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The determination by solution calorimetry of thermochemical data associated with the formation of environmentally important compounds such as lanthanide and actinide hydroxides, hydroxycarbonates and carbonates...requires the knowledge of the relevant cations in the medium- often hydrochloric acid solutions- selected for the dissolution of these compounds. Suprizingly enough, for a number of lanthanides, the data in such media are fragmentary and sometimes contradictory. In this paper, are reported new results on the enthalpy of solution of lanthanum, neodymium, gadolinium, erbium and lutetium, in hydrochloric acid solutions at concentrations up to 6 mol: dm(-3), using ultra high purity metal samples. The evolution of these enthalapies of solution as a function of the HCI concentration is discussed and compared to the corresponding literature data for trivalant actinides (mainly plutonium and americium). From the measurements of the enthalpies of solution of GdCI(3) (cr) and LuCI (3) (cr) in media ranging from 6.00 mol:dm(-3) HCI to 10(-3) mol:dm(-3) HCI, new values are reported for the standard molar enthalpies of formation of these compounds and of the gadolinium and lutetium ions. Based on these and other determinations which appeared recently in the literature, an evaluation of the status of the standard molar enthalpies of formation of several lanthanide trichlorides and ions is made.

Additional information

Authors: MERLI L, University of Liege (BE);RORIF F, University of Liege (BE);FUGER T, ITU Karlsruhe, Karlsruhe (DE)
Bibliographic Reference: Paper presnted: Migration 1997, Sendai (JP), October 26-31st, 1997
Availability: Available from DG XIII as Paper EN 41195 ORA
Record Number: 199910329 / Last updated on: 1999-03-12
Original language: en
Available languages: en