Study Of Biochars Adsorption Mechanisms Of Three Kinds Of Organic Contaminants

In this project,at first by choosing different rich organic carbon solid wastes,a variety of biochars were prepared by the use of temperature-programmed method;The scanning electron microscope,elemental analysis,specific surface area analysis,spectral analysis method will be used to analyze the structural properties of the biochar,and then by optimizing the production procedure to obtain fine biochars with high adsorption capacity.Secondly,using these biochars,a lot of isothermal and kinetics of adsorption experiments of biochar with different organic contaminants had be taken.The prepared biochar and the adsorption complex were analyzed by the infrared spectroscopy to study the adsorption processes of different organic pollutants on the biochar molecules surface;then to clarify the adsorption mechanism of the biochar with different organic pollutants by combining with the structural characteristics and adsorption properties of the biochars.The results showed:(1)The properties of biochars were decided by the nature of the raw materials.Corn straw chars had significant higher C content in comparison to those others and the poplar biochars had the more H and more N content,the ash content of sludge biochar was the most.With the increase of pyrolysis temperature,the aromaticity,adsorption capacity and specific surface area of biochar increased clearly.Infrared analysis revealed a significantly change of the key functional groups of the biochar,associating with consideriable increased specific surface area.As a consequence,it improved the biochar adsorptive capacity to organics.(2)The adsorption process of 2,4-D,atrazine and naphthalene these three kinds of organic pollutants on the biochars had the same pattern which was adsorpted fastly at the beginning then slow down,with the gradually reduce of adsorption sites,and then achieve adsorption equilibrium adsorption.Biochars adsorption of naphthalene in commonly after 15 hours to reach adsorption equilibrium,while 2,4-D and atrazine adsorption takes more than 24 hours to reach equilibrium.Batch adsorption experiments revealed that 2,4-D,atrazine and naphthalene isothermal adsorption curve to biochars accord with Frendlich model;the adsorption curve of naphthalene also conforms to the Langmuir model.(3)Pyrolysis temperature and particle size of biochar will affect its adsorption characteristics of organic matter.With increasing the pyrolysis temperature,straw char and poplar leaves char increases adsorption capability for three kinds of organics.Adsorption rate and adsorption of organic pollutants increaced with the decrease of the char particles diameter.(4)The adsorption solution environment can significantly affect the biochars adsorption to organic molecules.The optimum ionic strength condition for straw biochars adsobing 2,4-D and atrazine was 0.01 mol/L,and the adsorption capacity of poplar leaves biochars to 2,4-D and atrazine increased with the increase of the strength of the electrolyte in the solution.Biochars exhibited better adsorbance to 2,4-D in acid solution conditions.The adsoption capacity to atrazine is exerts a contrary change rule,when the pH values increased,the atrazine adsorption capacity increased.The pH of the solution has no significant effect the straw char's adsorption ability to naphthalene.(5)The adsorption mechanism of three organic pollutants and biochars are different.Naphthalene was non-polar molecules in aqueous solution and the sorption mechanism of cornstalk biochars to naphthalene mainly including van der waals force,hydrophobic function and?-? EDA interactions.2,4-D molecules was negative polarity,the adsorption mechanism between 2,4-D and poplar leaves biochars was electrostatic interactions,van der Waals force,?-? EDA interaction and hydrophobic interaction.Atrazine have positive charge in aqueous solution and the adsorption process of on cornstalk biochars were affected by electrostatic interactions,hydrophobic and hydrogen bonding.The adsorption mechanism of poplar leaves biochars to atrazine was relatively simple,and the electrostatic interaction was the main adsorption mechanism.