The Problem of Limestone Phosphatization
in Light of Experimental Studies

G. N. Baturin¹ and A. V. Savenko²

¹Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
²Geographical Faculty, Moscow State University, Moscow, Russia

Received December 6, 2000

Abstract—In order to estimate the possibility of limestone phosphatization upon contact with seawater, two
series of experiments have been performed—with respect to the solubility of natural phosphates and to the
phosphorus precipitation from solution over a carbonate phase. In the experiments on the solubility of the oce-
anic phosphorites and phosphatized rocks at temperatures of 5.5–17.5°C and pH values of 7.8–7.9, the phos-
phorus concentration in seawater ranged from 0.039 to 0.338 mg P/l. The minimum solubility is characteristic
of the ancient crystallized phosphates from seamounts, while the greatest solubility was observed for the
younger and less crystallized samples. The experiments on phosphorus precipitation in the presence of CaCO₃
showed that, at a dissolved phosphorus content in seawater up to 3 mg/l, it may be sorbed over a solid phase
without forming its own mineral; the latter is rapidly formed only if magnesium is removed from the solution.
In magnesium-free seawater, the phosphate precipitation proceeds at a dissolved phosphate concentration
greater than 0.9–1.2 mg P/l. The results of the experiments suggest that limestone phosphatization in seawater
occurs at the contact with the interstitial water during the diagenesis of the sediments beneath the water–bottom
interface rather than at the contact with the near-bottom seawater.

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