Adsorption Of Pb(?) By Several Biochars Loaded With Iron-Based Composite Oxides

Heavy metal ions are the highly toxic pollutants requiring preferential control.The research on the materials and methods for heavy metal ions adsorption has been the focus of attention in multidisciplinary fields such as chemistry,material science,environmental science,etc.Specifically,the development of new adsorbents which can efficiently remove the heavy metal ions from water has attracted considerable attention of researchers.In this study,several magnetic biological carbon-based composite materials featuring carriers,developed from the industrial grade corn core biological carbon and magnetic modifiers?MnFeO_x,CuFe₂O₄ and CoFe₂O₄?loaded on the carriers,were prepared.The as-prepared materials were systematically characterized by XRD,SEM,EDS,VSM,FTIR,XPS and pH drifting test.Pb?NO₃?₂ was used as the model pollutant in the heavy metal ion adsorption studies.The ability of the as-prepared magnetic composite materials to adsorb and remove Pb?II?and the influence of the typical factors were thoroughly studied through adsorption kinetics and thermodynamics.The Pb?II?adsorption mechanism was investigated by using various modern analysis methods.The main results obtained from the experimental studies are as follows:?1?Three types of magnetic corn core biological carbon materials could be prepared by loading iron-manganese oxides,CuFe₂O₄ and CoFe₂O₄ on the corn core biological carbon following a two-step dipping and oxalate pyrolysis method.Uniform and stable coatings of MnFeO_x,CuFe₂O₄ and CoFe₂O₄ were formed on the corn core biological carbon.?2?The coating on the surface of MnFeO_x@CCBC consists of MnFe₂O₄,amorphous?-MnO₂ or hydrated manganese oxide.The MnFeO_x@CCBC sample has a pH_ZPC of 6.0 and a specific surface area of 4 m²·g^-1.The behavior and mechanism of Pb²⁺adsorption by MnFeO_x@CCBC and CCBC were investigated.The results from the adsorption experiments can be summarized as follows:1)for pH,Pb²⁺concentration and temperature set at 5.0,200mg·L^-1 and 30°C,respectively,the adsorption rate and capacity of Pb²⁺by MnFeO_x@CCBC are significantly higher than CCBC,and the process of Pb²⁺adsorption by the two materials can be fitted with the pseudo-second order model.Compared with CCBC,the pseudo-second order adsorption rate constant and equilibrium adsorption capacity for MnFeO_x@CCBC are increased by 2.3 and 5.95 times,respectively;2)Pb²⁺adsorption by MnFeO_x@CCBC and CCBC can be fitted with the Langmuir model,with the process featuring a uniform single-layer adsorption.For the temperature and pH set at 30°C and 5.0,respectively,the maximum adsorption capacity of the two materials is noted to be 99.60 and 15.66 mg·g^-1,respectively.The maximum adsorption capacity is observed to increase with temperature.The Pb²⁺adsorption is an entropy-driven and endothermal process;3)Mn-OH on the surface of CoFe₂O₄@CCBC is the main binding site for Pb?II?.The adsorption of Pb²⁺can be mainly attributed to the ion exchange of Pb²⁺with H⁺in Mn-OH through which the inner-sphere surface complexes are generated.?3?CuFe₂O₄ on the surface of CuFe₂O₄@CCBC features a face-centered cubic structure.The composite material loaded with 5%?w/w?CuFe₂O₄?CuFe₂O₄@CCBC?5%??was characterized for its adsorption behavior.The findings from the corresponding experiments can be summarized as follows:1)the saturation magnetization,specific surface area pH_ZPC of the composite material are 5.75 emu·g^-1,75 m²·g^-1 and 7.0,respectively;2)the Pb²⁺adsorption on the surface of CuFe₂O₄@CCBC?5%?can also be fitted with the pseudo-second order model and Langmuir model.The simulation results demonstrate that the pseudo-second order adsorption rate constant and maximum adsorption capacity at 30°C are 7.68×10^-3g·mg^-1·min^-1 and 132.10 mg·g^-1,respectively.The value of the two parameters are observed to be significantly higher than those of the unmodified CCBC(4.38×10^-33 g·mg^-1·min^-1 and 11.66mg·g^-1);3)the adsorption reaction during the removal of Pb?II?by CuFe₂O₄@CCBC is an endothermic and entropy-driven process;4)the formation of CuFe₂O₄ coating on the surface of the composite material leads to a simultaneous enhancement in its specific surface area as well as the amount of functional groups?M-OH and-COOH?,thus,improving the Pb?II?adsorption capacity.The synergistic effect between the ion exchange process and inner-sphere surface complexation mechanism is the major adsorption mechanism exhibited by the composite material.?4?CoFe₂O₄ on the surface of CoFe₂O₄@CCBC features a spinel structure.The composite material loaded with 5%?w/w?CoFe₂O₄?CoFe₂O₄@CCBC?5%??was characterized for its Pb²⁺adsorption behavior.The findings from the corresponding experiments can be summarized as follows:1)the particle size,specific surface area,total pore volume,average pore size and pH_ZPC are observed to be 10-50?m,93 m²·g^-1,0.11 cm³·g^-1,2.09 nm and 6.4,respectively;2)the composite material has a saturation magnetization of 7.48 emu·g^-1,indicating that its optimal magnetic separation ability;3)as for the kinetic behaviour,for the pH and temperature values set to 5.0 and 30°C,the adsorption of Pb?II?by CoFe₂O₄@CCBC?5%?can be fitted with the pseudo-second order model,and the corresponding adsorption rate constant and theoretical equilibrium adsorption capacity are7.27×10^-3 g·mg^-1·min^-1 and 124.84 mg·g^-1,respectively;4)as for the thermodynamic behaviour,the adsorption of Pb?II?by CoFe₂O₄@CCBC?5%?can be fitted with the Langmuir model.The adsorption process exhibits the characteristics of a uniform single-layer chemisorption.Its saturated adsorption capacity is 127.55 mg·g^-1,with the value increasing with temperature;5)the process of Pb?II?adsorption on the surface of CoFe₂O₄@CCBC is an endothermic and entropy-driven process;6)the functional groups such as Co?II?-OH and carboxyl groups on the surface of CoFe₂O₄@CCBC are the main binding sites for Pb?II?.H⁺in Co?II?-OH or-COOH undergoes ion exchange with Pb²⁺through which the inner-sphere surface complexes are generated.The observed findings show that the as-prepared magnetic MnFeO_x@CCBC,CuFe₂O₄@CCBC and CoFe₂O₄@CCBC can be used as effective and environmentally friendly adsorption agents for heavy metal adsorption at commercial scale.