This paper investigates interaction processes of the Fe 3þ , Cu 2þ , Ni 2þ , and Co 2þ cations with humic acids isolated from brown coals of Ekibastuz basin. It was demonstrated that the sorption of heavy metal ions by humic acids (HA) depends on the concentration and nature of cations and decreases in the order of Fe 3þ > Cu 2þ > Ni 2þ > Co 2þ ; while increase in the concentration of humic acids (HA) results in the higher yield of ions and metals. The occurrence of ion exchange and complexation reactions in metal-humic acid systems is confirmed by the appearance of new bands and the shift of the absorption bands corresponding to stretching and deformation vibrations of carboxylate ions, C ¼ O and OH groups. The occurrence of these processes is also evidenced by spectrophotometric data, as well as a decrease in the pH of the solution due to deprotonation of humic acids during these reactions. Thus, based on the data on the degree of sorption of metal cations by humic acids, the results of infra-red spectroscopy and spectrophotometry, it can be concluded that the Fe 3þ , Ni 2þ , Co 2þ , Cu 2þ cations interact with HA by the ionic mechanism and by the complexation mechanism with electrondonating functional groups. Electrochemical studies of the Cu 2þhumic acid system carried out by the method of cyclic voltammetry also indicate the occurrence of the interaction of humic acid with copper cations. Modification of humic acid with copper ions shows the electrochemical activity of copper immobilized on the surface of dispersed humic acid, which is important for the implementation of electrocatalytic reactions on modified glassy carbonhumic electrodes.

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Processes involved in the electrodeposition of perrhenate ions were studied from two different potassium nitrate and sodium sulfate background electrolytes in the presence of citric acid on graphite electrode by cyclic voltammetry method. Anodic and cathodic potentials of deposited film were determined. After electrolysis process, morphology and content of obtained deposited layers were investigated by SEM and X-Ray methods. The coated film from sodium sulfate background electrolyte was not uniform and Re content was 60.83-65.5%, in case of potassium nitrate electrolyte, the deposited film was more densely located, and Re content was 80.94-82.52%. In the presence of nickel sulfate and citric acid, an alloy was formed with content of Re 80.94-82.52%, 14.10-11.83% of Ni, 4.96-5.66% of impurities, which were confirmed by X-Ray method. The current density decreased with addition of citric acid into sodium sulfate background electrolyte and in cathodic area, the reduction potential of perrhenate ions remained the same, but oxidation potentials changed from 0.25 to 0.35 V and from 0.5 to 0.6 V. The influence of citric acid on potentials of the processes of reduction and oxidation of perrhenate ions from potassium nitrate gave following results: reduction peaks shifted from -0.35 to -0.55 V, and multi peaks of oxidation appeared which were not noticeable without citric acid. It was shown that citric acid has inhibitory effect on reduction and oxidation of perrhenate ions. It is shown that the electrochemical reduction of perrhenate ions leads to the formation of rhenium dioxide in different forms.

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