Adsorption Characteristics Of Typical Pollutants On Magnetic Biochar

With the rapid development of China?s industry and agriculture,the problem of environmental pollutions has become increasingly prominent,and the control of various pollutants in aqueous phase is imminent.Biochar derived from a variety of waste materials under pyrolysis or incomplete combustion of biomass.It is recognized as a high-efficient,cost-effective sorbent for different kinds of pollutants removal due to its greater pore structure and the larger surface area.However,it is difficult to separate powdered biochar from aqueous phase because of its small particle sizes.In order to improve the separation effect,recent research has been focused on preparing magnetic biochar by inducing magnetic particles into biochar.The magnetic biochar then can be seprated from aqueous phase by magnet.In the present study,magnetic biochars were prepared by chemical co-precipitation of Fe3+/Fe²⁺ on willow wood biochar?LZ?which was pyrolyzed at the temperature of 600 ?.The surface structure,element composition and functional group of biochars were characterized by BET-N2 specific surface,scanning electron microscopy,powder X-ray diffraction and fourier transform infrared spectroscopy,respectively.The adsorption behavior of pyrene on biochars was studied to verify the removal effect of magnetic biochar on organic pollutants in aqueous phase.The adsorption behavior of heavy metals on biochars was also studied and the effects of contact time,initial concentration of heavy metals,initial pH value and biochar dosage on the adsorption were investigated.The removal effects of heavy metals in simulated wastewater by magnetic biochars and the desorption study of metal-loaded biochars by four different desorbents was studied.Main conclusions were obtained as following:1.Adsorption equilibrium of pyrene on LZ,LZ1.5 and LZ2.5 were obtained at 24 h and 72 h,respectively.The best adsorbent was LZ1.5,with the maximum adsorption capacity of 2758.6 ?g·g-1,followed by LZ2.5 and LZ.90% of pyrene was removed when LZ1.5 added dose was 375 mg·L-1.The adsorption of pyrene in aqueous by biochars could be well described by both the pseudo-one order and pseudo-second order adsorption kinetics models.Both the Freundlich and Langmuir equation fit the isothermal data well?P<0.05?.The enhanced adsorption of pyrene was partly due to the original aromatic functional groups.Additionally,the increased micropore structure and the hydroxylation of the magnetic biochar surface by introducing Fe3O4 were also contributed to the adsorption.2.Adsorption equilibrium of Pb²⁺,Cd²⁺ and Cr⁶⁺ on three biochars almost reached in 6 h,and it could be well described by pseudo-second order model and Langmuir equation.The optimum solution pH value for three heavy metals was 5.0,5.0 and 2.0,respectively.90% of three heavy metals were removed as the biochar dosage was 1000 mg·L-1.3.In a binary system,Pb²⁺ and Cd²⁺ adsorption process was better described by Langmuir isotherm than that by Freundlich isotherm.The removal effect Pb²⁺ is better than Cd²⁺,which was probably due to the selective ion exchange in the adsoprtion process.4.HNO3 with a concentration of 0.43 mol·L-1 is the best reagent for the desorption of Pb²⁺ and Cd²⁺ whose desorption amount is higher than 85%.NaOH with a concentration of 0.1 mol·L-1 is the best reagent for the desorption of Cr⁶⁺.The desorption amounts of co-loaded Pb²⁺ and Cd²⁺ by four desorption agents were below 70%,and the desorption of Pb²⁺ is higher than Cd²⁺.