Adsorption Characteristics Of Lead By Modified Sludge-based Biochar In Water Solution

Lead is persistent in the environment and bioaccumulates in the body over time.It has high gastrointestinal absorption and its ability to penetrate the blood-brain barrier makes children particularly vulnerable to lead exposure and subsequent brain damage.The methods commonly used to remove Pb²⁺in aqueous phase mainly include:ion exchange,membrane process,chemical precipitation,solvent extraction and electrodeposition.These techniques are expensive and time-consuming,however adsorption is a fast,inexpensive and versatile method.Although activated carbon has the advantages of high surface area,thermal stability,porous structure,and wide pH application range as a commonly used adsorbent,it is expensive to produce.Biochar has been proposed as an alternative to traditional adsorption techniques using activated carbon due to its low price.China produces a large amount of sewage sludge every year,which brings a huge burden to the environment.Therefore,this study used municipal sludge and traditional Chinese medicine factory sludge as raw materials to prepare biochar,and modified it to study its adsorption performance for Pb²⁺and explore its adsorption mechanism for Pb²⁺.（1）Municipal sludge and pharmaceutical sludge from traditional Chinese medicine factories were selected as raw materials,and municipal sludge biochar（MBC）and pharmaceutical sludge biochar（PBC）were prepared under the condition of 500 ^oC,respectively.MBC and PBC were modified with three substances,chitosan,and six kinds of modified biochars were prepared.The physicochemical properties of biochar were analyzed by scanning electron microscope analysis,Fourier transform infrared spectroscopy analysis,X-ray diffraction analysis,iso-charge point analysis and surface functional group titration analysis.The results showed that the adsorption effect of biochar before and after modification was mainly affected by the change of surface functional groups.Among them,tartaric acid-modified biochar will form more carboxyl groups on the surface of MBC and PBC,more carboxyl groups and amino groups will be formed after ammonium persulfate modification,and abundant amino groups will be formed after chitosan modification.（2）The experiment selected and changed the following single factors to explore the influence on the adsorption effect:the amount of adsorbent added,the adsorption time,the pH of the solution and the concentration of salt ions in the solution.The experimental results show that the optimum addition amount of adsorbent is 0.6 g/L;the unmodified original biochar reached adsorption equilibrium time in 180 min,the tartaric acid and ammonium persulfate modified biochar reached adsorption equilibrium time in 120min,and the chitosan modified biochar reached adsorption equilibrium in 60 min;the adsorption effect is best when the solution is acidic;in the presence of salt ions,the monovalent cations K⁺and Na⁺have a slight inhibitory effect on the adsorption effect,while the divalent cations Ca²⁺and Mg²⁺have a stronger inhibitory effect,and the inhibitory effect of Ca²⁺is greater than that of Mg²⁺.（3）The kinetic model was used for fitting,and it was found that pseudo-second-order kinetics can better describe the adsorption process;the nonlinear fitting analysis was carried out by the Langmuir and Freundlich isotherm models,and the linear fitting analysis was carried out for the Temkin isotherm model.The maximum adsorption capacities of MBC and PBC were calculated to be 18.56 mg/g and 19.07 mg/g,respectively,and the maximum adsorption capacities of tartaric acid-modified MBC-TA and PBC-TA were 22.58 mg/g and 22.86 mg/g,respectively.The maximum adsorption capacities of ammonium sulfate-modified MBC-AP and PBC-AP were 24.38 mg/g and 22.49 mg/g,respectively,and the maximum adsorption capacities of chitosan-modified MBC-CTS and PBC-CTS were 29.84 mg/g,respectively.g and 28.70 mg/g.（4）Sludge-based biochar can adsorb Pb²⁺mainly through physical adsorption,surface precipitation,electrostatic interaction,ion exchange and complexation.Among them,the surface precipitation is the main part,and the complexation is enhanced due to the increase of carboxyl and amino groups after modification,but the surface precipitation still ranks first.In this study,two kinds of sludge-based biochars were successfully prepared,and their modification effectively improved the adsorption effect of Pb²⁺in aqueous solution,and successfully quantitatively explored the adsorption mechanism.This study confirmed that the preparation of biochar by pyrolysis of sludge to remove Pb²⁺in aqueous solution can not only successfully solve the problem of sludge treatment and disposal,but also have significant advantages such as low production cost and large adsorption capacity.Contribute to the realization of the goal of"treating waste with waste".It has huge potential both for environmental benefits and economic benefits.