Adsorption Of Chromium (?) By Cationic Surfactant Modified Spent Substrate In Wastewater

With the development of industry,the pollution of hexavalent chromium Cr(?)in natural water and industrial wastewater has became an important environmental issue.The use of agricultural solid waste as a adsorbent for the treatment of Cr(?)-containing wastewater is economical,efficient and environmentally friendly.In this study,using the cationic surfactant dodecyldimethylammonium bromide(DDAB)to modify the Auricularia Auricular spent substrate(AASS)to explore its adsorption effect on Cr(?)(in the form of anionic)in water.The adsorption conditions were screened by static batch adsorption test and used the response surface to optimize more significant conditions;Zeta potential analyzer,Specific surface area meter(BET),Scanning electron microscope and energy spectrometer(SEM-EDX),Fourier infrared spectrophotometer(FTIR),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS)and other methods to characterize the modified adsorbent and analyze the adsorption mechanism;Immobilized modified adsorbent was subjected to dynamic fixed-bed adsorption test to deter mine the parameters of dynamic adsorption.This study provided a theoretical and practical basis for the treatment of Cr(?)-containing wastewater from agricultural solid waste.The main results were as follows:(1)The optimum conditions for the adsorption of Cr(?)by the modified spent mushroom substrate were: 2 g/L of adsorbent,p H value of 4.0,initial Cr(?)concentration of 20 mg/L,temperature of 298 K,adsorption time of 120 min,rotational speed of 150 r/min,respectively.At this time,the adsorption capacity of the modified spent mushroom substrate was 9.75 mg/g,and the adsorption capacity of the native spent mushroom substrate was 6.06 mg/g.After the optimization of the significant conditions(p H,initial Cr(?)concentration,adsorbent dosage),the adsorption capacity reached 12.16 mg/g.Coexisting cations and anions in binary systems could interfere with the adsorption of Cr(?)by the modified spent mushroom substrate,and Pb2+ and PO43-have the greatest influence,which reduced the adsorption capacity by 19.36% and 13.64%,respectively.In addition,both Langmuir and Freundlich isothermal models were well fitted to the adsorption process of Cr(?)by the modified adsorbent,indicating that the adsorption has both chemical and physical processes.The maximum theoretical adsorption capacity at room temperature could reach 25.85 mg/g.The adsorption process conformed to the pseudo-second-order kinetic model,with the initial stage of adsorption being faster and then gradually reaching equilibrium.(2)BET analysis showed that cationic surfactant modification increased the specific surface area and pore size of the adsorbent;Zeta potential analysis showed that the surface of the modified adsorbent was positively charged,which was beneficial to attract Cr(?)in the form of anion in solution;Changes in elemental content in EDX analysis indicated that DDAB increased the potential for ion exchange and complex formation;The results of FTIR analysis showed that the carboxyl group,amine group,hydroxyl group,alkyl chain and phosphate group on the surface of the adsorbent were involved in the adsorption of Cr(?);After adsorption,XRD analysis detected the crystal structure of Cr-O compound.Scanning electron microscopy also observed the appearance of flaky particles on the surface of the modified adsorbent.The peak and binding energy in XPS analysis confirmed that part of Cr(?)was reduced to Cr(III).In summary,the adsorption process of Cr(?)by the modified adsorbent was the result of a combination of mechanisms of ion exchange,electrostatic attraction,complexation and reduction.(3)The experiment on dynamic fixed-bed adsorption showed that the influent concentration of Cr(?),flow rate and bed height were all the key factors affecting the adsorption of Cr(?)by the adsorbent.With the increase of the influent concentration of Cr(?),the adsorption efficiency of the adsorbent on Cr(?)was improved,but the depletion of the adsorbent was accelerated.At the same time,the higher flow rate was not conducive to ad sorption,and the exhaustion time was shortened from 1295 min to 520 min.In addition,In addition,an increase in the height of the bed(from 10 cm to 30 cm)could increase the capacity of adsorption by 11%.The Thomas model had a better fitting effect on the adsorption of Cr(?)by the modified adsorbent under dynamic conditions.