Patent ID: 7514051

Claim:
A method for purifying aqueous crude sodium sulfate solution having from about 28 weight percent to about 38 weight percent sodium sulfate and at least one heavy metal impurity selected from the group of metals consisting of antimony, arsenic, iron, cadmium, lead, and combinations thereof, said method comprising: (a) adding ferric sulfate to said aqueous crude sodium sulfate solution to form a suspension; (b) progressively neutralizing said suspension from a pH of less than about 3.5 to a pH of greater than about 6 to form precipitate of ferric sulfate and said at least one heavy metal impurity, said progressively neutralizing comprising agitating said suspension at sustained pH increments, said progressively neutralizing further comprising testing a sample of said suspension for residual heavy metal impurities at a pH increment before incrementing said pH to a new pH increment in said suspension; and (c) separating said precipitate from said suspension.