Advanced Materials Research Vols. 634-638 (2013) pp 258-262
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.634-638.258
Recovery of nickel and cobalt from dimethyldithiocarbamate
precipitation of pyrolusite leaching process
Haifeng Su1,a, Boji Li1,2,b, Qing Lu3,c, Yanxuan Wen1,d,
Jing Su1,e
1
School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
2
Guangxi Institute of Metallurgy, Guangxi University, Nanning 530023, China
3
Guangxi Vocational & Technical Institute of Industry, Nanning 530004, China
a
[email protected], [email protected], [email protected], [email protected],
e
[email protected]
Keywords: nickel, cobalt, dimethyldithiocarbamate, oxidative leaching
Abstract. Dimethyldithiocarbamate precipitation is a secondary resource containing nickel and
cobalt, which are formed by adding sodium dimethyldithiocarbamate to purify the neutralized
filtrate of pyrolusite reductive leaching process. The extraction of nickel and cobalt from
dimethyldithiocarbamate precipitation was investigated using nitric acid as oxidant in dilute sulfuric
acid medium in this paper. The effects of concentrations of nitric acid and sulfuric acid, leaching
temperature as well as reaction time were discussed. The results showed that high nickel and cobalt
recovery could be obtained by analyzing the leaching efficiencies of nickel and cobalt during the
leaching process. The optimal leaching condition was 1.47 mol/L H2SO4 and 1.16 mol/L HNO3 for
30 min at 45 °C while using particles smaller than 0.420 mm. And the leaching efficiencies were
98% for Co and 95% for Ni, respectively.
Introduction
Nickel and cobalt have the advantage of excellent corrosion resistance, high melting temperature
and strong magnetism. They are important raw materials for the manufacture of special steel,
heat-resisting alloy, corrosion resistant alloy, magnetic alloy and cemented carbide. These products
are widely industrial applied in aviation spaceflight, machine facture, electric instruments and
chemical industry. Hence, nickel and cobalt are considered as strategic resources[1,2].
Many efforts have applied recently to develop a commercial hydrometallurgical process to
recover cobalt and nickel from different secondary resources such as laterite tailings[3], copper
residue[4], low-grade Ni–Cu sulfide tailings[5], waste from the production of electrolytic zinc and
cadmium[6], spent nickel oxide catalyst[7], spent battery material[8], spent Ni–Cd batteries[9],
waste dusts generated by the glass industry[10]. Because the main existing form for cobalt and
nickel is sulfide, it is an effective way to improve leaching efficiency using the oxidant assist
leaching including deep-sea manganese nodules[11], sodium persulfate[12] oxidation roasting[13],
oxygen in high pressure[14].
China owns abundant manganese resource, with some trace constituents like Co and Ni in
manganese ore. Generally after crush, gravity separation, magnetic separation of pyrolusite, Mn
content with a grade of 20% can be obtained. And the contents of Ni and Co in it are 0.01%～
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Advanced Materials Research Vols. 634-638
259
0.10% and 0.01%～0.08% respectively. Metals in this manganese ore form metallic sulphate by
sulfuric acid leaching. Dimethyldithiocarbamate are organic compounds with strong reducing
capacities in their sulfide ions, and metal complexing has an affinity for removing dissolved metals
from liquor[15]. Dimethyldithiocarbamate precipitation[16,17] is formed by adding sodium
dimethyldithiocarbamate into the neutralized filtrate of pyrolusite reductive leaching process. Me2+
(metallic cation included Ni2+ and Co2+) and dithiocarbamate anion to form chelate[18].
Dimethyldithiocarbamate，this chelate has the property of low charge and relative small dentate
distance, the resonant structure of it’s anion are:
Because there are two equivalent partial double-bonds in the predominant structure (Ⅲ) for
dimethyldithiocarbamate. One is the carbon-nitrogen bond and the other is the carbon-sulphur bond
with negative ion.This resonant structure (Ⅲ) can form bidentate ligand with a lot of metal ion [19].
