The methods applied in this study are several methods that are used in combination to create a whole system. The most important are:
- The main simulation method used is system dynamics modelling (Sverdrup et al., 2022). We analyse the system using stock-and-flow charts and causal loop diagrams (Senge 1990, Sverdrup et al., 2022). The flow charts describe the mass balances used in the model. The causal loop diagrams show the causal links and feedbacks in the system. The flow charts and the causal loop diagrams are used for constructing the system dynamics model.
- Program the scandium system into a system dynamics tool. The simulation model for the mass flows and economics of extraction, production and cycling of scandium in society, as a part of the WORLD7 model. The mass balance differential equations are numerically solved using the STELLA® Architect software. The zirconium and hafnium module was integrated into the WORLD7 model system (For a full explanation of the WORLD7 model, see Sverdrup et al., 2019a,b,d, 2021, Sverdrup and Olafsdottir 2019, and Olafsdottir and Sverdrup 2020).
- Parameterize the coefficients and constants of the model.
- The scandium demand was generated from a combination of potential future uses and general economic development. Identify the available sources of scandium and the estimate the available amounts that can be extracted, considering extraction technologies and the cut-off and costs of extraction as related to the market price. The reserves and resources estimates for the source metals are based on geological estimates, the interpretation of geological data, and the allocation of extractable amounts according to ore quality, considering yields and extraction costs (Sverdrup and Olafsdottir 2019, Sverdrup and Ragnarsdottir 2014, Sverdrup et al., 2018, Krautkraemer 1988). For the methodology of estimating the reserves and resources for metals, the works of Singer (2007) and Singer and Menzies 2010 was instructing. They use the geological characteristics of known and detected metal resources to predicts the amount of undiscovered resources, and estimating the amounts on a deposit-by-deposit basis.
- Validate the total model performance on historical data. The WORLD7 model is confined by mass balance and energy balances, and all parameterizations have a real world connection. The parameterization is based on measured or estimated parameters, leaving small room for free adjustments.
- Make model simulations for the system. Run the Business-as-usual scenario as a basis.
- Make sensitivity analysis for increased demand in the future. Finally, the model outputs are interpreted, the results studied and draw out consequences for the future.
4. About scandium production and resources for extraction
Scandium is found mainly in two minerals, there are no substantial occurrences of these in volume that would justify industrial mining, the minerals are called Thortveitite ScYSi2O7 and Kolbeckite ScPO4·2H2O (Nilson 1879a,b, Neumann 1961, Kristiansen 2003, Steffensen et al., 2020, Segalstad and Raade 2003). Madagascar and in the Iveland-Evje and Tørdal regions in Norway have the only deposits of Thortveitite and Kolbeckite minerals with high scandium content (Kristiansen 2003, Wilhelmsen 2020), but none these are being exploited at present. The typical scandium deposit is found as small isolated pockets in pegmatite formations and is not easy to exploit in an industrial way, even if they supply beautiful mineral samples. The dominating source of scandium is secondary extraction, from waste products after bauxite processing (Ackil et al., 2018, Altinsel et al., 2018). A smaller amount comes from scandium mining and from extraction from laterite soils (Altinsel et al., 2018, Botelho et al., 2020). Deposits with industrial potential are known from China, Kazakhstan, Australia, United States and Russia (Kristiansen 2003, Brown 1999). Chinese deposits are in tin ores, tungsten ores, and iron deposits and Rare Earth Element deposits The Russian deposits are associated with Rare Earth Element deposits and uranium mining. The Norwegian and Madagascan deposits are associated with gabbro and pegmatite formations, but are not used for production. Scandium is currently produced by calcio-thermic reduction of ScF3, which is obtained by fluorination of the oxide (Ackil et al., 2018). These are two reactions:
Sc2O3 + 6 HF → 2ScF3 + 3 H2O
2 ScF3 + 3 Ca → 3 CaF2 + 2 Sc
First scandium fluoride (ScF3) is produced from the scandium oxide (Sc2O3) and minerals by dissolution in hydrofluoric acid, then in a next step the metal is produced as a precipitate. The product is melted and distilled to produce either dendritic scandium or 99.9% pure cast scandium ingots. Use of scandium in aluminium alloys makes them harder, usual contents are 0.5-2%. With scandium, aluminium alloys can be given properties similar to titanium, but with only 25% of the specific weight. A probable market would be military aviation technologies.
Scandium is not really a very rare element in terms of occurrence, the average crustal content is 22 ppm. Scandium does not really participate in the processes that normally concentrate metals in ores, and thus, it is very rare to find deposits with higher concentrations of scandium (DeCarlo and Goodman 2003). Thus, there are very few scandium mines, and none are significant.
