Study On The Co-Utilization Of Red Mud Roasting Iron And Tailings

The increasing demand for aluminum due to economic development has led to an annual increase in the production of red mud as a byproduct of aluminum extraction.Red mud is rich in mineral and elemental resources,but its high alkalinity and radioactivity can cause pollution to the storage area.In this study,a red mud optimization mechanism was designed based on the decomposition characteristics of calcium iron garnet-based red mud,which includes a hydrothermal de-alkalization process,reduction roasting for magnetic metal recovery,and residue utilization.By regulating the composition of red mud through hydrothermal calcination and utilizing the reduction roasting process for the recovery of valuable elements,the red mud can be transformed into a cementitious material that can be directly applied to cement concrete materials,while achieving resource recovery and reducing the storage of red mud.This study focused on the composition regulation of red mud based on the calcium iron garnet phase,phase transformation of red mud under reduction roasting,and the hydration properties of the resulting cementitious material.（1）In this experiment,a hydrothermal calcination process was used to modify the red mud.The effects of hydrothermal parameters,such as temperature,time,alkaline concentration of hydrothermal solution,α_k（mass ratio of Na₂O to Al₂O₃）,and Ca/Si（Ca O to Si O₂ mass ratio）ratio,on the chemical composition,element distribution,and mineral composition of the calcined red mud were characterized and analyzed using X-ray fluorescence spectrometer（XRF）and X-ray diffractometer（XRD）.The leaching behavior of Na,Si,and Al elements in the red mud was investigated,and the ion solid solution in the calcium ferrite phase was analyzed.The key influencing factors and control methods for red mud composition were clarified.The optimal process parameters were determined as follows:40%Na OH,α_k of 40 for sodium aluminate solution,Ca/Si ratio of 2.5,temperature of 200°C,and hydrothermal time of 2 h.Under these conditions,the red mud composition is effectively regulated red mud de-alkalization rate of 89.7%,silicon dissolution rate of 22.2%,can achieve efficient de-alkalization and retain silicon,the minerals are hydrous calcium iron garnet（Ca₃Al Fe Si O₄（OH）₈,abbreviated as C₃（A,F）SH₄）,lime（Ca CO₃）,hematite（Fe₂O₃）rich in silica-aluminum iron,for the realization of cementing materials and iron recovery provides composition guarantee.（2）In this paper,the reduction roasting process is used to transform silicate minerals into dicalcium silicate gel phase,and XRD,Synchronous Thermal Analyzer（TG-DSC）and M?ssbauer spectrosmeter are used to characterize and analyze the influence of the composition of the charge,the roasting temperature and the concentration of the reducing atmosphere on the roasting products.The conversion process of calcium algarnet phase under the process of reduction roasting heat and the optimum conditions for the coexistence of magnetic minerals and non-magnetic gellite phases were explored.Then,the iron recovery efficiency and iron concentrate grade of red mud were studied by Inductively coupled plasma mass spectrometer（ICP）and vibrating sample magnetometer（VSM）.In this experiment,calcified red mud doped with 5%Ca O was placed in a tubular furnace at 1100℃and filled with 30%H₂ and 70%Ar₂for 120 min.After the reaction,the roasted products with more than 90%reusable components were obtained.The non-magnetic cementing material（REIC）is composed of C₂S,C₁₂A₇ and C₄AF,and the magnetic mineral is Fe.After magnetic separation,iron concentrate（RIP）with total iron content of 46.75%is obtained,which provides mineral composition basis for the regulation and preparation of red mud cementing material.（3）This study investigates the effect of adding gypsum and increasing the hydration temperature on the hydration performance and hydration products of red mud-based cementitious materials using methods such as hydration heat measurement,XRD,and TG-DSC.Effective control measures for the hydration performance of red mud-based cementitious materials are proposed.The results show that the addition of gypsum can slow down the phenomenon of rapid early strength increase and improve the early hydration performance of red mud-based cementitious materials,thus solving the problem of insufficient early strength of red mud-based cementitious materials.In addition,it is found that a wet and hot environment may have the potential to further optimize the hydration performance of red mud-based cementitious materials.Furthermore,the effect of red mud-based cementitious materials on the hydration process and mechanical properties of Portland cement is analyzed using XRD,Scanning Electron Microscope（SEM）and a compressive and flexural testing machine.It is found that red mud-based cementitious materials do not affect the hydration products of Portland cement,and that Portland cement with 5%red mud-based cementitious materials has good long-term strength.This study utilized a hydrothermal environment to modify red mud and achieved element separation through reduction roasting,promoting the enrichment of iron elements and the aggregation of non-magnetic minerals through magnetic separation.This resulted in the transformation of red mud into cementitious minerals while obtaining iron concentrate,which has significant environmental and economic benefits.