Lanthanum solubility constant

The solubility of lanthanum, neodymium and gadolinium hydroxide has been studied over an extensive temperature range, with data available for neodymium hydroxide available from 0 to 300 °C. All three solubility constants vary linearly with respect to the inverse of absolute temperature (Figure 8.8). The enthalpies of reaction calculated from the linear relationships are all within 10% indicating a similar functionality of the solubilities as a function of temperature as would be expected. The calculated enthalpy of reactions are -137.2 3.8, -139.8 1.7 and -129.5 4.4 kj mol for lanthanum, neodymium and gadolinium hydroxide, respectively. 

Figure Solubility constant (log of LnfOHjjfs) (lanthanum, neodymium and...

Deberdt et al. (1998) measured the solubility of lanthanum hydroxide from 40 to 150 °C and from the data obtained estimated a solubility constant at 25 °C. The latter value is in reasonable agreement with that found in other studies (Akselrud... 

There have been very few studies on the hydrolytic reactions of actinium(III). There is only one study on the solubility of Ac(OH)3(s) (Ziv and Shestakova, 1965). These authors studied the solubility in a medium of 0.001 moll NH4NO3 and at 22 "C. They corrected for the activities of the ions in the solution and obtained a solubility constant of log A jio = 21.10 0.05. This value appears consistent with the solubility constants obtained for scandium(lll), yttrium(III) and lanthanum(III), with actinium(III) hydroxide as expected being the most basic. The solubility constant obtained by Ziv and Shestakova is retained in the present study for zero ionic strength and 25 C, namely,... 

Marked differences are observed between the properties of the halides. The trifluorides are stable in air at room temperature and are non-hydroscopic. They are sparingly soluble in water with solubility product constants which vary from 10 for lanthanum to 10 for lutetium (DaDilva and Queimado, 1973). In liquid HF, the solubilities are less than 4x 10 mole/ (Ikrami et al., 1972). At high temperatures the trifluorides react with oxygen and moisture to form the oxide fluorides, ROF, which are stable in air at temperatures greater than 1000°C. Conversion of the fluorides to the oxides may be achieved by heating in steam at 1000°C (Stezowski and Eick, 1970). 

The chemical behaviour of actinium will be similar to that of lanthanum. Data are only available for two monomeric hydrolysis species and the solubility of the hydroxide phase. The solubility of this phase can be described by reaction (2.13) (M = Ac, x = 0), whereas the hydrolysis constants can be described by reaction (2.5) (M = = 1) for actinium(lll) in reaction (2.5),, the number of hydrox-... 

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