And cation is released by the oxidation of dimethyldithiocarbamate [20].
In this paper, the experimental studies were carried out on the leaching processes of cobalt and
nickel from the dimethyldithiocarbamate precipitation using nitric acid as oxidant in dilute sulfuric
acid medium, and the effect of concentrations of nitric acid and sulfuric acid, leaching temperature
and reaction time were investigated.
Materials and methods
Materials.
The sample of cobalt and nickel within dimethyldithiocarbamate precipitation was obtained from
CITIC (China International Trust and Investment Corporation) Dameng Mining Industries Ltd,
Guangxi, China. Within the precipitation a big portion of cobalt and nickel existed in the form of
Co(C3H6NS2)2 and Ni(C3H6NS2)2[18] . The general formula is showed by
C
S
N
C
S
M
C
S
C
C
S
N
C
( M represents cobalt and nickel ).
The precipitation sample was crushed and ground to the required particle size smaller than 0.420
mm (> 40 mesh). The precipitation material was also chemically analyzed for its major and minor
elements shown in Table 1. All the reagents and chemicals were analytical grade and used without
further purification.
Leaching procedure.
The leaching experiments were carried out in a 250 mL three-neck flask immersed in
thermostatically controlled water bath with mechanical stirring. In a typical experiment, 10.0 g of
sample was added to 50 mL H2SO4-HNO3 mixture with stirring (~200 r/min) at 45 oC, keeping the
solid : liquid ratio as 200 g/L. The initial concentrations of H2SO4 and HNO3 were 1.47 mol/L and
1.16 mol/L, respectively. After 30 min, the slurry was filtered and the residue was washed with
distilled water. The filtrate was poured into 500 mL volumetric flask and bring to volume by
laboratory-pure water, then it was diluted to 100-fold for analysis. The Co and Ni concentrations
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Advances in Chemical, Material and Metallurgical Engineering
during the leaching process were measured by an atomic absorption spectrometry (AAS, TAS-990
Persee).The leaching efficiency was calculated by referring the amount of leached metal in the
liquor to its original input quantity. All the experiments were repeated twice.
Table 1 Chemical composition of dimethyldithiocarbamate precipitation material
Component
wt.%
Co
0.75
Ni
1.16
Mn
6.15
Fe
4.88
Ca
7.56
Mg
1.50
Cu
0.041
Cr
0.035
S
16.01
Results and discussion
Effect of nitric acid concentration on leaching efficiency.
Nickel and cobalt dimethyldithiocarbamate precipitations cannot be leached by the sulfuric acid
directly. But their negative ions possess the capability of reduction. In order to obtain high leaching
efficiency of nickel and cobalt, it is necessary to add oxidants into the acidic solution.
A series of leaching experiments was carried out by varying concentrations of nitric acid from
0.00 to 1.44 mol/L, with the H2SO4 concentration fixed at 1.47 mol/L. It was shown in Fig.1 that
both leaching efficiencies of Co and Ni increased with the increasing of nitric acid concentration.
Nowever, the growth rate of nickel was faster than that of cobalt, and the reason is not fully
understood, but it is believed that cobalt is hard to be released in the oxidation because of the
semidiameter of cobalt is bigger than that of nickel and cobalt can form hexa-coordinate.
The strong oxidizing property of nitric acid destroyed the structure of metal
dimethyldithiocarbamate, lead to the exposure of it’s core which is hard to be passiviert. Hence, the
solution of the ore was accelerated [2]. When the concentration of nitric acid was low, reducing
substance in the dimethyldithiocarbamate precipitation consumed the oxidant, as the concentration
of oxidant has raise to a level, Co2+ and Ni2+ were released.
When the nitric acid concentration was 1.16 mol/L, cobalt and nickel were almost completely
dissolved. So an initial nitric acid concentration of 1.16 mol/L was sufficient to leach cobalt and
nickel dimethyldithiocarbamate refered to the precipitation efficiently.
