| With the rapid development of human industrialization,the situation of heavy metal pollution in water is becoming more and more serious,which seriously endangers human health.Adsorption is an efficient,convenient and widely used method for the treatment of heavy metal polluted water body,and its key and difficult point lies in the selection of adsorption materials.In this paper,the rice husk,a common agricultural byproduct,was carbonized at different temperatures,and the precursor of rice husk biochar with the best adsorption effect on cadmium and lead in simulated industrial wastewater was screened out,and then magnetic Fe3O4 was loaded by liquid phase reduction-coprecipitation method.Preparation of a novel Magnetic Biocarbon adsorption material(Fe3O4/BC),which can be recovered by external magnetic field and can be recycled for many times.Based on the basic influencing factors of Fe3O4/BC adsorption of Cd2+ and Pb2+in simulated industrial wastewater,the effects of pH value of solution,contact time,addition of Fe3O4/BC,initial concentration of solution and reaction temperature on Cd2+ in a single heavy metal adsorption system were investigated.At the same time,the adsorption kinetics and isothermal thermo-mechanical model of the whole adsorption process of Pb2+ were analyzed.In order to explore the possible adsorption mechanism of Fe3O4/BC to Cd2+ and Pb2+ in simulated industrial wastewater,a series of characterizations such as(BET)specific surface area,(SEM),(FTIR)infrared spectrum and(XPS)photoelectron spectroscopy of Fe3O4/BC were used to explore the possible adsorption mechanism of Cd2+ and Cd2+ in simulated industrial wastewater.At the same time,the adsorption-desorption test of Fe3O4/BC and the small scale test of simulated waste water were carried out.And the regeneration ability and practical application effect of Fe3O4/BC were discussed.The main results are as follows:(1)The adsorption efficiency of Cd2+ and Pb2+ on rice husk biochar at different pyrolysis temperatures is poor,and the removal rate increases at first and then decreases with the increase of carbonization temperature;The adsorption ability of rice husk biochar,Fe3O4 and Fe3O4/BC for Cd2+ and Pb2+ tended to be consistent,and the adsor:ption capacity Fe3O4/BC was higher than that of rice husk biochar,and Fe3O4 had no adsorption capacity.Moreover,Fe3O4/BC has the ability to treat multiple heavy metal ions at the same time,and the binding ability of Fe3O4/BC to Pb2+ is greater than that of Cd2+.Cd2+ and Pb2+ in mixed solution adsorption system There is competitive adsorption between two and the order of adsorption selection is Pb2+>Cd2+.(2)The characterization results show that many magnetic Fe3O4 particles are attached to the surface of Fe3O4/BC,which leads to uneven surface morphology.Compared with rice husk biochar,the specific surface area and total pore volume of Fe3O4/BC increase greatly,and the adsorption sites increase.In the process of magnetic Fe3O4 supported on rice husk biochar,the reductive groups on the surface are converted to carboxyl or carbon-oxygen double bonds,and the number and species of functional groups are increased.These functional groups combine with heavy metal ions through ion exchange and complexation to improve the adsorption.ability.The accurate magnetic source of Fe3O4/BC is Fe3O4,and its saturation magnetization satisfies the condition of recovering magnetic field from aqueous solution.(3)The adsorption of Cd2+ and Pb2+ by Fe3O4/BC is mainly influenced by pH value,initial concentration of solution,adding amount of material,contact time,temperature and so on.When the concentration of Fe3O4/BC is 0.1g,the volume of solution is 100ml,the absolute temperature is 303K,the contact time is 2h,the pH(Cd)value is 6.0,the pH(Pb)value is 5.5,and the initial concentration of Cd2+ and Pb2+wastewater is 100mg/L.The specific adsorption capacity of Fe3O4/BC for Cd2+ and Pb2+ in solution is 40.06mg/g and 59.43mg/g.The adsorption rate of Fe3O4/BC on Cd2+ was greater than that of Pb2+.The equilibrium adsorption time of Cd2+ was 1h and Pb2+ was 2h.(4)The kinetic analysis shows that the pseudo-second-order kinetic model can well fit the adsorption process of Cd2+ and Pb2+ by Fe3O4/BC,and R2 is more than 0.992.The adsorption process of Fe3O4/BC and Cd2+ is better than that of Fe3O4/BC and Cd2+.The ion exchange or valence bond sharing between Pb2+ is controlled by chemisorption.The good fitting of Elovich kinetic model also shows that the distribution of binding sites of Fe3O4/BC is uneven to some extent.The results of isothermal adsorption show that both Langmuir,Temkin and D-R isothermal model can fit the Fe3O4/BC well.For the adsor:ption process of Cd2+ and Pb2+,the main adsorption process of Langmuir isothermal model is surface monolayer chemisorption.The saturated adsorption capacity of(303K)Fe3O4/BC to Cd2+ and Pb2+ is 43.45mg/g and 66.83mg/g respectively.The Temkin isothermal model indicates that electrostatic interaction may be an important mechanism that affects the adsorption of Cd2+ and Pb2+ on Fe3O4/BC,and Dur model determines that the whole system of Fe3O4/BC for Cd2+ and Pb2+ belongs to chemisorption,and the adsorption mechanism may exist ion exchange.(5)The regeneration experiment of Fe3O4/BC shows that nitric acid can desorb Cd2+ attached to Fe3O4/BC surface,and Pb2+ can regenerate it.The regenerated Fe3O4/BC still has certain treatment ability for Cd2+ and Pb2+,and it has been subjected to five successive adsorption-desorption cycles.The urnit adsorption capacity of Fe3O4/BC for.Cd2+ and Pb2+ in aqueous solution was 21.80mg/L and 31.62mg/L respectively.The experimental results of simulated industrial wastewater show that Fe3O4/BC is a kind of heavy metal polluted wastewater with good adsorption performance and multiple recovery and regeneration properties.Materials,after the initial treatment of calcium oxide,Fe3O4/BC can quickly adsorb heavy metal pollutants in industrial wastewater,the removal efficiency is up to 97%,all of them reach the national wastewater discharge standard limit(GB8978-2017). |
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