Pyritic Sulfur In Coal Research Articles

Fine-grained pyrite in some Chinese coals

Fine-grained pyrite in some Chinese coals has been investigated, with analysis by optical microscopy and a scanning electron microscope equipped with energy dispersive X-ray spectrometer illustrating that the interaction between mineral and organic matters results in the irregular pyrite crystal present in coal. When considering the co-existing carbon, the density of fine-grained pyrite in coal is lower than that of mineral pyrite. Organic sulfur and pyritic sulfur in coal can be converted into each other under the favorable conditions. However, the fine-grained pyrite crystal pattern is still detected when the S/Fe ratio increases to 2:1, meaning that the fine-grained pyrite shifts from dissemination to crystallization. Fine-grained pyrite in coal has a strong activity and its surface is susceptible to be oxidized. Oxidized fine-grained pyrite usually forms sulfate (mainly gypsum), and sometimes may be converted to marcasite. Fine-grained pyrite in coal, when their granularity is small enough, may be chemically associated with organic components by non-pyritic Fe–S bond rather than physically embedded in coal matrix. So, it is not suitable to express the mineral using the FeS2 formula.

Mode of Occurrence and Thermal Stability of Mercury in Coal†

Mode of occurrence of mercury in three coals was studied using sequential selective extraction, physical separation, and thermal treatment methods. Mercury speciation in the selected coals was determined using a five step sequential selective extraction method showing associations of mercury fractions with the organic and mineral structure in the analyzed coals. One of the coals was further subjected to thermal treatment with results revealing release of the organo-complexed mercury from coal at temperatures below 400 °C, while the mercury fraction associated with the coal mineral lattice was found to be the more stable form, released at temperatures of 600 °C. The mercury content was also determined for a selected range of coal density fractions showing strong correlation between mercury concentration in coal and the coal density fractions. The heaviest density fraction of the coal exhibited the largest ash as well as the highest pyritic sulfur content. Previous studies have established a strong relationship between mercury and the pyritic sulfur in coal, which was also confirmed in this work.

Idle time in the washing and iron concentration in leachate removed: two basic parameters in the desulphurization of coal in a packed column

Column biodesulphurization of coal is at the experimental stage and is influenced by many variables including temperature, pH, particle size, concentration of iron in solution, among others. Idle time in the washing process and the concentration of dissolved iron in the purged leachate are two variables with a definite effect on the yield of the desulphurization system. In the laboratory, several trials were run with columns packed with coal for different idle times: 1, 2, 3, 5, 6 and 7 days, and for different concentrations of iron in the purged leachate: 500 to 4,000 mg/l. The optimal values for the two variables; that is, those allowing for the highest desulphurization yields, were idle times of 3 and 5 days, which give an elimination of 56% and 49% of pyritic sulphur, respectively, and 3,000 mg/l of iron concentration in the purged leachate, giving a decrease in pyritic sulphur in coal of 57%.

00/01131 Indirect determination of pyritic sulfur in coal by flame atomic absorption spectrometry

An atomic absorption spectrophotometric method for the determination of pyritic sulfur in coal was developed based on oxidizing pyritic sulfur in coal into sulfate, which then reacted on an excess of solid barium chromate,and was followed by collection of the unreacted barium chromate and barium sulfate precipitates, and AAS determination of free chromate (equivalent to the sulfur originally present) at 357.9nm. The method was applied satisfactorily to the determination of pyritic sulfur in coal samples. The recovery of sulfur was 95 -102% and relative standard deviation 3-5%.

Direct quantitative analysis of mineral matter and different forms of pyritic sulfur in coal by electron probe microanalysis (EPMA) and automated image analysis (AIA)

Coal contains mineral matter that can appear in various states of aggregation: as small inclusions in organic matter, as euhedral crystals and as extensive horizontal layers. Sulfur in coal is present in three forms: pyritic, sulfate and organic. The term ‘pyritic sulfur’ covers different forms of iron sulfides, such as pyrite (FeS 2), marcasite (FeS 2) and pyrrhotite (Fe 1 − X S). Previously, mineral matter is coal has been quantified indirectly, that is, the ash yield has been determined and the result converted to mineral matter by applying one of three formulae, i.e. Parr, King or ASTM. This study shows that the mineral matter can be directly and rapidly determined quantitatively by using electron probe microanalysis (EPMA) together with automated image analysis (AIA). The concentrations of the iron sulfides can also be determined by this technique. The results obtained for all three of the iron sulfides determined by this technique also show good concordance with those of the ISO and ASTM methods. Heavy metals such as Hg and As, which usually occur as impurities in the sulfidic minerals, can also be qualitatively analysed simultaneously by this method.

