Kinetics and Mechanism of Extraction of Zinc, Nickel, Cobalt, and Cadmium with Diphenylthiocarbazone, Di-o-Tolylthiocarbazone, and Di-α-Naphthylthiocarbazone.

Abstract

The kinetics of extraction of zinc, nickel, cobalt, and cadmium with diphenylthiocarbazone, di-o-tolylthiocarbazone, and di-a-naphthylthiocarbazone were studied. Each of these reactions were first order in metal ion and, with one exception, first order in reagent anion. The reaction of zinc with di-a-naphthylthiocarbazone was second order in reagent anion. The rate constants for each metal ion paralleled the rate at which water dissociates from the hydrated metal ion. In every case sterically hindering substituents on the phenyl rings of the reagents increased the rate of the reaction. A mechanism is proposed in which the rate-controlling step is the reaction involving the change in configuration of the monodithizonate complex from six-to-four-coordinate metal ion, accompanied by the dissociation of water. Values of the distribution coefficients, Kd" of the reagents between CHCI3 and water are reported.

Zur Kinetik der Komplexbildung an flüssig/flüssig‐Phasengrenzen

“…Abgesehen vom ,,Kobalt/Chloroform-System" wurde fur die Plateauraten eine erste Ordnung fur den Metallionen-und den DithizoneinfluB ermittelt und eine reziproke erste Ordnung fur die Protonenkonzentration entsprechend dem ersten Glied in Gleichung (6). Die Folge ist die einfachste Entsprechung des kinetischen Befundes, wobei die Einzelschritte als Grenzflachenreaktionen ablaufen, abweichend von der in [18,19]…”

Kinetics of solvent extraction of metal ions with HEDHP. III. The kinetics and mechanism of solvent extraction of Cr(III) from acidic aqueous solutions with bis-(2-ethyl hexyl) phosphoric acid in benzene

“…The first order dependence of Cr(I1I) concentration on the rate is in agreement w~t h the general observation that the order w.r.t. the metal ions is found to be unity (2, 7, 13-17, 22, 23), except in the case of extraction of Ti(IV) with HDEHP (1) and of Zn(I1) with di-r*-naphthyl dithiocarbazone (24). Thus, at lower acidities Cr(III), present as polynuclear form, breaks down rapidly to mononuclear form which then reacts.…”

Proposal of a simple screening method for a rapid preliminary evaluation of “heavy metals” mobility in soils of contaminated sites

“…It is possible that there is a contribution of other elements other than Zn, Cu, Pb and Cd to the total titrated, but the essential of the expected information is retained. Nevertheless, we evaluated the behaviour of other trace elements under the same conditions: Ni is not titred, while the relevance (with respect to the total) of other elements that could be titred (as Co) becomes negligible due to less favourable kinetic of the complexation reaction and the relatively short chosen extraction time (Freiser 1984;McClellan and Freiser 1964). Moreover, the abundance of Co and other not-considered trace elements in the earth's crust is relatively low (Taylor 1964;Wedepohl 1995;Kabata-Pendias and Mukherjee 2007), not exceeding in the major part of cases 15-20 mg kg −1 .…”