Effects of Chlorine Addition on Nitrogen Oxide Reduction and Mercury Oxidation over Selective Catalytic Reduction Catalysts.

The effect of chlorine on mercury oxidation and nitrogen oxides (NO x ) reduction over selective catalytic reduction (SCR) catalysts was investigated in this study. Commercial SCR catalysts achieved a high Hg0 oxidation efficiency when Cl2 was sprayed into the flue gas. Results indicated that an appropriate concentration of Cl2 was found to promote NO x reduction and Hg0 oxidation significantly. An optimal concentration of Cl2 (25 ppm) was found to significantly promote NO x reduction and Hg0 oxidation. Moreover, we studied the effects of Cl2 on NO x reduction and Hg0 oxidation over SCR catalysts under different concentrations of SO2. The SO2 poisoning effect was decreased by Cl2 when the SO2 concentration was low (below 1500 ppm). However, sulfate gradually covered the catalyst surface over time during the reaction, which limited the impact of Cl2. Finally, different sulfur-poisoned catalysts were examined in the presence of Cl2. The NO x reduction and Hg0 oxidation performances of sulfate-poisoned catalysts improved when Cl2 was added to the flue gas. Mechanisms for NO x reduction and Hg0 oxidation over fresh catalysts and sulfate-poisoned catalysts in the presence of Cl2 were proposed in this study. The mechanism of Cl2-influenced NO x reduction was similar to that for the NH3-SCR process. With Cl2 in the flue gas, the number of Brønsted active sites increased, which improved catalytic activity. Furthermore, Cl2 reoxidized V4+-OH to V5+=O and caused the NH3-SCR process to operate continuously. The Langmuir-Hinshelwood mechanism was followed for Hg0 oxidation by SCR catalysts when Cl2 was in the flue gas. Cl2 increased the number of Lewis active sites, and catalytic activity increased. Hg0 adsorbed on the surface of the catalysts and was then oxidized to HgCl2. Adding Cl2 to the flue gas increased the strength and number of acid sites on sulfate-poisoned catalysts.

Removal of elemental mercury from flue gas using the magnetic attapulgite by Mn-Cu oxides modification.

Mercury pollution has become one of the most concerned environmental issues in the world because of its high toxicity, non-degradability, and bioaccumulation. Attapulgite adsorbents modified by magnetic manganese-copper (MnxCuy-MATP) were fabricated by co-precipitation and ultrasonic impregnation method, aiming at removing Hg0 from coal-fired flue gas. BET, SEM, XRD, VSM, and XPS were used to systematically explore the physical and chemical properties of the adsorbents, the effects of manganese and copper additions, reaction temperature, and various components in the flue gas on the efficiency of Hg0 removal were investigated. Mn8Cu5-MATP exhibited the optimal properties, and excessive copper loadings led to the aggregation of the active components. The efficiency of mercury removal can be effectively improved by NO and HCl regardless of the absence and presence of O2, because the NO+, NO3, NO2, and Cl* produced during the reaction can promote the adsorption and oxidation of Hg0. SO2 and H2O inhibited the oxidation of Hg0 because of the competitive adsorption at the active sites, while a large amount of sulfite and sulfate were formed to block the pores. However, the introduction of copper caused the sample to obtain SO2 resistance, which resulted in a mercury removal efficiency of 84.3% even under 1500 ppm SO2. In addition, after 5 cycles of adsorption and regeneration, Mn8Cu5-MATP can still maintain excellent Hg0 removal ability. The fabricated adsorbent can save the actual production cost and effectively improve the mercury removal efficiency in sulfur-containing flue gas.

Microalgae Chlorella vulgaris and Scenedesmus dimorphus co-cultivation with landfill leachate for pollutant removal and lipid production.

In this study, landfill leachate was pre-treated with NaClO, and then diluted to 5%, 10% and 15% for microalgae growth of Chlorella vulgaris and Scenedesmus dimorphus in the mono- and co-culture modes to investigate the nutrient removal and growth characteristics of microalgae. The results revealed that landfill leachate with the 10% dilution rate was conducive for microalgae growth and exhibited robust biomass growth and the highest nutrient removal efficiency. The co-culture biomass in 10% landfill leachate achieved 0.266 g/L within 10 days and demonstrated the improved nutrient utilisation efficiency of microalgae. In addition, the chemical oxygen demand, ammonia nitrogen, total nitrate and total phosphorus removal efficiencies accordingly reached 81.0%, 80.1%, 72.1% and 86.0% in 10% landfill leachate. Meanwhile, both the enzyme activity and fluorescence parameters proved that the cell activity of co-culture was higher than that of mono-culture.

Removal of elemental mercury from flue gas using the magnetic Fe-containing carbon prepared from the sludge flocculated with ferrous sulfate.

The sewage sludge flocculated with ferrous sulfate (SFS) was prepared by one-step pyrolysis to obtain magnetic Fe-containing carbon. Results showed that only a small amount of FexOy as well as extremely weak magnetism were observed at pyrolysis temperatures of less than 500 °C. SFS tended to exhibit intensive agglomeration, leading to the drastic increase of the crystalline-phase particle size at high pyrolysis temperature. The optimal pyrolysis temperature is 700 °C, corresponding to the production of some sulfides, an optimal content of FexOy, and a suitable BET surface. Hg0 removal efficiency of SFS700 (SFS pyrolyzed at 700 °C) reached 80.7% at the reaction temperature of 125 °C. The presence of O2 and low concentration of SO2 enhanced the Hg0 removal, while the H2O vapor and high SO2 concentration inhibited it. Meanwhile, good resistance for the adsorbent to moderate concentrations of SO2 and H2O was observed. Moreover, the good magnetism performance is conducive to the recovery and utilization of the SFS700 in flue gas. Therefore, SFS can be used for Hg0 removal without any chemical modification after undergoing one-step pyrolysis and this study has guiding significance for the resource utilization and engineering practices.

Removal of Elemental Mercury from Flue Gas Using Cobalt-Containing Biomaterial Carbon Prepared from Contaminated Iris sibirica Biomass.

Iris sibirica biomass (ISBM) used for cobalt (Co) pollution remediation was prepared by one-step pyrolysis and employed to remove elemental mercury (Hg0) from flue gas. Results showed that the ISBM pyrolyzed at 700 °C (ISBM700) exhibited good Hg0 removal performance (about 86%) at 150 °C. The existence of NO and O2 facilitated the removal of Hg0, while SO2 and water vapor inhibited it. Characterization analysis (including N2 adsorption-desorption, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry) showed that ISBM700 has a relatively higher specific surface area, a quantity of lattice oxygen derived from well-dispersed amorphous-phase CoO x , and abundant oxygen functional groups. A Mars-Maessen mechanism is thought to be involved in the Hg0 removal process. The adsorbed Hg0 could be oxidized to HgO by the surface oxygen species derived from CoO x , and then, the consumed surface oxygen species can be replenished by O2. Therefore, the Co-contaminated I. sibirica biomass (CCIB) from phytoremediation could be utilized for Hg0 removal after being pyrolyzed instead of any chemical modification.