Experimental study of the influence of SiO2 on the solubility of cobalt and iron in silicate melts

The solubility of cobalt and iron in silicate melts with variable SiO2 content was experimentally determined under controlled oxygen fugacity. It was shown that, independent of temperature and oxygen fugacity, the solubility of the two metals reaches a maximum ( minimum of CoO and FeO activity coefficients) in melts of intermediate compositions. The analysis of available published data demonstrated that the gamma(MeO) values of at least four metals (Ni, Co, Fe, and Cr) dissolving in melts as divalent oxides show a minimum in melts with XSiO2 approximate to 57 +/- 2mol %. The position of the minimum is essentially independent of the element, melt temperature, and oxide concentration ( from a few ppm to 13 wt %). The extremes of iron solubility (lambda FeO) in Fe-rich MgO-free melts may shift toward significantly lower values, although this inference requires additional experimental verification. Using a numerical example, some problems were discussed in the use of experimental data obtained in different laboratories for the development of a general model for the. MeO dependence on melt composition.