Distribution of the activation energies for the thermal decomposition of organic and pyritic sulphur in coal

The activation energies for the thermal cracking of the organic sulphur of several coals ranking from lignite to subbituminous have been calculated. Likewise, the activation energies for the thermal decomposition of the pyrite associated with different density fractions obtained from a subbituminous coal by sink-float analysis have been determined. The model of multiple, parallel, independent (MPI) first order reaction has been assumed for the thermal cracking. The kinetic equations associated with a Gaussian distribution of the activation energies (DAE) have been used for calculating the average activation energy, E 0, and the standard distribution, σ. The results obtained show small differences between the parameters calculated for the cracking of the organic sulphur contained in the different coals tested. Decomposition of pyritic sulphur needs a higher activation energy than the organic sulphur. The decomposition of the pyrite associated with coal fractions with different density shows that a correlationship can be stablished between the pyrite content, E 0 and σ. The higher content in pyrite, the lower E 0 and the higher σ. It is probably due to a larger variety of pyritic sulphur forms, as the pyritic content increases, which leads to a more dispersive distribution of activation energies.

Thermomagnetometry and evolved gas analysis in the identification of organic and pyritic sulphur in coal and oil shale

Potential difficulties of using a new TG/TM technique for measuring the pyrite content of coals that also contain siderite are discussed briefly. Direct measurement of the SO 2 evolved on heating pyrite in an oxidizing atmosphere is a possible alternative and this may also provide information on amounts of organic sulphur in the coal.

Mossbauer studies of coal and coke: quantitative phase identification and direct determination of pyritic and iron sulphide sulphur content

Mössbauer spectroscopy has been used to analyse the included minerals and mineral-derived phases of a large suite of coal, coke, and other coal-related samples. Scanning electron microscopy, chemical analysis, and X-ray diffraction were used as supplementary techniques. Most of the samples studied were bituminous coals, and the dominant Fe-bearing minerals observed were pyrite, carbonate phases (siderite, ankerite), and ferrous silicates (principally illite). Pyrite was present in all coals investigated and was the dominant Fe-bearing phase in approximately 70% of the samples. Absorption peaks from ferrous Fe contained in illite and other clay minerals were observed for 90% of the coals, and were dominant for approximately 20% of the samples. The carbonates siderite and ankerite were present in approximately half of the coals, and siderite was the dominant Fe-bearing phase in four samples. In weathered coals and coal refuse, Fe sulphates, oxides and oxyhydroxides were also observed. Mössbauer data obtained from numerous coals before and after coking established that the following transformations occur during high-temperature carbonization: 1. (1) pyrite → troilite ( FeS) + pyrrhotite ( Fe 1 − x S); 2. (2) illite + other silicates → ferrous glass; 3. (3) siderite → metallic Fe. A new method was developed for making direct, quantitative determinations of the amount of pyritic sulphur in coal, which involves comparing the observed Mössbauer mass absorption coefficient for pyrite in coal to a standard calibration curve. Preliminary data for coke samples show that the same technique can be applied to determine the amount of sulphur contained in the Fe sulphide phases, troilite and pyrrhotite.

Reaction of pyritic sulphur in coal with lime and calcined dolomite during the coking process

Various reactions occur between pyrite (FeS 2) in coal and CaO to form CaS when a finely pulverized intimate mixture of coal and CaO is coked at 900 °C in an inert atmosphere. The effectiveness of lime and calcined dolomite (CaO.MgO) in promoting this reaction has been evaluated; calcined dolomite is somewhat more effective than lime over coal/ oxide weight ratios from 2.8 to 14. The degree of conversion of pyrite to calcium sulphide at a coal/calcined dolomite weight ratio of 7 has been determined as a function of time at 900 °C; coking time in excess of 2.5 h does not have a significant effect. It has been shown that the total sulphur lost on coking coal/lime mixtures decreases and the percentage of FeS, originating from the dissociation of pyrite, converted to CaS increases as the amount of lime added increases. But although the total sulphur content of coke produced in the presence of CaO is then higher than when the coal is coked without lime, the pyritic sulphur has been converted to CaS which is more amenable to chemical conversion to H 2S. A method is outlined for determining CaS in the coked mixture in the presence of FeS.

Sulphur in oil shale or torbanite

AbstractMott's rapid method for the determination of sulphate and pyritic sulphur in coal can be applied to oil shale or torbanite, the pyrites content being calculated from the iron extracted. The organic sulphur is best calculated by subtracting the pyritic sulphur from the total sulphur content of the hydrochloric acid‐extracted material as determined by the quartz‐tube method [I.P.63/42(T), 1949].On the pyrolysis of the torbanite approximately only I% of added pyritic sulphur appears as organic sulphur in the oil. Similarly the addition of calcium carbonate had no effect and calcium hydroxide had only a slight effect on the organic sulphur content of the oil. None of these materials affected the oil yield significantly.