Zirconium sulfate precipitation

Abstract

Zirconium containing less than about 400 ppm aluminum/zirconium is produced by precipitating zirconium sulfate from an aqueous stream containing from 0.5 M to 2 M zirconium oxychloride and contaminated with from 1000 to 3000 ppm aluminum/zirconium and having an acidity of greater than 1.5 N total acid per M zirconium. Ammonium hydroxide having a concentration of at least 14% by weight is added to the zirconium-containing solution to adjust the acidity to between 0.6 and 1.2 N total acid/M zirconium. Because the acidity adjustment results in the premature and undesired precipitation of zirconium hydroxide and aluminum hydroxide, the solution is maintained at a temperature of 60.degree. C. or more for 15 minutes to 60 minutes to dissolve at least some of the zirconium hydroxide without permitting the undissolved zirconium hydroxide to dehydrate to the extent that a gelatinous zirconium oxide precipitate forms. Ammonium sulfate or sulfuric acid is then added to the acid adjusted solution to provide a 0.6 to 0.9 M sulfur/M zirconium ratio for precipitating zirconium sulfate from the solution without coprecipitating aluminum. After mixing the precipitation agent and the zirconium-containing solution together to precipitate some of the zirconium, the slurry is maintained at a temperature of between 90.degree. C. and the boiling point of the solution for at least 15 minutes to precipitate additional zirconium sulfate. The zirconium sulfate is filtered to produce an asfiltered cake contaminated with less than 400 ppm aluminum/zirconium.

Dependencies are inferred from the claim text.