Dissolution of iron electrodes during polarization with three-phase AC in hydrochloric and sulfuric acids solutions

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In present work the regularities of electrochemicaldissolution of iron with the participation of industrial three-phase AC50Hz in aqueous solutions of HCl and H 2SO4 were studied the first time. The features of the dissolution of iron electrodes at
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   American Journal of Advanced Drug Delivery  www.ajadd.co.uk   American Journal of Advanced Drug Delivery  www.ajadd.co.uk     󰁏󰁲󰁩󰁧󰁩󰁮󰁡󰁬 󰁁󰁲󰁴󰁩󰁣󰁬󰁥 Dissolution of iron electrodes during polarization with three-phase AC in hydrochloric and sulfuric acids solutions Sarbayeva M.T.*, Bayeshev A.B., Sarbayeva G.T., Sarbayeva K.T., Bayesheva A.K. and Zhurinov M.Zh.   Institute of organic catalysis and electrochemistry after D.V. Sokolskiy, Almaty, Kazakhstan ABSTRACT   In present work the regularities of electrochemical dissolution of iron with the participation of industrial three-phase AC 50Hz in aqueous solutions of HCl and H 2 SO 4  were studied the first time. The features of the dissolution of iron electrodes at polarization with alternating current in acid solution to form ions of iron (II) were studied and the influence of various factors was examined. Based on the study results a new and efficient method of synthesis of iron salts which are widely used as a coagulant in water treatment was proposed. Keywords : Three-phase alternating current, current efficiency, iron, chloride iron, sulfate iron, polarization. INTRODUCTION This article examines ways of electrochemical obtaining chloride and ferric sulfate, which are used as coagulants in the treatment of contaminated water. In this regard, in this paper the patterns of electrochemical dissolution of iron electrode during polarization in industrial three-phase alternating current with a frequency of 50 Hz in solutions of hydrochloric acid and sulfuric acid were studied the first time. High efficiency and quality of an industrial alternating current polarization to obtain compounds of many sparingly metals are listed in earlier reports 1,2 . It is known that coagulation is a consolidation process of the colloidal and dispersed particles as a result of sticking, connection with one another depending on the values of their electrical charge. Typically, many substances which  pollute and stain natural water are in the form of colloids. The addition of coagulants lightens such water and increases the treatment efficiency. Water treatment plants mainly use compounds such as chlorides and sulfates of iron and aluminum 1,3 . Our research is devoted to the synthesis of ferric sulfate and chloride by electrolysis of waste iron at the polarization Date of Receipt- 25/2/2014 Date of Revision- 07/3/2014 Date of Acceptance- 05/7/2014 Address for Correspondence 󰁉󰁮󰁳󰁴󰁩󰁴󰁵󰁴󰁥 󰁯󰁦 󰁯󰁲󰁧󰁡󰁮󰁩󰁣 󰁣󰁡󰁴󰁡󰁬󰁹󰁳󰁩󰁳 󰁡󰁮󰁤 󰁥󰁬󰁥󰁣󰁴󰁲󰁯󰁣󰁨󰁥󰁭󰁩󰁳󰁴󰁲󰁹 󰁡󰁦󰁴󰁥󰁲 󰁄.󰁖. 󰁓󰁯󰁫󰁯󰁬󰁳󰁫󰁩󰁹, 󰁁󰁬󰁭󰁡󰁴󰁹, 󰁋󰁡󰁺󰁡󰁫󰁨󰁳󰁴󰁡󰁮 E-mail: 󰁭󰁡󰁫󰁫󰁥󰁮󰁺󰁥󰁀󰁭󰁡󰁩󰁬.