The Effect of Gypsum on the Fixation of Selenium in the Iron/Calcium-Selenium Coprecipitation Process

The coprecipitation of selenium (IV) (Se) with iron (III) (Fe) is a widely practiced method for the removal of Se from mineral processing effluents, but the effect of gypsum as a major secondary mineral on the iron-selenium coprecipitation process is still of concern. In our work we first investigated the effects of pH, Fe/Se molar ratio and the neutralizing agent on the removal efficiency of Se by iron-selenium coprecipitation method. The developed two-step Fe-Se coprecipitation method (Fe/Se molar ratio of 4) was superior to the one-step Fe-Se coprecipitation method at pH 4 using CaO as base in terms of the stability of the generated Fe-Se coprecipitates. Raman experimental results indicated the iron-selenium coprecipitates had the by-product of calcium selenite. We then investigated the effect of incorporation of Se into gypsum on the coprecipitation process at different pHs. The fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM) of the calcium-selenium coprecipitates showed that the Se incorporated into the structure of gypsum at pH 8–10. Therefore, this work has important implications for the development of new technologies for efficient Se removal.