EFFECT OF ORGANIC IMPURITIES ON NICKEL ELETROWINNING
Authors: FREIRE, N.H.J.1: [email protected] / [email protected]
MAJUSTE, D.1,2: [email protected]
CIMINELLI, V.S.T. 1,2: [email protected]
1- UFMG (Federal University of Minas Gerais – Department of Metallurgical and Materials
Engineering)
2- INCT – acqua (National Institute of Science and Technology on Mineral Resources, Water and
Biodiversity
The present work discusses the effect of some organic compounds, such as flocculant, SX diluent, SX
extractant, lubricating oil and an acid mist supressant on the current efficiency of nickel electrowinning and
on the product morphology. The electrowinning experiments were carried out using synthetic sulfate
solutions consisting of 80 g.L- 1 Ni2+ and 50 g.L-1 Na+ at pH 2.8 and 60 °C. 6 h electrowinning tests at 300
A/m2 indicated that low levels of organic contamination of the electrolyte do not affect considerably the
process. The current efficiency remained almost constant, within the experimental error, when 10 mg/L of
organic was added. On the other hand, in the presence of 50 or 100 mg.L -1 of extractant in the solution, the
current efficiency slight increased, while at similar concentrations of flocculant the current efficiency slight
decreased. When the acid mist suppressant was added, the current efficiency decreased 2 and 12% at 50 and
100 mg.L- 1, respectively. The cell voltage measurements revealed that the addition of organics to the
electrolyte does not significantly change this parameter; variations are within the experimental error. The
scanning electron microscopy analysis showed that the Ni deposits produced from solutions containing
extractant, flocculant, diluent and oil were smooth, compact, and bright, thereby indicating that the presence
of any of these organic compounds in the electrolyte did not have significant effects on the morphology of
the metal product, except at the higher concentration of extractant and oil. While pitting was observed for
the higher extractant and oil concentrations, the presence of 50 and 100 mg.L-1 of acid mist suppressant
resulted in low adhesion, peeling and cracking of deposits. Microhardness analysis of Ni deposits indicated
that the addition of flocculant and acid mist suppressant to the electrolyte increased the hardness.
Figure 1 – SEM micrograph of electrowon nickel produced at acid mist supressant concentration of
100mg.L-1.
95
Current Efficiency
94
93
92
Acid mist supressant
Flocculant
Extractant
Diluent
Oil
88
86
84
82
0
10
20
30
40
50
60
70
80
90
100
-1
Organic concentration (mg.L )
Figure 2 – Effect of organic impurities concentration on the current efficiency of nickel electrowinning.
KEYWORDS
Nickel electrowinning, Organic impurities, Organic coumpound.