󰁲󰁵   Sarbayeva  et al__________________________________________________    ISSN 2321-547X   󰁁󰁊󰁁󰁄󰁄󰁛󰀲󰁝󰁛󰀴󰁝󰁛󰀲󰀰󰀱󰀴󰁝󰀴󰀵󰀴󰀭󰀴󰀶󰀲  with three-phase alternating current in solutions of hydrochloric and sulfuric acid, and is aimed at implementing the principle of non-waste technology. In addition, electrochemical methods are one of the important areas of clean sustainable technology. In this context, the synthesis of important metal compounds in different aquatic media using industrial AC gives the opportunity to solve many problems. Standard electrode potentials of transition iron ions have negative value: Fe – 2e → Fe 2+  Е 0  = -0,44 В …(1) Fe – 3e → Fe 3+  Е 0  = -0,04 В …(2) However, under normal conditions an oxide film forming on its surface keeps the metal from being dissolved in water. Whereas in acids, for example in hydrochloric or sulfuric acid, iron dissolves significantly, but with a small rate 5 : 2Fe + 6HCl → 2FeCl 3  + 3H 2  ………(3) Fe + H 2 SO 4  = FeSO 4 + H 2  ………(4) Our researches have shown that in 80 g/l hydrochloric acid at 25 0 C the rate of chemical dissolution of the iron is 88 g/(m 2 ·hour), and in 100 g/l sulfuric acid solution it is equal to 47g/(m 2 · hour). Obviously, acidity of the solution plays a special role in iron dissolution. This is due to the participation of metal hydrocomplexes in electrode reactions. Researches are done on the effect of the AC density, acid concentration, temperature and time of electrolysis for dissolution of iron electrodes during  polarization by three-phase industrial alternating current at frequency 50 Hz in solutions of hydrochloric acid and sulfuric acid 3,4 . EXPERIMENTAL Method Experiments were conducted in an 200 ml electrolytic cell without stirring of the solution. Electrodes were made from iron  plates. Solutions of hydrochloric acid and sulfuric acid were used as electrolytes. Three- phase alternating current obtained from special setup (three-phase transformer). Line current was regulated by a three-phase laboratory transformer (Fig. 1). Current yield was calculated by the amplitude of the anode half-cycle of each  phase weight change of iron electrodes before and after electrolysis. In each phase of the anode half-cycle of AC, the iron on the electrode dissolves according to reactions (1) and (2) to form their ions. Whereas, in the cathode half cycle of AC hydrogen ions recover on the surface of iron electrodes:  2 Н +  + 2е → Н 2 The results show that under optimal conditions in the anodic half cycle on the surface of the iron electrodes appears the formation reaction, generally of the divalent iron ion, as in the cathode half cycle hydrogen is produced as a gas 6,7 . RESULTS AND DISCUSSION Fourier transform infrared spectral measurements The effect of current density in the range of 500-2500 A/m 2  on the formation of iron ions(II) in hydrochloric acid and sulfuric acid solutions during electrolysis and the dissolution rate of the iron electrode was studied. During polarization of iron electrode  by three-phase AC in a hydrochloric acid solution the current output on production of iron ions (II) greatly increases with