Lanthanide Solid Phase Speciation

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Abstract
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.
Funding Information
  • Water Resources Center, University of Minnesota

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