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A Pd/CuCl2/γ-Al2O3 catalyst of high activity (up to 87%) and of sulfur-poisoning resistance to SO2 as high as 10,000 ppm was designed for the selective catalytic oxidation of Hg0 for the first time. It was found that Pd and CuCl2 function as active sites of Hg0 adsorption and HCl activation, respectively. The combination of these two phases could improve the regeneration and migration of active chlorine, hinder the simultaneously competitive adsorption of Hg0 and SO2 on the active sites of CuCl2 and reduce the production and accumulation of sulfates, such as CuSO4. These mechanisms contributed to the outstanding catalytic performance of Pd/CuCl2/γ-Al2O3.

Reducing mercury emission is hot topic for international society. The first step for controlling mercury in fuel gas is to investigate mercury distribution and during the flue gas treatment process. The mercury transport and transformation in wet flue gas cleaning process of nonferrous smelting industry was studied in the paper with critical important parameters, such as the solution temperature, Hg0 concentration, SO2 concentration, and Hg2+ concentration at the laboratory scale. The mass ratio of the mercury distribution in the solution, flue gas, sludge, and acid fog from the simulated flue gas containing Hg2+ and Hg0 was 49.12~65.54, 18.34~35.42, 11.89~14.47, and 1.74~3.54%, respectively. The primary mercury species in the flue gas and acid fog were gaseous Hg0 and dissolved Hg2+. The mercury species in the cleaning solution were dissolved Hg2+ and colloidal mercury, which accounted for 56.56 and 7.34% of the total mercury, respectively. Various mercury compounds, including Hg2Cl2, HgS, HgCl2, HgSO4, and HgO, existed in the sludge. These results for mercury distribution and speciation are highly useful in understanding mercury transport and transformation during the wet flue gas cleaning process. This research is conducive for controlling mercury emissions from nonferrous smelting flue gas and by-products.

Nonferrous metals smelting industry is a major anthropogenic Hg emission source in China. A new method using transition metal-Tu (thiourea) solution was proposed to selectively remove Hg0 from high SO2 concentration flue gas. It is found that this solution displays significantly high Hg0 removal efficiency, up to above 88.7%, under optimal conditions, whereas the loss of SO2 is only 6.8%. High Tu concentration, low solution pH, and low temperature are helpful for Hg0 removal. The promoting effect of Fe3+ is better than that of Cu2+. The mechanism of selective Hg0 removal was studied by various methods. First, the cyclic voltammetry (CV) curves show that part of Tu could be oxidized to FDS (formamidine disulfide), which could combine with Hg0 to form Hg–Tu complex. Additionally, the UV–vis spectra indicate H2SO3 could improve the stability of FDS and facilitate Hg0 removal. In summary, the use of transition metal-Tu solution to selectively remove Hg0 from smelting flue gas displays excellent efficiency, an...

Regenerable flue gas desulfurization (FGD) is highly attractive because of the transformation of sulfur dioxide (SO2) to high-value products. In this study, selenium-assisted SO2 reduction by carbon monoxide (CO) in the liquid phase [dimethylformamide (DMF) + water (H2O) mixture] is proposed and applied in the FGD process. This process realizes recycle of the elemental sulfur product under room temperature. Moreover, results show that both the selenium catalyst and DMF solvent have good stability and can be well recycled, implying that this process is economically feasible. Furthermore, the mechanism of selenium-assisted SO2 reduction by CO in DMF/H2O is investigated. Results show that the selenium catalyst dissolves in solution and forms Sen2– species, which are the active intermediates and promote formation of the sulfur product.

