A combined Raman, Fourier transform infrared, and X‐ray diffraction study of thermally treated nesquehonite

Abstract Nesquehonite synthesized by mixing MgCl 2 ·6H 2 O and Na 2 CO 3 at T 25°C, was thermally treated at various temperatures (170°C, 200°C, 295°C, 350°C, and 390°C), based on thermal analysis study of raw nesquehonite. The mineral phases formed at each temperature were studied by means of Raman microspectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. After thermal treatment of raw nesquehonite above 295°C, its dominant Raman peak at 1,100 cm −1 , which corresponds to the v 1 CO 3 2− antisymmetric stretching vibrations, exhibits broadening and upshift of up to 10 cm −1 , whereas the Raman peaks at 707 cm −1 , at 770 cm −1 , at 1,425 cm −1 , and at 1,710 cm −1 disappear, and new Raman peaks arise at 1,282 cm −1 and at 1,386 cm −1 . The latter have been attributed to the decomposition of HCO 3 − , in accordance with the Fourier transform infrared spectroscopy study. According to the differential thermal analysis study, water of crystallization is lost in two steps until 295°C; therefore, the phase studied above this temperature corresponds to Mg (HCO 3 )(OH). The Raman peak at 3,550 cm −1 assigned to the existence of OH − , exhibits weakening after thermal treatment. Our results corroborate a Mg (HCO 3 )OH·2H 2 O nesquehonite formula.