Limits of solution of trace elements in minerals according to Henry's law: review of experimental data

Results of a survey of experimental data on trace element partitioning between crystals and coexisting liquid and between crystals and coexisting aqueous fluid are reported. These studies involve combinations of elements such as Cs, Rb, K, Na, Li, Ba, Sr, Ni, and Sm dissolved in minerals such as feldspars, micas, feldspathoids, garnets, pyroxenes, amphibole, and olivine. It is shown that the concentration ranges of these elements in minerals with solution behaviour according to Henry's Law appear to extend to less than 1 wt.% and often to less than 100 ppm of the element in the crystalline phase. The available data indicate that the concentration ranges of solution in minerals according to Henry's Law can be positively correlated with the difference of ionic radii between trace element and the host element for which the tracer is assumed to substitute. Furthermore, studies involving crystals and coexisting aqueous fluid have been used to determine whether Henry's Law or Raoult's Law adequately describes the solution. Based on the assumption that the aqueous fluid solution can be considered ideal, models have been proposed stating that if the difference between the ionic radii of the tracer and the host element in the crystalline phase is less than about 10% (relative to the host element), the solution is ideal (Raoult's Law). With larger differences between the ionic radii, there is an excess free energy of mixing, although Henry's Law is still obeyed in the concentration ranges where crystal-fluid partition coefficients are independent of element concentration. (author)