In recent years, Hg re-emission from the wet scrubber has become a hot topic in the field of Hg abatement since wet scrubber has been considered as an effective way to remove Hg. In this paper, the effects of Cu ions on Hg re-emission were investigated for the first time in the presence of SO32−. The effect of CuCl32− was proved to directly reduce Hg2+ to insoluble Hg0 and to catalytically decompose Hg(SO3)22− to Hg0 and SO42− in the presence of SO32−. When adding the Cu2+ into solution with low concentration, Hg re-emission was increased due to the generation of Cu+ from the reduction of Cu2+ by SO32−. Further increase of Cu2+ concentration inhibited Hg re-emission, which was possibly owing to the formation of metal Cu which could absorb Hg0 to form amalgam. The decomposition of Hg(SO3)22− by CuCl32− and Cu+ meet pseudo-first-order reaction with respect to Hg0 and the activation energy parameters are 64.43 and 48.78 kJ/mol, respectively. Difference of electron transfer path in the decomposition of Hg(SO3)22− with Cu+ was proposed to be the reason of low activation energy.

To improve the safety and efficiency of the Se/CO/H2O redox process, five ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, [bmin][BF4], 1-propyl-3-methylimidazolium tetrafluoroborate, [pmim][BF4], 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, [bdmim][BF4], N-ethylimidazolium tetrafluoroborate, [eim][BF4], and 1-butyl-3-methyl-imidazolium trifluoromethanesulfonate, [bmim][OTf]) were used as solvents instead of dimethyl formamide. The effect of the structure of anions and cations in ionic liquid, and water content on the Se reduction rate was investigated. In addition, the Se reduction pathway was also explored using UV-vis spectroscopy. The results show that the Se reduction rate is significantly increased by ∼1.4 times using [bmim][BF4], mainly by activating the water molecules.

Recently, the mercury re-emission from the scrubbing solution has become a hot topic in wet flue gas desulfurization process (WFGD). Selenite is one of the most important matters in the solution. It is discovered that selenite have great effect on the mercury re-emission in the WFGD process in this paper. Several important parameters, such as selenite concentration, pH value, temperature and chloride concentration, and reaction mechanisms were studied on the Hg 0 re-emission. The experimental results indicate that mercury reduction and re-emission can be effectively inhibited with high selenite and chloride concentrations, low temperature and pH value. The mechanisms for inhibition of mercury reduction and re-emission are proved to be different under acid and alkaline conditions respectively. Under acid condition, it is the formation of stable HgSe that decrease Hg 0 re-emission. However, the formation of more stable HgSeO 3 SO 3 2 - or Hg ( SeO 3 ) 2 2 - than Hg ( SO 3 ) 2 2 - contributes to avoid the oxidized mercury reduction by sulfite ions and then the mercury re-emission under the alkaline condition. In addition, it is also found that Cl - ions can further enhance the inhibition effect and suppress Hg 0 re-emission by the formation of stable HgSeO 3 Cl - and HgSeO 3 Cl 2 2 - complexes.

Zinc oxide formation in seed-assisted and controlled double-jet precipitation (CDJP) was explored. Results show that the formation of ZnO involves the initial surface precipitation of β-Zn(OH)2 intermediates on seed surfaces, followed by fast surface phase transformation to ZnO. During this process, the seeds play the role of crystallization catalysts to promote ZnO formation in a short time at room temperature via changing the precipitation pathway. Meanwhile, CDJP ensures the effects of the seeds by controlling the solution supersaturation.

Microwave was employed to prepare sodium bisulfate crystal using equimolar quantities of sulfuric acid and sodium sulfate. The effects of microwave on heating behavior and water content changes were studied by monitoring the temperature and weight. To embody the positive effect of microwave on dehydrating speed and crystal transformation, thermal conductive heating was compared. The phase transformation and micro morphology of the product were characterized by X-ray diffraction and scanning electron microscopy. It was observed that crystallization with lower water content obtained higher percentage of sodium bisulfate. Microwave can significantly speed up dehydration and the dehydrating efficiency increase over the output power. According to the phase transformation process, a possible mechanism for H + -dependent sodium bisulfate crystallization is proposed. Moreover, regular crystal with greater size was obtained under microwave irradiation. The specific phenomenon may be ascribed to the oriented attachment of hydrogen sulfate in alternating electromagnetic field.

