Feasibility studies on cleaning of high sulfur coals by using ionic liquids

Coal has been used as an energy resource around the world, primarily for the generation of electricity. The cleaning of coal by removing its unwanted sulfur and mineral matter components is utmost essential before their gainful utilizations. The ionic liquids （ILs） are considered as non-toxic solvents for using in different industrial processes. The effect of two ILs namely, 1-n-butyl, 3-methylimidazolium tetrafluoro borate （ILl） and 1-n-butyl, 3-methylimidazolium chloride （IL2） in oxidative de-sulfurization and de-ashing of two industrially important high sulfur coal samples from Meghalaya （India） is discussed in this paper. The maximum removal of total sulfur, pyritic sulfur, sulfate sulfur and organic sulfur are observed to be 37.36 %, 62.50 %, 83.33 % and 31.63 % respectively during this oxidative process. The quantitative diffuse reflectance Fourier transform-infrared spectroscopy analysis supports the formation of sulfoxides （S--O） and sulfones （-SO2） and their subsequent removal during the oxidation of the coals in presence of ILs. The X-ray fluorescence combined with near edge X-ray absorption fine structure and scanning electron microscopic studies reveal the removal of mineral matters （ash yields） from the coal samples. The thermogravimetric analysis of the raw and clean coals indicates their high combustion efficiencies and suitability for using in thermal plants. The method is partially green and the ILs could be recovered and reused in the process.

Physico-chemical and elemental investigation of aqueous leaching of high sulfur coal and mine overburden from Ledo coalfield of Northeast India

Acid mine drainage （AMD） is one of the major problems in high sulfur coal mining areas generating acidic water. The acidic mine water generated contain hazardous elements in varying concentrations. The Northeastern Indian coalfield produces considerable amounts of AMD. The AMD and metal leaching from coal and mine over burden （OB） are the two important naturally occurring processes. In order to know the AMD potential, the aqueous leaching experiment of a few coal and OB samples from the Ledo colliery of the Northeastern coalfield, Mergherita （India）, at different time periods （1, 3, 5, and 8 h） and at different temperatures （25, 45, 65, and 90℃） were performed in the laboratory. The physico- chemical analysis of the aqueous leachates shows the pH, electrical conductivity （EC）, and total dissolved solid （TDS） in the range of 1.62-3.52, 106-2006 μs/cm, and 106-1003 ppm for the raw coal samples respectively. The OB samples produced pH, EC, and TDS in the range of 3.68-6.92, 48.6-480 μs/cm, and 69.5-240 ppm respectively. From the study, it was revealed that the concentrations of major （Si, A1, K, Na, Fe, Ca, Mg）, minor （Mn） and trace/hazardous elements （As, Ba, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se, Zn） considerably change with leaching time as well as with leaching temperature. Out of these elements As, Cd, Hg, Pb, Cr, and Se are of greater environmental importance. Alteration of the physico-chemical structure of the coal and OB samples resulting from leaching was also studied by field emission scanning electron microscope- energy-dispersive X-ray spectroscopy method. The release of the potentially hazardous elements from the raw coal and OB during leaching time periods to the leachates was detected by inductively coupled plasma-atomic emission spectroscopy and ion-chromatographic analyses. The major minerals found in coal and OB are quartz （SiO2）, pyrite （FeS2）, hematite, marcasite, and kaolinite. The association of different functional groups in minerals and their mode of association were studied by Fourier-transform infrared spectroscopy and X-ray diffraction analytical techniques. The present laboratory study will be useful in relating the characteristics of aqueous leaching from coal and mine OB with the natural weathering condition at the coal mine area.

THE APPLICATION OF REVERSE FLOCCULATION METHOD IN HIGH SULFUR COAL DESULFURIZATION

The reverse flocculation method for removing pyritic sulfur from high sulfor coals has been conceptually beveloped and investigated. The tentative tests on China high sulfur coals have shown that this advanced physical separation techaique can be very efficient in coal desulfurization, provided the process parameters are properly optimized. Under the circumsances of acquiring high coal recovery, the total sulfur rejection with four kinds of coal samples normally falls in tbe range 57% to 71 % by one-step reverse flocculation, and within the range 40% to 59% by one-step normal flocculation process.

