The original examples of lanthanide tetrad effect in solvent extraction: A new interpretation compatible with recent progress in REE geochemistry.

Abstract

Geochmeical studies reporting lanthanide tetrad effects in natural samples often cite the original examples of tetrad effect depicted by logK d (org/aq) for Ln(III) in the two solvent-extraction systems (Peppard et al., 1969) and its theoretical interpretation (Jørgensen, 1970;Nugent, 1970). An improved equation for the refined spin-pairing energy theory (RSPET), which has been developed in pursuing tetrad effects in geochemical studies, makes it possible to examine more thoroughly the original examples of tetrad effect by using the digitized logK d (org/aq) data. The logK d (org/aq) values are found to be successfully described by the RSPET equation. Our analyses show that the ratios of relative differences in Racah parameters for Ln 3+ ions in aqueous and organic phases, ∆E 3 /∆E 1 , are 0.29 ± 0.07 and 0.25 ± 0.06 for the two extraction systems. They are comparable with the spectroscopic observations of nephelauxetic effect in Nd(III) compounds (∆E 3 /∆E 1 = 0.23 ± 0.02). The tetrad effects in logK d (org/aq) are experimental evidence for the thermochemical consequence of the nephelauxetic effect in Ln(III) complexes. Although Ln 3+ ions in condensed phases are atomic-like, it is rather surprising that logK d (org/aq) can easily be reproduced by the simple RSPET equation derived from the Slater-Condon-Racah theory for free Ln 3+ ions in vacuum. The effect of coordination change of Ln 3+ ion across the Ln 3+ (aq) series is not obvious in the series variations of logK d (org/aq), suggesting that the coordination changes in the two Ln(III) complex series in the extraction systems are significantly canceled out in ∆G r°. The two sets of logK d (org/aq) are analogous to the Masuda-Coryell plot in REE geochemistry with respect to their coordinates. This gives an insight into the fact that the Masuda-Coryell plot also depicts tetrad effects in the REE patterns for geochemical samples.

Experimental REE partitioning between calcite and aqueous solution at 25.DEG.C. and 1atm: Constraints on the incorporation of seawater REE into seamount-type limestones

“…According to the result of speciation calculation by Ohta and Kawabe (2000a), REE 3+ (aq) and REESO 4 + (aq) were also considered when logK d (REE) Liu and Byrne (1998). (Kawabe, 1999;Kawabe and Masuda, 2001).…”

“…Seawater shows a representative concave tetrad effect of W-type, whereas evolved granitic rocks often indicate convex tetrad effects of M-type. Brief reviews of recent studies of tetrad effects in REE geochemistry are given in Kawabe and Masuda (2001) and Monecke et al (2002).Japanese seamount-type Permian limestones also have seawater-like REE characteristics such as concave tetrad effects, negative Ce anomalies, negative Eu anomalies and higher Y/Ho ratios than the chondritic one in their chondrite-normalized REE abundance patterns (Kawabe et al, 1991;Tanaka et al, 2003). This strongly suggests that seawater REEs have been incorporated into seamount-…”

“…Seawater shows a representative concave tetrad effect of W-type, whereas evolved granitic rocks often indicate convex tetrad effects of M-type. Brief reviews of recent studies of tetrad effects in REE geochemistry are given in Kawabe and Masuda (2001) and Monecke et al (2002).…”

Characteristics of rare earth element abundances in shallow marine continental platform carbonates of Late Neoproterozoic successions from India.

“…(2)) between REE(III) complexes in seawater (Kawabe et al, 1998), 3 ) parameters for 4f electron repulsion in REE 3+ , the logarithms of concentration ratios between the pair of species show a REE fractionation trend characterized by tetrad effect (Jørgensen, 1979;Kawabe, 1992;Minami et al, 1998;Kawabe and Masuda, 2001). In fact Racah E 1 and E 3 parameters for REE sesquioxide (REEO 1.5 ) and REE(OH) 3 are significantly smaller than those for REECO 3 + (aq) and slightly smaller than those of REE(CO 3 ) 2 -(aq) in seawater solution (Ohta and Kawabe, 2000).…”

Adsorption of lanthanides on mordenite from nitrate medium

“…Let us evaluate quantitatively the changes of Racah parameters. According to Kawabe and Masuda [37] the following equation, the so-called refined spin energy (RSPET) equation, describes the changes of the lanthanides distribution constants log K d in the two-phase system:…”