Study On The Collaborative Adsorption Of Dyes And Heavy Metals By Modified Straw Adsorbent In Water

Printing and dyeing wastewater,as a kind of industrial wastewater with large quantity and high difficulty in treatment,had attracted the attention of many researchers.Therefore,it was urgent to study an efficient treatment method for different types of pollutants.At the same time,straw,as a biomass resource,due to a large number of improper treatment,had become a waste of resources and even become a kind of pollution sources.In this paper,the straw was modified and optimized by the two-step method of citric acid and acrylamide,and the adsorption properties of dye pollutants and heavy metal pollutants in high-salinity printing and dyeing wastewater were studied.1)The citric acid was grafted to the straw material through the esterification reaction between citric acid and the hydroxyl group on the cellulose in the straw,and then the carbon-carbon double bond on the acrylamide was opened through the initiator to polymerize with the hydroxyl group.And the acrylamide was grafted to the straw material,and finally the modified straw material,called WS-CA-AM,was formed.Then the formula was optimized by using the cationic dye methylene blue(MB)and the anionic dye methyl orange(MO)as the characterwastic pollutants.With SEM,FT-IR,TGA,specific surface aera,Zeta potential and other characterization methods,the success of material grafting was confirmed and various physical and chemical properties of the material were detected.2)The adsorption experiments of MO,MB,Cu2+ and Cr6+(Cr2O72-)were carried out with WS-CA-AM.WS,WS-CA and WS-AM were used as the transverse comparwason materials of WS-CA-AM.It was confirmed that the pH sensitive region of WS-CA-AM for dye pollutants of different properties was that the pH for MO should be less than 4,no less than 4 for Cu2+,no less than 3.5 for Cr6+(Cr2O72-)and larger than 5 for MB.The adsorption wasotherm and kinetics of a single pollutant were studied.WS-CA-AM had excellent adsorption capacity for MO,MB,Cu2+ and Cr6+(Cr2O72-).Langmuir isotherm fitting and pseudo-secondary kinetics fitting were performed on experimental data,and the adsorption capacity for MB was 120.84 mg/g,13.82 mg/g for Cu2+,53.88 mg/g for Cr6+(Cr2O72-)and 3053.48 mg/g for MO.At the same time,with four kinds of straw materials,the mixing system of MB,MO,Cu2+ and Cr6+(Cr2O72-)adsorption experiment was carried out,compared with single system under the adsorption quantity.It could be found that the WS-CA-AM has synergwastic adsorption capacity for two kinds of pollutants under the mixed system,and with the FT-IR,SEM and EDS for the material after absorption to explain adsorption mechanwasm.3)In order to investigate the adsorption of WS-CA-AM in high salinity wastewater,the adsorption effects of different NaCl concentrations on MB,MO,Cu2+ and Cr6+(Cr2O72-)were studied.Under the influence of salinity,the adsorption effect of WS-CA-AM on the four pollutants was reduced.Among them,the maximum adsorption capacity of cationic pollutants MB and Cu2+under the influence of maximum 10000 mg/L NaCl was about 60%and 25%of the original,while the anionic dye MO was the least affected,with the maximum adsorption capacity being about 70%of the original.And the anionic heavy metal Cr6+(Cr2O72-)was also affected,with the maximum adsorption capacity being about 20%of the original.At the same time,the adsorption in the mixed system was investigated,and it was found that the mixed cooperative adsorption effect still existed in the first two chapters under high salinity.The cooperative adsorption could effectively improve the adsorption efficiency in the mixed system of anions and cations pollutants.For isoelectric pollutant mixture system,it had competitive adsorption effect.Then the dynamic adsorption experiment was carried out on the adsorption column to study the adsorption effect of the material in the dynamic adsorption.The adsorption amount of the material was smaller than that in the static adsorption,but the effect was still excellent.At last,two dye pollutants Malachite Green(MG)and Acid Red 26(AR 26)were used in adsorption column experiment,and the adsorption effect was still very good.It could be considered that the cooperative adsorption of pollutants by materials was of generality.