Crystal Research and Technology
Cryst. Res. Technol. 40, 370 (2005) - Abstract -

Adsorption of 3d-elements onto zinc oxalate dihydrate in aqueous oxalate solutions

J. Pencheva, B. Donkova*, M. Djarova*, and S. Maksimova*

University of Rousse, ul. Student 8, 7000 Rousse, Bulgaria
*Faculty of Chemistry, University of Sofia, Av. 1 J. Bourchier, 1164 Sofia, Bulgaria

Keywords crystallization, impurity, inclusion, sorption, zinc(II) oxalate
PACS 61.66.Fn, 61.72.Ss, 64.75.+g, 68.45.Da
DOI 10.1002/crat.200410353

A study of the sorption of 3d-transition elements onto ZnC2O4.2H2O has been carried out.To reveal the mechanism of the process, the experiments were performed in two media of different oxalate ion concentrations –1x10-2 and 4x10-4 mol/l, by the separate and by the joint presence of the microcomponents in the system. In the latter case, copper was also added, the sorption of which has been previously well studied. Different mechanisms of sorption in the different media were found, the determining role of the neutral oxalate complexes having been manifested. In the case of manganese and cobalt, in the medium with oxalate ions deficit, sorption by neutral complexes in the adsorption layer A is supplemented by ion-exchange sorption in the first surface layer S. The sorption of nickel under oxalate ion excess is proved to be an irreversible process, and the concept of its sorption by a mixed complex with the participation of the macrocomponent, Zn[Ni(C2O4)2], is advanced. The experimental data show the occurrence of segregation of Mn and Ni by their sorption onto the growth steps, and the absence of segregation of Co by its sorption. An interesting result is the extension of the validity of the Paneth-Fajans rule in the case of so-called complex oxalates, growing by neutral oxalate complexes, such as the oxalates of the macro- and microcompoments, studied in the present work.




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