Sample Preparation Guide pt7: Samples Containing Scandium

• The Metal
• Sc Oxide, Hydroxide, Carbonate
• Minerals and Ores
• Alloys
• Organic Matrices
• Hydrolytic Stability and Preferred Matrices
• Detailed Elemental Profile
• Further Reading

The Metal

Scandium (Sc) is a silvery white metal resembling aluminum and the Rare Earth elements. The metal is insoluble in NaOH or NH₄OH, reacts slowly with water, liberating H₂, and is readily soluble in acids forming the Sc⁺³ and Sc(OH)⁺² ions.

Sc Oxide, Hydroxide, Carbonate

The Sc oxide, hydroxide and carbonate are soluble in dilute acids where some heat is typically required. The ignited oxides are much less soluble. Most analysts prefer dilute (1:1) nitric acid.

Minerals and Ores

Scandium is very widely distributed in minute quantities in almost all rocks, but it is found in appreciable quantity in only a few minerals.

Since Sc minerals contain such a wide assortment of other elements, a variety of sample preparation methods exist including fusions with Na₂O₂, Na₂CO₃, Li₂CO₃ and Li₂B₄O₇. The fuseate is dissolved in dilute nitric or HCl. Consult the following method for the preparation of limestone for Ca, Mg, Fe, Al, Mn, and Si using a lithium carbonate fusion: Sample Preparation Procedure.

Lithium tetraborate (Li₂B₄O₇) has proven to be a very useful way of opening out any of the minerals associated with Sc. This fusion is carried out in Pt for ~ 10 minutes at 1000 °C and the fuseate is dissolved at room temperature by stirring with dilute (5 % v/v) nitric acid. When metal ions are present that are readily hydrolyzed, dissolution in the presence of EDTA in 0.01 M HCl is advantageous.

Many analysts prefer to acid digest/extract the mineral using 1:1 HNO₃ or 1:1:1 HNO₃/HCl/H₂O. The extraction is typically performed for 2-4 hours using heat. Both glass and Teflon vessels are commonly used. If silica is absent, an acid digestion/extraction is particularly useful.

Alloys

Sc metal is not used to a great extent, nor are it's alloys. Although commercial alloys are relatively rare, their dissolution can be effected using dilute nitric or nitric/HCl mixtures.

Organic Matrices

This includes a wide variety of materials including oil additives, petroleum matrices, coal, organic plant material, biological material, synthetic organics, etc. Samples can be digested with nitric/perchloric. For more detailed information about acid digestions of organics, please see the following article: Acid Digestions of Organic Samples.

It is also very acceptable to dry ash organic samples for Sc analysis in a Pt crucible and then bring the resulting oxides into solution using a sodium carbonate fusion or if Sc alone is sought, dissolution in dilute nitric or HCl. For more information, see the portion of our Trace Analysis Guide that discusses Ashing.

The following is a general guide for carbonate fusions:

1. Make certain that the sample is well mixed with the sodium carbonate.
2. A 5-9's pure sodium carbonate is recommended and available from EM Science.
3. Mix the sample with the flux at no more than a 1:20 ratio. Typical sample to flux ratios are in the 1:10 area.
4. If organic matter is present, either the sample is mixed with the flux initially and heated slowly to 500 °C for ~ 2 hours before bring up to full temperature, or the sample can be pre-ashed at 500 °C and then the ash mixed with the flux.
5. Use Pt as the crucible container material.
6. Perform the fusion at 1000 °C in a muffle furnace. Avoid flames since this fusion is difficult to perform in a flame due to the high melting point of the sodium carbonate.
7. Most fusions are complete in 15 minutes and some require up to 45 minutes.
8. Dissolve the fuseate in dilute HCl (1:1).

Hydrolytic Stability and Preferred Matrices

• Sc is particularly prone to hydrolysis due to its small ionic radius.
• Sc begins to precipitate from solution as Sc(OH)3 and ScO(OH) at a pH of between 2 (high conc. Sc) to 4 ( low conc. Sc).
• Scandium oxide, hydroxide, carbonate, fluoride, oxalate, and phosphate are all insoluble in water and neutral to basic media. The fluoride is readily soluble in excess HF forming the ScF₆^3-. The scandium hydroxide dissolves readily in NaOH.
• Sc sulfate is readily soluble.
• The following table shows the improvements in the hydrolytic stability of Sc⁺³ with different complexing agents. The pH where precipitation of ScO(OH) begins is shown for 0.1 M solutions of each complexing agent:

• Sc can be mixed with any of the elements at high concentrations (200 to 2000 µg/mL) with the exception of the fluoride containing elements (Ti, Zr, Hf, Nb, Ta, W, Si, Ge, Sn, Sb, Mo), unless excess HF is present. Moderate to low levels (≥ 100 µg/mL) can be mixed with all of the elements except low levels of fluoride (F^-). Sc is more stable in relatively high (> 5% v/v) levels of acid.
• Sc has a moderately complex emission spectrum primarily in the 200 to 450 nm region. A popular Sc emission line is the 440.037 nm line with a DL of ~ 0.002 µg/mL (axial view) because of it's relative freedom from spectral interference combined with high sensitivity.

Detailed Elemental Profile

Chemical compatibility, stability, preparation, and atomic spectroscopic information is available by clicking the element below. For additional elements, visit our Interactive Periodic Table.

Further Reading

• Part 8: Samples Containing Rare Earth Elements
• Sample Preparation Guide: Table of Contents
• More Guides and Papers