Preparation Of CeO₂/Fe₂O₃/FA Composite Adsorbent And Its Adsorptive Characteristics For Simulated Wastewater Of Direct Dyes

The CeO2/Fe2O3/ fly asn composite aasorbent (CeO2/Fe2O3/ FA) was prepared by HCl treatment and precipition reaction using solid waste fly ash (FA) which from the Inner Mongolia Datang International Power Generation Co., Ltd. various precipition conditions (including raw material ratio, modifier HCl concentration, temperature, reaction time, standing temperature, standing time, calcination temperature and time) were optimized. The composite adsorbent were characterized by chemical composition, XRD, SEM, EDS, FT-IR, and the specific surface area and pore size analysis. The CeO2/Fe2O3/FA composite adsorbent was used for the removal of direct pink 12B and direct blue 2B from aqueous solution, and the optimum adsorption conditions was received, The adsorption kinetics and thermodynamics were researched, and the recycling of materials and heavy metals leaching in FA were further discussed. The future of the experimental work was prospected and some feasible suggestions were put forward. The detailed results are as follows:(1) The CeO2/Fe2O3/FA composite adsorbent was prepared by HCl treatment and precipition reaction using FA as the main material, and the optimum conditions were studied. The composite adsorbent were characterized by XRD, SEM, EDS, FT-IR, and the specific surface area and pore size analysis. The results show that when the FA were activated with 4mol/L HCl at 80℃, and then mixed with FeCl3·6H2O and Ce(SO4)2·4H2O with mass ratio of 160:4:1, and the producting solid material was roasted at 300℃ for 1h and obtained CeO2/Fe2O3/FA composite adsorbent with the best adsorption performance.(2) The adsorption properties and influencing factors of CeO2/Fe2O3/FA composite adsorbent were investigated the direct pink 12B and direct blue 2B. The results show that amount of adsorbent, the adsorption temperature and solution pH are the main factors affecting the adsorption. The best adsorption temperature is 25℃. Adsorption kinetics show that CeO2/Fe2O3/FA adsorbent has faster adsorption rate for the direct pink 12B and direct blue 2B and adsorption can reach the basic equilibrium at 30 min. Kinetic experimental data at different temperatures were primary used for Lagergren adsorption kinetics equation, pseudo second-order equation and the diffusion equation, and the results are found that the adsorption process can be explained very well by pseudo second-order equation, the second-order kinetics rate constant k2 decreases with increasing temperature The values of adsorption activation energy Ea for direct pink 12B and direct blue 2B are 19.78kJ/mol and 17.02kJ/mol. Respectively which indicate that the adsorption process may be mainly completed through physical adsorption.(3) The experimental isotherm data were analyzed using Langmuir and Freundlich isotherm models. The results revealed that the adsorption behavior fitted better with the Langmuir model (R2> 0.99) than Freundlich isotherm models (R2>0.92 and R2>0.83) at different temperatures. The Langmuir adsorption coefficient b decreased with increasing temperature, further illustrating the temperature rise was not conducive to the reaction proceeds, indicting that the adsorption is of exothermic nature; The RL value calculated by Langmuir equation were defined within the range of 0.004 to 0.022 and 0.003 to 0.023 range, iduminaling that adsorption of CeO2/Fe2O3/FA composite for direct pink 12B and direct blue 2B is very easy. Adsorption thermodynamics studies showed that at the temperature of 298K,308K,318K and 328K, thermodynamics capacities of direct pink 12B obtained through the experiment and calculation △ G was -26.95 to -28.12 kJ/mol range, △ H was-15.28 kJ/mol, △ S was 0.0395 J/mol/K; thermodynamics capacities of direct blue 2B obtained through the experiment and calculation △ G was -27.37 to-28.79 kJ/mol range, △ H was-14.01 kJ/mol, △ S was 0.0448 J/mol/K, indicating that the adsorption process of direct pink 12B and direct blue 2B was spontaneous exothermic process and adsorption process was based on physical adsorption.(4) Leaching characteristics of heavy metalions from CeO2/Fe2O3/FA composite adsorbent are studied by horizontal vibration method, and the results show that the adsorbent is no leaching toxicity according to Identification standard for hazardous wastes——Identification for extraction pwcednre inxicity GB5085.3-1996 and Control standards of pollutants in fly ash for agricultural use GB8173-87; The adsorbent will not cause pollution for surface water according to Integrated wastewater discharge standard; The measured amounts of Cd, Zn, Mn, Cu, Ni, Co, Pb, and Cr ions were far below the standard limit of each pollution index in the water environment according to Surface Water Environment Quality Standard GB3838-2002. In summary, the CeO2/Fe2O3/FA composite adsorbent is safe and feasible for dye wastewater treatment.(5) The recycling performance of the adsorbent was investigated by regeneration experiments, and the results show that the CeO2/Fe2O3/FA composite adsorbent saturated with the adsorption of direct pink 12B and direct blue 2B with NaOH solutions of 0.01 mol/L and 0.008 mol/L, by shaking 3h and 6h at 25℃ respectively and can achieve the best regeneration rate. Direct pink 12B-saturated CeO2/Fe2O3/FA can be regenerated three times and direct blue 2B-saturated CeO2/Fe2O3/FA can be regenerated twice.