No abstract

e desulfurization and denitrification wastewater (DDW) from the wet flue gas treatment project is difficult to be treated and recycled because of high chloride ion (Cl − ) concentration. Cl − can cause equipment and piping corrosion. However, there is a lack of cost-effective treatment technologies for the removal of Cl − from the DDW. In this research, the feasibility of Cl − removal from the DDW using Friedel's salt precipitation method was evaluated. Factors affecting the Cl − removal, such as Ca(OH) 2 dosage, NaAlO 2 dosage, solution's initial pH, solution's temperature, reaction time, stirring speed, and anions (SO 4 2− , NO 3 − , and F − ), were investigated, and the optimal experimental conditions for Cl − removal were determined. Experimental results showed that Friedel's salt precipitation method can remove Cl − effectively and can achieve synergistic removal of SO 4 2− , F − , and heavy metal ions. Under the best experimental conditions, the average removal efficiencies of Cl − , SO 4 2− , F − , and heavy metal ions reach more than 85%, 98%, 94%, and 99%, respectively. e Cl − removal mechanism studies showed that Cl − can be removed by precipitation as Ca 4 Al 2 Cl 2 (OH) 12 . e purified wastewater and the precipitated solid can be reused to reduce the consumption of water and alkali. Friedel's salt precipitation method is an effective control technology for the synergistic removal of Cl − , SO 4 2− , F − , and heavy metal ions and has enormous potential to be applied in the industrial wastewater treatment field.

e feasibility of removal of sulfate ions from the sodium alkali FGD wastewater using the ettringite precipitation method was evaluated. Factors affecting the removal of sulfate ions, such as NaAlO 2 dosage, Ca(OH) 2 dosage, solution temperature, anions (Cl − , NO 3 − and F − ), and heavy metal ions (Mg 2+ and Mn 2+ ), were investigated, and the optimal experimental conditions for the removal of sulfate ions were determined. Experimental results indicate that the ettringite precipitation method can effectively remove SO 4 2− with removal efficiency of more than 98%. All the investigated factors have influences on the removal of sulfate ions, and among them, the dosage of reagents, solution temperature, and fluoride ions have the strongest influence. In addition, the method can effectively synergistically remove F − and heavy metal ions with removal efficiencies of more than 90% and 99%, respectively; meanwhile, Cl − and NO 3 − also can be removed minimally by the method. e result of actual wastewater treatment shows that the method is feasible for treating high-concentration sulfate wastewater. e ettringite precipitation method has the potential to be a commercial application in the future.

In this paper, a new method of split, partial oxidation and mixed absorption for the synergistic removal of SO 2 , NOx, and Hg 0 is proposed. Factors that affect the multipollutant removal, such as the flue gas split ratio, NaClO 2 concentration, initial pH and temperature of NaClO 2 solution in the oxidation reactor, SO 2 , NO, O 2 , and CO 2 concentrations, gas flow rate, and species of alkali absorbent in the absorption reactor are investigated, with a special focus on NOx removal. Results show that SO 2 and Hg 0 are removed quite efficiently and are slightly affected by reaction conditions, whereas NOx removal is seriously affected by the above factors, except for O 2 and CO 2 concentrations. Under the best experimental conditions, the average removal efficiencies of SO 2 , NOx, and Hg 0 reach more than 99, 82, and 95%, respectively. Meanwhile, the mechanism of multipollutant removal is deduced based on related literature, experimental phenomena, and reaction products. The novel process has enormous potential in the removal of multipollutants from flue gas.