REE Geochemistry of Moderate-and High-Sulfur Coals from North Shanxi, China

Contents of the rare-earth elements (REE) in two coal seams from North Shanxi Province, China, were determined using the instrumental neutron activation method. Based on the REE distribution patterns, and correlation analysis and cluster analysis, the main conclusions were drawn as follows. The REE contents are controlled mainly by the coal-forming environments, but might be affected by acidic solution leaching after peat sedimentation. The REE distribution patterns should be nearly the same in the sublayers of the same coal seam, and the occurrence of abnormal patterns might indicate the geological effect during post-sedimentation. The REE in coals are present mainly in the inorganic phase, and might be derived mainly from terrigenous detrital minerals. Some harmful elements, such as V, P, Mo, Cr, Cu, Mo, Th and Cd, might have cleaning potential during processing and dressing by washing because they are associated with REE.

Research on Factors Affecting Flotation and Desulfurization of Coal by Electrochemical Method

Influence of factors such as potential of electrolyte, electrolyzing time, concentration of electrolyte, and pH value on flotation and desulfurization of coal was researched. The result shows that the electrochemical reduction can enhance the desulfurization effect and increase the yield of clean coal under certain conditions. So it is an effective method.

STUDY ON REGULATIONS OF SULFUR OCCURRENCE AND PYRITE MAGNETISM OF LATE PERMIAN COALS IN SOUTHWEST CHINA

The Permian coal in southwest China contains highest sulfur among the Chinese coal .Compositional variations of sumir in coal are mainly controlled by palaogeographital environmentsduring peat accumulation. High organic sulfur coal is formed in peat swamp developing in tidal flat of limited carbonate platform, and it is provided with especial petrologital and geochemical characteristics, and its organoschr-containing compounds are mainly thiophene series. The macroscopitaland microscopical shapes or types of pyrites in Late Permisn coal are diversined. Bituminous coal and anthracite are diamagnetic, but the pyrites are paramagnetic. The magnetic susceptibility oftbe pyrites is depended on the content of paramagnatic elements associnted with pyrites.

Secondary ion mass spectrometry of high-sulfur coal:Observation and interpretation of polysulfur ions

The chemical state of sulfur existing in superhigh-sulfur coal has been studied with high-performance static secondary mass spectrometry. A species of polysulfur ions, as most reasonable mass spectrometric fragments of molecules of elemental sulfur or sulfurite, is observed and exactly determined through accurate mass analysis and isotopic pattern analysis.From the observation, the chemical form of elemental sulfur is considered to occur naturally in coal, particularly in its organic phases or maceral such as telocollinite.

Sulfur-accumulating Model of Superhigh Organosulfur Coal From Guiding, China

Superhigh organosulfur coal has received considerable attention 'chemically as well as geologically,because from it we could get much useful chemical information for removing organosulfur from coal.By studying it, we could also find out the factors af-

Sulfur Isotopic Characteristics of Coal in China and Sulfur Isotopic Fractionation during Coal-burning Process

The determined results of the sulfur contents and isotopic composition of coal samples from major coal mines in 15 provinces and regions of China show that the coal mined in the north of China is characterized by higher ^34S and lower sulfur content, but that in the south of China has lower ^34S and higher sulfur content.During the coal-burning process in both indrstrial and daily use of coal as fuel the released sulfur dioxide is always enriched in lighter sulfur isotope relative to the corresponding coal;the particles are always enriched in heavier sulfur isotope.The discussion on the environmental geochemical significance of the above-mentioned results also has been made.

Leaching of vanadium from stone coal with sulfuric acid

The effects of roasting, mass ratio of H2SO4 to stone coal, leaching temperature, liquid-to-solid ratio, grinding fineness of stone coal, and two-stage counter-current leaching on the vanadium leaching ratio were studied. The results show that the vanadium leaching ratio of roasted stone coal through two-stage counter-current leaching can reach 65.1% at the mass ratio of H2SO4 to stone coal of 20%, leaching temperature of 95℃, leaching time of 30 h, liquid-to-solid ratio of 1.1 mL·g^-1, and grinding fineness of 0.1 mm, which can serve as an experimental basis for the production of vanadium from stone coal.

