Synthesis of protodolomite from coral reef sand

Protodolomite (calcium carbonate, PD) is widely used in calcium (Ca) and magnesium (Mg) nutritional supplements because it is rich in Ca (>20%) and Mg (>10%). Synthesis of PD usually involves the use of a NaCl solution with Ca2+ and Mg2+. In this study, we synthesized PD from coral reef sand (CRS) and magnesium chloride (MgCl2). First, CRS was dissolved in hydrogen chloride (HCl). MgCl2 was then added to the solution and the concentrations of Ca2+ and Mg2+ in the solution were adjusted to 150 and 350 mM, respectively. The solution was mixed with sodium carbonate (Na2CO3 = 156 mM) and incubated at 40 °C for 2 days in order to precipitate PD. The precipitate was identified as PD by X-ray diffraction analysis and atomic absorption analysis. This is the first study to synthesize PD from CRS, providing a new source of PD for the food industry.