Alkaline metal fluoride synthesis as a subproduct of beta-spodumene leaching

GUSTAVO D. ROSALES; MARÍA DEL CARMEN RUIZ; MARIO H. RODRIGUEZ

HYDROMETALLURGY (AMSTERDAM)

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 139 p. 73 - 78

0304-386X

This paper investigated the development of new techniques to recover fluorine as three valuable fluorides:cryolithionite (Li3Na3Al2F12), sodium hexafluorosilicate (Na2SiF6) and cryolite (Na3AlF6). The synthesis of thesecompounds was carried out through three routes: I) by precipitation "in situ" during the leaching processof beta-spodumene at different temperatures and different HF concentrations, to produce Li3Na3Al2F12; II) by precipitationadding NaOH to the leach liquor of beta-spodumene, to produce Na2SiF6 and Na3AlF6; and III) by coprecipitationfrom pure reagents, to separately produce Li3Na3Al2F12, Na2SiF6 and Na3AlF6. Reagents and productswere characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), atomic absorption spectroscopy(AAS), scanning electronic microscopy (SEM) and electron probe microanalysis (EPMA). The experimental resultsindicate that the production of the fluorinated compounds was possible. Following route I), an enhancementof the crystal size was observed after increasing the concentrations of HF. It was also observed that adecrease in temperature favors precipitation of the solid. Furthermore, the presence of Na+ fromalbite (gangue)was essential for the formation of Li3Na3Al2F12. The compounds Na2SiF6 and Na3AlF6 were synthesized togetherusing route II), with a recovery of 92%. Through route III) the three compounds were synthesized separately andthese compounds were used as standards for XRD analysis.