Comparative chemical and mineral characterization of some Bulgarian coals

The mineralogy and chemical composition of lignitic, subbituminous and bituminous coal and coal-ash samples from six Bulgarian deposits, namely Maritza West (MW), Sofia (S), Maritza East (ME), Bobov Dol (BD), Pernik (P) and Balkan (B), were studied and a model for comparative characterization of their composition was done. Major minerals identified in the crystalline matter of Bulgarian coals are commonly quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum and occasionally dolomite, siderite, Fe oxyhydroxides and Fe sulphates. Some genetic features of the inorganic matter in coal and coal ash are described and compared. The coals studied show high detrital (P, B, BD, ME) or high authigenic (S, MW) mineral abundance with sulphide–sulphate (P, BD, ME, MW) or mixed carbonate and sulphide–sulphate (B, S) authigenic mineral tendencies. The high-temperature ashes of these coals belong to sialic (P), sialoferricalcic (B, BD), sialoferric (ME) or ferricalsialic (MW, S) chemical types. They have high (B, P, BD) or low (ME, MW, S) silicate mineral abundance with sulphate (B, P, ME, MW, S) or oxyhydroxide (BD) mineral tendencies.     

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.     

Clay and non-clay minerals in the pharmaceutical industry: Part I. Excipients and medical applications

Minerals are widely used in the pharmaceutical industry as lubricants, desiccants, disintegrants, diluents, binders, pigments and opacifiers, as well as emulsifying, thickening, isotonic agents, and anticaking agents, and flavour correctors and carriers of active ingredients.A variety of minerals are used as excipients in pharmaceutical preparations because they have certain desirable physical and physico-chemical properties, such as high adsorption capacity, specific surface area, swelling capacity, and reactivity to acids. Other important properties are water solubility and dispersivity, hygroscopicity, unctuosity, thixotropy, slightly alkaline reaction (pH), plasticity, opacity, and colour. Clearly such minerals must not be toxic to humans. The following minerals are commonly used as excipients: oxides (rutile, zincite, periclase, hematite, maghemite, magnetite), hydroxides (goethite), carbonates (calcite, magnesite), sulfates (gypsum, anhydrite), chlorides (halite, sylvite), phosphates (hydroxyapatite), and phyllosilicates (palygorskite, sepiolite, kaolinite, talc, montmorillonite, saponite and hectorite). More recently, some tectosilicates (zeolites) also feature in pharmaceutical preparations.Minerals also enjoy the following medical/health applications: a) contrast diagnostic techniques, b) production of dental cements and dental molds in odontology, c) immobilization of limbs and fractures or dental and craniofacial surgical procedures in traumatology, d) bone grafts or construction of orbital implants, and e) spas and aesthetic centers. Examples of such minerals are oxides (zincite, magnetite and maghemite), sulphates (gypsum and barite), phosphates (hydroxyapatite) and phyllosilicates (clay minerals).     

Identification of clay minerals in coal and wastes from main coal washery, Zonguldak, Turkey

Identification of clay minerals present in coal and washery wastes is important in cleaning fine coal by froth flotation and in flocculation and dewatering. Therefore samples of wastes from jigs and the flotation cell at the Zonguldak main coal washery were collected and analyzed petrographically for their mineral matter content and by X-ray diffraction for their clay content. The “loss on ignition” method was carried out to determine their organic carbon and carbonates. The waste samples contain 48–68% clay minerals in addition to silicates, carbonates, sulfides and coal. Three clay minerals were identified, namely illite, kaolinite and chlorite. Illite seemed to be the dominant clay mineral in washery wastes. Loss on ignition indicated high percentages of organic matter in the fine jig tailings (21%) and flotation tailings (33%). 3%–6.5% of carbonates have also been found.     

Clay and non-clay minerals in the pharmaceutical and cosmetic industries Part II. Active ingredients

A wide range and variety of minerals are used in the pharmaceutical industry as active ingredients. Such minerals may be administered either orally as antacids, gastrointestinal protectors, antidiarrhoeaics, osmotic oral laxatives, homeostatics, direct emetics, antianemics and mineral supplements, or parenterally as antianemics and homeostatics. They may also be used topically as antiseptics, disinfectants, dermatological protectors, anti-inflammatories, local anesthetics, keratolytic reducers and decongestive eye drops. In all cases the LADME process of the minerals is described. In the cosmetic industry minerals are used as solar protectors as well as in toothpastes, creams, powder and emulsions, bathroom salts and deodorants.The minerals in use belong to the following groups: oxides (rutile, periclase, zincite), carbonates (calcite, magnesite, hydrocincite, smithsonite), sulphates (epsomite, mirabilite, melanterite, chalcanthite, zincosite, goslarite, alum), chlorides (halite, sylvite), hydroxides (brucite, gibbsite, hydrotalcite), elements (sulphur), sulphides (greenockite), phosphates (hydroxyapatite), nitrates (niter), borates (borax) and phyllosilicates (smectite, palygorskite, sepiolite, kaolinite, talc, mica).The therapeutic activity of these minerals is controlled by their physical and physico-chemical properties as well as their chemical composition. The important properties are high sorption capacity, large specific surface area, solubility in water, reactivity toward acids, high refractive index, high heat retention capacity, opacity, low hardness, astringency, and high reflectance.     

