Preparation Of Manganese Sulfate By Reduction Leaching Of Pyrolusite With Crap Iron And Its Electrolytic Techniques

With the development of economy, demand for the products of manganese-containing products will be increasing. Rhodochrosite resources can not meet thegrowing demand for manganese products in china. So development and utilization ofpyrolusite resources is of gerat significance. Because of the low grade of pyrolusiteresources in china, Choosing a reasonable reducing agent has been the key problemfor the development of pyrolusite. The traditional high-temperature roasting methodconsumes a lot of energy and is not conducive to the sustainable development ofmanganese ores. So, it is necessary to develop new reduction technologies.Manganese and manganese dioxide play important role in many fields. Therefore, it isvery important how to reasonably utilize manganese resources and obtain manganeseand manganese dioxide.This paper used scrap iron, generated in the mechanical manufacturing process,as the reductant to leach manganese sulfate from pyrolusite. The leaching solution iscomposed of the anodic solution from the electrolytic production of metal manganeseor the cycle solution from electrolytic production of manganese dioxide. Manganesesulfate solution will be obtained under certain leaching conditions. After beingsubjected to the purification treatment, the manganese sulfate solution was used to beelectro-reduced in cathodic compartment. Effect of various experiemtal factors onleaching rate of pyrolusite, effect of various electrolytic conditions on the currentefficiency were determined by the single factor method. Electrolytic kinetics ofmanganese sulfate was studied by electrochemical techniques. The main researchcontent and conclusions are as follows:（1） Scrap iron reduction of pyrolusite was thermodynamically analyzed. Standardequilibrium constants of the main reactions were obtained. The results show thatmanganese dioxide in pyrolusite has been leached out under the conditions ofleaching temperature50℃, molar ratio of sulfuric acid to manganese dioxide inpyrolusite:2.1, molar ratio of scrap iron to manganese dioxide in pyrolusite:0.78,leaching time80min. Ferric ions were removed by forming ammoniojarosite salts at80℃. Other ions （Co、Ni etc） in solution were removed by adding barium sulfide orsodium dimethyl dithiocarbamate. Fluorinating agent was added to the leachingsolution to remove calcium, magnesium and other ions.（2） Electrochemical dynamics for the Mn2+reduction were studid by using linearweep voltammetry（LSV） and cyclic voltammetry（CV） at different concentration of manganese ions. Electron transfer coefficient （α） and exchange current density （i0） atdifferent concentrations of manganese ion were obtained according to Tafel equation.At potentials of-1.14V and-1.20V, the apparent activation energies （ΔG） were37.11KJ·mol-1and30.87KJ·mol-1according to the polarization curves at differenttemperatures at20g·L-1Mn2+.（3） The high-quality of manganese of manganese metal was obtained when theeletro-reduction of Mn2+was carried out in the cathodic compartment separated fromthe anodic one with an anion-exchang membrane. SEM showed that electrolyticmanganese metal particles were uniformly dispersed and tightly packed with theparticle size of about10μm, showing a screw dislocation growing mechanism. Theobtaine manganese-chip on the cathode plate was a hard, brittle, surface smooth, andsilver-white metal. Product quality has reached the industry standard of DJMnB inYB/T051-2003. It is a high-purity grade electrolytic manganese.（4） Industrial scale tests were performed for the electrolytic manganeseproduction on the basis of experiemental results. Results showed that high-qualitymanganese metal was produced by utilizing the scrap iron reduction process. Productquality also meets the standards DJMnB;（5） In order to recover the iron in residues, residues were analyzed and treatedwith alkaline solids or high-temperature. Iron species in residues will be converted toiron hydroxide or iron oxide. The latter is then to form ferric sulfate solution byadding dilute sulfuric acid to it.（6） Reductive leaching of pyrolusite by scrap iorn in the solution produced duringthe production of electrolytic manganese dioxide particles was also studied. Theoptimal molar ratio of scrap iron to manganese dioxide in pyrolusite was0.81. Ironwas removed by forming iron hydroxide. Optimal electrolytic process parameters forthe production of electrolytic manganese dioxide particles were determined by thesingle factor method: Mn²⁺:55g·L^-1, sulfuric acid concentration:3.0mol·L⁽-1_,temperature（T）:40℃, current density（J）:300mA·cm-2. Current efficiency can reach85%at the optimal condition. Scanning electron microscopy of particles manganesedioxide showed that the particles present spherical shape with the relatively uniformsize of less than1μm.