Preparation And Application Of Polymerized Aluminum Ferric Sulfate From Coal Gangue Acid Leaching Solution

My country's total raw coal producti on in 2019 accounted for 68.6%of the total primary energy production,and the accompanying solid waste coal gangue is produced in the process of raw coal mining and washing.The gangue output is about20%to 25%of the raw coal,And every 1 t of raw coal selected will produce 3.0?5.0m³ of slime wastewater.With the increase in energy demand for social development,the accumulation of coal gangue and the discharge of coal slime wastewater have also increased,and at the same time it has brought about ecolo gical environmental pollution in terms of soil,atmosphere,and water quality.In recent years,a single inorganic polymer flocculant has been widely used in water treatment research,but it still has shortcomings such as low degree of polymerization and po or flocculation performance.Therefore,the development of inorganic polymer composite flocculants with more significant performance has been widely favored.However,coal gangue with large quantity and low price contains a large amount of valuable elements aluminum and iron,which are used as raw materials for the preparation of inorganic polymer composite flocculant polyaluminum iron sulfate(PAFS).It is hoped to achieve the goal of turning coal gangue waste into treasure and treating waste by waste.This article takes the high iron content coal gangue and sulfuric acid leaching solution in Panzhou,Guizhou Province as the research object.In order to explore the process of using coal gangue acid leaching solution to prepare PAFS flocculant,a preliminary study was carried out through a simulation system with the same aluminum and iron content as the acid leaching solution.The basicity of PAFS flocculant products and the flocculation performance used in the treatment of coal slime wastewater are used as eval uation indicators,and the initial experimental conditions for preparing PAFS from coal gangue acid leaching solution(real system)are set based on this.The preparation experimental conditions were optimized through orthogonal experiments,and the PAFS pr epared under the optimized conditions was applied to the treatment of coal slime wastewater.The flocculation performance of the self-made PAFS product in the process of slime wastewater treatment was explored,and the more suitable water treatment conditi ons were obtained through single factor experiments.The kinetics of the self-made PAFS treatment of the sedimentation process of slime wastewater was preliminarily studied.At the same time,the stability of self-made PAFS products was explored.It provides a certain foundation for the preparation of PAFS from coal gangue acid leaching and its application in coal slime wastewater.This paper draws the following conclusions:(1)Using FeSO₄·7H₂O and Al₂(SO₄)₃·18H₂O as raw materials,the flocculant PAFS was prepared by simulating the content of aluminum and iron in the acid leaching solution of coal gangue for the treatment of coal slime wastewater.The optimal process conditions for its preparation are:polymerization temperature of60?,polymerization time of 60 min,polymerization pH of 2.3 0,and stirring speed of 250 r/min during polymeriza tion.The liquid product of PAFS obtained under this condition is reddish brown,and the solid product is light ye llow.The basicity of the product reached 43.56%.When the product was applied to the treatment of coal slime wastewater,the turbidity removal efficiency reached 98.99%,and the COD removal efficiency reached 81.67%.(2)Using infrared spectroscopy analysi s,it can be seen that the aluminum and iron ions in the polymer PAFS have undergone polymerization reaction,and are combined by hydroxyl bridge;through the SEM characterization diagram,it can be seen that the microstructure of the polymer surface is a dense network.The structure increases the surface area,enhances the adsorption and net trapping cohesion,and shows good flocculation performance;X-ray photoelectron spectroscopy proves that the chemical form of iron on the surface of the product is tri valent,that is,the hydroxyl bridge is trivalent.The form of iron and trivalent aluminum.(3)The coal gangue acid leaching solution is used as the raw material for the preparation of PAFS,and the polymerization temperature,polymerization time,stirring speed,OH/(Al+Fe)molar ratio and other factors are investigated,and the value of each factor is set on the basis of the simulation system range.The optimal conditions for the preparation of PAFS are:polymerization temperature is 35?,polymerization time is 60 min,polymerization process stirring speed is 250 r/min,and the molar ratio of OH/(Al+Fe)is 2.4 0.The liquid product of polyaluminum iron sulfate obtained under this condition is reddish brown,and the solid product is light yellow,and the color is lighter than that of the analog system product.The basicity of the product reached 32.18%.When the product was applied to the treatment of slime wastewater,the turbidity removal rate reached 95.62%,and the COD removal efficiency reached 77.50%.(4)The conditions for preparing PAFS from coal gangue acid leaching solution were optimized by orthogonal experiment.The optimal solution is:the molar ratio of OH/(Al+Fe)is 2.50,the polymerization temperature is 35?,the polymerization time is 60 min,and the stirring speed during the polymerization is 150 r/min.(5)PAFS prepared from coal gangue acid leaching solution is applied to the treatment of coal slime wastewater,and the optimal process conditions are as follows:the dosage of flocculant is 80 m g/L,the pH of the water body is 8.00,the sedimentation temperature is 25?,and 400 Stir rapidly at r/min for 1.5 min,then stir at 200 r/min at slow speed for 2.5 min,and let it settle for 0.5 h.Under the above conditions,the turbidity removal efficiency of the treated coal slime wastewater reached 98.73%,and the COD removal efficiency reached 78.46%.(6)The self-made PAFS is used in the treatment of coal slime wastewater,steel slag wastewater,and lake water in a university.The turbidity removal efficiency is above 96.20%,and the COD removal efficiency is above 77.80%.(7)PAFS is applied to the sedimentation process of coal slime wastewater.When the hyperbolic model is used for fitting,the fitting coefficient is R²=0.8703,and when the two-stage kinetic model is used for fitting,the fitting coefficient is R²=0.9624.The sedimentation kinetics of PAFS prepared from coal gangue acid leaching solution used in the process of slime wastewater treatment is more suitable for fitting with a two-stage kinetic model.(8)The form of aluminum and iron in the product w ill continue to change with time.After 9 days of standing,0.80%of the monomer state(Al+Fe)_a is transformed into the low-medium polymerization state,with 1.87%of the medium-low polymerization state.The oligomeric state(Al+Fe)_b transformed into a high polymerization state or precipitated sol,while the high polymer or precipitated sol state(Al+Fe)_c increased by 2.673%.As time continues to increase,the monomers or oligomers in the product will gradually undergo further maturation polymerization,moving towards a higher polymerization state,in which the content of active aluminum and iron,which plays a major role in flocculation,will continue to decrease,which is prone to precipitate or The sol causes the stability to deteriorate.(9)With the increase of the storage time,the turbidity removal efficiency of self-made PAFS applied to coal slime wastewater treatment decreased from 97.19%to 95.94%,indicating that the flocculation performance of PAFS was reduced.According to the Zeta potential data,the stability of PAFS will become worse with time.