the  Sarbayeva  et al__________________________________________________    ISSN 2321-547X   󰁁󰁊󰁁󰁄󰁄󰁛󰀲󰁝󰁛󰀴󰁝󰁛󰀲󰀰󰀱󰀴󰁝󰀴󰀵󰀴󰀭󰀴󰀶󰀲  increase of the current density (Figure 2, curve 1). As it can be seen from Figure 2, at current densities of the electrodes 1000 A/m 2  and higher, the current output on dissolution of iron exceeds 100%. It was found that in the sulfuric acid solution the current output of the iron ions (II) decreases with increase of current density (Figure 2, curve 2). This  phenomenon is explained by the fact that depending on the concentration increase of oxygen containing sulfate anion increases the  possibility of iron oxide formation on the electrode surface. In two acids, the increase of the current density increases the dissolution rate of iron electrode according to Faraday's law (Figure 3) The effect of hydrochloric acid and sulfuric acid concentration on current output of iron dissolution and the dissolution rate of the iron electrode during the polarization of electrodes by three-phase alternating current was studied. As seen in Figure 4, with concentration increase of hydrochloric acid increases the output current and reaches a maximum value (105.9 %). Even when the current is stopped on the line intensive chemical self-dissolution of the iron electrode continues. Which is explained by the influence of active chloride ions. Therefore, at high concentrations of HCl solution, not only electrochemical but also a chemical dissolution of iron is going and the output current of the iron ions (II) exceeds one hundred percent. Increasing the concentration of hydrochloric acid increases the dissolution rate of iron electrode (Figure 5, curve 1). When the concentration of sulfuric acid is increased up to 100g/l the iron dissolution rate increases to 1485 g/(m 2 ·hour). Further increase of the concentration of sulfuric acid leads to a decrease in the dissolution rate (Figure 5, curve 2). This is because of the  possibility of iron oxide formation on the electrode surface due to the concentration increase of oxygen containing sulfate ion. It is shown that during polarization by a three-phase AC of the iron electrode in a hydrochloric acid solution, the temperature change of the electrolyte does not affect the electrode processes. Figures 6, 7 show that during the  polarization by AC in acidic solutions the output by current of iron ion formation (II) and the dissolution rate initially increases and then decreases with the increase of electrolysis time. These dependences pass through a maximum. Reducing the current yield and the dissolution rate of iron over time can be explained by the gradual passivation of the electrode surface by the electrolysis  products and the appearance of concentrative  polarization. After the electrolysis, the solution was evaporated, then cooled to obtain crystals of ferrous sulfate and chloride. X-ray phase analysis of the crystals obtained in hydrochloric acid solution showed the formation of FeCl 2  · 6H 2 O compound (Figure 8). All reflexes correspond to the phases of ferric chloride (ІІ): 5,78 А 0 ; 4,37 А 0 ; 3,15 А 0 ; 2-9; 2,43 А 0 . Results of X-ray phase analysis of the crystals obtained in the sulfuric acid solution revealed the formation of a compound of FeSO 4 . 