| Adsorption is one of the most effective technologies as it can be used to remove different types of refractory and toxic organcic pollutants. Fly ash is industrial waste, which can be used as adsorbent in wastewater treatment because of its active groups and porous structure. In recent years, the high value use of fly ash has abtained more attention. However, the adsorption capation of fly ash is low becacue its surface is dense. Besides that when adsorbents were used to adsorb lots of pollution, it becomes a hazardous waste that should be treated or disposed properly to avoid secondary pollution. Therefore, the study of regeneration has bcome a focus of attention of researchers.In this paper, the washed fly ash (FA) as raw material was used to prepare acid modified fly ash (MFA) as to increase the adsorption capacity of FA. The optimal conditons of modified process were:the acid concentration of 0.5 mol/L,60 min of modified time, fly:acid =1:5 (g:mL), stitting speed 150 r/min. The physicochemical properties and surface morphlogy of FA and MFA were investigated by SEM, BET and XRF methods.FA and MFA were used as adsorbents for the treatment of p-nitrophenol (PNP) and methylene blue (MB) wastewater. The adsorption kinetics, adsorption isotherms, and factors were studied. The results showed that the rate of adsorption process of PNP and MB onto FA and MFA followed the second order better, and the adsorptions followed Langmuir isotherms better. The monolayer adsorption capacity of PNP onto FA and MFA were 0.98 mg/g and 1.09 mg/g, while that of MB were 6.97 mg/g and 7.10 mg/g. The adsorption capability of MFA was larger than that of FA. The adsorption capacity of PNP when using FA and MFA decreased with the increase of pH, the adsorption capacity of MB increased with the increase of pH. Electrostatic adsorption was the major factor on the adsorption capaticy. The optimal temperature and stitting speed were 10℃and 150 r/min.Fenton-drive oxidation regeneration was used for regeneration of FA and MFA after the adsorption of PNP (FA-P and MFA-P). Around 106% and 97% percentage regeneration (PR) were abtained for FA and MFA repectively when 9.80 mmol/L H2O2 and 2.88 mmol/L Fe2+ were used at pH 3. The percentage regeneration of FA and MFA decreased with the regeneration times in 27 cycles of adsorption-regeneration equilibrium. The PRs of FA using new regeneration reagent was higher than that of MFA and FA using using intial regeneration reagent repeatedly.Two methods, Fenton-drive oxidation regeneration and thermal regeneration, were used for regeneration of the FA and MFA after the sorption of MB (FA-M and MFA-M). Around 61.2% and 54.6% percentage regeneration (PR) were abtained for FA and MFA repectively when 78.40 mmol/L H2O2 and 0.72 mmol/L Fe2+ were used at pH 3. When the conditions of thermal regeneration were 400℃and 2 h, around 101.8% and 82% PRs of FA and MFA were obtained. Positive correlation can be found between the PRs of FA and regeneration times, the PRs were 101.8%,104.1% and 107% in three cycles of adsorption-thermal regeneration process. However negative correlation can be found between the PRs of MFA and regeneration times, the PRs were 82%,75% and 73.9% in three cycles of adsorption-thermal regeneration process. The PR of FA was larger than that of MFA, and thermal regeneration was superior to Fenton-drive oxidation regeneration. |
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