Preparation Of Absorbent For Dye From Flax Shive And Its Adsorption Mechanism

A large quantity of dye wastewater is produced by texitile,leather,paper-making and plastic industries each year.As many dyes are significantly toxic,and can cause abnormal,cancerous and mutagenic,which carries a great threat on human health and life,and eco-environment good development.Therefore,dye wastewater treatment is of importance.Dye waste water treatment is very difficult.However methods in use is expensive and complicated for the process.Bio-absorbent is abounding in resource and easily obtained,also naturally porous,which is good purification material for dye wastewater.Flax shive(FS)is a kind of byproduct of fiber production.It has the similar chemical components as popular wood.However,it has not been researched in the adsorption of dyes.The studies on its theory and application on dyes adsorption need to further improvement.In this paper,dye absorbent was prepared from FS as raw material.Researches on the adsorption of malachite green(MG)on FS particle,the adsorption of reactive red and reactive yellow on chitosan-modified flax shive(CFS),and the adsorption of reactive red and reactive blue on flax shive cellulose quaternary ammonium salt(FSCQAS)were carried out.The effects of absorbent dosage,contact time,dye initial concentration,pH value and temperature on the adsorption were investigated.Focusing on kinetics equation,adsorption isotherms,thermodynamics and the parameters,the adsorption mechanisms were discussed by combing SEM,FTIR,XPS and XRD analysis.(1)The adsorption of MG on FS particleThe adsorption capacity of MG on 80～100 mesh FS particle in 10mg/L and 30mg/L solution reached 9.54mg/g and 18.1mg/g,respectively.Improving temperature is good for the adsorption of MG on FS with the increasing of initial concentration of dye solution,the adsorption capacity increased and the removal rate decreased.pH value of the dye solution has obvious effect on the adsorption.And the adsorption effect became better with the pH increasing.The adsorption is the best in a wide pH value range higher than pH 6.The experimental data were fitted to kinetic equations.It is found that the adsorption of MG on FS follows Pseudo-second-order and Elovich kinetics equations.The correlation degree is higher.But,it didn’t fit the Pseudo-order kinetic equation well.It is shown by intraparticle studies that the adsorption of MG on FS proceeded in three consecutive steps.The adsorption rate gradually decreased.Also,the intraparticle diffusion is not the only process controlling the adsorption rate.The adsorption of MG complies both Langmuir and Freundlich isotherms well.It is shown by thermodynamic equations that the adsorption of MG on FS is a spontaneous and exothermal process.The confusion degree of the system decreased after MG was absorbed on FS.FS contains SiO2,and the structure didn’t changed after the adsorption of MG.Physical and chemical adsorption promoted the adsorption,in that,the chemical one is the main effect.(2)The adsorption of reactive red and reactive yellow dyes on CFSCFS has the adsorption capacity 17 times higher than that of FS.The removal rate of the reactive red(RR)and reactive yellow(RY)dyes improves with the increasing of the absorbent dosage.When the dosage is 0.5g,the removal rates of the two dyes are about 98%and 95%,respectively.Lower pH is better for the adsorption of the dyes on CFS.When pH value of the solution is 2,the adsorption is the highest.The adsorption capacity of RR on CFS is higher than that of RY under the same conditions.The desorption of RY is easier than RR by NaOH solution.It is indicated by kinetics model studies that the adsorption of the two dyes on CFS can be well described by Pseudo-second-order and Elovich kinetics equations.The adsorption data highly correlated to Langmuir isotherm,Freundlich isotherm,as well as Temkin equation.Chemical interaction is the main adsorption for the two dyes on CFS,in which most amino groups took part in the adsorption.The dye molecules absorbed on the surface of CFS form a disorder array so that no crystalline structure occurred.(3)The adsorption of reactive red and reactive blue dyes on FSCQASFSCQAS has strong adsorption for reactive red(RR)and reactive blue(RB)dyes.When the dosage is 40mg,the capacity of the two dyes reached more than 200mg/g.pH value has significant effect on the adsorption.The adsorption became worse with the increasing of the pH value of the solution.The adsorption of RB is better than that of RR on FSCQAS.RB is more easily desorbed from FSCQAS than RR in NaOH solution.The adsorption processes of RR and RB well follow Pseudo-second-order and Elovich kinetics models and Langmuir isotherm.The adsorption of RR on FSCQAS is a spontaneous and exothermic process,but that of RB is a spontaneous and endothermic process.It is shown by SEM analysis that surface morphology of FSCQAS is obviously different from that of pristine FS cellulose.Uniform scalelike twinkle structure formed on the surface of FSCQAS.After adsorption of dyes,the twinkle grain became smoother and shallower.The FTIR and XPS results show that FSCQAS was successfully synthesized and it absorbed dyes through electrostatic force between positive and negative electric charges.It is shown by XRD analysis that FSCQAS has amorphous structure,and amorphous dyes were absorbed and uniformly distributed on the surface of FSCQAS.FS and FS-based absorbent has ideal adsorption performance of dyes,which is helpful for its application to wastewater treating practice.Furthermore,absorbent became colorful after adsorption so that it can be also utilized as a raw material.