Preparation Of Electrolytic Manganese Slag Base Polymers And Characterisation Of Contaminant Migration Under Road Use Conditions

The most dangerous source of pollution in the manganese electrolysis industry is the electrolytic manganese slag.At present,the open pile of electrolytic manganese slag in China exceeds 120 million tons,with 12 million tons of new slag added every year,in which pollutants such as manganese and ammonia and nitrogen are easily released into the external environment and cause pollution.There is an urgent need to promote clean production and speed up the promotion of economical and applicable technologies such as harmless treatment of manganese electrolysis slag and comprehensive utilization of resources,so as to achieve the goal of minimizing the risk of environmental pollution of manganese electrolysis slag.The construction of road transport infrastructure requires a large amount of road building materials,and the main phase of electrolytic manganese slag is the same as that of ordinary silicate materials,which provides the preconditions for the realisation of road resource utilisation of electrolytic manganese slag.This paper takes electrolytic manganese slag as the research object,based on the study of physical and chemical properties and leaching toxicity of electrolytic manganese slag,the volcanic ash activity of electrolytic manganese slag and fly ash is stimulated by alkali exciter and prepared into geopolymer to replace some raw materials in road surface and subgrade,then the leaching characteristics,release law,release mechanism and model fitting of long-term cumulative release of characteristic pollutants manganese and ammonia nitrogen are studied,finally the migration characteristics of pollutants in soil and groundwater are studied based on groundwater environmental safety,the main findings are as follows:1)The results show that electrolytic manganese slag is an industrial waste slag with high water content,high content of soluble salts and weak acidity,mainly composed of SO₃,Si O₂,Ca O,Fe₂O₃,Al₂O₃,Mn O,K₂O and Mg O,etc.The main physical phases are quartz and gypsum,and the microstructure is mostly irregular columnar or lumpy,with a large number of particles attached to its surface.The microstructure is mostly irregular columnar or blocky,with a large number of particles attached to its surface,such as flakes or spheres of uneven size.Leaching toxicity experiments showed that Mn and ammonia nitrogen were the main pollutants in the electrolytic manganese slag,with the average concentrations of Mn and ammonia nitrogen in the leachate being 1863.16 mg/L and1062.00 mg/L respectively.2)During the preparation of electrolytic manganese slag-based polymers,the effects of Ca O,Na OH/Na₂Si O₃ and Ca（OH）₂/Na₂Si O₃,the mass ratio of electrolytic manganese slag to fly ash,the liquid-solid ratio and the reaction temperature on the removal of pollutants were investigated,and the optimum conditions for the preparation of electrolytic manganese slag-based polymers were determined as follows:6wt%Ca O and 3wt%Na OH/Na₂Si O₃ for the addition of alkali exciter,60:40 mass ratio of electrolytic manganese slag to fly ash,50%liquid-solid ratio and 60°C curing temperature.3)The NEN7375 continuous leaching experiment was used to simulate the leaching of pollutants from the electrolytic manganese slag base aggregates in the surface and substrate.The predicted 15-year cumulative release of Mn from the surface and substrate was 4.8607 mg/m² and 12.8400 mg/m² respectively,while the predicted release of ammonia was 0.0991 mg/m² and 0.2861 mg/m² respectively.4)Due to the karst topography of the study area and the complex groundwater recharge pattern,the transport of contaminants in soil was then simulated using hydrus-1D and Visual MODFLOW based on groundwater environmental safety.The simulation assumes that the background value of manganese in groundwater in the study area has no effect on groundwater,and only considers the effect on groundwater of manganese leaching by rainwater drenching when the base aggregates of electrolytic manganese slag are used for resource recovery in road structures.The results showed that the pollutant transported in the soil for 15 years,corresponding to the burial depth of groundwater in the rainy season and dry season,the manganese concentration was 2.10×10^-4 mg/L and2.00×10^-4 mg/L respectively,which satisfied the Class III standard of Groundwater Quality Standard（GB/T14848-2017）;the pollutant transported in the groundwater for 15 years,the manganese concentration in the contaminated plume also satisfied the Groundwater Class III standard.The risk of groundwater contamination from the release of pollutants from the electrolytic manganese slag base aggregates when applied to road projects is considered manageable.