Study On Recovery Of Manganese From Biomass Hydrothermal Reduction Electrolytic Manganese Residue And Heavy Metal Immobilization

As the grade of manganese ore decreases,more and more research has been carried out on the resource utilisation of manganese slag,but most of the research on manganese slag has been on the use of valuable components with high content,such as calcium sulphate.There are also studies on the recycling of manganese elements,but the specific forms and valence distribution of manganese elements have not been analysed.In this study,the basic physicochemical properties of manganese slag are studied,and the form of the manganese element is investigated in terms of its valence distribution and content,the form of the mineral phase present,and the form of the different reactivity of the element,in order to gain a better understanding of the manganese slag and to provide some guidance for the study of the form of other metals.In this study,we aim to find a method to recover manganese from manganese slag that is easy to find in terms of raw materials,simple process,mild conditions and high efficiency.The results show that manganese in electrolytic manganese slag exists in very complex forms,mainly in the form of+2,+3 and+4 valence,and the possible phases are MnO2,Mn2O3,MnFe2O4,MnSO4-2H2O and a small amount of MnSO4-2H2O in complex salts with other metal elements.The metal elements are present in the form of complex salts.Of these,+2 valent manganese accounts for 24%of the total manganese.The high valence manganese elements account for 76%of the total manganese.Studies have shown that the mass fraction of residual manganese elements in electrolytic manganese slag is approximately 8.40%and that its content is not negligible compared to the abundance of manganese elements in manganese ores,for example 21.68%in high grade rhodochrosite,and as a heavy metal,its content is well above national safety emission standards.In order to better recycle the manganese in the electrolytic manganese slag,this study removes the elemental manganese from the electrolytic manganese slag by cellulose,glucose and other biomass under acidic hydrothermal conditions.The resulting glucose as well as other small molecule organic acids can be used as reducing agents to reduce the high valent manganese in the slag to the low valent state,while the resulting organic acids can be used as acidic leaching agents to enhance the leaching of the elemental manganese.After hydrothermal completion,the solid-liquid was separated and the leaching rate of elemental manganese was analysed by ICP-MS.The optimum reaction conditions for the leaching of elemental manganese from electrolytic manganese slag by hydrothermal biomass leaching were:mass to slag ratio of 1:1,reaction temperature of 250℃,reaction time of 60 min and the use of 5%sulphuric acid solution at 20 mL to achieve the maximum leaching efficiency of 92.47%.The components that play a major role in the reaction are the small molecule organic acids and some of the reducing sugars produced by the degradation of the biomass.Finally,in this study,after the recovery of manganese from the electrolytic manganese slag,the residual electrolytic manganese slag was analysed for leaching toxicity and the heavy metal content in the leachate measured by ICP-MS was compared with the National Comprehensive Effluent Discharge Standard(NCDS)and it was found that some of the heavy metal content in the manganese slag still exceeded the NCDS,and by using the electrolytic slag to co-cure the heavy metals in the electrolytic manganese slag the study It can be intuitively felt that the accelerated carbonate treatment process before and after the reaction produced significant physical,chemical and mineralogical changes in the electrolytic manganese slag,and these changes were also clearly related to the degree of carbonation.Mineralogical analysis shows that Ca is the dominant element in the process and largely determines the composition of the carbonated material,not only that,but other elements including Mg,Fe and Mn are also involved in the process.Although XRD analysis detected carbonate minerals such as calcite,these carbonates are all effective in reducing the leaching of heavy metals.Harmlessness can be achieved.The analysis of the combined test results led to the following experimental conditions for the optimal carbonation:30%calcium carbide slag addition,0.6 MPa pressure,90 min reaction time,25:1 liquid to solid ratio and 60℃reaction temperature.The characterisation of the carbonated samples demonstrated that the addition of calcium carbide slag to the manganese slag and the introduction of CO2 was able to generate a large amount of calcium carbonate,which could reach 23%.The generation of calcium carbonate is accompanied by the generation of heavy metal carbonates and some heavy metal hydroxides,which are doped with each other.The calcium carbonate covers the heavy metal carbonates and hydroxides,and the two aspects work together to immobilise the heavy metals and make them less likely to leach out,thus achieving a harmless treatment.