Research On The Adsorption Of Heavy Metal Ions In Water By Lignin-based Activated Carbon

Lignin is a kind of abundant renewable resource,and the aromatic polymer in nature.Therefore,it is used as the carbon source to prepare low-cost,high-performance activated carbon and that is used to treat heavy metals in water,including the adsorption of multiple mixed heavy metal ions,which has important application significance.So based on the black liquid lignin as raw material,active carbon is prepared.And with the common three kinds of heavy metal ions(lead,copper,chromium)as the research object,the effects of different preparation conditions and adsorption conditions on the adsorption properties of heavy metals in activated carbon are inspected.The activated carbon with the best adsorption performance is obtained.The lignin and activated carbon are characterized and resolved.The adsorption kinetics of its adsorption process is analyzed.Finally,the mixed adsorption characteristics of various heavy metal ions on lignin-based activated carbon are studied.Firstly,the effects of different preparation conditions on the adsorption performance of activated carbon show that the optimum preparation conditions of activated carbon are impregnation ratio of1.5:1,the activation of 600?and the activation time of 90 mins.The BET specific surface area and pore volume of the lignin activated carbon under optimal working conditions are 1593.69m~2/g and 0.91cm~3/g respectively.At the same time,the activated carbon has a lower isoelectric point(3.5),which is rich in oxygen-containing functional groups such as hydroxyl group and carboxyl group.Secondly,the result of the effects of solution pH,adsorption temperature,adsorption time and initial concentration on the adsorption of lignin-based activated carbon on single heavy metal ions(lead ions and chromium ions,copper ions)shows that the adsorption equilibrium time of Pb,Cr,and Cu ions by lignin-based activated carbon is 90min,90min,and 80min,respectively.The pH has a great influence on the adsorption effect,but with the increase of pH,the adsorption of Pb and Cu increases,and the adsorption capacity of Cr is reduced.At pH 5.0-6.0,the lignin-based activated carbon has a good adsorption capacity for Cr ions and Pb ions.At pH 7.0-8.0,it has a good adsorption capacity for Cu ions.With the increase of initial concentration,the adsorption of three heavy metal ions increases.With the increase of temperature,the adsorption of Cr ions increases,but the adsorption of Pb and Cu ions decreases.The quasi-first/secondary kinetics model and intragranular diffusion model are used to fit the adsorption process of heavy metals with time.The results show that the adsorption of heavy metal ions by lignin-based activated carbon is more consistent with the quasi-second-order kinetics.The internal diffusion model presents two stages.By fitting to the second stage,it is concluded that intragranular diffusion is not the main rate-limiting step for controlling the adsorption process.Finally,the adsorption characteristics of lignin-based activated carbon for two heavy metal ions and three heavy metal ions are respectively studied.For the study on mixed adsorption of two heavy metal ions,The three heavy metals Pb,Cr,and Cu are classified into three binary heavy metal systems(Pb,Cr),(Pb,Cu),and(Cr,Cu).For each group of binary systems at the same and different concentration ratio,the adsorption detection experiment of adsorption process and the heavy metal interaction experiments are conducted.The results showed that the adsorption time of various heavy metals in three binary systems is at least 90min.The adsorption promotion of Cr on Pb is not significant,but the adsorption inhibition of Cu on Pb is relatively large.Pb does not have an inhibitory effect on Cr so large,but later transforms into a promoting effect.Cu inhibits Cr.Pb and Cr inhibit the adsorption of Cu.For the mixed adsorption of three heavy metal ions,the orthogonal test method is used.From the experimental results and analysis,it can be seen that the order of the adsorption capacity in the mixed system is Cr adsorption>Pb adsorption>Cu adsorption.The order of lignin-based activated carbon adsorption sensitivity for heavy metal ions in three heavy metal ions mixing systems is Cr>Pb>Cu.