Samples Containing Rare Earth Elements

Hydrolytic Stability and Preferred Matrices

• The hydrolytic instability of the RE elements increases with increasing atomic number. The hydrolytic stability is related to the ionic radius, which decreases with atomic number (the lanthanide contraction). None of the RE elements are as prone to hydrolysis as is Sc, which has a smaller ionic radius than any of the REEs.
• For comparison purposes, Sc begins to precipitate from solution at a pH of between 2 (high conc. Sc) to 4 (low conc. Sc), whereas Ce begins to precipitate from pH 6 (high conc Ce) to 8 (low conc Ce) and Yb begins to precipitate from pH 5 (high conc Yb) to pH 7 (low conc Yb).
• The RE element oxides, hydroxides, carbonates, fluorides, oxalates, sulfates, and phosphate are all insoluble in water and neutral to basic media. The fluorides and oxalates are insoluble in dilute nitric acid. The fluorides may be dissolved in 1:4 nitric acid : water that is saturated with boric acid. The chlorides are soluble in water.
• The RE elements 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). Low levels (≤ 1 µg/mL) can be mixed with all of the elements, provided the nitric acid content is 5 to 10 % v/v. In general, the RE elements are more stable in relatively high (> 5% v/v) levels of acid.

Was this helpful?  Tell a Friend | Let us know