Lanthanides oxalate

While there have been many non-isothermal studies of the decompositions of lanthanide oxalates, fewer detailed kinetic investigations have been reported. The anhydrous salts are difficult to prepare. La, Pr and Nd oxalates decompose [1097] to the oxide with intervention of a stable oxycarbonate, but no intermediate was detected during decomposition of the other lanthanide oxalates. The product CO disproportionates exten-... 

The a—time curves for the vacuum decomposition at 593—693 K of lanthanum oxalate [1098] are sigmoid. Following a short induction period (E = 164 kJ mole-1), the inflexion point occurred at a 0.15 and the Prout—Tompkins equation [eqn. (9)] was applied (E = 133 kJ mole-1). Young [29] has suggested, however, that a more appropriate analysis is that exponential behaviour [eqn. (8)] is followed by obedience to the contracting volume equation [eqn. (7), n = 3]. Similar kinetic characteristics were found [1098] for several other lanthanide oxalates and the sequence of relative stabilities established was Gd > Sm > Nd > La > Pr > Ce. The behaviour of europium(III) oxalate [1100] is exceptional in that Eu3+ is readily reduced... 

Now the pressure-jump technique will be described with a system consisting of lanthanide oxalate complexes [17]. The technique used a sudden change in pressure to perturb the equilibrium and a conductivity bridge to detect and follow the changes in the system. The course of re-equilibration is recorded by the use of an oscilloscope and a camera. 

Formation kinetics of some lanthanide oxalate complexes [22], ... 

Continuous Precipitation of Actinide-Lanthanide Oxalates from HLLW... 

Figure 3. Equipment flowsheet for continuous precipitation of lanthanide oxalates...

Table II. Experimental Conditions and Results of Continuous Precipitation of Lanthanide Oxalates...

The behaviour of yttrium oxalate (573 K) was [82] generally similar to Aat of the lanthanide oxalates. No carbonate could be detected, suggesting that the carbonate is less stable than the oxalate. Carbon monoxide disproportionation proceeded to about 60%, accompanied by carbon deposition. 

Other hydrated salts include Sc2 (C2 04)3-61120, Sc (N03)3-4H20, and Sc2(S04)3-5H20 the structure of the oxalate shows approximately dodecahedral coordination of scandium by two water molecules and six oxygens from bridging oxalates. The oxalate is, unlike lanthanide oxalates, slightly soluble in water and also dissolves in excess oxalate as 80(0204)2. No structural data are available for the nitrate, although it should be noted that eight-coordinate Sc(N03)3(H20)2 and nine-coordinate Sc(N03)3(H20)3 molecules are present in crown ether... 

Fig. 14. Plot of the log of the formation rate constant, log f, of the lanthanide oxalate complex as a function of the inverse cation radius.

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