Your problem looks technological, I mean a large scale process. Besides, I can guess that you have solid impure sodium sulfate. In this case, the patent you cite may be useful if you adapt it to the composition of the impurities (the patent was intended for purifying the thenardite mineral without dissolving it). Therefore, you need to know the composition of the impurities quite accurately. According to this patent, anhydrous sodium sulfate is obtained. Decahydrate can be obtained by recrystallization. Carbonates and fluorides are relatively easy to remove, but you need to think about what to do with waste sodium chloride containing about half the sodium sulfate by mass.