Microwave-enhanced Pyrite Reduction Of Pyrolusite By Wet Method

Manganese is an important strategic reserve resource of the country,widely used in metallurgy,batteries,fertilizers and other fields,and plays an irreplaceable role in social production and national economy.However,my country's abundant low-grade pyrolusite(Mn%<30%)resources are difficult to industrialize due to its high mining cost,low ore utilization rate,high unit energy consumption ratio and serious pollution.Compared with conventional heating,microwave heating not only has the characteristics of rapid heating and can increase the reaction rate of the reduction process;at the same time,as one of the raw materials for the production of sulfuric acid,pyrite can not only be used as a reducing agent in the process of reducing pyrolusite,but also can reduce the amount of sulfuric acid.Therefore,based on the current urgency to develop environment-friendly and cost-effective low-grade pyrolusite reduction technology,this paper proposes a new technology for microwave-heated pyrite wet reduction of low-grade pyrolusite,which is provided by a Guangxi ore company Low-grade pyrolusite is the research object.The following researches have been carried out on the process of pyrolusite reduction and leaching of pyrolusite and microwave heating:(1)The low-grade pyrolusite wet leaching experiment was carried out under different heating methods with pyrite as the reducing agent.The experimental results show that under the same experimental conditions,microwave can strengthen the leaching of manganese from low-grade pyrolusite,and under the same leaching rate,it can reduce the used amount of pyrite by 25%and the used amount of sulfuric acid by more than 10%;At the same time,under the optimal conditions,the leaching rate of manganese under the microwave heating is increased by more than 19%compared with the conventional heating.Subsequently,the analysis of leaching kinetics showed that the microwave-enhanced reductive leaching process of low-grade pyrolusite is controlled by surface chemical reaction control,the apparent activation energy is 45.03k J/mol,and the control equation is:1-(1-x)^1/3=3425.32/r₀·[H₂SO₄]^1.316·[FeS₂/Mn O₂]^0.907·exp(-45.03/(RT))·t.And through the phase analysis of the leaching residues,it is shown that microwave can reduce the production of elemental sulfur,thereby reducing the adsorption of elemental sulfur on the surface of mineral particles,making the electrons between the Mn O₂/Fe²⁺and FeS₂/Fe³⁺corrosion potentials in the system.The channel remains unblocked,thereby increasing the leaching rate of manganese in the low-grade pyrolusite;at the same time,the electromagnetic radiation of the microwave aggravates the turbulent motion of the solution to a certain extent,and aggravates the process of the redox reaction to a certain extent.(2)The dielectric study of the pyrolusite-pyrite-sulfuric acid system indicated that the value of microwave dielectric constant of the single sulfuric acid system is 36.886(F/M),which is lower than that of the mixed system of the two ores with acid(37.787(F/M)),uncovered that the microwave absorption of the mixed system can be enhanced by the addition of minerals,indicated that microwave heating can not only heat the liquid,but also directly act on the internal minerals.Thus,the efficient reduction of low grade pyrolusite is realized.And by studying and comparing the morphology of minerals after conventional heating and microwave heating,it can be found that the manganese ore reduced by microwave has a loose and porous structure,and there were many cracks and holes on the surface,which was due to the selective heating characteristics of microwave heating.(3)Production mechanism and influence of elemental sulfur.Based on the phase analysis of slag which was obtained from the experiment,it is shown that the oxidation process of sulfur in pyrite is mainly composed of S_x^2-?S⁰?S_xO_y^2-and other different valence sulfides,in which the passivation layer formed by elemental sulfur was an important reason for the low leaching rate of manganese in the acid process of the two ores at present.The results illustrated that microwave heating can effectively alleviate the formation of sulfur,promote the redox reaction of low-valent sulfur,and greatly improve the leaching efficiency of manganese.To sum up,the reduction of low grade pyrolusite by pyrite through microwave heating can greatly improve the leaching of manganese from low grade pyrolusite,reduce the disposal cost,and provide a new direction for low-energy production and efficient clean utilization of low-grade pyrolusite in the future.