Preparation And Characterization Of Zirconium-loaded Modified Fly Ash Adsorbent And Its Adsorption For Weak Acid Dyes

Dye wastewater is one of the important sources of water pollution.Fly ash with a certain adsorption capacity is used as an adsorbent for dye wastewater treatment because it contains many active substances,but its adsorption capacity is low due to its compact surface structure.In order to solve this problem,a novel zirconium-supported modified fly ash(Zr/MFA)adsorbent was prepared by acid modification and solution reaction method using waste fly ash(FA)as the main raw material and a small amount of zirconium ions supported on the acid modified fly ash.The preparation conditions of the adsorbent were optimized.The structure,morphology and composition of FA,MFA and Zr/MFA adsorbents were characterized and analyzed by specific surface area,pore size analysis,SEM,EDS,XRD,FT-IR and UV-Vis DRS.Weak acid brilliant blue RAW and weak acid red RAW in aqueous solution were adsorbed on Zr/MFA adsorbents,and the optimized adsorption conditions were obtained.The regeneration and utilization of Zr/MFA adsorbents were also investigated,and the adsorption mechanism was discussed.The mainly results were showed as follows:(1)Optimun preparation conditions of Zr/MFA adsorbent,FA is modified by 2 mol/L HCl solution at 25?for 30 min and then it is named MFA,MFA was mixed with Zr(?)solution for 20 min,according to the mass ratios of Zr(?)ions to FA was 1:20.Zr/MFA adsorbent was obtained by drying,grinding and over 250 mesh sieve.Under the same adsorption conditions,the adsorption capacity of weak acid brilliant blue RAW and weak acid red GRS on Zr/MFA adsorbents are increased by 4.0 and 8.6 times than that of FA.The characterization results show that acid modification makes the surface of FA become rough and uneven,the pore impurities are reduced,the specific surface area and total porosity are increased,and Zr(?)ions are successfully loaded on MFA.(2)The weak acid brilliant blue RAW and weak acid red GRS adsorption properties of Zr/MFA adsorbent showed that When the dosage of Zr/MFA adsorbent is 0.10 g,the pH value of weak acid brilliant blue RAW solution is 5.0,the oscillation frequency is 180 r/min,the dye is adsorbed with Zr/MFA adsorbent for 2 h at 25?,the adsorption capacity can reach 239.3mg/g.At 25?,0.12g Zr/MFA adsorbent is put into weak acid red GRS solution(pH=6.0).When the oscillating frequency is 180 r/min,the adsorption capacity of weak acid red GRS is 125.5 mg/g when the adsorption time was 2 h.(3)The adsorption kinetics results show that Zr/MFA adsorbent has faster adsorption rates for the weak acid brilliant blue RAW and weak acid red GRS.The adsorption equilibrium state can be reached in 2 h.The pseudo-second-order model shows good correlation for the adsorption of weak acid brilliant blue RAW and weak acid red GRS on Zr/MFA adsorbents,their adsorption rates are is easily effected by the Intragranular diffusion,but it is not the only control step.(4)The adsorption isotherms of weak acid brilliant blue RAW and weak acid red GRS on Zr/MFA adsorbent were linear fitted by Langmuirn Freundlich and D-R isotherms,respectively.The results show that all the isotherms of weak acid brilliant blue RAW and weak acid red GRS by Zr/MFA adsorbent are followed the Langmuir isotherm model,and the maximum adsorption capacities of weak acid brilliant blue RAW and weak acid red GRS are 285.7 mg/g and 185.2 mg/g,respectively,the separation factor R_L is between 0 and 1,indicating that the adsorption reaction is easy to occur.(5)Theadsorptionthermodynamicsresultsshowthatthe thermodynamic constants?G°and?H°are negative at different temperatures,which show that the adsorption processes are spontaneous and exothermic.Combined with the apparent activation energy(Ea)of two weak acid dyes on Zr/MFA adsorbent,the average adsorption free energy E,The analysis of FT-IR and UV-Vis DRS before and after the adsorption of two weak acid dyes by Zr/MFA adsorbent showed that the adsorption is mainly physical adsorption and chemical adsorption.(6)Optimun regeneration conditions of Zr/MFA adsorbent:when the regeneration agent is distilled water,the regeneration time is 2 h and the temperature is 25?,Zr/MFA adsorbent has saturated weak acid brilliant blue RAW or weak acid red GRS can be regenerated at least three times and one time,respectively.The Zr/MFA adsorbent prepared in this study has the advantages of simple preparation,less time consuming,low cost and high efficiency,which provides a theoretical basis for the preparation of fly ash based adsorbent and the treatment of dye wastewater.It is expected to be widely used in fly ash and wastewater treatment.