Download Recovery of Scandium from Lateritic Nickel Ores

UCTEA Chamber of Metallurgical & Materials Engineers
Recovery of Scandium from Lateritic Nickel Ores
Proceedings Book
Ece Ferizoğlu¹,², Şerif Kaya¹, Yavuz Topkaya²
¹Middle East Technical University, ²Meta Nikel Kobalt A.Ş. - Türkiye
Abstract
The aim of this study was to extract and recover scandium
from a lateritic Ni-Co ore by means of hydrometallurgical
techniques. Nickel laterites are very important type of
nickel ore deposits and they also contain considerable
amount of scandium in addition to nickel and cobalt.
Scandium is the most important and strategic metal that
can be obtained as a by-product from lateritic ores. In this
research, as a result of two-step pH controlled purification
processes, a scandium enriched concentrate was obtained
during mixed nickel-cobalt hydroxide precipitate (MHP)
production process. After these precipitation processes,
the obtained precipitate was leached by sulfuric acid and
the experiments showed that considerable amount of
scandium could be taken into the leach solution.
1.
Introduction
Scandium, which is classified as a rare earth element, is
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crust. It is mainly substitutes for major elements in the
minerals such as; iron, aluminum. Thus, due to low
concentration and complex structure of the mineral,
scandium can generally be recovered as a by-product from
effluents, wastes, slags and so on. The main valuable
scandium resources are effluents or slags which form
during processing of uranium, iron, tungsten, nickel, tin,
titanium, zirconium, tantalum, aluminum and other rare
earth elements.[1] The annual production of scandium is
around 5-12 tons and the price of 99.9% Sc2O3 ranges
between 2000-3000$ per kg[2] The production rate cannot
reach to high levels due to the main supply of scandium as
a by-product of other metals.
In spite of the low availability, various uses of scandium
have been identified up to the present. However, scandium
cannot be produced with high production rate and as a
result of this in the literature; the application of scandium
is classified in mainly three different areas. The first and
widespread consumption area of scandium is in aluminum
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alloys. It is stated that the addition of small amount of
scandium (0.1-0.8%) into aluminum improves corrosion,
mechanical and welding properties [3]. Al-Sc alloys are
generally used in fighter jets, aerospace industry and high
technical sporting equipment. Since scandium has low
availability at the present, Al-Sc alloys are generally used
in the area where the performance is much more important
than the cost. If the price of scandium can be reduced by
developing new and easier methods of production of
scandium, the industrial uses of Al-Sc alloy will increase
due to high potential for the use of this alloy in many areas
such as, sporting goods, aerospace and automotive
industries. The other consumption area of scandium is in
solid oxide fuel cells as solid electrolytes. The addition of
scandium oxide into stabilized zirconium oxide in the fuel
cells improves the long term stability of the electrolyte,
enhances the conductivity, allows low operating
temperatures and extends operating life. Finally, since
scandium can provide replication of sunlight effectively,
its compounds can be used in lighting applications such as
high intensity vapor lamps which are used in stadium
lights and in studios for the film and television industry.
Scandium can be also recovered as a by-product from the
hydrometallurgical extraction process of lateritic nickel
cobalt ores. The high pressure sulphuric acid leaching
(HPAL) behavior of typical lateritic ore was studied
previously [4]. The studied lateritic ore contained 106 g/t
scandium and 80.6% scandium in the ore could be
extracted into leach solution together with nickel, cobalt
and other impurities. The analysis of the obtained leach
solution (PLS) is given in Table 1.
During MSP (Mixed Sulphide Precipitate) method or
MHP (Mixed Hydroxide Precipitate) method, this type of
solutions (pregnant leach solutions) can be processed for
the recovery of nickel and cobalt as intermediate product.
In MSP method, hydrogen sulphide gas is directly used in
treatment of solution in order to precipitate mixed sulphide
product of nickel and cobalt. On the other hand, in MHP
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method, the control pH and temperature of the solution are
important to remove the impurities from the solution
before the precipitation of nickel and cobalt by MgO.
Figure 2. For this aim, a synthetic leach solution was
prepared according to the data given in Table 1.
