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Flue gas from coal combustion contains significant amounts of volatile selenium (Se). The capture of Se in the flue gas desulfurization (FGD) scrubber unit has resulted in a generation of metal-laden residues. It is important to determine Se speciation to understand the environmental impact of its disposal. A simple method has been developed for selective inorganic Se(IV), Se(VI) and organic Se determination in the liquid-phase FGD residues by hydride generation atomic fluorescence spectrometry (AFS). It has been determined that Se(IV), Se(VI) and organic Se can be accurately determined with detection limits (DL) of 0.05, 0.06 and 0.06 microg/L, respectively. The accuracy of the proposed method was evaluated by analyzing the certified reference material, NIST CRM 1632c, and also by analyzing spiked tap-water samples. Analysis indicates that the concentration of Se is high in FGD liquid residues and primarily exists in a reduced state as selenite (Se(IV)). The toxicity of Se(IV) is the strongest of all Se species. Flue gas desulfurization residues pose a serious environmental risk.

Two Chinese coals were selected to investigate the effects of flotation on the release behavior of sulfur and nitrogen during pyrolysis. The results show that the removal rate of minerals and sulfur-containing compounds from raw coal by flotation are closely related to coal properties. The significant alterations of sulfur and nitrogen forms on coal surface are mainly presented in the decrease of sulfidic-S, thiophenic-S, and pyridinic-N, the increase of sulfones-S and quaternary-N after flotation. The release of sulfur- and nitrogen-containing gases during pyrolysis of raw and clean coals has evident differences, which are mainly caused by the change of the relative proportions of different sulfur and nitrogen forms in the process of flotation. [ABSTRACT FROM PUBLISHER]

Porous carbon-based sorbents are considered as one of the most promising materials for solving atmospheric mercury pollution. In this study, a novel porous carbon-based sorbents ZnS/AC were prepared from high sulfur petroleum coke (HSPC) and zinc nitrate by in-situ method. The as-prepared ZnS/AC sorbents were characterized by BET, XRD, ICP-OES and XPS analyses, and the element mercury removal performance of these sorbents from the simulated coal derived fuel gas were evaluated using a bench-scale fixed-bed reactor. The effects of atmospheres and temperatures on the Hg0 removal performance of ZnS/AC sorbents were also studied. The mercury removal efficiency could maintain above 84% within 4 h at ≤120 °C under N 2 + H 2 + H 2 S atmospheres. The higher temperature was not conducive to mercury removal. The average mercury removal efficiency was only 30% within 2 h at 180 °C. Hydrogen sulfide (H 2 S) significantly improved the mercury removal performance of the ZnS/AC sorbent, while the concentration of H 2 S hardly affected the mercury removal efficiency. The mercury removal efficiency of the regenerated ZnS/AC sorbents after mercury capture still maintained above 85% within 6 h at 120 °C after three cycles of capture-regeneration, it can be concluded that ZnS/AC sorbent is a promising and efficient sorbent for removing elemental mercury from fuel gases. Unlabelled Image • ZnS/AC was prepared with HSPC and Zn(NO 3) 2 by in-situ method. • Providing a novel application of high sulfur petroleum coke for mercury removal. • Effect of H 2 S on Hg adsorption ability of ZnS/AC was investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two-step craft was proposed to prepare Hg0 sorbent from high organic sulfur coal. • Fe 2 O 3 doping changed organic sulfur to FeS x during carbonization process. • KOH changed FeS x to various active sulfur during activation process. • This two-step craft can be expanded to other organic sulfur materials. It is a win–win strategy to prepare mercury sorbents from low-cost high-sulfur raw materials. In part 1, mercury sorbents with excellent performance were prepared from high inorganic sulfur coal through KOH activation. However, this method does not work for high organic sulfur coal. In this work, a two-step preparation method is developed to prepare mercury sorbents from high organic sulfur coal. The first step is the co-pyrolysis/carbonization of Fe 2 O 3 and coal, during which organic sulfur in coal is converted into FeS x. XPS shows that the percentage of S x 2–/S on the surface of the carbonized samples gradually increases from 5.4% to 22.2% with the m(Fe):m(S o) ratio from 0:4 to 5:4. The second step is KOH activation, and it converts FeS x into various S species, including C-S, S0, S 2 2− and S2−. Among the prepared mercury sorbents, LF+3Fe/4S-A (m(Fe):m(S o) = 3:4) shows the best mercury removal performance, and its mercury removal efficiency remains above 84% for 120 min under N 2 +O 2 at 120 °C. The Hg-TPDD and XPS results indicate that S*, including C-S, S0 and S 2 2−, are the major active sites for mercury removal rather than Fe element, and HgS is the main existing form of mercury on the used sorbents. Besides LF coal, this two-step process is also applicable to other high organic sulfur coals (such as LL coal, WJZ coal, and SY coal) and high-sulfur petroleum coke. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel mercury sorbent was prepared from a high inorganic sulfur coal (HISC). • The sorbent shows high Hg0 removal efficiency under complex gas conditions. • The active sulfur in the sorbent reacts with Hg0 to form stable HgS. A novel sulfur hybrid mercury sorbent was successfully prepared by chemically activating high inorganic sulfur coal using potassium hydroxide (KOH). The optimal conditions for preparing the sorbent are at 800 °C with the ratio of KOH/coal at 2:4 by mass. The prepared sorbent, named ZY-2:4-800, containing 0.92% sulfur with a high specific surface area of 353 m2·g−1, has a wide temperature range for mercury removal. Between 60 and 180 °C, the Hg0 removal efficiencies of this sorbent keep above 95% within 2 hr under N 2 +O 2 +NO+SO 2 +H 2 O. This is because that O 2 can slightly improve the mercury removal ability of the sorbent, and it shows great resistance to acid gas (NO and SO 2) and H 2 O. The calculated Hg0 adsorption capacity of ZY-2:4-800 is 214.7 μg·g−1, which is much higher than that of activated carbon sorbent (ACs) reported in the literature. Based on XPS and Hg-TPDD analysis, it is revealed that the iron sulfide compounds in coal can be converted into active sites as S0, S 2 2–, and C-S during the preparation of the sorbents, and Hg interacts with these active sites and forms β-HgS (metacinnabar). The excellent mercury removal performance and the low cost indicate that the as-prepared sorbent from the blend of the high inorganic-sulfur coal and KOH is a promising sorbent for mercury removal from flue gas. It is expected that this method could be applicable in converting other high-inorganic sulfur coals into efficient mercury sorbents. [ABSTRACT FROM AUTHOR]