BACKGROUND SO2 is an important gaseous pollutant that seriously affects the environment and human health. The most common method for SO2 removal is absorption by NaOH solution and then forming HSO3−. Since generation of high-value products and reduction of alkali consumption are important for the economy and practical application, selenium-catalyzed HSO3− disproportionation was developed in this study. RESULTS Selenium decreased the reaction temperature of HSO3− disproportionation from >433 K to 343 K. The effects of HSO3− concentration, temperature, selenium dosage, and stirring intensity were investigated. Selenium could be used at least five times with stable catalytic performance, indicating satisfactory reusability. More importantly, a catalytic mechanism was proposed using dynamic light scattering, differential scanning calorimetry and UV-visible transmittance spectrophotometry. Results showed that selenium-catalyzed HSO3− disproportionation experienced a solid–liquid–solid phase transformation process. During this process, SeSO32− and HSe− were identified as the intermediates. Furthermore, products, i.e. sulfur and sodium bisulfate, were characterized to demonstrate their structure and composition. CONCLUSION Selenium was an efficient catalyst for HSO3− disproportionation. This catalytic process offered the advantages of less consumption of alkali and production of high-valuable products, and thus was a potential alternative to other technology for SO2 removal in practical applications. © 2015 Society of Chemical Industry

Fe(II)-EDTA, a typical chelated iron, is able to coordinate with nitric oxide (NO) which accelerates the rates and kinetics of the absorption of flue gas. However, Fe(II)-EDTA can be easily oxidized to Fe(III)-EDTA which is unable to absorb NO. Therefore, the regeneration of fresh Fe(II)-EDTA, which actually is the reduction of Fe(III)-EDTA to Fe(II)-EDTA, becomes a crucial step in the denitrification process. To enhance the reduction rate of Fe(III)-EDTA, selenium was introduced into the SO3 2−/Fe(III)-EDTA system as catalyst for the first time. By comparison, the reduction rate was enhanced by four times after adding selenium even at room temperature (25 °C). Encouragingly, elemental Se could precipitate out when SO3 2− was consumed up by oxidation to achieve self-separation. A catalysis mechanism was proposed with the aid of ultraviolet–visible (UV–Vis) spectroscopy, Tyndall scattering, horizontal attenuated total reflection Fourier transform infrared (HATR-FTIR) spectroscopy, and X-ray diffraction (XRD). In the catalysis process, the interconversion between SeSO3 2− and nascent Se formed a catalysis circle for Fe(III)-EDTA reduction in SO3 2− circumstance.

Solid–liquid separation is a fundamental and ubiquitous process in water purification. Previously, an abiological granular sludge (ABGS) formation strategy was developed to improve the solid–liquid separation in heavy metal wastewater treatment. Although this strategy can be effectively applied in hydroxide precipitation, it remains challenging to apply it to other precipitation processes and real wastewater. Here, conditions for ABGS formation in the sulfide precipitation were first optimized. The effect of pH, seed dosage, and flocculant dosage on settling velocity and metal removal was systematically investigated. The results showed that the settling velocity of ABGS reached up to 3.7 cm/s and the volume of ABGS was compressed to one fifth of the original under optimal conditions, that is, pH of 8.5, seeds dosage of 0.25 g/L, and polyacrylamide dosage of 10 mg/L. Moreover, the ABGS formed in the process was analyzed for morphology and phase composition to provide insight into the formation mechanism, involving surface nucleation and aggregation, flocculation, and rearrangement. Under the optimized conditions, real Pb–Zn smelting wastewater was treated. The settling velocity (3.4 cm/s) of ABGS formed in real wastewater was as high as that in synthetic wastewater. Therefore, the ABGS strategy is potential to be scaled up to industrial application.