Table1. Conc. of PLS and the prepared synthetic solution
Element
PLS Comp. (mg/L)
Synt. Soln. (mg/L)
Nickel
Cobalt
Scandium
Iron
Aluminum
Chromium
Manganese
Magnesium
Copper
Zinc
5502
321
34
1688
3985
342
2110
1285
28
73
5827
371
30
1814
4317
150
2056
1369
29
74
According to Figure 1, which is based on the solubility
product data of ions at 25ƒC, the precipitated cations with
increasing pH can predicted. As a result of hydrolysis
reactions in the solution, precipitation occurs in the
following order: Fe(III) > Al(III) > Sc(III) > Cr(III) > Cu(II) >
Fe(II) > Zn(II) > Ni(II) > Co(II) > Mn(II) > Mg(II) > Ca(II). The
conventional MHP process generally consists of two
impurity removal steps. The aim of the first step is to
eliminate some of the Al (III), Cr (III) and most of the Fe
(III). This step is carried out between 80-95ƒC. In the
second impurity removal step, the remaining Fe(III),
Al(III) and Cr(III) are removed by increasing pH to 4.5 5.0 at around 60ƒC. After these two steps, nickel and
cobalt are precipitated from the purified solution at a
higher pH in order to obtain mixed hydroxide product.
Figure 1. The solubility product data of ions at 25ƒ&
according to molar concentration of ions [5]
According to Figure 1. scandium is predicted to be
precipitated in the second impurity removal step. Thus, the
aim of the study is the recovery of Sc from an MHP Circuit
without affecting conventional production route given in
Figure 2. Conventional MHP Circuit
2.
Experimental Procedure
Synthetic solution as given in Table 1 was prepared by
reagent grade salts of existing ions in order to investigate
the behavior of metal ion with changing pH. Precipitation
experiments were performed in two steps by using a hot
plate with magnetic stirrer and a four-necked glass
balloon, for condenser, temperature, pH measurement and
reagent addition.
In the first step of the precipitation, in order to stabilize the
pH and temperature at desired value, small amounts of
CaCO3 slurry (25g/100cc water) was added by
micropipette to avoid excessive pH increase at a local
point. At the end, the slurry was filtrated by a Buchner
funnel and a vacuum pump. After filtration, the solid
remaining in the Buchner funnel was washed with deionized water at suitable pH to avoid precipitation. Then,
in order to make mass balance, the solid and liquid
samples were analyzed with ICP-OES. According to
experiment results of the 1st impurity removal step, the
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suitable pH was determined and the stock solution was
prepared at this pH in order to use it for the second
impurity removal stage. In the second step of the
precipitation, small amounts of CaCO3 slurry
(12.5g/100cc water) was added into previously prepared
stock solution using the same procedure.
The aim of the study was to obtain maximum scandium
precipitation and recovery with minimum nickel and
cobalt co-precipitation. In accordance with the aim of the
study, the optimum pH was determined for each
precipitation step and then the scandium enriched
precipitate was tried to be re-leached under the determined
optimum conditions.
3.
Results and Discussion
1st Impurity Removal
The aim of the 1st impurity removal part of the study was
to obtain maximum amount of iron and limited amounts of
aluminum and chromium precipitations with minimum
nickel, cobalt and scandium losses.
Proceedings Book
a stock solution was prepared as a result of series of
experiments which were performed at pH 2.75 and the
analysis of this solution is given in Table 2.
Table 2. Chemical composition of stock solution obtained
after 1st impurity removal step
2nd Impurity Removal
The main aim of the second precipitation stage in
conventional MHP process is to remove impurities still
remaining after the first impurity removal step with the
minimum nickel and cobalt precipitations. However, since
the aim of the study was to provide maximum scandium
precipitation with minimum nickel and cobalt losses, the
pH of this step should be chosen with respect to
precipitation behavior of scandium.
Figure 4. Precipitation behavior of the metal ions with
increasing pH at constant temperature (60ƒC) for 180
minutes
Figure 3. Precipitation behavior of metal ions with
changing pH at 90oC for 120 minutes
According to Figure 3, in which precipitation behavior of
the metal ions is given with respect to pH, the significant
Ni and Co precipitation occurred after pH 4.00 and the
removal of impurities increased with increasing pH.
