Abstract
The kinetics of extraction of Ni(II) in the Ni2+-SO4 2_AC- (Na+, H+)-Cyanex 272 (H2A2)-kerosene-3% (v/v) octan-1-ol system using the single falling drop technique have been reported. The flux of Ni2+ transfer (F) at 303 K in presence of 3% (v/v) octan-1-ol (de-emulsifier) can be represented as:.Depending on reaction parameters, the activation energy (Ea) and enthalpy change in activation (DH±) varies within 17 - 58 kJ/mol and 17 - 67 kJ/mol, respectively. Entropy change in activation (DS±) is always negative. Based on the empirical flux equation, Ea and DS± values, mechanisms of extractions in different parametric conditions are proposed. At low and [Ac-], and pH, the chemical controlled step is: Ni2+ + A- → NiA+; and this reaction occurs via an SN2 mechanism. But in most parametric conditions, the process is under intermediate control; and at high SO42- and [Ac-], and pH, the extraction process is under diffusion control.
Highlights
Cobalt has no natural deposit as its mine; and all nickel deposits contain invariably small proportion of cobalt
The Co2+/Ni2+ separation is a challenge to hydrometallurgists, who extract nickel following 1) leaching of ores, 2) purification of leach solution and 3) either reduction by hydrogen or electrolysis of purified solution
The purification of leach solution by solvent extraction is complicated by the difficult separation of Co2+ from Ni2+
Summary
Cobalt has no natural deposit as its mine; and all nickel deposits contain invariably small proportion of cobalt. In order to obtain purified nickel and to isolate cobalt, it is necessary to separate Co(II) from Ni(II). The Co2+/Ni2+ separation is a challenge to hydrometallurgists, who extract nickel following 1) leaching of ores, 2) purification of leach solution and 3) either reduction by hydrogen or electrolysis of purified solution. The purification of leach solution by solvent extraction is complicated by the difficult separation of Co2+ from Ni2+.
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