Study On Preparation Of Biomass Magnetic Activated Carbons And Their Adsorption Properties For Industrial Dye Wastewater

In this paper,peanut shells?PS?with high yield,low price,high fixed carbon and low ash content were used as raw materials for the synthesis of magnetic biomass activated carbons?MACs?by one-step method.MAC is a kind of functional activated carbon with high adsorption and magnetic property,which was applied to deal with malachite green?MG?dye wastewater.The application of biomass waste to the treatment of industrial wastewater not only reduced the cost of wastewater treatment but also relieved the burden of biomass waste on environment,which achieved the purpose of waste control by waste.Based on the thermal transformation and magnetism mechanism of FeCl₃,the characteristics of one-step method for the preparation of MAC were studied.The research on the modified adsorption properties of MgO nanoparticles was carried out.Moreover,the rapid recovery and efficient regeneration of MAC were realized.The specific research work is as follows:?1?Monometallic Fe-MAC was synthesized in the CO₂ atmosphere using the PS impregnated by FeCl₃ as the precursor by one-step method which realized the simultaneous chemical-physical activation and magnetization.The results confirmed that CO₂ not only played a significant role in the development of pore structure through C-CO₂ reaction but also converted FeCl₃ into Fe₃O₄ magnetic particles as an oxidizing atmosphere.Good adsorption perfoamance of Fe-MAC was found for MG dye with the Langmuir monolayer saturated adsorption amount of 1106.40 mg/g obtained at 298 K.Physical adsorption dominated the main force of Fe-MAC towards MG and chemical adsorption existed in the meanwhile.The main driving forces came from the internal and external mass transfer caused by the concentration difference of MG between solid and liquid phase,which is limited by the number of available active sites.?-?stacking and H-bonding interactions widely existed between Fe-MAC and MG molecules.Under alkaline conditions,electrostatic attraction promoted stable high adsorption capacity.From the thermodynamic point of view,the adsorption of MG onto Fe-MAC was a spontaneous,enthalpy-driven and exothermic process.The decrease of temperature was favorable for adsorption.?2?Bimetallic Fe-Mg-BAC with high adsorption potential was synthesized by introducing MgCl₂ as the second component other than FeCl₃.The results indicated that MgCl₂ was thermally decomposed and recrystallized into MgO nanoparticles in CO₂atmosphere,coated and aggregated on the surface of Fe₃O₄ to form Fe₃O₄/MgO composite nanostructures.A large number of MgO nanoparticles formed H-boding with N atoms in MG in the state of Mg-OH active sites in both acidic and alkaline conditions,remarkably enhancing the affinity of Fe-Mg-BAC to MG.The adsorption amount of MG with an initial concentration of 800 mg/g onto Fe-Mg15?the optimum sample?at298 K reached 3240.43 mg/g.The adsorption process was dominated by chemical adsorption,the high affinity of the MgO active site promoted the randomness at the solid-solution interface,resulting the adsorption of MG onto Fe-Mg-BAC a spontaneous,entropy-driven and endothermic process in which the increasing temperature was favorable.?3?The regeneration and cycle characteristics of Fe-MAC and Fe-Mg-BAC were studied based on the surface characteristics and adsorption mechanism of adsorbents as well as the molecular structure and decomposition characteristics of MG.The results indicated that it was difficult to remove MG from the adsorbents effectively by chemical desorption since that chemical adsorption played an important role in the adsorption of MG onto Fe-MAC and Fe-Mg-BAC.However,in the process of thermal regeneration,due to the low thermal decomposition rate of MG,a large amount of amorphous carbon in MG molecules adsorbed onto the adsorbent which cannot be decomposed and removed was crystallized into graphite crystal or partially graphite microcrystalline,which became a part of"carbon skeleton"in the adsorbent and reconstructed the pore structure of MAC,gradually increasing the adsorption performance of regenerated MAC by a limited number of thermal regeneration cycles.