| Fulvic acid is a typical representative of natural dissolved organic matter in surface water resources, which removal efficiency is poor by conventional drinking water treatment process. In the chlorine disinfection process, fulvic acid react with chlorine will generate disinfection by-products with carcinogenic, teratogenic and mutagenic effects which serious harm to human health. Therefore, the search for removal of the fulvic acid of natural dissolved organic matter in water method has important significance.This study firstly proposed a method of potassium ferrate preparation based on calcium hypochlorite. Then the single factor and orthogonal test method was conducted to study the characteristics of fulvic acid removal in raw water by potassium ferrate oxidation. And then adopt the static adsorption method to analyze the properties, adsorption kinetics, equilibrium and thermodynamics of fulvic acid adsorbed by MIEX resin. Finally, a preliminary study on potassium ferrate + MIEX resin combination process was conducted.Firstly proposed the hypochlorite oxidation method based on calcium hypochlorite and potassium carbonate with potassium chlorate saturated solution to prepare solid potassium ferrate. The results show that the potassium hypochlorite solution concentration, potassium hypochlorite concentration of alkali solution, re-crystallization solution concentration of alkali and reaction time have different effects on the purity and yield of potassium ferrate preparation. The higher purity and yield of potassium ferrate was prepared in the conditions: potassium hypochlorite solution concentration 1.15mol/L, potassium hypochlorite concentration of alkali solution for 10.71mol/L, re-crystallization concentration of alkali solution for 15.48mol/L and reaction time in 40-60 minutes.The research of fulvic acid removal by potassium ferrate oxidation show that the oxidation reaction was faster in 10 min, but the flocculation process with generated ferric by oxidation takes longer. And the removal rate of fulvic acid increased with the dosage of potassium ferrate increasing, but decreased with the increase of the initial concentration of fulvic acid and high temperature. The optimal process parameters for the removal of fulvic acid by potassium ferrate: the initial concentration of fulvic acid was 5 mg/L, p H value was 3, the flocculation reaction time was 70 min, the oxidation reaction time was 80 min, and the dosage of potassium ferrate was 0.10g/L. The removal rates of UV254 and UV410 were 83.54% and 95.36% on the conditions, respectively.The research of fulvic acid removal adsorbed by MIEX resin show that prolong stirring time, increase the amount of resin, acid and higher temperature conditions can improve the removal rate of fulvic acid. But it decreased with the increase of the initial concentration of fulvic acid and coexisting anions. Various factors on MIEX resin adsorption indicated that the impacted degree of primary and secondary factors influencing the removal of fulvic acid is in the order of initial FA concentration > adsorption dosage > stirring time > coexisting anions > p H of solution. The optimizing process parameters of UV254 adsorption removal are: the initial concentration of fulvic acid was 1mg / L, the stirring reaction time was 180 min, the adsorbent dosage was 1.4ml/L, the p H of solution was 7 and coexisting anions was HCO3-. The study of adsorption kinetics indicated that pseudo second order model and Elovich model were suitable for describing the MIEX resin adsorption kinetic process on fulvic acid. And the Freundlich and Redlich-Peterson model can fit the adsorption equilibrium process well. The calculation of thermodynamic shows that the adsorption process was entropy increasing.The preliminary research of potassium ferrate pre-oxidation + MIEX resin adsorption combined process shows that the combination process can effectively remove the fulvic acid in raw water. And the removal rate increased 30% compared with the separate process by potassium ferrate or MIEX resin. The removal efficiency decreased with the increase of p H value. The temperature effect was not obvious, indicating that the combination process can effectively remove fulvic acid in raw water in winter and summer. |
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