The largest producers are as far as is known Russia, Ukraine, Kazakhstan and China. The United States have mined scandium in the past, but at present no running operations are known. The dominating use in 2022 was for solid state fuel cells and aluminium alloys. We estimate the annual production to be about 35 ton/year in 2022, in 2014, it was about 15 ton/year (Riva et al., 2016). Alloys based on scandium, titanium, zirconium and hafnium are also being developed. These would serves as hybrid superalloys, probably suitable for military hardware (Riva et al., 2016).
About 80 kg/yr of scandium is used in metal-halide lamps/light bulbs globally per year. The alloy Al20Li20Mg10Sc20Ti30 is as strong as titanium, is as lightweight as aluminium, and as hard as some ceramics (Youssef et al., 2015). When bauxite is processed for making alumina (Al2O3), two types of waste are produced: red mud (a solid waste) and a Bayer liquid. From the red mud, scandium, iron ore, titanium oxide and yttrium can be extracted. From the Bayer liquid, gallium, indium and germanium can be extracted. One ton of bauxite normally yields 0.2 ton of aluminium. The scandium resources were estimated from the equation (Sverdrup and Olafsdottir 2023, Sverdrup et al., 2023):
Where M is the available mother metal or ore amount, X is the amount of scandium in that material and Y is the extraction yield for obtaining it from the total resource. Y consists of the access yield, the utilization yield (it is reachable, but how much of the possibility is utilized), and the extraction yield.
Table 1 shows guess-assisted estimates of production volumes of scandium production in 2022. About 65% of the total volume is used as metal for alloys. The rate of scandium recycling is unknown, there are no numbers found in any of the references.
Figure 3 shows some of the available data for scandium contents in bauxite used for scandium extraction in Russia (Boyarintsev et al., 2022). For other mother materials, only anecdotical information is available (Duyvesteyn et al., 2014). The ranges found are for uranium 1-10 ppm in the ore, corresponding to 110-200 per uranium content. For tinstone, a scandium content of 125-200 ppm is given, for zirconium about 50-120 ppm, 12 ppm in ilmenite or about 22 ppm per titanium content (Ackil et al., 2018, Botelho et al., 2020, 2021, Borra et al., 2016). An estimated 12,000 ton of scandium is believed to be present in primary Australian deposits that would support scandium mining. What is shown in Table 1 is what will be explored and broadened with the model simulations. The total primary scandium resources may be of the order of 30,000-40,000 ton of scandium content.
Table 2 shows the resource estimates for scandium as done by the authors. For Rare Earth Element deposits there are some more data points and the contents vary a lot, from as low as 26 ppm to more than 110 ppm in India and China, other locations have averaged at 220-400 ppm, but some deposits may have as much as 2,000 ppm (Phoung et al., 2023, Kalashnikov et al., 2016). Single deposits have significantly higher contents in smaller sections of the ore bodies (Ulrich et al., 2019, Wang et al., 2021). None of this is geostatistically representative for whole regions, and only represents single random samples. Thus, the data is tentative. The available data and information has been used to make educated guesses. The estimated yields are very variable.
Table 1. Estimates of production volumes of scandium production in 2022. Most scandium secondary resources are co-located with bauxite and rare earth element deposits.
|
Country
|
Total
2022
|
Metal
2020
|
Forecast
2030
|
Scandium
resource
ton
|
Source of Scandium
|
Reference, where did the information come from?
|
Ton/year
|
China
|
12
|
8
|
80
|
?
|
REE, Ti, Zr, Sn, W, Bauxite
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999, Cordier 2022. Acil et al., 202018. No public information available on resources.
|
United States of America
|
1
|
5
|
80
|
?
|
REE, mining, Nb, Cu
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999, Cordier 2022. Potential for about 70 ton/year scandium in ongoing project from a Nb-Ta-Sc mining project in Nebraska.
|
Russia
|
10
|
7
|
16
|
?
|
REE, U, Fe, Y, Bauxite
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999, Boyarintsev et al., 2022, Naumov 2008, Cordier 2022, Arbuzov et al., 2014
|
Philippines
|
7.5
|
5
|
15
|
?
|
Ni, Cu
|
de Carlo and Goodman 2003, Gambogi 2021, Cordier 2022
|
Canada
|
3
|
?
|
6
|
?
|
Ni, Cu
|
Gambogi 2021, Cordier 2022
|
Australia
|
?
|
?
|
6
|
12,000
|
REE, Ti, Bauxite, some mineral deposits
|
de Carlo and Goodman 2003, Gambogi 2021, Cordier 2022. Rio Tinto 2023a,b.
|
Malaysia
|
4
|
3
|
5
|
?
|
REE
|
Wikipedia, Cordier 2022
|
Kazakstan
|
3
|
0
|
3
|
?
