Method for the production of iron oxide pigment or pigment intermediate and hydrochloric acid

A method for producing hydrochloric acid and a metal precipitate with reduced or substantially eliminated waste streams, the method comprising:

• providing a metal chloride solution;
• neutralizing the metal chloride solution with one or both of ammonia and ammonium hydroxide to form a slurry of a metal compound solid component and an ammonium chloride solution;
• separating the metal compound solid component from the ammonium chloride solution, wherein the metal compound solid component is a metal precipitate;
• reacting the ammonium chloride solution with an alkaline-earth metal solid to form an alkaline-earth metal chloride solution and to evolve ammonia as a vapor, wherein at least a portion of the evolved ammonia reacts with water to form ammonium hydroxide;
• recycling one or both of the evolved ammonia and the formed ammonium hydroxide for use in connection with the neutralization step;
• and
• pyrohydrolyzing the alkaline-earth metal chloride solution to form hydrochloric acid and to regenerate the alkaline-earth metal solid.

A method for producing an iron pigment and hydrochloric acid with reduced or substantially eliminated waste streams, the method comprising:

• providing an iron chloride solution, wherein the iron chloride solution includes one or both of iron (II) chloride and iron (III) chloride;
• neutralizing the iron chloride solution with one or both of ammonia and ammonium hydroxide to form a slurry of an iron oxide solid component and an ammonium chloride solution;
• separating the iron oxide solid component from the ammonium chloride solution;
• drying and calcining the iron oxide solid component to form an iron pigment or pigment intermediate;
• reacting the ammonium chloride solution with an alkaline-earth metal solid to form an alkaline-earth metal chloride solution and to evolve ammonia as a vapor, wherein at least a portion of the evolved ammonia reacts with water to form ammonium hydroxide, and wherein the alkaline-earth metal solid includes one or more of magnesium oxide, magnesium hydroxide, magnesium oxychloride, calcium oxide, or calcium hydroxide;
• recycling one or both of the evolved ammonia and the formed ammonium hydroxide for use in connection with the neutralization step;
• pyrohydrolyzing the alkaline-earth metal chloride solution to form hydrochloric acid and to regenerate the alkaline-earth metal solid, wherein a concentration of the formed hydrochloric acid is between about 22 wt % and about 36 wt %;
• and
• recycling at least a portion of the regenerated alkaline-earth metal solid for use in the reaction with the ammonium chloride solution.