The mobility of titanium and niobium during low temperature hydrothermal transformation and weathering of oxides of niobium (pyrochlore, lueshite) and titanium (rutile, anatase)

Abstract

Niobium and titanium are refractory metals, which are both included as impurities in the composition of many minerals and form their own ore minerals. These metals are considered inactive under conditions of low-temperature hydrothermal transformation and weathering, and their minerals are considered resistant to such processes. On the other hand, there is evidence of crystallization of niobium and titanium oxides during low-temperature transformations, which indicates the possibility of their mass transfer by solutions. A number of experimental works indirectly confirms this. However, the studies were carried out under conditions corresponding to earlier and high-temperature stages of the formation of magmatic objects for systems with simple composition. The present article presents the results of studies on the complex dissolution of rutile and anatase crystals mixed with pyrochlore or lueschite in 1.0 M solutions of HF, HCl, H₂SO₄ at 50 and 200 °C for 4 hours. Rutile and anatase turned out to be resistant to acids, and luesite was moderately resistant. Solutions of hydrochloric and sulfuric acids caused leaching of pyrochlore components. It was found that sulfuric acid solution has a more aggressive effect than hydrochloric acid solution, and this effect increases with increasing temperature. Exposure to fluoride solutions caused the replacement of pyrochlore with fluorite. At the same time, the solutions themselves were most intensively saturated with both niobium and titanium: during the experiments, >70% Nb₂O₅ and up to 3% TiO₂ from the initial amounts went into solution. It has been shown that under low-temperature conditions, a chloride solution is an unlikely agent for the mass transfer of titanium and niobium; sulfate solutions have the ability to dissolve and transfer the elements in question in significant quantities, but their effectiveness decreases with decreasing temperature; fluoride solutions have demonstrated the best ability to transport niobium and titanium.

Keywords:

rutile, anatase, pyrochlore, lueshite, weathering, mobility of niobium, mobility of titanium