Process for the preparation of very pure cryolite from sodium fluosilicate and ammonia

Abstract

Abstract D R A W I N G NA2SIF6+4NH4OH$2NAF+4NH4F+SIO2+2H2O A PROCESS FOR THE PREPARATION OF CRYOLITE STARTING FROM SODIUM FLUOSILICATE IS DISCLOSED WHICH INVOLVES THE STEPS OF: (A) A REACTION, AT TEMPERATURE BETWEEN 35*C. AND 80* C., OF SODIUM FLUOSILICATE WITH A DILUTE AQUEOUS SOLUTION OF AMMONIA, SAID AMMONIA BEING IN EXCESS OF 20-30% BY WEIGHT ON THE STOICHIOMETRIC QUANTITIES NECESSARY TO SATISFY THE REACTION: SO THAT THE FINAL PH IS BETWEEN 7.9 AND 9.2; THUS OBTAINING AN AQUEOUS SOLUTION OF SODIUM AND AMMONIUM FLUORIDES AND A PRECIPITATE OF SILICA. (B) SEPARATION OF SILICA. (C) TREATMENT OF THE SOLUTION OF SODIUM AND AMMONIUM FLUORIDES WITH A FERRIC SALT IN EXCESS WITH RESPECT TO THE SILICA AND PHOPHATE ION STILL CONTAINED IN THE SOLUTION, AND SEPARATING THE PRECIPITATED IMPURTIES. (D) INCOMPLETE PRECIPITATION OF THE CRYOLITE OBTAINABLE FROM THE ABOVE SOLUTION BY ADDING SODIUM METAALUMINATE IN AN AMOUNT LESS THAN THE STOICHIOMETRIC QUANTITY NECESSARY TO PRECIPTATE ALL THE CRYOLITE, SO THAT A SUBSTANTIAL QUANITY OF FLORIDE ION REMAINS IN THE SOLUTION. (E) RECYCLING OF ALL OR PART OF THE MOTHER LIQUOR OF THE CRYOLITE FOR REACTION WITH SODIUM FLOSILICATE.

Inventors

• 👤 Giovanni Cuneo
• 👤 Pietro Saccardo
• 👤 Giuseppe Muratori

Bibliographic Details