STABILITY-CONSTANTS FOR THE FORMATION OF RARE-EARTH INORGANIC COMPLEXES AS A FUNCTION OF IONIC-STRENGTH
STABILITY-CONSTANTS FOR THE FORMATION OF RARE-EARTH INORGANIC COMPLEXES AS A FUNCTION OF IONIC-STRENGTH
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DOI：
10.1016/0016-7037(92)90293-r
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发表时间：
1992-08-01
影响因子：
5
通讯作者：
MILLERO, FJ
中科院分区：
文献类型：
--
作者：
MILLERO, FJ
近年来，人们研究了稀土元素（La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Th、Dy、Ho、Er、Tm、Yb、Lu）在天然沃茨中的分布及其在页岩中的含量。这些金属也被用作三价锕系元素行为的模型。采用离子相互作用模型对天然沃茨中稀土元素的形态进行了模拟。本文用Pitzer相互作用模型，将在不同离子强度下，在NaClO_4中测定的镧系元素与Cl ~-、NO_3 ~-、SO_4 ~（2-）、OH ~-、HCO_3 ~-、H_2PO_4 ~（2-）和CO_3 ~（2-）形成配合物的稳定常数（K（MX）~*）外推至无限稀释。外推所需的游离离子的活度系数（γ（M），γ（X））已从Pitzer方程中估算。根据ln（K（MX）*/gamma（M）gamma（X）= ln K（MX）+ ln（gamma（MX））确定各种离子对的热力学稳定常数（K（MX））和活度系数（gamma（MX））。用离子对的活度系数确定了稀土配合物的Pitzer参数（B（MX））。发现相同电荷的络合物的B（MX）值相同。这些结果使人们有可能估计在很宽的离子强度范围内形成稀土配合物的稳定常数。稳定常数已被用于确定海水和卤水中镧系元素的形态。碳酸盐络合物在所有天然沃茨中占主导地位，其中碳酸盐碱度在pH接近8时大于0.001 eq/L。
Recent studies have been made on the distribution of the rare earths (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, Lu) in natural waters relative to their concentration in shales. These metals have also been used as models for the behavior of the trivalent actinides. The speciation of the rare earths in natural waters is modelled by using ionic interaction models which require reliable stability constants. In this paper the stability constants for the formation of lanthanide complexes (K(MX)*) with Cl-, NO3-, SO42-, OH-, HCO3-, H2PO42-, and CO32- determined in NaClO4 at various ionic strengths have been extrapolated to infinite dilution using the Pitzer interaction model. The activity coefficients for free ions (gamma(M), gamma(X) needed for this extrapolation have been estimated from the Pitzer equations. The thermodynamic stability constants (K(MX)) and activity coefficients of the various ion pairs (gamma(MX) were determined from ln (K(MX)*/gamma(M)gamma(X) = ln K(MX) + ln (gamma(MX)). The activity coefficients of the ion pairs have been used to determine Pitzer parameters (B(MX)) for the rare earth complexes. The values of B(MX) were found to be the same for complexes of the same charge. These results make it possible to estimate the stability constants for the formation of rare earth complexes over a wide range of ionic strengths. The stability constants have been used to determine the speciation of the lanthanides in seawater and in brines. The carbonate complexes dominate for all natural waters where the carbonate alkalinity is greater than 0.001 eq/L at a pH near 8.