The Research And Application Of Preparing Electrolytic Manganese Cleanly Without Selenium And Chromium

As there are much hexavalent chromium and selenium dioxide were used in the process of electrolytic manganese production,causing some serious environment problems and product quality problem.Thesis devotes to the research the electrolysis additives without selenium of electrolytic manganese and clean passivator.According to the characteristics of the electrolytic manganese and product requirements, the clean production process of electrolytic manganese without selenium and chromium was established.Through selection in laboratory experiments, a new type of electrolytic manganese additives has been developed, and set thiocarbamide as the main additives, the organic compounds Y as the auxiliary additives. The concentration of the both are0.1g·L-1;0.05g·L-1Y. respectively.The optimum technological conditions of new additives are:Current density for400A·m-2; The value of electrolyte’s pH is8; Concentration of ammonium sulfate for130g·L-1; Electrolytic temperature at35℃, the cathode current efficiency could be above65%. The effect of new additive on the surface morphology and crystal structure of electrolytic manganese was investigated by SEM and XRD. Respectively. Showing new additives can cause manganese metal generate stable α-Mn; And it is advantageous to the cathode to generate compact flat metal layer; EDX analysis shows that the manganese element mass fraction of the product surface is99.9%, reach the DJMnB product standard of YB/T051-2003.On the basis of experimental results, further to explore the mechanism of new additives in manganese electrodeposition process,conforms to the "closed effect","Ψ1effect" and "selective adsorption theory".Compound passivation solution without chromium was achieved by orthogonal test method,The optimization formula is:sodium silicate20g·L-1; Sodium tetraborate3g·L-1; Complexing agent9g·L-1; Chelating agent9ml·L-1; The value of passivation solution’s pH3. The samples corrosion resistance wre test by spot test of nitric acid and potassium permanganate, salt water immersion test, precision chromatic meter analysis and ventilation hanging pieces.The results showed that, after passivated by chromium-free composite, The nitric acid and potassium permanganate time the electrolytic manganese obviously prolonged (from35.4s to35.4s); the time of corrosion to occur in brine immersion delay (from5min to30min); Placed in the air, black was significantly weakened due to oxidation. Tafel polarization curve and electrochemical impedance spectroscopy (EIS) test showed that, after passivated by chromium-free composite,the total linear polarization resistance of electrolytic manganese significantly increased (from50.4ohm to845.9ohm), the corrosion current density decreased by one order of magnitude, effectively inhibit the electrochemical corrosion of metal manganese greatly reduces the corrosion rate of electrolytic manganese. Otard microscope after the passivation of manganese metal surface morphology analysis, combined with the experimental results, discuss without chromium passivation liquid composite film and the corrosion mechanism of passivation film. There are30figures,13tables and97references in this paper.