Effect of temperature on leaching efficiency.
Metal extraction from the dimethyldithiocarbamate precipitation also tightly depends on reaction
temperature. When temperatures were increased from 35 to 75 °C, the leaching efficiencies of Co
increased from 49 % to 98 % shown in Fig. 2. However, there is little change in Ni with the
efficiency of 95 %. Considering the equipment and leaching cost, the leaching temperature should
not be higher than 45 °C.
The dilute nitric acid was assumed to be reduced to NO2, but this NO2 was reduced forward to
NO before escaping from the reaction system[20]. In addition, nitric acid is volatile acid. With the
increase of temperature, the escape of NO2 and volatilization of nitric acid was fiercer. For this
reason, both the concentrations of oxidant and the extraction ratio decreased.
Advanced Materials Research Vols. 634-638
261
100
100
80
90
Leaching efficiency, %
Leaching efficiency, %
Effect of sulfuric acid concentration on leaching efficiency.
The result of leaching experiments at different initial H2SO4 concentrations (0.00 to 1.84 mol/L)
was shown in Fig. 3. The result demonstrates that the leaching efficiencies of Co and Ni increased
with the increasing of H2SO4 concentration. When the acid concentration were 1.47 mol/L for Co
and 1.10 mol/L for Ni, this two metals were almost completely dissolved. Increasing the H2SO4
concentration from 1.47 to 1.84 mol/L had slightly improved the leaching efficiency. Therefore, an
initial H2SO4 concentration of 1.47 mol/L is sufficient for the complete recovery of cobalt and
nickel.
Co
Ni
60
40
20
80
Co
Ni
70
60
50
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
30
40
Concentration of HNO3, mol/L
50
60
70
80
o
Temperature, C
Fig. 1 Effects of HNO3 concentration on
the leaching efficiencies of Co and Ni.
Fig. 2 Effects of temperature on the
leaching efficiencies of Co and Ni
100
100
80
80
Leaching efficiency, %
Leaching efficiency, %
Effect of time on leaching efficiency.
Fig. 4 presents the effect of leaching time (< 60 min) on the leaching efficiencies of Co and Ni at
45 °C. The other leaching conditions were fixed in the experiments. Enough leaching time helped
the extraction of Co which raise to 98% after 30 min. The effect of time on leaching efficiency of Ni
was different from that of Co, there was little change for Ni with a higher efficiency after 10 min.
Hence, oxidative leaching process for 30 min at 45 °C could be considered as optimum. And the
leaching efficiencies under this condition were 98 % for Co and 95% for Ni.
Co
Ni
60
40
20
0
0.0
60
40
20
0
0.4
0.8
1.2
1.6
2.0
Concentration of H2SO4, mol/L
Fig. 3 Effects of H2SO4 concentration on
the leaching efficiencies of Co and Ni
Co
Ni
0
10
20
30
40
50
60
Time, min
Fig. 4 Effects of time on the leaching
efficiencies of Co and Ni
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Advances in Chemical, Material and Metallurgical Engineering
Conclusions
An oxidative leaching process for a dimethyldithiocarbamate precipitation has been successfully
demonstrated using a mixture of sulfuric acid and nitric acid as oxidant. The results indicate that the
leaching efficiencies of Co and Ni increase with the H2SO4 and HNO3 concentration and reaction
time increase. Metal extraction from the dimethyldithiocarbamate precipitation depends on the
reaction temperature. The optimum leach conditions were 1.47 mol/L H2SO4 and 1.16 mol/L HNO3
at 45°C for 30 min. Under these conditions, the recovery of cobalt and nickel was 98 % and 95%
respectively.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (No.
51164002 and No. 21166003), the Doctoral Discipline Foundation of China Ministry of Education
(No.20114501110004) and the Province Science and Technology Key Projects of Guangxi
(11107021-1-4,11107021-4-4).
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