However, the aim of the study was to provide also
minimum scandium loss and scandium precipitation
started to increase after pH 2.75. For example, at pH 2.75
about 8% scandium precipitated, but it increased to about
26% at pH 3.00. As a result, it can be said that pH should
be controlled very carefully for avoiding scandium loss.
Thus, pH of the 1st impurity removal stage was chosen to
be as 2.75. In order to use for the other parts of the study,
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According to Figure 4, scandium can be precipitated and
separated from MHP circuit up to pH 4.25. On the other
hand, the nickel and cobalt precipitations start to increase
at pH values higher than 4.75. Because of this reason, the
selection of pH as 4.75 will be the best choice for the
precipitation and separation of scandium from MHP
circuit. After this determination, a series of experiments
were performed at 60ƒC, pH 4.75 for 180 minutes.
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Table 3. Composition of precipitate and the solution
obtained after 2nd impurity removal step
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in order not to increase acid consumption and amount of
impurity elements in the solution.
4.
According to Table 3, at which the composition of the
obtained precipitate and the solution remaining after
precipitation are given, the initial concentration of
scandium in the ore could be increased to 703 g/ton in the
precipitate and the removal of impurities such as; iron,
aluminum and chromium was achieved.
Scandium Re-leaching
For the extraction of scandium, Sc enriched precipitate,
which was obtained in the previous part of the study,
should be re-leached in sulphuric acid. The aim of this part
of the study was to achieve maximum scandium extraction
with minimum impurity dissolution. In order to investigate
these conditions for re-leaching, in which the maximum
amount of scandium with limited impurities can be releached, a series of agitation leach experiments were
conducted with 0.2 solid to acid- water mixture ratio at
60ƒC for 60 minutes. The metal concentrations of re-leach
solution and the leaching parameters are given in Table 4.
Thus, according to the experimental findings, if 1st
impurity removal step is conducted at 90ƒC, pH 2.75 for
120 minutes and 2nd impurity removal is done at 60ƒC, pH
4.75 for 180 minutes, scandium can be precipitated and
separated efficiently from MHP circuit with minimum
nickel-cobalt losses after two-step pH controlled
precipitation process. After the precipitation and
concentration, scandium can be re-leached efficiently, if
the re-leach process is conducted at 60ƒC for 60 minutes
with 100 g/L of H2SO4 acid with 0.2 solid to acid-water
mixture ratio. In the future, scandium is being planned be
recovered from the purified re-leach solution by ion
exchange and/or solvent extraction methods.
Acknowledgements
The authors would like to express their special thanks to
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and financial support given.
References
[1]
Table 4.The analysis of re-leach solution and re-leaching
parameters
[2]
[3]
[4]
According to Table 4, it can be said that the concentration
of all of the elements in the re-leach solution increased
with increasing acid concentration. High amount of
scandium could be extracted with minor impurity
dissolution with the addition of 100 g/L H2SO4 acid. Thus,
although scandium extraction might increase with further
increase in acid addition, 100 g/L acid seems to be suitable
Conclusion
[5]
Semenov, S., Reznik, A., & Yurchenko, L.
(1983).Scandium extraction at
complex
processing of different type of raw material by
Semenov, S.A.; Reznik, A.M.; Yurchenko, L.D.
Tsvetnye Metally, 15(10), 12th ser., 43-47.
Riggall, S. Australian scandium supply - A
paradigm shift for a strategic metal in AeroMat
2015. Long Beach, California.
Duyvestyeyn, W. P. (2012). U.S. Patent No. US
2012/0207656. Washington, DC: U.S. Patent and
Trademark Office.
.D\DùDQG7RSND\D<$ High pressure acid
leaching of a nickel laterite ore to extract
scandium. in ERES 2014- 1st International
Conference on European Rare Earth Resources.
2015. Milos Island, Greece.
Franzen, S., Solubility Product Constants Online
Database. 2015, NC State University.
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