Geochemical Journal, Vol. 12, pp. 183 to 189, 1978 183

Coprecipitation of borate-boron with calcium carbonate

YASUSHI KITANO1, MINORU OKUMURA2 and MASATOSHI IDOGAKI2

Water Research Institute, Nagoya Univ., Nagoya1 andFaculty of Literature and Science, Shimane Univ., Matsue2, Japan

(Received March 20, 1978; accepted in revised form April 19, 1978)

The behavior of borate-boron in a calcium bicarbonate parent solution during the precipitation ofcalcium carbonate has been studied experimentally.

The amount of borate-boron coprecipitated with calcium carbonate is proportional to the concentra-tion of borate-boron dissolved in a parent solution, and this relationship is affected by the crystal formof calcium carbonate precipitated and the concentration of sodium chloride dissolved in the parentsolution. Borate -boron is easily coprecipitated with aragonite rather than with calcite. These experimentalresults agree with the trend of boron content in carbonate skeletons of marine organisms such as bivalvedmollusks. There is a difference in the influence of sodium chloride dissolved in a parent solution on thecoprecipitation between calcite and aragonite: The amount of borate-boron coprecipitated with calciteincreases with increasing concentration of sodium chloride in a parent solution, whereas the amount ofborate-boron coprecipitated with aragonite decreases with increasing concentration of sodium chloridein the parent solution. This fact suggests that the mechanism of the coprecipitation of borate-boron withcalcite is different from that with aragonite. Borate-boron dissolved in a parent solution has little influenceon the crystal form of precipitated calcium carbonate.