|
REE
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999
|
Finland
|
?
|
?
|
3
|
2,200
|
Ni, Zn, Cu
|
Gambogi 2021, Cordier 2022
|
South Africa
|
1
|
0
|
3
|
?
|
Ni
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999
|
Ukraine
|
1
|
0
|
2
|
?
|
U, Fe
|
de Carlo and Goodman 2003, Gambogi 2021, Brown 1999
|
Norway
|
0.05
|
0.025
|
5
|
6,000
|
Scandium minerals
|
Kristiansen 2003, Sverdrup and Ragnarsdottir 2014, Neumann 1961
|
Madagascar
|
0
|
0
|
?
|
2,000
|
Scandium minerals
|
Kristiansen 2003
|
Others
|
2.5
|
3
|
5
|
?
|
Secondary
|
Cordier 2022
|
Sum
|
42
|
31
|
220
|
6,000,000
|
-
|
Taken from Table 2
|
Data on yields are only available for fly-ash and bauxite (Duyvesteyn et al., 2014, Naumov 2008, a low value of 15-20% is given). The other yields have been guessed looking at extraction yields for other secondary metals like indium (Sverdrup et al., 2023), germanium or tellurium from different mother metal refining wastes. Values given scandium contents in mother metals ore are approximate, and only mother metal ores in the high end of the scandium content range are used for scandium extraction at present (Williams-Jones, and Vasyukova 2018). In Table 2, we estimate the total scandium extraction potential to be 6 million ton. The yields reported are very variable and come from a small number of studies. The raw scandium metal trades at 70% of the price of a 99.99% scandium metal ingot. The oxide trades at 1.6% of the metal price. The metal price for 99.99% (Electronics grade) has been systematically in the range of 185,000-210,000 $/kg, but occasionally higher. In April 2023 the price was 348,000 $/kg and 517,000 $/kg (Scrapmonster 2023). The price is comparable to the price of the platinum group metals such as rhodium or iridium. The high price effectively prevents any mass use or meaningless applications in mass produced consumer goods. Very little information on global scandium production is available. Information on the processes from taking scandium from different substrates is available (Gosh et al., 2023, Salman et al., 2022). Examples are for bauxite waste extraction (Ackil et al., 2018, Botelho et al., 2020, 2021, Gu et al., 2018), Rare Earth Element mining (Borra et al., 2016, Ribagnac et al., 2017), from nickel-cobalt mining wastes (Altinsel et al., 2018, Chernoburova and Chagnes 2021, Kaya et al., 2017), from coal and coal ash (Arbuzov et al., 2014), from titanium substrates (Gao et al., 2019, Zhou et al., 2008, Zhou et al., 2021).
Table 2. Results for resource basis for scandium production. Resource estimates for indium as estimated by the authors. The estimated yields are very variable and approximate. Real data on yields are only available for scandium extraction from fly-ash and bauxite (Duyvesteyn et al., 2014, Naumov 2008). Mother ore contents are approximate, and only ores in the high end of the range are used for extraction at present. No scandium is extracted from coal fly-ash at the moment, and no plans to do so exists. The scandium content in the refining waste is normally higher than in the raw ore.
|
Mother metal
|
Resource
million ton
|
Contents, ppm Sc
|
Resource ore grade, ppm Sc
|
Potentially
extractable, ton
|
Extraction yield
2023
%
|
Extractable
amount, ton
|
Yield
2030
%
|
Extractable
amount, ton
|
Nickel
|
700
|
10-100
|
30
|
2,100
|
50
|
1,050
|
70
|
1,500
|
Uranium
|
16
|
40-110
|
80
|
1,280
|
50
|
740
|
70
|
900
|
REE
|
310
|
500-2,000
|
800
|
248,000
|
65
|
161,200
|
70
|
174,000
|
Bauxite
|
112,500
|
10-110
|
55
|
4,500,000
|
7
|
337,500
|
20
|
900,000
|
Coal ash
|
40,000
|
5-100
|
30
|
1,200,000
|
5
|
60,000
|
10
|
120,000
|
Yttrium
|
24
|
2,000-20,000
|
3,000
|
72,000
|
65
|
46,800
|
70
|
50,000
|
Titanium
|
1,570
|
5-10
|
60
|
34,540
|
40
|
13,816
|
70
|
24,000
|
Scandium deposits
|
0.1
|
30,000-100,000
|
40,000
|
101,000
|
65
|
65,000
|
80
|
80,000
|
Sum
|
|
|
|
6,158,920
|
11
|
686,106
|
22
|
1,350,000
|
Scandium comes mostly from secondary extraction from major metal primary extraction operations, and there are very few scandium mines being operated. Scandium is mined in the sense that some mines are multi-metal mines, where no single metal can alone cover the extraction and mining costs. The United States Geological Survey (Gambogi 2021, Cordier 2022, Hedrick 1996, Brown 1999) reports that they have no real numbers on total scandium production and resources. They guess that the world production of scandium is in the order of 15-20 ton per year, in the form of scandium oxide (Sc2O3). Numbers for production rates and resources are withheld in the United States, Russia and China. Scandium was apparently to 80% produced from TiO2 pigment processing residuals in China (Zhou et al., 2022). Many projects are under way (Rio Tinto 2023a,b are one example), but not very much is known about the projects in the USA, Russia and China. Apparently, it appears as the use of scandium is of military strategic importance. From different extractions, mainly the scandium oxide is extracted. Scandium metal is made from scandium oxide by reduction with either calcium metal, magnesium metal or lithium metal (Boyarintsev et al., 2022). The scandium demand is higher, and both the scandium production and demand keep increasing (Boyarintsev et al., 2022).
