Hydrothermal Modification Of Agricultural Waste Biomass Charcoal And Study Of Its Adsorption Performance

Laying hens and corn are the main livestock breeding and crop planting objects in the rural areas of China,and the annual output is huge.At the same time,these bring huge economic benefits to local farmers,and a large amount of unused agricultural waste biomass which chicken manure?CM?and corncob?CC?were also produced.Biomass contains a large amount of carbon elements,which is an ideal precursor of carbon materials.At present,the development of carbon materials with high performance is the main research topic for many researchers.In this paper,the hydrothermal modified pyrolysis biochar?HMPC?has been modified by hydrothermal reaction with pyrolysis biochar precursor?BPC?that using the mixtures of chicken manure and corn cob as raw materials,urea as hydrothermal modifier.The physicochemical properties of BPC and HMPC were characterized by EA,FTIR,SEM and so on.Using HMPC as adsorbent,the adsorption properties of heavy metal Cr?VI?and organic dye methyl orange MO in water were systematically studied.Several main conclusions of this research are as follows:?1?The effects of pyrolysis temperature of?600,700,800,900,1000??and the ratio of raw materials?chicken manure,3:1,1:1,1:3,corncob?on the physicochemical properties of BPC were investigated.It was found that the conditions of high temperature and low corncob content were favorable to the formation of"hard carbon"with porous structure.Comprehensive yield and the results of pre-adsorption Cr?VI?and MO.Pyrolytic biochar with pyrolysis temperature of 900?,ratio of 1:3 and carbon content of 70.28%was chosen as the best precursor,which could provide carbon skeleton structure for the subsequent preparation of HMPC.?2?The BPC prepared under the optimum conditions was modified by hydrothermal method.The effects of hydrothermal reaction temperature,hydrothermal reaction time and the ratio of solid to liquid?biochar mass ratio and urea aqueous solution volume ratio?on the adsorption properties of HMPC were investigated by orthogonal experiments.The preparation conditions of HMPC were optimized,and the results showed that the optimum preparation conditions of HMPC were as follows:150?hydrothermal reaction temperature,1hhydrothermal reaction time and 1:10 solid-liquid ratio.Compared with the unmodified BPC,the specific surface area and pore size structure changed less,but the element composition,surface electronegativity and functional groups changed greatly:the nitrogen content was1.38%of the unmodified BPC change to 3.06%of HMPC.The increase indicates that a large number of amino functional groups have been added to the surface of HMPC.?3?The results of static adsorption experiments show that the adsorption and removal rates of Cr?VI?and MO increase with the increase of stirring rate in the range of 50²50 rpm,and the acidic conditions are more favorable for the adsorption of Cr?VI?and MO by HMPC.For both of them,the adsorption capacity decreased with the increase of HMPC dosage,while the adsorption removal rate increased firstly,and then tended to be stable,and when the initial concentration of Cr?VI?and MO were both 60²50 mg·L^-1,the adsorption removal rate decreased gradually with the increase of the concentration,and the adsorption capacity will eventually be maintained in a certain range and no longer be significant.The final results show that the temperature is 25?,the initial pH value of Cr?VI?and MO are 2.0 and 6.5,the stirring speed is 150 rpm,and the dosage of HMPC is 1 g·L^-1,the adsorption amount of Cr?VI?and MO with initial mass concentration 100 mg·L^-11 reaches 56.26 mg·g^-11 and 73.31 mg·g^-1,respectively.?4?The adsorption of HMPC for Cr?VI?and MO comply with the pseudo-second-order kinetics model.Langmuir isotherm model can simulate the adsorption behaviors of HMPC for Cr?VI?and MO better.The thermodynamic function analysis shows that the adsorption of Cr?VI?and MO by HMPC is spontaneous and endothermic,and the increase of temperature is favorable to the adsorption.After 5 adsorption-ultrasonic regeneration cycles,the regeneration efficiency is still over 75%.The adsorption mechanism of HMPC on Cr?VI?and MO is mainly composed of chemical adsorption and electrostatic gravitational adsorption.