Investigation of the Properties of Hard Clam （Mercenaria mercenaria） Shells as a Source of Calcium-based Materials

Abstract

Hard clams （Mercenaria mercenaria）, an invasive species in Japan, are increasing in population every year. In this study, we discussed the effective utilization of discarded hard clam shells by analyzing their properties. X-ray diffraction patterns and Fourier transform-infrared absorption spectra of powdered shells confirmed their structure to be of a single-phase aragonite-type. In addition, to improve the crystal quality of calcium carbonate, the powdered shells were dissolved in 35.0–37.0 % hydrochloric acid to prepare a calcium solution and exposed to CO₂ and NH₃ gases in order to reprecipitate high value-added calcium carbonate. X-ray diffraction measurements of the obtained reprecipitated calcium carbonate showed the formation of a single-phase calcite-type structure. The particle shape was uniformly spindle-shaped, and the particle size was approximately 5 μm. The dissolution and reprecipitation of the hard clam is expected to avail calcium carbonate that can act as a valuable industrial source for calcium-based materials.