achieved at х = 1.4–1.6, which corresponds to redox potential of 1.4 V. Deviation of x meaning from 1.4–1.6 results in the reduction of the dilution reaction speed. That is why dissolving of NiO or NiO₂ stoichiometric oxides runs at a lower speed.

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