Influence of amorphous calcium carbonate on strontium ion removability from aqueous solution

Abstract

The Fukushima nuclear power plant accident caused an outflow of pollutants. Thus, precautionary measures must be taken by using preventive materials for the deterrence of such accidents. Herein, we aimed to develop inexpensive materials that can remove radioactive elements from an aqueous solution. We found that powders obtained from milling scallop shells, which were discarded in large quantities, removed Sr²⁺ from aqueous solutions. The Sr²⁺ removability of the scallop shell powder improved with milling time, indicating the influence of increase in the specific surface area on Sr²⁺ removability. Despite of the same specific surface area, the scallop shell powder exhibited higher Sr²⁺ removability than that of the unmilled CaCO₃. Differential scanning calorimetry evaluation for the investigation of factors other than the specific surface area revealed that the milled scallop shell powder contained amorphous calcium carbonate. Moreover, we synthesized amorphous calcium carbonate and found that it exhibited 60-times higher Sr²⁺ removability than that of crystalline calcium carbonate. We concluded that the amorphous structure of calcium carbonate significantly affects the Sr²⁺ removability from aqueous solutions. It was hypothesized that amorphous calcium carbonate removes Sr²⁺ by incorporating Sr²⁺ into the structure during crystallization in an aqueous solution.