Production of fumed silica

A method of producing fumed silica and a fluorine-containing compound from a source of silica and a solid fluoride-containing material selected from the group consisting of sodium aluminum tetrafluoride, cryolite, aluminum fluosilicate, ammonium bifluoride, sodium aluminum silicofluoride, and sodium fluosilicate, the method comprising the steps of:

• (a) digesting said silica and said solid material selected from the group consisting of sodium aluminum tetrafluoride, cryolite, aluminum fluosilicate, ammonium bifluoride, sodium aluminum silicofluoride, and sodium fluosilicate in a sulfuric acid digester at a temperature range of 100° to 300° C. to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor, said digesting being carried out for 30 to 180 minutes, said digester maintained under negative pressure;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester to a temperature in the range of 750° to 850° C. to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing fumed silica and a fluorine-containing compound from a source of silica and sodium aluminum tetrafluoride, the method comprising the steps of:

• (a) digesting said silica and said solid sodium aluminum tetrafluoride in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing fumed silica and a fluorine-containing compound from a source of silica and cryolite, the method comprising the steps of:

• (a) digesting said silica and said cryolite in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing filmed silica and a fluorine-containing compound from a source of silica and aluminum fluosilicate, the method comprising the steps of:

• (a) digesting said silica and said aluminum fluosilicate in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing finned silica and a fluorine-containing compound from a source of silica and ammonium bifluoride, the method comprising the steps of:

• (a) digesting said silica and said ammonium bifluoride in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing fumed silica and a fluorine-containing compound from a source of silica and sodium aluminum silicofluoride, the method comprising the steps of:

• (a) digesting said silica and said sodium aluminum silicofluoride in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said fumed silica from said hydrogen fluoride.

A method of producing fumed silica and a fluorine-containing compound from a source of silica and sodium fluosilicate, the method comprising the steps of:

• (a) digesting said silica and said sodium fluosilicate in a sulfuric acid digester to produce a gas component comprised of silicon tetrafluoride, hydrogen fluoride and water vapor;
• (b) removing said gas component from said digester;
• (c) heating said gas component recovered from said digester in the presence of an oxygen source to a temperature sufficiently high to convert said silicon tetrafluoride to fumed silica in the presence of said hydrogen fluoride;
• and
• (d) separating said filmed silica from said hydrogen fluoride.