Preparation Of Peanut Shell Adsorbent And Its Adsorption Performance On Water Heavy Metals

In this paper,the peanut shell(PS)of biomass material was used as adsorbent,Pb(Ⅱ),Cu(Ⅱ),and Cr(Ⅵ)water samples were used as research objects,and the adsorption capacity and removal rate of Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)were used as evaluation indexes,and the effect of PS on the adsorption performance of three heavy metal ions was studied by univariate experiment,and the adsorption mechanism of PS on Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)was discussed.On this basis,L-cysteine(L-Cys)was used as a modifier to modify PS,and the modification conditions were gradually optimized by single-factor test,orthogonal test,response surface test,etc.and the modified peanut shell(PS)and L-cysteine modified peanut shell(CPS)were characterized by SEM,EDS and FT-IR and other characterization methods,and univariate tests such as adsorbent dosage,adsorption time,adsorption temperature,aqueous p H and coexisting ions were carried out.The adsorption performance and adsorption mechanism of peanut shell(CPS)modified by L-Cys on Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)were continued.The main conclusions of the study are as follows:(1)When the PS dosage is 4g/L,the adsorption time is 120 min and the p H is 6,the adsorption effect of Pb(Ⅱ)is the best,the removal rate can reach 74.57%,the adsorption capacity is 9.32mg/g,and the adsorption of Pb(Ⅱ)can be completed at room temperature.When the PS dosage was 4g/L,the temperature was 25°C,the adsorption time was 120 min,and the p H was6,the adsorption effect of Cu(Ⅱ)was the best,the removal rate was 87.29%,and the adsorption capacity was 10.91mg/g.When the PS dosage is 5g/L and the p H is 2,the adsorption effect of Cr(Ⅵ)is the best,and the adsorption of Cr(Ⅵ)can be completed at room temperature,and the adsorption reaction can reach equilibrium within 120 min,the maximum removal rate is83.81%,and the adsorption capacity is 8.38mg/g.(2)The coexistence of Cu(Ⅱ)and Cr(Ⅵ)and Pb(Ⅱ)had a certain effect on the adsorption of Pb(Ⅱ)by PS,and with the gradual increase of the concentration of Cu(Ⅱ)and Cr(Ⅵ)in the same system,the removal efficiency of PS to Pb(Ⅱ)gradually decreased,and the adsorption capacity also decreased.The coexistence of Pb(Ⅱ)and Cr(Ⅵ)and Cu(Ⅱ)has a certain effect on the adsorption of Cu(Ⅱ)by PS,and when the concentration of coexistence ions Pb(Ⅱ)and Cr(Ⅵ)in the solution increases,the removal rate and adsorption capacity of Cu(Ⅱ)by PS decreases significantly.When Cr(Ⅵ),Cu(Ⅱ)and Pb(Ⅱ)coexist in the same reaction system,the adsorption of Cr(Ⅵ)by PS is completely not affected by the concentration of coexisting ions,and with the increasing concentration of Pb(Ⅱ)and Cu(Ⅱ)in the solution,the removal efficiency and adsorption capacity of Cr(Ⅵ)by PS also gradually increase,indicating that the adsorption of Cr(Ⅵ)by PS has extremely high selectivity.(3)The adsorption kinetic model and adsorption isotherm studies showed that the adsorption of Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)by PS conformed to the quasi-secondary kinetic model and the Langmuir adsorption isotherm model,and the adsorption reaction was dominated by chemical adsorption,the adsorption process was easy to carry out,and there was monolayer adsorption.Adsorption thermodynamic studies have shown that the adsorption of Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)by PS is a spontaneous and endothermic process,which can be completed at room temperature.