Purification Efficiency And Risk Assessment Of Red Mud For Treating Acid Mine Drainage

The serious pollution of acid mine drainage(AMD)and a large amount of red mud storage is an urgent need and a key difficulty in ecological environmental protection.AMD contains a lot of hydrogen ions and sulfate radicals.Due to low p H,heavy metals are eaiser to migrate.At present,the commonly used treatment method is lime.Because red mud has good dispersibility,small particle size,large specific surface area and pores.It has a cemented pore-frame structure and good stability in water medium.Red mud can provide better stability than other traditional neutralizers with stronger heavy metal ion adsorption capacity.In this paper,the effects of red mud dosage,reaction time and p H of influent water were investigated for three concentrations of AMD₁₀₀₀,AMD₅₀₀ and AMD₁₀₀ on the removal efficiency of iron and manganese ions.Combined with effluent p H,suspended solids content,and iron and manganese ion removal efficiency,the optimal red mud usage for each mine inflow waters is summarized.After processing AMD₁₀₀₀,AMD₅₀₀ and AMD₁₀₀,the red mud is analyzed for properties,such as zeta potential,SEM,EDX,three-dimensional fluorescence,infrared spectroscopy,XRD,etc.Based on the analysis of diameter,suspended matter content and zeta potential,the appropriate ratio of red mud to control acid mine drainage and the related mechanism of action were discussed.Adding biochar and humic acid to the reacted red mud was used to explore the effect on the physical and chemical properties of red mud.The removal process of ferrous ions mainly relies on precipitation,manganese ions mainly rely on mineral adsorption.The removal of iron ions was greatly affected by the reaction time,removal rate of manganese ions increased with the extension of the reaction time.Therefore,the optimal reaction time is 2 h.When iron and manganese ions were up to the standard,the mud-water separation effect is different.Comparing the mud-water separation effect of AMD₁₀₀₀,AMD₅₀₀ and AMD₁₀₀,the results show that AMD1000>AMD500>AMD100.Because the surface zeta potential value of AMD₁₀₀₀suspended red mud is low,the particle size of the suspension is large,and the system is unstable which is prone to sedimentation.Mainly due to the increased flocculation of hydroxide precipitates formed.AMD₁₀₀ supernatant had the worst sedimentation effect,probably because the absolute value of zeta potential is large.The p H of the supernatant is higher,system tends to be stable,and the sedimentation performance becomes worse.XRD analysis showed that the red mud was mainly concentrated in the bottom layer.The ions in AMD are ferrous.XPS shows that part of the ferrous ions in the adsorption process is oxidized into three iron ions.The adsorbed manganese ions are oxidized into trivalent manganese and tetravalent manganese which are concentrated in the bottom and middle layers.Combined with EDX analysis,the adsorbed iron was mainly concentrated on the red mud surface of the middle layer supernatant.In contrast,the red mud surface area of AMD₁₀₀₀ and AMD₅₀₀ decreased.However,the red mud surface area of AMD₁₀₀ increased.Biochar and humic acid can provide organic matter for the reacted red mud,and can also adjust the conductivity and p H.Adding biochar decreased the conductivity of red mud while adding humic acid increased the conductivity of red mud.Due to the dissolution of a metal salt and minerals in red mud was dissolved by humic acid.Adding biochar and humic acid have lower p H while red muds charge is zero.Biochar organic matter exists for a short time in reacted red mud.The humic acid can exist in red mud for a long time,up to 30 days.The risk assessment of red mud with biochar and humic acid addition is lower than the hazardous waste standard value,according to the German standard leaching method(DIN 38414-S4 standard)and our country's solid waste toxic leaching method(HJ/T 299-2007).During the mixing process,we found that the fixation ability of humic acid was stronger than biochar.The leaching concentration of the fixed red mud was lower than the leaching standard of hazardous waste.