Phosphate Induced Metal Stabilization

using Apatite II



The development of Apatite II resulted from Wright's original work from the 1980's in paleochemical oceanography where she used rare earth elements and trace metals sequestered in the fossil apatite mineral of conodonts, the original marine organism that developed the first teeth and bone structures made of hydroxycalcium phosphate. Her research showed that once deceased and fallen to the sediment/water interface in the ocean, the apatite absorbed trace metals and elements from the seawater, concentrated six to ten orders of magnitude above ambient concentrations, and locked in for geologic time, in the face of subsequent changes in aqueous chemistry, diagenisis, burial and uplift, heating and erosion, for over 500 million years. Notably, the relative elemental concentrations in the original waters, e.g., the rare earth element pattern, was maintained even with the elevated concentrations. Concentrations of metals like Ce relative to La and Nd could be used to determine the redox state of the original waters in which the organism lived as well as for other aqueous chemical properties, such that chemostratigraphic correlations could be done across these ancient ocean basins.

Subsequent studies on all types and sources of apatite in the 1990's by Wright showed that the apatites from fish bones and teeth were the optimal form of apatite for metal remediation because of its unique structural and chemical properties, sorbing and removing up to 20% of its weight in metals like Pb, U, Cu, Zn, Cd and Mn. This type of apatite is non-weight-bearing and highly substituted with carbonate and Na but with no F, having random nanocrystals of well-crystallized apatite in a matrix of poorly-crystallized and amorphous hydroxycalcium phosphate. This combination provides high surface reactivity as well as seed crystals for precipitation of metal-apatite phases such as pyromorphites and autunites. This work dovetailed nicely with others such as Nriagu and the Ohio State University group lead by Traina and Logan whose seminal works determined the precipitation mechanics of Pb on apatites. Further work with the organic constituents in the fish bones broadened their application to other metals and contaminants such as anions and organics.

Read more in these papers:



 Variation in ocean redox through time using the Ce-anomaly and trace metals sequestered in fossil apatite.


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