No abstract

Sulfuric acid is present in many enterprises for metal processing and manufacturing of metal parts. Existing methods of regeneration of spent solutions are not effective, in particular, spent sulfate solutions are neutralized with lye or waste from other industries containing solid carbonates and hydroxides. At the same time, sulfate waste is formed, which requires disposal at special landfills. Electrochemical regeneration of spent solutions of sulfate-acid treatment of steel solves the problem of disposal of such spent sulfate solutions with the inclusion of iron sulfates. The kinetics of combined cathodic processes in aqueous solutions of iron (II) sulfate at a concentration of 0.5 mol.·dm–3 of iron (II) sulfate, depending on the cathode material was studied. The research methodology was as follows: model aqueous solutions with a composition (mol∙dm–3): 0.5 iron (II) sulfate with the addition of 0.5 sulfuric acid and a control solution – 1.0 sulfuric acid were prepared from chemicals of high stage of purification by dissolution in distilled water. The study of the kinetics of combined cathodic processes in model aqueous solutions was carried out by the method of linear voltammetry using the MTech PGP-500 S potentiostat. The auxiliary electrode is platinum. The reference electrode is mercury sulfate. Determination of iron (II) ions in the solution was carried out by the permanganatometric method. Based on the analysis of the obtained current-voltage curves, the effectiveness of the application of electrochemical regeneration of model solutions of iron (II) sulfate with sulfuric acid was established, which makes it possible to cathodically deposit iron in the form of foil or metal powder, and through the course of the anodic process - convert sulfates into sulfuric acid. During this process, oxidation of Fe2+ to Fe3+ takes place at the slightly soluble anode. Therefore, it is proposed to use polymer porous diaphragms to prevent Fe2+ from entering the anode space. Platinum and copper were used as cathode material. The choice of cathode material was based on different electrochemical properties of these metals in relation to the hydrogen reaction. The balance research on the regeneration of the model solution was carried out in a three-chamber electrolyzer. The initial test solution was fed into the middle chamber. The cathodic current density was 0.025 and 0.035 A∙cm–2, the working area of the anode and cathode was 85 cm2. A compact iron deposit was obtained on the cathode with 08X12N10T, which peeled off. The analysis of the cathode deposit showed the presence of 0.065% hydrogen in iron. Output according to the current of iron was 92%. The end of the Tafel section of the course of cathodic reduction of iron with electrochemical control occurs due to Fe2+ concentration limitations and the ohmic resistance of adsorbed hydrogen at the boundary of heterogeneous phases. It is proposed to eliminate these limitations due to electrolyte mixing.

The possibility of chemical and electrochemical dissolution of secondary raw materials on the basis of tungsten carbides electrolytes from solutions of acids HNO3, HCl, H2SO4 has been considered. The influence of nature and concentration of electrolyte on the process of anodic dissolution of the alloy WC–Co has been studied. It has been established that the final product of the dissolution of the WC–Co alloy in acid solutions is the higher tungsten oxide WO3. The reduction of the electrochemical process efficiency in the series HNO3 + HF > HCl > H2SO4 has been shown. In order to obtain tungsten carbide or tungsten powder, during the electrochemical treatment of the WC–Co alloy, the introduction of an admixture-reductant in a solution of sulfate acid has been proposed for the preparation of tungsten powder. On the basis of the conducted studies, a working electrolyte has been selected which allows to obtain the target product WC or W. Bibl. 10, Fig. 6.

Widespread use of specialized tools, the component part of which is tungsten, leads to the accumulation of its secondary raw materials (worked tools, cutters, drills, etc.). That is why there is a need to create technologies for recycling of the demanded metals, in particular tungsten. The purpose of this work is to study the anode behavior of carbide pseudoalloy type WC-Co in solutions of nitric acid with the addition of fluoride acid to obtain, as a target product, higher tungsten oxide in one stage. The corrosion behavior of carbide type pseudoalloy in acid solutions has been studied, and it has been found that the highest oxidation rate occurs in a concentrated solution of nitric acid. In order to accelerate the process and to increase the yield on the substance, adding to the fluoride acid working electrolyte has been proposed. As a result of the researches, it has been found that the behavior of the dissolution of pseudoalloys of the carbide type is characterized by the properties of the main component — tungsten. An electrolyte for obtaining higher tungsten oxide in one stage has been proposed. Bibl. 10, Fig. 1, Tab. 1.

The current state of regeneration of sulfate solutions was analyzed, it was established that the existing physico-chemical methods do not solve the problem of regeneration of sulfuric acid, but only neutralize it, for transfer according to the standards of the MPC to neutralization and into the sewage system with subsequent disposal. It has been confirmed that it is advisable to carry out the regeneration by an electrochemical method using a three-chamber electrolyzer, when the solution is fed into the middle chamber, the concentration of regenerated sulfuric acid increases to 180-200 g/l, with simultaneous iron deposition, with a current yield of 65-70%. This method reduces waste and allows switching to a closed cycle on sulfuric acid. It was found that in the process of digestion, the concentration of sulfuric acid decreases from 2.0 to 0.5 mol·dm-3, and the concentration of iron (II) sulfate increases accordingly. Under the conditions of a decrease in the concentration of sulfuric acid, its chemical activity also decreases when interacting with iron oxides and hydroxides. To increase the reactivity of pickling solutions, an increase in the temperature of the entire process is used. The kinetic regularity of combined cathodic processes in model solutions of iron (II) sulfate with sulfuric acid was established. Platinum, copper and carbon steel were used as cathode material. The choice of the cathode material was based on the different electrochemical properties of these selected metals with respect to the hydrogen reaction. The main process at the platinum cathode is hydrogen release in a wide range of current densities. At current densities greater than 0.1 A/cm2, a sharp increase in potential was observed due to the incorporation of Fe2+ into the composition of the cathode-electrolyte interface, but Fe2+ reduction potentials were not reached. When replacing the cathode material from platinum to carbon steel, a significant inhibition of hydrogen release was observed, which made it possible to reach the potentials for the simultaneous reduction of hydrogen and iron, however, the maximum current of the rectilinear section of the electrochemical process with electrochemical control was reduced from 10 at 20 0C to 3 times at 80 0C. The use of a copper cathode made it possible to reveal the influence of the hydrogen reaction on the course of Fe2+ reduction. The release of hydrogen at the copper cathode was accompanied by a significant inhibition of the hydrogen ion discharge. When using an iron cathode, electrochemical desorption is the limiting stage, which leads to the existence of layers of adsorbed hydrogen firmly attached to the surface of the iron cathode. A comparative analysis of the voltage-current dependences for the final investigated temperatures indicates a significant effect of an increase in temperature from 20 0C to 80 0C by approximately 120-150 mV. The cathodic process at 20 0C takes place in the mode of increased kinetics for both combined processes. At 80 0С, rectilinear sections of electrochemical control of the cathodic process appear on the voltage–voltage dependences, at Fe2+ concentrations of 1.0 and 1.5 mol/dm3. These areas range from 20 to 60 mA/cm2. The concentration of iron ions and the temperature of electrolysis have a significant effect on the process of electrochemical reduction of Fe2+, which was confirmed experimentally. Since the target process in the electrochemical regeneration of spent pickling solutions is the regeneration of sulfuric acid itself, and not the removal of Fe2+ from this solution, the cathodic mode of operation of the electrode unit was determined according to the technological indicators of the anodic process.