| A widely generated byproduct of coal-fired power plants, fly ash was explored as raw material to extract the aluminum and iron components into a solution by acid soaking and silicon component by base soaking. Then a Na2CO3 solution was slowly added to the acid solution to prepare the poly aluminum ferric sulfate(PAFS).On the basis of characterization of fly ash, types of acid solution, H2SO4 concentration, ratio of H2SO4 to fly ash and stirring time were respectively examined as factors that influenced the converting efficiencies of iron and aluminum when soaking fly ash with acid solution at atmosphere and room temperature. However, due to the limitation of utilization of acid solution and low converting efficiencies, pretreatment of fly ash to increase the acid lixiviate property was needed. The method was as follows: fly ash of 33.333g was baked with Na2CO3 of 2g in the muffle furnace at 805℃for 1h, and then the sinter was soaked by H2SO4 of 4M at boiling point in a glass reactor with the water vapor condensed. The reaction was conducted for 0.5h, then the mixture was cooled for 0.5h before filtrated. The filtrated sample contained Al of 0.207M and Fe of 0.040M.Acid soaking didn't give high conversion efficiency of silicon of fly ash while base did. The conversion efficiency for silicon compound increased with an increase in either NaOH concentration or ratio of NaOH to fly ash. A similar trend is shown with an increase in either stirring time or reaction temperature. A silicate solution was attained at the condition of NaOH-fly ash ratio of 20mL/g, NaOH of 4mol/L, reaction time of 0.5h and cooling time of 0.5h with conversion efficiency of 32.83%, a higher value than at the condition of acid soaking or room temperature. The XRD pattern of NaOH treated fly ash suggested that major phases were quartz, Al2SiO5 and Na2Al2XO3x+1.The acid solution could be used as coagulant. When treating soybean wastewater, the optimum pH range of coagulation was 68 with a wide coagulation dosage range. The COD reduction was 28.04% when the coagulant dosage of 12mL/L was employed. When treating dairy wastewater, the optimum pH range of coagulation was 48. Out of the optimum coagulation pH range, the acid solution achieved worse coagulation performance at higher pH side because of SO42-. The formed floc could settle in 10min in neutral medium. Removal efficiencies of COD and SS reached 59.35% and 92.62%, respectively when the coagulant dosage of 1.2mL/L was employed. Through researches done on affection to coagulation performance of PAFS by checking various Al/Fe mol ratios, Na2CO3 concentration, pH of PAFS, Al+Fe concentration and types of base solution, it was proved a successful condition when Na2CO3 of 100g/L was slowly added to the acid solution until the pH of the acid solution raised to 1.11.2.A ferron timed complexation colorimetric method was employed to classify the hydrolysis-polymerization law of Al(Ⅲ) and Fe(Ⅲ). The hydrolysis- polymerization process of aluminum ions and ferric ions in acid solution was investigated by pH titration. Interaction between Al(Ⅲ) and Fe(Ⅲ) was studied by using Near-infrared Spectroscopy. The result showed that [Al,Fe]a decreased as pH of PAFS was raised while [Al+Fe]b and [Al+Fe]c increased. For PAFS with pH of 1.11.2, the [Al,Fe]a species was the main component, 57.06%, with 5.58% of [Al+Fe]b and 37.36% of [Al+Fe]c. The change of pH of PAFS with aging time to a lower value was in agreement with the transformation of Al and Fe species of oligomers to high polymers. PAFS was composed of OH-Al complexes and OH-Fe complexes.PAFS had shown a high coagulation effect, superior to that of PAC for dairy wastewater treatment at the same dosage. The optimum coagulation pH range of PAFS is 69. After sedimentation period of 15min, removal efficiencies of COD and SS by this type of coagulant reached 63.9% and 94.4%, respectively.
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