THE INFLUENCE OF THE ANODE MATERIAL ON THE COURSE OF COMBINED PROCESSES DURING THE REGENERATION OF SULPHATE-ACID SOLUTIONS
Authors: Kravchenko K. , Tulsky G. 
Published: January 2023

The existing methods of regeneration of sulfo-acidic solutions, which contain iron sulfate, formed after technological operations for the preparation and etching of metal parts at metalworking enterprises are not effective and therefore are not used at Ukrainian enterprises. They are either aimed at sedimentation of the sludge of sparingly soluble iron compounds after neutralization of unreacted sulfuric acid or at dilution of the formed spent sulfo-acid solutions. The electrochemical method of regeneration of such spent sulfo-acid solutions is not properly researched. A feature of the development of technology and equipment for regeneration is a decrease in the content of iron ions and an increase in the concentration of sulfuric acid during the regeneration process. The process of electrochemical regeneration of spent steel etching solutions is characterized by a significant change in the composition of the etching solution and the temperature of the etching process. At the beginning of work, the initial solution of sulfuric acid reaches a concentration of 2.0 mol·dm-3 and does not contain iron (II) sulfate. In the process of digestion, the concentration of sulfuric acid decreases to 0.5 mol·dm-3, and the concentration of iron (II) sulfate increases accordingly. Therefore, the course of the anodic process was studied for the following solution compositions: 0.5 mol·dm-3; 1.0 mol·dm-3 and 1.5 mol·dm-3 H2SO4. Under the conditions of a decrease in the concentration of sulfuric acid, its chemical activity also decreases when interacting with iron oxides and hydroxides. An increase in the temperature of the entire process is used to increase the reactivity of the pickling solutions. The main process at the platinum anode is the release of oxygen in a wide range of current densities and a significant overvoltage of the entire process. Taking into account the obtained voltage-voltage dependences, it can be seen that the current rises when reaching potentials that significantly exceed the standard potential for obtaining oxygen from water. The advantage of the platinum anode is the slight influence of the concentration of sulfuric acid on the kinetics of the anode process. The obtained results were used for comparison with other alternative anode materials. Manganese dioxide was obtained by the method of pyrolysis of a coating solution of manganese monoacid applied to a titanium current lead, which can be represented by reaction (5) of the decomposition of manganese nitrate on a titanium plate. Due to the developed surface, the real current density was more than an order of magnitude lower on the TDMA than on the platinum anode with the same geometric dimensions. A lower current density contributed to a decrease in the steady-state potentials of oxygen release. The current density can be increased by an order of magnitude if surfactants are added to the working solution. A comparison of voltage-voltage dependences on platinum and TDMA indicates that the use of TDMA gives a more significant gain in energy consumption during the regeneration process. Taking into account that the range of current densities of 4-5 A/dm2 was determined for the cathode process according to the research results, the difference in the reduced polarization of the anode on TDMA, compared to platinum, is more than 400 mV, which will significantly reduce costs during unit operation. The use of TDMA is expedient in the galvanostatic mode of operation of the electrode unit for the process of electrochemical regeneration of spent sulfo-acid solutions of steel pickling.