Study On The Adsorption Of Sulfate And Nitrate In Water By Polypyrrole-modified Mushroom Residue Activated Carbon

Sulfate and nitrate are common inorganic anionic pollutants in water,and high concentrations can cause potential harm to the natural environment and human health.Common methods for removing sulfate and nitrate from water include membrane filtration,ion-exchange,chemical,biological,electrodialysis,and adsorption methods.Activated carbon（AC）adsorption has been widely used in wastewater treatment due to its selectivity,simple operation,economical,and environmental protection,but the preparation cost of AC is expensive.Biomass materials are wastes produced by agriculture and forestry that contain natural macromolecules,such as lignin and cellulose.Using them to prepare AC has outstanding performance and cost advantages.China is a major producer of edible fungi.With the rapid development of the edible fungus industry,rational disposal and effective use of mushroom residue（MR）have become issues that cannot be ignored.MR is produced by the fermentation of fungi in a culture medium.It is rich in cellulose,protein,and hydroxyl functional groups,which is conducive to the penetration of the activator into the interior to form a loose and porous structure.It is also an excellent material for preparing AC.In this study,mushroom residue activated carbon（MRAC）was prepared using agricultural waste MR as raw material and Zn Cl₂ as activator.A new type of adsorption material,polypyrrole-modified mushroom residue activated carbon（Ppy-MRAC）,was prepared by compounding MRAC and polypyrrole（Ppy）using a dipping method.The adsorption effect and adsorption mechanism of Ppy-MRAC on sulfate(SO₄^2-)and nitrate（NO₃^-）in water were studied by batch adsorption experiments,adsorption model fitting,and characterization analysis.The regeneration and practical application of Ppy-MRAC were also studied which provided an environmentally sustainable adsorbent for the removal of inorganic anions from water.The main research contents and experimental results were as follows:（1）Optimized preparation of MRAC and Ppy-MRAC.Taking the adsorption of SO₄^2-in water as the optimization index,the preparation conditions of MRAC and Ppy-MRAC were optimized by single factor experiment and response surface methodology.The experimental results showed that the optimal preparation conditions of MRAC were:activation temperature600°C,activation time 2 h,impregnation ratio（the mass ratio of Zn Cl₂ to MR）2,and impregnation time 12 h;the optimal preparation conditions of Ppy-MRAC were:pyrrole concentration 0.8 mol/L,ferric chloride concentration 2 mol/L,modification time 4 h,and modification temperature 25°C.SEM-EDS,FTIR,BET,and Zeta characterization analysis showed that MRAC could be used as a carrier to support Ppy,effectively combining hydroxyl-rich MRAC with coordinating chloride-rich Ppy,giving full play to the synergistic effect of each functional group.The prepared Ppy-MRAC was a mesoporous material with a zero-point potential of 10.2,which was beneficial to the adsorption of anionic pollutants in water.（2）Study on the adsorption of SO₄^2-and NO₃^-in water by Ppy-MRAC.Through batch adsorption experiments,the effects of initial concentration,dosage of Ppy-MRAC,adsorption time,initial p H value,and adsorption temperature on the adsorption of SO₄^2-and NO₃^-in water by Ppy-MRAC were studied.The experimental results showed that when the dosage of Ppy-MRAC was 0.4 g,the adsorption time was 180 min,and the initial p H value was 7,the adsorption capacities of Ppy-MRAC for 500 mg/L SO₄^2-at 35°C and 50 mg/L NO₃^-at 15°C were 39.41 mg/g and 10.33 mg/g,respectively The adsorption model fitting revealed adsorption of SO₄^2-and NO₃^-via spontaneous endothermic and exothermic reactions,respectively,which fit the Langmuir isotherm model and pseudo-second-order kinetic model.Through SEM-EDS,FTIR,and XPS characterization analysis,and competitive adsorption experiments,it was confirmed that the adsorption mechanisms of Ppy-MRAC on SO₄^2-and NO₃^-in water were mainly ion exchange,electrostatic attraction,and hydrogen bond,and Ppy-MRAC had a strong effect on NO₃^-selective adsorption.（3）Ppy-MRAC regeneration and application.0.1 mol/L Na OH was used to conduct regeneration experiments on Ppy-MRAC adsorbing saturated SO₄^2-and NO₃^-.The experimental results showed that the adsorption-saturated Ppy-MRAC could be regenerated by 6 cycles after Na OH elution,and had good stability.Ppy-MRAC had a high adsorption capacity for SO₄^2-and NO₃^-in real wastewater,which was a promising environment-friendly adsorbent.