ABSTRACT

The behavior of borate-boron in a calcium bicarbonate parent solution during the precipitation of calcium carbonate has been studied experimentally. The amount of borate-boron coprecipitated with calcium carbonate is proportional to the concentration of borate-boron dissolved in a parent solution, and this relationship is affected by the crystal form of calcium carbonate precipitated and the concentration of sodium chloride dissolved in the parent solution. Borate-boron is easily coprecipitated with aragonite rather than with calcite. These experimental results agree with the trend of boron content in carbonate skeletons of marine organisms such as bivalved mollusks. There is a difference in the influence of sodium chloride dissolved in a parent solution on the coprecipitation between calcite and aragonite: The amount of borate-boron coprecipitated with calcite increases with increasing concentration of sodium chloride in a parent solution, whereas the amount of borate-boron coprecipitated with aragonite decreases with increasing concentration of sodium chloride in the parent solution. This fact suggests that the mechanism of the coprecipitation of borate-boron with calcite is different from that with aragonite. Borate-boron dissolved in a parent solution has little influence on the crystal form of precipitated calcium carbonate.