Characterization Of Biochar From Co-pyrolysis Of Sludge And Attapulgite

Pyrolytic biochar is a carbon-rich substance obtained by pyrolysis of biomass under hypoxic environment at high temperature,because of its unique structure and its good effects in agricultural soil improvement and environmental remediation.And attapulgite as a cheap,and inorganic mineral materials are more likely to win,because it has unique structure and fibre structure,making it the heavy metal ions have a strong adsorption ability,and attapulgite under 300-400 ? after thermal modification will be exposed more inner surface and reactive group,improve its adsorption capacity.On the basis of summarizing the relevant researches in recent years,this paper explored the influence mechanism of the structure and properties of biochar obtained by adding different proportions of attapulgite to sludge to prepare biochar.The experimental materials of this study were based on the sludge of anning qilihe sewage plant in lanzhou and attapulgite in banqiao town,linze county,gansu province.0%,5%,10%,15%,20%,25% and 30% attapulgite powder were added into the sludge according to the dry matter quality.Then,7 kinds of sludge-attapulgite co-pyrolysis biochar were prepared in vacuum tube pyrolysis furnace,and the basic physical and chemical properties and surface characteristics of the biochar were measured.The bioavailability of heavy metals and the morphology distribution of BCR continuous extraction method were analyzed by measuring the total amount of heavy metals in biochar during the co-pyrolysis of 7 sludge-attapulgite,as well as the total amount of heavy metals Cu,Zn,Cd,Cr and Ni in biochar.The main factors affecting the properties of biochar and its mechanism were analyzed from the aspects of physicochemical properties,characterization,availability of heavy metals and chemical morphology of heavy metals.Key findings include:The physicochemical properties and characterization of co-pyrolysis biochar were analyzed by adding different amounts of attapulgite.The results show that pH,CEC,EC and OM all change to different degrees.However,the highest heavy metal content in biochar is Zn and Cu.The general rule of heavy metal content in biochar is: Zn>Cu>Cr>Ni>Cd.With the increase of attapulgite addition,it was found that the pH value in biochar showed a trend of gradually increasing,and reached the highest value at B5,and the proportion of most heavy metals in the mass of biochar gradually increased,and the leacheability and bioavailability of heavy metals decreased to some extent.The bioavailability of heavy metals in biochar was analyzed,as well as the DTPA and TCLP contents of heavy metals Cd,Cu,Zn,Ni and Cr in biochar.Attapulgite reduced the content of heavy metal cu-dtpa in co-pyrolysis biochar,and fixed heavy metal Cu,but the overall decline was small.The variation trend of heavy metal Zn-DTPA content is similar to that of heavy metal Cu,and also shows a decreasing trend.Cd-DTPA leaching rate in biochar was significantly reduced.The Cr-DTPA content in biochar was significantly affected.The content of Ni-DTPA in biochar increased.Attapulgite addition has obvious influence on cu-tclp leaching rate in biochar,but the overall difference is not big.The leaching rate of zn-tclp was not significant in biochar with low content of attapulgite.Attapulgite can fix cd-tclp in biochar obviously.Attapulgite has a significant effect on the leaching rate of heavy metal cr-tclp in biochar.The addition of attapulgite has no obvious fixation effect on the heavy metal ni-tclp in the biochar,and it can even promote the release of Ni in the biochar and improve the bioavailable state of the heavy metal Ni.The morphological distribution of heavy metals in biochar was determined by BCR continuous extraction method.The morphological changes of heavy metals Cd,Cu,Zn,Ni and Cr in biochar all showed a tendency from instability to stability.B3(15% attapulgite added to sludge)has the best fixation effect on heavy metal Cd and Cr.B5(25% attapulgite is added to sludge)has the best fixation effect on heavy metals Cu and Zn.B0(0% attapulgite added to sludge)treatment has the best fixation effect on heavy metal Ni.It was found that the content sequence of heavy metal Cd in biochar was the oxidation state of > in the residue state of > in the acid soluble state.The content sequence of Cu in biochar is reduced > residue > acid soluble > oxidation state.The order of Zn content in biochar is reduced > residue > acid soluble > oxidation state.Biochar heavy metal Ni content ranking is reduced > residue > acid soluble > oxidation state.The content sequence of biochar heavy metal Cr is residue > oxidation > acid soluble > reduced state.