Lanthanide Solid Phase Speciation
1985
Essington, M. E. | Mattigod, S. V.
The solid phase speciation of La, Ce, and Nd in the Ln₂O₃-CaO-SO₄-PO₄-F-O₂-CO₂-H₂O (where Ln = La, Ce, and Nd) equilibrium system were evaluated using three-dimensional activity diagrams. Diagrams were constructed from thermodynamic data and interpreted with a knowledge of the ligands associated with La, Ce, and Nd in sewage sludge and sludge-amended soil particles as characterized by scanning electron microscopy. Throughout a wide range of equilibrium conditions at 298.15 K and 0.101 MPa, the activities of dissolved lanthanides were controlled by a small number of solid phases. These solids were cerianite [CeO₂], lanthanite [La₂(CO₃)₃·8H₂O] and Nd-lanthanite [Nd₂(CO₃)₃·8H₂O], and La and Nd sulfates [(La,Nd)₂(SO₄)₃·8H₂O] in the presence of gypsum. In general, the stable lanthanide solid phases predicted from the thermochemical evaluation were consistent with those directly observed in chemically well-defined sewage sludge and sludge-amended soil; thus, illustrating the applicability of such an evaluation when applied to well characterized environments.
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