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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.
1 Contribution of the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521. Support by the Univ. of California and the Water Resources Center, as part of Water Resources Project UCAL-WRC-W-85, is gratefully acknowledged. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at the Univ. of California, Riverside.
2 Former Graduate Research Assistant and Graduate Fellow, Univ. of California, Riverside, presently Scientist II, Western Research Institute, Univ. of Wyoming Research Corp., P. O. Box 3395, Laramie, WY, 82071, and Assistant Professor of Soil Science, Univ. of California, Riverside, CA, respectively.
Received for publication February 7, 1985. Accepted for publication July 12, 1985.
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