Densities and apparent molal volumes of some aqueous rare earth solutions at 25.deg.. I. Rare earth chlorides

Apparent molar heat capacities and apparent molar volumes ofY2(SO4)3(aq),La2(SO4)3(aq),Pr2(SO4)3(aq),Nd2(SO4)3(aq),Eu2(SO4)3(aq),Dy2(SO4)3(aq),Ho2(SO4)3(aq), andLu2(SO4)3(aq)atT= 298.15 K andp= 0.1 MPa

“…(8) It should be apparent from the brief summary above that thermodynamic information for the rare-earth ions in aqueous chloride and sulfate solutions is needed in order to understand the hydrometallurgical extraction of the REEs from natural minerals, and to model the solubility and speciation of fission product waste dissolving into ground water or natural brines. Assessed values are available for the thermodynamic formation constants of RCl 2+ (aq), RSO + 4 (aq), and R(SO 4 ) − 2 (aq) complexes at T = 298.15 K. (5,7) Fairly comprehensive sets of thermodynamic measurements are already available for the RCl 3 (aq), excluding CeCl 3 (aq) and PmCl 3 (aq), at T = 298.15 K. (9)(10)(11)(12)(13)(14)(15)(16) More recently, Xiao and Tremaine (17) reported apparent molar volumes and apparent molar heat capacities of LaCl 3 (aq) from T = (283.2 to 333.2) K. Other thermodynamic measurements are summarized in the following paragraphs.…”

“…Fairly extensive density information is available for most of the RCl 3 (aq), R(ClO 4 ) 3 (aq), and R(NO 3 ) 3 (aq) at T = 298.15 K. (9,10,12,17,(49)(50)(51)(52)(53)(54) Because these electrolytes are either essentially uncomplexed {R(ClO 4 ) 3 (aq)}, slightly complexed {RCl 3 (aq)}, or moderately complexed {R(NO 3 ) 3 (aq)} at the lower molalities, their V φ can be extrapolated to infinite dilution to obtain values of V • φ (R 3+ , aq, 298.15 K). Some of these densities were measured with pycnometers, (10,12,(49)(50)(51) others with a magnetically controlled float, (9,52) and the remainder with vibrating-tube densimeters.…”

“…Some of these densities were measured with pycnometers, (10,12,(49)(50)(51) others with a magnetically controlled float, (9,52) and the remainder with vibrating-tube densimeters. (17,53,54) The latter two types of measurements are capable of much greater precision than pycnometric measurements, and thus may yield much more reliable values of V • φ {R 3+ , aq, 298.15 K}.…”

“…Only pycnometric measurements are available for yttrium salts. (10,12) Table 9 lists the references for all the experimental values of V φ used for evaluating the parameters of equation (10).…”

“…In contrast, values of V φ for La(NO 3 ) 3 (aq) through Gd(NO 3 ) 3 (aq) exhibit positive deviations from the DHLL as a result of larger amounts of complex formation. (9,52) Because the largest deviations from additivity occur for values of V • φ (R 3+ , aq, 298.15 K) calculated from the V φ of the lighter R(NO 3 ) 3 (aq), for which the extent of complex formation is greatest, these deviations seem to be due to residual effects of complex formation that are not removed by the extrapolations of equation (10). Consequently, we evaluated the values of V • φ (R 3+ , aq, 298.15 K) only from the molar volumes of RCl 3 (aq) and R(ClO 4 ) 3 (aq) solutions, for which complex formation does not affect the extrapolations to any significant extent.…”