Preparation of Extra-pure Na2CO3 Powder with Crystallization Techniques for Low-Background Scintillation Crystal Growth

A method for the preparation of extra-pure Na2CO3 powder has been developed. The method is based on a fractional crystallization of Na2CO3 from its saturated solutions and its conversion into sodium formate, followed by a melt crystallization. To obtain the final product Na2CO3, the recrystallized sodium formate was thermally decomposed. The contents of Th and U in the purified powder were below 10 ppt, the concentrations of Mn, Co, Ba, and Pb were not above 3 ppb, the concentrations of Cu and Sr were on the level of tens of ppb, and the K concentration was about 200 ppb. The ICP-MS analysis showed that the purity of the obtained powder significantly surpasses that for commercial products in 99.997 and 99.999% purity grades. The sodium carbonate powder thus obtained is going to be used as initial material for growing scintillation single crystals in experiments searching for the neutrinoless double beta decay (0νββ) or dark matter.