An intensive development of science and technology, creation of new products with new
properties comes in contradiction with the functioning of natural environment. Among the other
pollutants, the heavy metal ions belong to the most dangerous ones. A promising ecological
approach was shown to be the prevention of the discharges of used high-concentrated
technological solutions, due to their regeneration and repeated using. A new technological
principle was proposed, involving the selective reducing of Fe(III) to Fe(II) ions in the
“oxidized” iron plating electrolytes in an electrochemical, reagent-free way, without the
depositing of solid metal phase on electrode. This has become possible due to the using of flowthrough
three-dimension electrodes. The kinetic parameters have been determined of the
reduction-oxidation processes in the studied multicomponent system, which liquid phase
contains four main components: Fe3+, Fe2+, H+, O2, taking part in the following electrode
reactions:
Fe(III) Fe(II); Fe(II) Fe0; 2Н+ Н2; О2 Н2О2 2Н2О.
The theoretical studies were carried out using the numerical calculations of the processes
distribution within the three-dimensional electrodes, based on the mathematical model [1]. For
this scope, physical and kinetic parameters specific for the studied complex system have been
used. The physical parameters have been considered for the electrolyte containing 2.5 mol/l
Fe(II), concentration of Fe(III) varying within the range 1.8·10-3–1.8·10-1 mоl/l. The calculations
made it possible to study the electrode processes within the electrodes under the various
conditions, and compare the numerical results with the experimental data, the target process
being the electrochemical reduction of iron (III) to iron (II).
Thus, it was found that for all the studied values of current density (100-1500 А/cm2), the
increase of the electrolyte linear flow rate from 0.1 to 0.8 cm/s results in the polarization increase
along the entire electrode thickness. An increase in the flow rate, as well as the electrode depth,
cathodic current density were found to intensify the electrochemical processes up to the certain
limits, after which the target process rate has remained unchanged.
The kinetic regularities, technological regimes and distribution of electrode processes within the
flow-through electrodes in the multicomponent system have been studied on the base of
mathematical approach and experimental tests. The optimal parameters of the electrochemical
stabilization of iron electrolytes composition were determined. The data obtained were used to
propose the processes and reactors [2], which made it possible to realize the continuous
regeneration of electrolytes and prevent the discharges of used concentrated solutions into the
natural environment.
References:
[1] Koshev, А.N. et al. In: Reviews of Siberian Branch of AS, Chemical Sciences, 1984, is.6, №
17, 24–27.
[2] Covaliova, O. Technology and ecological safety of plating industry (Rus.). Chisinau: CEP
MSU, 2008, 373 p.