Electroconductive qualities of the membranes МС-40 and МА-41, researched by the method of impedance high-frequency spectroscopy

One of the most important factors defining the complex of operational characteristics of heterogeneous ion-exchange membranes that represent a composite material is their structure. Composite material electroconductivity depends on the nature of phases setting the system and on their relative position. Impedance spectroscopy is one of the effective methods of structure definition and electrochemical characteristics not only of the composite material generaly but also the phases which it consists of. In this paper by the method of impedance spectroscopy the electrochemical characteristics of the heterogeneous ion-exchange membranes МС-40 (H+, Na+, К+, NH4+ - forms) and МА-41 (Cl- and NO3- - forms) in the range of the alternating current frequencies 100 KHz – 20 MHz are researched. The comparison of the contact and contact-differential ways of measuring membrane impedance is done. It is shown that in the case of impedance contact measuring of the sample the borders “electrode/membrane” influence the electrochemical impedance system spectrum greatly. In connection with this the contact-differential variant of the experimental procedure in the impedance measuring of the membrane system is more preferable. The interpretation of the received electrochemical impedance spectra in terms of the composite material conductivity is given. Basing on the method of equivalent circuits it is suggested representing the impedance of the heterogeneous ion-exchange membrane as a sum of pure resistance (resistance of ion-exchanger particles), sequentially connected with the impedance of the dielectric layers (resistance and capacity of polyethylene and dissolvent). The analysis of the spectra of electrochemical impedance of ion-exchange membranes in different ion forms showed that the quantity of the semicircle locus impedance radius is inversely proportional to the coefficient of counter-ion diffusion and directly proportional to the part of the membrane intergel phase

Corrosion of steel St3 in technological water solutions of calcium nitrate

By the voltammetry method studied corrosion behavior of low carbon alloy structural steel St3 in aqueous solution of calcium nitrate. The effect of ammonation solution and additions of monoethanolamine and potassium dichromate on the basic parameters of the corrosion process was detected

ELECTRODIALYSIS IN THE CONVERSION STEP OF THE CONCENTRATED SALT SOLUTIONS IN THE PROCESS OF BATTERY SCRAP

Summary. The concentrated sodium sulfate solution is formed during the processing of waste battery scrap. A promising way to further treatment of the concentrated salt solution could be the conversion of these salts into acid and bases by electrodialysis, that can be reused in the same technical process cycle. For carrying out the process of conversion of salts into the corresponding acid and base several cells schemes with different combinations of cation, anion and bipolar membranes are used. At this article a comparative analysis of these cells is carried out. In the cells there were used the membranes МC-40, МА-41 and МB-2I. Acid and base solutions with higher concentration may be obtained during the process of electrodialysis in the circulation mode, when a predetermined amount of salt in the closed loop is run through a set of membranes to obtain the desired concentration of the product. The disadvantages of this method are the high cost of buffer tanks and the need to work with small volumes of treated solutions. In industrial applications it is advisable to use continuous electrodialysis with bipolar membranes, since this configuration allows to increase the number of repeating sections, which is necessary to reduce the energy costs. The increase of the removal rate of salts can be achieved by increasing the process steps, and to produce a more concentrated products after the conversion step can be applied electrodialysis-concentrator or evaporator