Effect of thiosulfate, sulfide, copper(II), cobalt(II)/(III) and iron oxides on the ammoniacal carbonate leaching of nickel and ferronickel in the Caron process
Senanayake, G., Senaputra, A. and Nicol, M.J. (2010) Effect of thiosulfate, sulfide, copper(II), cobalt(II)/(III) and iron oxides on the ammoniacal carbonate leaching of nickel and ferronickel in the Caron process. Hydrometallurgy, 105 (1-2). pp. 60-68.
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Previous studies have related the low recovery of nickel and cobalt in the Caron roast-leach process to the formation of less reactive sulfides during roasting and/or the passivation or surface blockage of ferronickel by oxides and/or sulfides. This study examines the different types of reactions and background reagents which may affect the dissolution of nickel and ferronickel alloy in oxygenated NH3/NH4+/HCO 3- solutions at 45 °C based on equilibrium constants and measured leach results at a low solid/liquid ratio of 1 g/dm3. Some of the additives tested in the present study represent interim leach products. Initial leaching rates of nickel during oxygenation of presoaked Fe-Ni alloys decreases with increasing iron mole fraction. The Fe-Ni(45%) alloy continues to react and dissolve about 90% Ni over the first 15-40 min, depending upon the additives. In contrast, iron leaching reaches a broad maximum of ~ 10% over 20-35 min, or a sharp maximum of 6% after 5 min in the absence or presence of additives, respectively. This is followed by a decrease in iron extraction to ≤ 2% after 45-60 min due to the precipitation of red/black oxides and sulfides. Direct involvement of S2O32- and redox mediation by Cu(II) or Co(III) is evident from the enhanced initial rates of nickel leaching from Fe-Ni(45%) alloy in the order: O2/HS - O2 < O2/S2O32- < O2/Co(III)/S2O32- < O2/Cu(II)/S2O32-. While the added S2O32- has a detrimental effect on iron leaching, HS- retards the leaching of both iron and nickel from Fe-Ni(45%) alloy to < 1%. The final leaching of 95% Ni from Fe-Ni(45%) alloy after 3 h is unaffected by Fe2O3 and Fe3O 4, but FeOOH causes about 5% decrease in nickel leaching. Thermodynamics predict the passivation of nickel and ferronickel by M(OH) 3-MOOH as well as the formation of MFe2O4.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions|
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