7H 2 O, i.e. ferrous sulfate heptahydrate (Figure 9), which by the common name is iron copperas. All reflexes correspond to iron sulfate  phases (ІІ): 6,9 А 0 ; 5,48 А 0 ; 5,4 А 0 ; 4,5А 0 ; 4,0 А 0 ; 3,61 А 0 ; 3,40 А 0 ; 3,28 А 0 ; 3,23 А 0  and others, which belong to compound FeSO 4 · 4H 2 O (АSТМ 19-632).   Reflexes 4,92 А 0 ; 4,88 А 0 ; correspond to phase FeSO 4 · 7H 2 O to compound (АSТМ 19-632). The formation of this compound is also shown by Mossbauer spectroscopy method (Chart, Figure 10).    Sarbayeva  et al__________________________________________________    ISSN 2321-547X   󰁁󰁊󰁁󰁄󰁄󰁛󰀲󰁝󰁛󰀴󰁝󰁛󰀲󰀰󰀱󰀴󰁝󰀴󰀵󰀴󰀭󰀴󰀶󰀲  Chart Determination of the obtained compound by Mossbauer spectroscopy. Thus, the results of the research made  possible to obtain new information about the  patterns of the iron electrochemical dissolution during the polarization by industrial three-phase alternating current. An efficient synthesis method of inorganic iron salts (II) chloride (FeCl 2  · 6H 2 O) and sulfate (FeSO 4 · 7H 2 O),  polarization of iron electrodes by three-phase alternating current in solutions of hydrochloric and sulfuric acids is proposed. Obtained salts have high purity and the compositions do correspond to the chemical formula, so no doubt to use them as chemical reagents. REFERENCES 1.    Bayeshev A., Bayesheva А.К. Electrochemical methods of obtaining inorganic substances,   Lambert, Academic Publishing, Germany, 2012 – 72 с. 2.    Bayeshev A., Bayesheva А.К., Sarbayeva G.T. Innovation patent of RK № 20681 от 26.06.2007. Iron chloride obtaining method (ІІ). Published in bulletin №1, 2009 3.   Weizer Yu.I. Coagulants and substances that promote coagulation Chemical society journal after D.I. Mendeleev. Т.5, №6, 1960  4.    Proskuryayev V.A., Schmidt L.I. Wastewater treatment in the chemical industry. L.: Chemistry, 1977.  5.    Bayeshev A., Andamasov R.S., Galiyeva  A.S.  About the formation of iron hydroxide (II) during the polarization by alternating current. Comprehensive use of minerals.N.5,1993, 86с  6.    Rosin I.V., Tomina L.D.  General and inorganic chemistry. Modern course.– М.: Textbook for bachelors and specialists, 2012, 967с.   7.    Bayeshev A.  Electrochemical processes in polarization by non-stationary currents. News of NSS of RK, 2011, №2,С.3−23.   󰁓󰁡󰁭󰁰󰁬󰁥 󰁉󰁳󰀬 мм󰀯с 󰁑󰁳󰀬 мм󰀯с 󰁓* отн󰀮󰀬 % 󰁓󰁡󰁭󰁰󰁬󰁥 󰁦󰁯󰁲󰁭󰁵󰁬󰁡 1.26 3.22 100 󰁆󰁥󰁓󰁏 4 *7󰁈 2 󰁏  Sarbayeva  et al__________________________________________________    ISSN 2321-547X   󰁁󰁊󰁁󰁄󰁄󰁛󰀲󰁝󰁛󰀴󰁝󰁛󰀲󰀰󰀱󰀴󰁝󰀴󰀵󰀴󰀭󰀴󰀶󰀲  󰁆󰁩󰁧󰀮 󰀱󰀺  󰁄󰁲󰁡󰁷󰁩󰁮󰁧 󰁯󰁦 󰁴󰁨󰁥 󰁳󰁥󰁴󰁵󰁰 󰁦󰁯󰁲 󰁳󰁴󰁵󰁤󰁹 󰁯󰁦 󰁩󰁲󰁯󰁮 󰁥󰁬󰁥󰁣󰁴󰁲󰁯󰁤󰁥󰁳 󰁤󰁩󰁳󰁳󰁯󰁬󰁵󰁴󰁩󰁯󰁮 󰁩󰁮 󰁴󰁨󰁥 󰁡󰁣󰁩󰁤󰁩󰁣 󰁭󰁥󰁤󰁩󰁵󰁭 󰁤󰁵󰁲󰁩󰁮󰁧 󰁰󰁯󰁬󰁡󰁲󰁩󰁺󰁡󰁴󰁩󰁯󰁮 󰁢󰁹 󰁴󰁨󰁲󰁥󰁥󰀭󰁰󰁨󰁡󰁳󰁥 󰁁󰁃. 1󰀭 󰁉󰁲󰁯󰁮 󰁥󰁬󰁥󰁣󰁴󰁲󰁯󰁤󰁥󰁳 2󰀭 󰁔󰁨󰁲󰁥󰁥󰀭󰁰󰁨󰁡󰁳󰁥 󰁬󰁡󰁢󰁯󰁲󰁡󰁴󰁯󰁲󰁹 󰁴󰁲󰁡󰁮󰁳󰁦󰁯󰁲󰁭󰁥󰁲 3󰀭 󰁅󰁬󰁥󰁣󰁴󰁲󰁯󰁬󰁹󰁺󰁥󰁲 󰁆󰁩󰁧󰀮 󰀲󰀺  󰁔󰁨󰁥 󰁥󰁦󰁦󰁥󰁣󰁴 󰁯󰁦 󰁴󰁨󰁥 󰁣󰁵󰁲󰁲󰁥󰁮󰁴 󰁤󰁥󰁮󰁳󰁩󰁴󰁹 󰁩󰁮 󰁴󰁨󰁥 󰁥󰁬󰁥󰁣󰁴󰁲󰁯󰁤󰁥󰁳 󰁯󰁮 󰁦󰁯󰁲󰁭󰁡󰁴󰁩󰁯󰁮 󰁯󰁦 󰁩󰁲󰁯󰁮 󰁩󰁯󰁮 󰁢󰁹 󰁴󰁨󰁥 󰁣󰁵󰁲󰁲󰁥󰁮󰁴. 1󰀭80 󰁧/󰁬 󰁈󰁃󰁬; 2 󰀭 100 󰁧/󰁬 󰁈 2 󰁓󰁏 4 ; τ 󰀽 0,5 󰁨󰁯󰁵󰁲.
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