Changes in sulfur form during coal desulfurization with microwave:Effect on coal properties

The changes in sulfur form in coal were analyzed by sulfur K-XANES(K-edge X-ray absorption near edge structures) spectra before and after the coal microwave desulfurization in a Na OH solution. After the desulfurization, the pyritic sulfur content of coal decreased significantly from 53.6% to 39.2%, while the sulfate sulfur content increased from 17.3% to 34.6%. Only a small amount of thiophene sulfur(20.1–16.1%) was removed. Some sulfur-containing components were oxidized to sulfate sulfur. Under the optimum conditions, the ash content decreased, while the volatile content increased. The calorific value of coal slightly decreased with a slight variation in the amplitudes. The overall structure of coal did not change significantly based on Fourier transform infrared(FTIR) spectral analyses. Thus, the desulfurization of coal with microwave irradiation in a Na OH solution did not significantly change the properties of coal.

Sulfur in Coal and Its Environmental Impact from Yanzhou Mining District, China

Sulfur is one of the hazardous elements in coal. The concentrations of sulfur are relatively high in coal. The major forms of sulfur in coal are pyritic, organic and sulfate. Pyritic and organic sulfur generally account for the bulk of sulfur in coal. Elemental sulfur also occurs in coal, but only in trace to minor amounts. When coals are burned, leached and washed, sulfur will be released in the form of sulfide and H\-2S, which then react with O\-2, water and other substances to change into vitriol, and in some places it may form acid rain. And they will impact water environment, acidify the soil and do great harm to plants and human health. In this paper, on the basis of the data from the Yanzhou mining district, the distribution and concentrations of sulfur are analyzed and the existing forms of sulfur are studied. The variation of sulfur and its impact on the environments also are described when coal is used.

Distribution Characteristics of Sulfur and the Main Harmful Trace Elements in China's Coal

To promote the rational development and use of clean coal resources in China, data on the regional and age distribution of sulfur, arsenic and other harmful elements in Chinese coal was broadly collected, tested for content, and analyzed. Coal in northwestern China is characterized by low to extremely low levels of sulfur; the coal of the Taiyuan Formation in northern China mainly has high-sulfur content; that of the Shanxi Formation is mainly characterized by low sulfur coal; and the Late Permian coal in southern China has overall higher sulfur content; other regions have low sulfur coal. The average content of harmful trace elements in the bulk of China＇s coal is similar to the corresponding content in the coal of the North America and the rest of the world, whereas the content of various elements （Hg, Sb and Se） is different in magnitude to the corresponding percentage in the crust. The average content of the elements Cr, Se, Co, Be, U, Br in Late Permian coal in S China ranks first in the country whereas the average content of Hg and CI in the coals of Late Carboniferous to Early Permian age in N China are the highest. The average content of Mn in Early and Middle Jurassic coal is higher in NW China. The high content of harmful elements in some coal should cause particular concern both in the development and utilization of coal.

Effects of Coal Rank and High Organic Sulfur on the Structure and Optical Properties of Coal-based Graphene Quantum Dots

Coal-based graphene quantum dots(GQDs) were successfully produced via a one-step chemical synthesis from six different coal ranks, from which two superhigh organic sulfur(SHOS) coals were selected as natural S-doped carbon sources for the preparation of S-doped GQDs. The effects of coal properties on coal-based GQDs were analyzed by means of high-resolution transmission electron microscopy(HRTEM), X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, X-ray photoelectron spectroscopy(XPS), ultraviolet-visible(UV-Vis) absorption spectroscopy, and fluorescence emission spectra. It was shown that all coal samples can be used to prepare GQDs, which emit bluegreen and blue fluorescence under ultraviolet light. Anthracite-based GQDs have a hexagonal crystal structure without defects, the largest size, and densely arranged carbon rings in their lamellae; the highrank bituminous coal-based GQDs are relatively reduced in size, with their hexagonal crystal structure being only faintly visible; the low-rank bituminous coal-based GQDs are the smallest, with sparse lattice fringes and visible internal defects. As the metamorphism of raw coals increases, the yield decreases and the fluorescence quantum yield(QY) initially increases and then decreases. Additionally, the surface of GQDs that were prepared using high-rank SHOS coal(high-rank bituminous coal) preserves rich sulfur content even after strong oxidation, which effectively adjusts the bandgap and improves the fluorescence QY. Thus, high-rank bituminous coal with SHOS content can be used as a natural S-doped carbon source to prepare S-doped GQDs, extending the clean utilization of low-grade coal.