(4)The univariate test determined the optimal influence range of PS to L-Cys mass ratio,modification time,modification temperature,modified p H and other factors in the modification conditions.Through orthogonal tests,p H was determined as the main influencing factor,and the mass ratio of PS and L-Cys was the second,and the time effect was the smallest.The response surface test showed that the significance of the effect of each factor on the removal effect of 50mg/L Pb(Ⅱ)was different,and in the 50mg/L Pb(Ⅱ)water sample,p H had the most significant effect on the removal of Pb(Ⅱ)from modified peanut shell CPS,the mass ratio of PS to L-Cys was the second,and the temperature effect was the least significant.(5)The best preparation conditions for L-Cys modified PS were: m(PS): m(LCys)=1:3.70,the reaction temperature was 66.1°C,the reaction time was 4h,and the p H was11.67,and the CPS prepared under this condition had the best effect on 50 m L of Pb(II)wastewater with an initial mass concentration of 50mg/L.(6)By SEM,EDS and FT-IR characterization analysis,the apparent morphology of PS and CPS before and after modification was observed,the PS surface was smooth,the number of pores was small,the pore size was different,the adsorption site was less,and the modified CPS surface showed many depressions and folds,the specific surface area increased,the sense of hierarchy was enhanced,the pore structure was rich,and the adsorption sites were increased.The results of EDS element content analysis showed that the content of CPS modified by L-Cys increased significantly,indicating that-SH had been successfully introduced to the PS surface.It can be seen from the FT-IR infrared spectrum that there are obvious-CO-NH-amide characteristic absorption peaks and-SH vibration absorption peaks on the surface of CPS,indicating that L-Cys is successfully introduced to the PS molecular structure in the form of amide groups.(7)The optimal adsorption conditions of CPS modified by L-Cys for Pb(II),Cu(II)and Cr(VI)were as follows: CPS dosage was 4g/L,reaction time was 120 min,p H was 4,the removal rate of Pb(II)reached the highest 95.78%,and the adsorption capacity was 11.97mg/g.When the CPS dosage was 4g/L,the reaction time was 120 min,and the p H was 5,the highest removal rate of Cu(II)was 99.46%,and the adsorption capacity was 12.43mg/g.When the CPS dosage was 4g/L and the p H was 2,the removal efficiency of Cr(VI)reached the best,which was97.26%,and the adsorption capacity was 12.16mg/g,and the adsorption of three heavy metal ions by CPS could be carried out at room temperature.After four cycles of recycling,the removal rate of Pb(II),Cu(II)and Cr(VI)of CPS is still above 85%,and the regeneration performance is good.(8)When three heavy metal ions coexist in the same system,the adsorption of CPS on Pb(Ⅱ)is affected by the concentration of Cu(Ⅱ)and Cr(Ⅵ),when the concentration of Cu(Ⅱ)and Cr(Ⅵ)is increasing,the adsorption efficiency of CPS on Pb(Ⅱ)gradually decreases,when CPS adsorbs Cu(Ⅱ),the presence of Pb(Ⅱ)and Cr(Ⅵ)also inhibits the adsorption of Cu(Ⅱ),but when Pb(Ⅱ)and Cu(Ⅱ)coexist with Cr(Ⅵ),Pb(Ⅱ)and Cu(Ⅱ)The concentration change basically had no effect on the adsorption of Cr(Ⅵ)by CPS,and the adsorption capacity and removal rate of Cr(Ⅵ)by CPS gradually increased as the concentrations of the coexisting ions Cu(Ⅱ)and Pb(Ⅱ)gradually increased.(9)The adsorption mechanism of CPS on Pb(Ⅱ),Cu(Ⅱ),and Cr(Ⅵ)may include: chelation coordination,electrostatic attraction,ion exchange and redox,and physical adsorption accompanies the entire adsorption process.(10)The adsorption of Pb(Ⅱ),Cu(Ⅱ)and Cr(Ⅵ)heavy metal ions by CPS conformed to the quasi-secondary kinetic model,and chemical adsorption was dominant.The Langmuir model can illustrate the adsorption isothermal process of CPS on three heavy metal ions.All three adsorption processes are spontaneous endothermic processes.