Characteristics And Mechanisms Of Cr(?) Removal By Modified Solidago Canadensis And Spartina Alterniflora

China is one of the countries who suffer the most severe invasion of alien species.Spartina alterniflora and Solidago canadensis are harmful invasive plants in Eastern China,and their stalks are rich in cellulose,hemicelluloses and lignin.In addition,the hydrophilic groups of the cellulose surface are partly taken place by hydrophobic epoxy,which can strengthen fiber self-bonding.Cellulose structure has a large amount of reactive hydroxyl groups and can be used for the preparation of various functional polymers.Spartina alterniflora and Solidago Canadensis can be modified into an anionic adsorbent for the removal of anionic contaminants from aqueous solutions after treatment with suitable chemicals.This method could solve the problem of malignant propagation of Spartina alterniflora and Solidago Canadensis.Meanwhile it reuses solid waste to treat wastewater,which means it is an environmental friendly wastewater treatment technique.In this work,Spartina alterniflora(SA)and Solidago Canadensis(SC)were modified into anionic adsorbent by alkalization,etherification and graft copolymerization,and the modification mechanism was investigated.The modified Spartina alterniflora and Solidago Canadensis were characterized by element analyzer,infrared spectroscopy(FTIR),scanning electron microscopy(SEM),nitrogen adsorption,X-ray photoelectron spectroscopy(XPS)and nuclear magnetic resonance(NMR).The modified Spartina alterniflora and Solidago Canadensis were used to remove hexavalent metal chromium.The influences of adsorbent mass,initial concentration,contact time,temperature and pH on the adsorption were investigated by conducting a series of batch adsorption experiments,and the equilibrium adsorption isotherms and kinetics were investigated too.Furthermore,the removal of hexavalent metal chromium using modified Spartina alterniflora and Solidago Canadensis was studied using column technique as well.The primary results were summarized as follows:(1)To prepare MSC and MSA,Spartina alterniflora and Solidago Canadensis were modified using sodium hydroxide as the alkaline agent,epichlorohydrin as etherifing agent and triethylamine as grafting agent.The results showed that NaOH dosage didn't affect absorbent efficiency of MSC and MSA,but the dosage of epichlorohydrin and triethylamine affected absorbent efficiency obviously.The optimum preparation condition of MSC was found as follows,the ratio of SC/NaOH/ECH/TEA was 1: 13: 13: 6.7.Under the optimum condition,the absorbent efficiency of MSC could be reached 88.5% in the 10mg/L Cr(?)solution.The optimal preparation condition of MSA was found as follows,the ratio of SA/NaOH/ECH/TEA was 1: 13: 6.7: 5.3.Under the optimal condition,the absorbent efficiency of MSA could be reached 92.9% in the 20mg/L Cr(?)solution.(2)Element analyzer showed that the total nitrogen content of SC and SA increased 32% and 46%,respectively.FTIR spectra and XPS spectra indicated that the surface group structure of SC and SA had been changed after modification.In addition,a large amount of amino groups were successfully grafted onto the surface of MSC and MSA.(3)Batch adsorption experimental results indicated that adsorption behavior of MSC and MSA was significantly depending on pH,contact time,and initial concentration of Cr(?).The adsorption equilibrium time of MSC was about 3 hours,and the adsorption capacity increased obviously with the increasing concentration of Cr(?).The removal efficiency of MSC for Cr(?)significantly increased with the increasing solid/liquid ratio.When the solid/liquid ratio was 2g/L,the removal efficiency of MSC was 71%,which was higher than that of SC(9%).The pH of solution was a key parameter influencing the uptake of Cr(?),because it could change the Cr(?)ionic state and the charge property of the adsorbent surface.The proper p H scale was 1~5.Kinetic data were best fitted with the pseudo-second-order kinetic model.The batch equilibrium data was fitted well to both Langmuir and Freundlich adsorption model(R2>0.95).Maximum adsorption capacity of MSC for Cr(?)was 29.62 mg/g at 298 K.The adsorption equilibrium time of MSA was about 6 hours,and the proper pH scale was 3.When the solid/liquid ratio was 2g/L,the removal efficiency of MSA was 98%,which was higher than that of SA(7%).The adsorption process of Cr(?)on MSA was fitted with pseudo-second-order kinetic model,and the equilibrium adsorption data was fitted well to Langmuir adsorption model.Thermodynamic parameters were evaluated by applying the Van?t Hoff equation.The obtained thermodynamic parameters showed that the adsorption of Cr(?)onto MSC and MSA was a spontaneous and endothermic process.The adsorption process was enhanced with the rising temperature.(4)Dynamic adsorption results showed that initial concentration of Cr(?)and bed depth affected significantly the fixed-bed column adsorption of Cr(?).The higher initial concentration of Cr(?)and shorter bed depth shortened penetration time.The Thomas model well described the behavior of Cr(?)on MSC.Dynamic column of MSC was good at removing lower concentration of Cr(?),and adsorption ability was very stable.