Preparation Of Modified Biochars And Study On Dyes And Heavy Metals Removal Performance

With the continuous progress of society and the rapid development of light and heavy industries in China,more and more industrial wastewater is produced,and the problem of water pollution has become increasingly prominent.Heavy metal and organic dye wastewater has become the representative of water pollution.In recent years,biochar has become a new type of adsorbent that may replace activated carbon because of its low cost,excellent adsorption performance and wide source of raw materials.1.In this paper,algae,coconut shell and coconut coat were used as raw materials of biochar,and three kinds of biochar were modified by KOH and H₃PO₄,respectively.The structure of biochar was characterized by SEM,BET and FT-IR,and the adsorption properties of modified biochar for three dyes（MO,MB and Rh B）were studied.The main conclusions are as follows:（1）N₂protection,700℃pyrolysis and KOH modification were used to prepare three kinds of biochar with large specific surface area and well-developed pores.The adsorption experiments showed that KOH pyrolysis modified seaweed biochar（KABc）showed a more balanced and excellent removal effect on the three dyes.When the amount of modified seaweed biochar was 20mg and the temperature was 25℃,the removal rates of three dyes（MO,MB,Rh B）were 97.24%,96.96%and 91.82%,respectively.（2）The biochar prepared by H₃PO₄as solvent and wet pyrolysis at 200℃did not show a good removal effect on methyl orange,but algae and coconut shell biochar showed a excellent effect on methylene blue.When the amount of modified biochar was 10mg and the temperature was 25℃,the removal rates of methylene blue by modified biochar（PABc,PCSBc）were 97.43%and 95.60%,respectively.（3）Through dye adsorption experiments,kinetic equation fitting and isotherm equation fitting,it is found that the adsorption of modified biochar dyes accords with quasi-second-order kinetic model and Langmuir thermodynamic model,which shows that chemical adsorption is dominant in the adsorption process.Among them,the adsorption effect of seaweed biochar modified by KOH pyrolysis on dyes is more prominent.2.Magnetic algae biochar（Fe₃O₄/KABc）and magnetic coconut biochar（Fe₃O₄/KCCBc）composites were prepared by in-situ precipitation method.The structure of the composites was characterized by SEM,BET,FT-IR,XRD and VSM,and the oxidation removal of three dyes（MO,MB,Rh B）by biochar composites was studied.The main conclusions are as follows:（1）When the temperature is 35℃,the amount of H₂O₂is 50μL and the initial p H value is3,the removal effect of methyl orange by biochar composite was the best.（2）Under the optimum conditions,the removal rates of methyl orange were 99.40%and99.44%when Fe₃O₄/KABC and Fe₃O₄/KCCBc were 5mg and 10mg,respectively.（3）KABC and KCCBc showed only adsorption properties for methyl orange solution before magnetic modification.After magnetic modification,the two composites showed the synergistic effect of catalytic degradation and adsorption when removing methyl orange solution,and the removal rate was obviously improved,which made them a catalyst with high stability,easy magnetic separation and high reuse efficiency.3.Na/N co-doped biochar composites NKABc were prepared by impregnation and calcination.The structure of biochar composites was characterized by SEM,BET,FT-IR,XRD and XPS,and the adsorption properties of biochar composites for three dyes（MO,MB,Rh B）and heavy metals Pb（II）,Cu（II）were studied.The main conclusions are as follows:（1）The removal rates of MO,MB and Rh B of modified NKABc 1%composites were39.70%,96.10%and 99.40%,respectively,when the amount of the modified NKABC 1%composites was 20mg.It can be seen that the modified composites have poor removal effect on anions,while the removal effect on cations is better.（2）Two kinds of cationic heavy metals were selected for adsorption.The results showed that the best removal conditions of Pb（II）by NKABc 10%composites were as follows:the addition of 10mg,temperature 25℃,pollutant concentration 100mg/L,the maximum removal rate was 99.80%.The best removal conditions of Cu（II）by NKABc 10%composites were as follows:the addition of 20mg,temperature 25℃,pollutant concentration50mg/L,the maximum removal rate was 96.90%.（3）The reaction mechanism of Na/N co-doped biochar composites with Pb（II）,Cu（II）was investigated by means of SEM-EDS,FT-IR and XPS;The removal mechanism of Pb（II）and Cu（II）by Na/N co-doped biochar composites includes physical adsorption（electrostatic interaction）and chemical adsorption（ion exchange,complexation and precipitation）.Chemical adsorption is the main mechanism of adsorption of Pb（II）and Cu（II）.