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The 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 NaAlO2 dosage, Ca(OH)2 dosage, solution temperature, anions (Cl−, NO3− and F−), and heavy metal ions (Mg2+ and Mn2+), 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 SO42− 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 NO3− also can be removed minimally by the method. The result of actual wastewater treatment shows that the method is feasible for treating high-concentration sulfate wastewater. The ettringite precipitation method has the potential to be a commercial application in the future.

The 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, NaAlO2 dosage, solution’s initial pH, solution’s temperature, reaction time, stirring speed, and anions (SO42−, NO3−, 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 SO42−, F−, and heavy metal ions. Under the best experimental conditions, the average removal efficiencies of Cl−, SO42−, F−, and heavy metal ions reach more than 85%, 98%, 94%, and 99%, respectively. The Cl− removal mechanism studies showed that Cl− can be removed by precipitation as Ca4Al2Cl2(OH)12. The 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−, SO42−, F−, and heavy metal ions and has enormous potential to be applied in the industrial wastewater treatment field.

A new paraffin/surfactant/water emulsion (PSW) for volatile organic compounds (VOCs) controlling was prepared and its potential for VOCs removal was investigated. Results indicated that PSW-5 (5%, v/v) provided higher toluene absorption efficiency (90.77%) than the other absorbents used. The saturation pressure, Henry’s constant, and activity coefficient of toluene in PSW-5 were significantly lower than those in water, and toluene solubility (1.331 g·L−1) in the PSW-5 was more than 2.5 times higher than the value in water. Several factors potentially affecting the toluene absorption efficiency were systematically investigated. The results suggested that concentration and pH of PSW, absorption temperature, and gas flow rate all had a strong influence on the toluene absorption, but the inlet concentration of toluene had little effect on the toluene absorption. There were different absorbing performances of PSW-5 on different VOCs, and the ketones, esters, and aromatics were more easily removed by the PSW-5 than the alkanes. Regeneration and reuse of the PSW were possible; after 3 runs of regeneration the absorption efficiency of PSW-5 for toluene also could reach 82.42%. So, the PSW is an economic, efficient, and safe absorbent and has a great prospect in organic waste gas treatment.