| About 80%of the global electrolytic manganese is produced in China,which has thus become the largest producer of electrolytic manganese metal in the world.Every 1 ton of product generated in the electrolytic manganese metal industry discharges 7–9 tons of waste,corresponding to about 20 million tons per year and more than·130 million tons accumulated over the years,with huge stockpiles.The Law of the People’s Republic of China on the Prevention and Control of Environmental Pollution by Solid Waste has been implemented since September 2020.It stipulates in Article 42 that mining enterprises should adopt scientific mining methods and beneficiation processes to reduce the production and storage of mining solid waste,such as tailings,coal gangue,and waste rock.Accordingly,identifying a method for the harmless,reduction,and resource utilization of electrolytic-manganese residue in open dumps is urgently needed.In this dissertation,we selected electrolytic manganese dioxide residue as the research object,we found that the elemental composition of electrolytic manganese dioxide residue was complex and contained some valuable metals after a thorough analysis of physicochemical properties,so first extracted the valuable metal fraction from it,and used the residue of electrolytic manganese after recovering the valuable fraction to prepare three environmental functional materials,namely,soil conditioner,curing agent and analcime.Performance research was then conducted to realize the reduction of electrolytic manganese residue and efficient stepwise resource utilization.The main research results were as follows.(1)The combination process of oxidation and weak-acid complexation was used for the harmless and resourceful utilization of electrolytic manganese residue,and the optimal process parameters and mechanism were investigated.After the oxalic acid leaching step,silicon became the main element in the acid-leaching slag.Meanwhile,the leachate generated by the acid-leaching treatment could be recovered by crystallization.This leachate contained valuable components.The mechanism of recovery was investigated and we concluded that the iron element in the electrolytic manganese residue was recovered by redox leaching,whereas the manganese element was obtained by dissolution leaching during acid leaching.Soil conditioner materials were further prepared by materializing them from the slag of electrolytic manganese residue after recovering valuable components.The alkaline soil conditioner,containing 9.81%effective silicon,which was prepared by adding acid-leaching residue and activation aid(sodium carbonate)at a ratio of 1:0.5,roasting temperature of 750°C,and roasting time of 2 h.(2)The soil improver prepared using the residue of electrolytic manganese dioxide residue was found to have applications in pot-planting experiments.When the re-greening landscape plants were grown in soil contaminated by electrolytic manganese residue,the application of 0.5%–1%soil improver caused the plants to have thick stems and highly resistant to environmental stress in the face of poor soil.The soil amendment also improved the soil environment to a certain extent and had a positive impact on enriching the microbial and fungal communities in soil.Specifically,1)phyla Actinomycetes,Acidobacteria,and Aspergillus maintained high relative abundances due to the application of soil amendment;2)the growth of Micrococcaceae was promoted and it became the dominant species,and Rhodobacteria with denitrification function lost their dominant position;and 3)the addition of an appropriate amount of soil amendment maintained the balance among fungal communities in soil,such as the significantly increased relative abundance of Cryptococcaceae community followed by a slight decrease to a new equilibrium state.Thus,the application of soil amendments effectively reduced the environmental stress on plant growth.From the differential transcriptome-expression data,we observed numerous enriched transcripts in the carbon–water metabolism,material transport,and sulfur metabolism pathways after soil-amendment application.This finding indicated that the application of soil amendment can effectively promote the root growth and metabolism of Dianthus caryophyllus L.(3)Residue of electrolytic manganese dioxide residue was used as curing material to cure and stabilize electrolytic manganese residue containing ammonia nitrogen and heavy metals Mn,Cd and Pb.Indoor and field demonstration tests were conducted,and it was found that the gelling activity of electrolytic manganese dioxide residue could reach more than 78%,which has gelling performance.At the same time,Mn,Pb and Cd in the solidified body were reduced from 781,0.05 and 0.003 mg/L to 0.038,0.01 and 0.002 mg/L respectively,all of which were lower than the level of hazardous waste identification in the Hazardous Waste Classification.All of them are lower than the limit values in"Hazardous Waste Identification Standard Leaching Toxicity Identification"(GB5085.3-2007),and almost no harm to the environment.These indicate that the residue-based environmental functional material has immobilization effect on the main pollutant-manganese element in the electrolytic manganese slag,which will not be leached out by the natural water body under the natural environment,and the leaching concentration of lead and cadmium in the leaching solution is also lower than the concentration limits of the above-mentioned standards,which are all lower than 0.005 mg/L.This indicates that the solid body has the function of safe disposal of electrolytic manganese residue,and can make electrolytic manganese residue were transformed from a Class II solid waste in general industrial solid waste to a Class I solid waste in general industrial solid waste("General Industrial Solid Waste Storage and Landfill Pollution Control Standards"(GB18599-2020)).(4)The other was zeolite material,which was synthesized by hydrothermal synthesis under the conditions of adjusted silica-to-alumina mole ratio of 16,p H 9–10,and hydrothermal reaction at 180°C for 6 h.The mineral phase of the zeolite material was primarily analcime with an average pore size of 3.1143 nm and a specific surface area of138.4 m~2/g.Results showed that the applied silica source and hydrothermal reaction duration jointly affected the properties of synthetic zeolites.Moreover,the appropriate hydrothermal reaction duration could regulate the particle size of synthetic zeolites and improve the specific surface area,pore volume,and pore size of zeolite materials,thereby providing ideas and theoretical support to guide the high value-added resource utilization of electrolytic manganese residue.Analcime materials prepared from the residue of electrolytic manganese dioxide residue were applied to adsorb two antibiotics,namely,roxithromycin and azithromycin.The maximum adsorption amounts of azithromycin and roxithromycin were 68 and 54.45 mg/g,respectively,at an initial concentration of 500 mg/L and a volume of 100 m L of the antibiotic solution with 0.2 g of analcime,maintaining an oscillation speed of 140 rpm,an adsorption time of 1260 min,and a temperature of 30°C.Different kinetic and isothermal models were used to analyze the adsorption behavior.Analysis of the adsorption behavior revealed that the adsorption of the two antibiotics by analcime was well in accordance with the quasi-level kinetic model and the Langmuir isothermal adsorption line model,i.e.,they showed single-molecular-layer physical adsorption.Thermodynamic analysis demonstrated that the adsorption was a heat-absorbing process and the increase in temperature contributed to the adsorption process.Based on the characterization of the samples before and after adsorption and density functional theory calculations,we concluded that the mechanism of adsorption of antibiotics by analcime was primarily due to the formation of abundant hydrogen bonds between the hydroxyl adsorption sites on the surface of analcime and the oxygen-containing groups on the antibiotic molecules for the purpose of binding antibiotics. |
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