Samples Containing Strontium or Barium

Minerals and Ores

Since the ores contain such a wide assortment of other elements it is considered best to prepare them by fusion with either lithium carbonate in graphite crucibles or sodium carbonate in Pt crucibles. If barium sulfate is present, the fusion converts it to the barium carbonate and the corresponding sodium sulfate, which can be leached out from the fuseate with water prior to dissolution of the fuseate in dilute HCl. The following method is for the preparation of limestone for Ca, Mg, Fe, Al, Mn and Si using a lithium carbonate fusion but can be applied to samples high in Sr and Ba: Sample Preparation Procedure.

The following is a general guide for sodium 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 E.M. 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 deg 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).

When Ba is associated with sulfate as BaSO₄ or the fluoride, it is suggested that the analyst fuse the sample with H₃BO₃ or B₂O₃ . This fusion is carried out in Pt crucibles at 1000 °C where the sample to flux ratio is at least 1:8 and can be as high as 1:30. The SO₃ is expelled due to the high temperature of the acidic melt. The MF₂ is opened out by this fusion procedure and the fluoride is tied up with the boron, making the dissolution of the fuseate in water or dilute acid possible without reformation of the MF₂.

Lithium tetraborate (Li₂B₄O₇) has also proven to be a very useful way of opening out many of the ores associated with Ba and Sr. 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 that are readily hydrolyzed are present, dissolution in the presence of EDTA in 0.01 M HCl is advantageous.

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