Catalysis in Metal Extraction Kinetics

The extraction kinetics of Ni(II) and Zn(II) with //-alkyl-substituted dithizone (HL) in chloroform has been studied by HSS method [7]. The observed extraction rate constants was linearly proportional to both metal ion concentration in the aqueous phase [M2+] and ligand concentration in the organic phase [HL]0, and inversely to the hydrogen ion concentration [H + ] in the aqueous phase. Thus, the rate law for the extraction was determined as 

the observed extraction rate constant If was rewritten as 

From this study, one can understand that the liquid-liquid interface has a role of catalyst in the extraction rate through the adsorption of extractants like 

The adsorptivity and the orientation of the 2-hydroxyoxime molecule were well simulated by the MD simulations [65], In Fig. 17, the polar groups of -OH 

Pyridylazo ligands have been widely used in the extraction photometry of various metal ions. For example, l-(2-pyridylazo)-2-naphthol (Hpan) is one of the most well-known reagents, but it shows slow extraction rate for some metal ions such as Ni(II) and Pd(II). 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a relatively new reagent, which is more sensitive than Hpan for Cu(II), Ni(II), Co(II), and Zn(II), giving the metal complexes of molar absorptivities in the order of 105M-1 cm-1. 

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