Study On The Effect Of Electrolysis Conditions On Cathode Manganese Deposition Mechanism

In the hydrometallurgical process of metal manganese,because the standard electrode potential of manganese is relatively negative,the current efficiency is lower than that of other metal,it is only about 70%.In its industrial production,most energy consumption is used in the electrodeposition of manganese,so it has certain theoretical and practical significance to carry out the research of its electrodeposition.Based on the continuity of the previous team's work,this paper studies the cathode manganese electrodeposition mechanism on the changes of Mg²⁺concentration,(NH₄)₂SO₄concentration and current density,it is expected to provide theoretical support for electrolytic manganese production.(1)The electrochemical study of manganese deposition.With the increase of Mg²⁺concentration,the basic characteristics of the cyclic voltammetry curve remain unchanged,and the slope of the cathodic current curve and the slope of the oxidation peak current curve gradually decrease,that is,the manganese deposition rate becomes slower.9The change of electrochemical impedance spectroscopy shows that the difficulty of charge transfer between the solution and the electrode interface increases,and the Faraday resistance increases,which is manifested by the decrease of the amount of manganese electrodeposited on the electrode surface;As the concentration of(NH₄)₂SO₄ increases,the basic characteristics of the cyclic voltammetry curve remain unchanged,and the overpotential for manganese precipitation decreases,which is more conducive to the precipitation of manganese.Both the slope of the cathodic current curve and the slope of the oxidation peak current gradually increase,which inhibits the hydrogen evolution reaction to a certain extent and promotes the manganese evolution reaction.The change of electrochemical impedance spectroscopy shows that the difficulty of charge transfer between the solution and the electrode interface is reduced,and the cell voltage is effectively reduced.Although the hydrogen evolution reaction is catalyzed,it is ultimately manifested as an increase in the amount of manganese electrodeposited on the electrode surface.(2)The growth law of manganese deposition.The growth of metallic manganese generally conforms to the growth mechanism of screw dislocations.With the increase of Mg²⁺concentration and the extension of the electrodeposition time,the growth of manganese grains changes from pyramidal lamellae to polygonal grains with stepped stripes and pyramid top.When the Mg²⁺concentration increases from 10 g/L to 30 g/L,the grain growth rate increases from 13.213?m/h to 18.785?m/h;With the increase of the concentration of(NH₄)₂SO₄ and the extension of the electrodeposition time,the growth of manganese crystal grains finally turned into a cauliflower shape with more adsorption points.When the concentration of(NH₄)₂SO₄ increases from 80 g/L to 100g/L,the grain growth rate decreases from 19.553?m/h to 16.288?m/h.When the concentration increasing to 120 g/L,the grain growth rate increases to 20.238?m/h;With the increase of the current density and the extension of the electrodeposition time,the grain growth eventually turns into a non-uniform growth and a spherical shape.When the current density increases from 350 A/m² to 550 A/m²,the grain growth rate increases from 15.196?m/h to 19.791?m/h.(3)Economic and technical indexes of manganese deposition:current efficiency,cell voltage and energy consumption.The change of Mg²⁺concentration has a greater impact on current efficiency and energy consumption,and has a negative correlation with current efficiency,and has a small impact on cell voltage;The concentration of(NH₄)₂SO₄ has a greater impact on current efficiency and energy consumption and is positively correlated with current efficiency,and has a small impact on cell voltage;With the increase of current density,the amount of change in current efficiency shows a trend that the amount of increase gradually decreases to a negative growth.The fluctuation of the cell voltage causes the change trend of the energy consumption to be similar to that of the cell voltage on the whole,and at any current density,it gradually increases with the extension of the electrodeposition time.