Table 3. Results for resource basis for scandium production. Production estimated from mother metal production rates and assumed average scandium content at present as estimated by the authors. Exact production data are not available for the research community (Hedrick 2022). 1-average content, 2-content in Chines deposits, 3-content in Australian deposits (Williams-Jones, and Vasyukova 2018).
|
Mother metal
|
Production
mill ton/yr
|
Content
ppm Sc
|
Potential,
ton/yr
|
Yield
%
|
Potential extraction
ton/yr
|
Fraction of potential used, %
|
Extraction 2023
ton/yr
|
Nickel
|
3.5
|
60-110
|
385
|
50
|
167
|
0.6
|
1
|
Uranium
|
0.100
|
60-110
|
11
|
50
|
6
|
0.18
|
1-2
|
REE
|
0.220
|
1,000-2,000
|
440
|
65
|
285
|
2
|
6-8
|
Bauxite
|
100
|
50-100
|
5,000
|
15
|
750
|
2.7
|
20
|
Fly-ash
|
150
|
10-25
|
1,500
|
15
|
225
|
0
|
0
|
Yttrium
|
0.006
|
20,000
|
120
|
65
|
78
|
19
|
15
|
Titanium, world
Titanium, China
Titanium, Australia
|
3
0.8
0.2
|
221
1002
2003
|
66
80
40
|
40
65
60
|
14
52
24
|
7
|
1-2
|
Sum secondary
|
|
|
7,559
|
0.6
|
1,596
|
3
|
44-48
|
Primary mining
|
5
|
0.2
|
5
|
85
|
4
|
-
|
3
|
Sum all
|
|
|
7,564
|
|
1,600
|
|
47-51
|
In 2003, three mines produced scandium as a by-product (Naumov 2014):
- Ukraine: uranium and iron mines in Zhovti Vody
- China: the rare earth mines in Bayan Obo
- Russia: the apatite mines in the Kola peninsula; yttrium extraction from the mineral loparite can yield scandium as a by-product
After 2003, scandium is mostly produced from red mud after bauxite processing, and from titanium and nickel processing residuals (Williams-Jones, and Vasyukova 2018, Rio Tinto 2023). Every site only produce small amounts, measured in kg/yr rather than ton/yr. Since then, many other countries have built scandium-producing facilities (United States of America, Canada, Malaysia, Philippines). In each case, scandium is a by-product from the extraction of other elements and is sold as scandium oxide. The absence of reliable, secure, stable, and long-term production of scandium has limited commercial applications of scandium, beside the fact that the scandium metal is at present in the same price range as precious metals like gold and rhodium. Despite this low level of use, scandium offers significant benefits. Particularly promising is the strengthening of aluminium alloys with as little as 0.5% scandium. Scandium-stabilized zirconia enjoys a growing market demand for use as a high efficiency electrolyte in solid oxide fuel cells. The potential for extraction is about 7,400 ton/year of scandium content. At present access and opportunity fraction, and at present chemical extraction yields, the maximum production would be about 1,500 ton/year. Total scandium extraction yield from potentials are very low (About 11%, see Table 2), and it would probably be feasible to increase that to 40% on average, allowing a scandium production of about 3,700 ton/year, where probably 3,500 ton/year would be scandium metal. Increasing the yield to 65% would allow for a scandium production of 4,810 ton/year. The approximate scandium production was estimated with (Sverdrup and Olafsdottir 2021, Sverdrup et al., 2023):
where ri is the rate of extraction of the mother material i, with yield Yi and mother metal scandium content fraction Xi. Table 3 shows the approximate scandium production potentials from the different possibilities. Production estimated from mother metal production rates and assumed average scandium content at present as estimated by the authors.