In-situ Raman analysis of the precipitation sequence of sulphate minerals using small droplets: application to Rio Tinto (Spain)

Raman spectroscopy has been used for a comparative study of the sulphates mineral sequence precipitation in Rio Tinto (Huelva, Spain) under natural and laboratory conditions. In natural conditions spectra were performed in-situ with portable instruments. In laboratory, spectra were performed using a simulator of the riverbank conditions and also small droplets of liquid on different substrates. The capability of the micro-Raman spectroscopy to detect in a fast and reliable way the mineral phases at the mineral grain scale allow a precise identification of these phases as function of time. The use of small droplets increases this capability reducing the experimental time and allowing reproducing the process under greater supersaturation conditions. Finally, a series of computer modeling algorithms have been developed to compare the experimental process with the theory based on the equilibrium properties of the solutions and precipitation kinetics.