Fe-Si promoter for sulfur capture during coal briquette combustion

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Removal of sulfur in coke oven gas by mixing ZnO-based additive into coal

A new technology for recycling EAF dust and removal of sulfur from coking oven gas was investigated. The new technology does not need to set up special equipment to treat COG (coke oven gas), and it is only acquired by mixing the ZnO base additive into the coke coal. In the stage of pyrolysis of the coal volatile, ZnO of the additive combines with H 2S, CS 2, COS and C 2H 2SH of coal gas, forming ZnS in coal char. In the stage of coking of the coal char, Zn is gasified with S, then the gas Zn react with H 2S, CS 2, COS and C 2H 2SH, forming ZnS in coal gas and depositing as dust. After the collected ZnS dust was regenerated, it can be recycling as the additive again. The sulfur in coal gas can be completely removed if the mole ratio of the added Zn to the volatilized S is more than 1, and the sulfur in coke is also slightly decreased comparing with the coke without the additive. The EAF dust containing ZnO and Fe 2O 3 can be the base material of the desulfurizing additive.

The Formation Models of Sulfur in the Late Permian Coal of Sichuan

On the basis of the study on the occurrence and distribution of sulfur in the Late Permiau high-sulrur coals of Sichuan .Southwest China,the paper discusses the geological ractors influencing sulfur occurrence in coals, and suggests two evolutionary motlels, i. e. a directly depositional pyrite series(euhedral crystal→aggregate→glomerocryst ) and complex genetic series (mini→granular, framboid→spherical→nodular,lumpy pyrite). They are of theoretically and actually important significance not only in the explanation to the difference in composition of varioas types of coal pyrites,but also in the understanding of the mechanism of physical properties (magnetic,surface property) of pyrites. By a comprehansive analysis,a genetic model of sulfur in the Late Permian coal of Sichuan has been established.

Mechanism of sulfur capture during coal briquette combustion

The mechanisms of sulfur capturing during coal briquette combustion was discussed. Various factors affecting sulfur removal efficiency have been studied. Characterization of the slag left after combustion has been carried out by using X ray diffraction (XRD), Messbauer spectroscopy (MS), scanning electron microscopy (SEM), energy dispersion X ray analysis (EDAX), and electron spectroscopy for chemical analysis (ESCA). No other sulfur containing species besides CaSO 4 was found. Small amount of CaFe 3(SiO 4) 2OH, some complexes of CaO SiO 2 Fe 2O 3 and vitreous iron oxides were identified on the surface of CaSO 4 grains. This might explain the mechanism of sulfur fixation during coal briquettes combustion.

Combustion and Sulfur-fixing Performance of Pulping Black Liquor Coal-water Slurry

The effects of adding pulping black liquor and other additives to coal-water slurry(CWS) on the sulfur-fixing performance of the resultant mixture(pulping black liquor coal-water slurry) were evaluated. The experimental results demonstrated that the ash content of the black liquor coalwater slurry decreased as the addition of pulping black liquor in the mixture increased. Nevertheless, the addition amount should be appropriately selected to ensure that the black liquor coal-water slurry had a moderate calorific value. Addition of black liquor improved the combustion performance of CWS by lowering the ignition point and stabilizing the combustion process; moreover, the sulfur-fixation ratio after combustion increased by 12 to 16 percentage points than that of CWS, and the content of high-melting-point salt in the ash from CWS after adding black liquor was low. The sulfur-fixing ratio of CWS after adding a sulfur-fixing agent was effectively increased by 25 to 30 percenatge points, but with compromise of the fluidity and stability of the CWS; thus, the addition amount of a sulfur-fixing agent should be optimized.