Mineralogy of combustion wastes from coal-fired power stations

A combination of methods, including separation procedures, light microscopy, SEM, TEM, XRD and DTA-TGA methods, were used to characterize the phase-mineralogical and chemical composition, microstructural and some genetic phase peculiarities of solid waste products from coal burning. Fly ashes, bottom ashes and lagooned ashes from eleven Bulgarian thermoelectric power stations were studied. These products comprise inorganic and organic constituents. The inorganic part consists mainly of non-crystalline (amorphous) components and lesser amounts of crystalline components represented by various major, minor and accessory mineral phases. The organic constituent contains unburnt coal components represented by slightly changed, semicoked and coked coal particles. The origin of solid phases could be: primary — minerals and phases contained in coal and having undergone no phase transition (silicates, oxides, volcanic glass, coal particles); secondary — phases formed during burning (magnetite, hematite, metakaolinite, mullite, anhydrite, lime, periclase, CaMg silicates, glass, semicoke, coke); or tertiary — minerals and phases formed during the transport and storage of fly ashes and bottom ashes (sulphates, carbonates and oxyhydroxides).     

Mineralogy of ash of some American coals: variations with temperature and source

Ten samples of mineral-matter residue were obtained by the radio-frequency low-temperature ashing of subbituminous and bituminous coals. The low-temperature ash samples were then heated progressively from 400 °C to 1400 °C at 100 °C intervals. Mineral phases present at each temperature interval were determined by X-ray diffraction analyses. The minerals originally present in the coals (quartz, kaolinite, illite, pyrite, calcite, gypsum, dolomite, and sphalerite) were all altered to higher temperature phases. Several of these phases, including kaolinite, metakaolinite, mullite, anhydrite, and anorthite, were found only in limited temperature ranges. Therefore the temperature of formation of the ashes in which they occur may be determined. Mineralogical differences were observed between coal samples from the Rocky Mountain Province, the Illinois Basin, and the Appalachians; and as a result of these mineralogical differences, different high-temperature phases resulted as the samples were heated. However, regional generalizations cannot be made until a greater number of samples have been studied.     

Partitioning of minerals and elements during preparation of Taixi coal, China

Mineralogy, sulfur and 40 other element contents were determined on eight samples of the Taixi coal and its preparation products from the Rujigou mining district, China. INAA, ICP-AES, CV-AAS, GAAS, XRD, SEM/EDX, conventional chemical and maceral analysis were carried out on the samples. This study is focused on the partitioning behavior of the minerals and elements during the coal cleaning, and the main factors influencing the partitioning behavior of elements were also discussed.The clay minerals (kaolinite, illite, montmorillonite and chlorite), quartz and, to a lesser extent, carbonate minerals (calcite, dolomite and siderite) dominate the mineralogy of Taixi coal. There is also minor amounts of pyrite and trace amounts of gypsum and feldspar. The quartz is dominantly epigenetic in origin, and clay minerals were modified by the thermal metamorphism. They are easily liberated from the coal by cleaning. However, although the majority of carbonate minerals are also mainly epigenetic in origin, its degree of removal is relatively low, especially with respect to dolomite and siderite, which are often finely dispersed in coal macerals, so that they are mostly retained in cleaned coal. Most of the elements studied could be removed effectively during the cleaning processes, especially for the elements predominantly hosted in coarse, epigenetic minerals. Compared with other sized cleaned coals, the coarse-grained cleaned coal is cleanest and has a relatively low potential of environmental risk. The majority of the potentially hazardous elements are notably enriched in the coal waste so that the waste is not feasible to be used as fuel. The partitioning of elements during the coal cleaning processes is essentially controlled by some factors such as the modes of occurrence of elements, maceral type, grain size and textural relation of minerals, and types of cleaning technique used.     

Characterization of four petrologic end members from Alberta oil sands and comparison between different mines and sampling times

The current research was performed on four petrologic end members samples from Syncrude's North Mine collected in 2012 (NM12), i.e. marine clay (MC), marine sand (MS), estuarine clay (EC), and estuarine sand (ES). The mineralogical compositions of the four petrological end members were determined using X‐ray diffraction (XRD), quantitative XRD (QXRD), elemental analysis, and particle size distribution (PSD) measurements. Bulk samples from the four petrologic end members, after bitumen removal, were mainly composed of clay minerals (kaolinite, illite, chlorite, and mixed‐layer expandable clays) and non‐clay minerals such as quartz, carbonates, feldspars, and traces of TiO₂ minerals, gypsum, and pyrite. Bulk samples of the clay end members were composed of significantly higher amounts of clay minerals and lower amounts of quartz compared with the bulk samples of the sand end members. XRD analysis of oriented preparations (air dried‐54 % RH and ethylene glycolated) of the < 0.2 μm fractions of the four end members showed that interstratified illite‐smectite of high (～30 %) and low (～10 %) expandability were observed only in clay‐rich end members, i.e. NM12‐EC and MC, respectively. Kaolinite‐smectite was only found in the < 0.2 μm fraction of the NM12‐MC with an expandability between 5 and 10 %. Interstratification of illite‐smectite was observed in the < 0.2 μm fraction of NM09‐MC and EC samples but the expandability was only 10 % for both fractions. However, kaolinite‐smectite was not found in the same fraction for NM09‐MC and EC. ES and EC had the highest and lowest bitumen contents, respectively, for the NM12, NM09, and AM10 samples.     

皖北刘二煤在Shell气流床气化过程中熔渣形成机理初探

选取安庆石化sheu气化炉使用的皖北刘二煤（简称AQ007）及气化过程产生的大块渣和细渣样品，利用X-射线衍射仪（XRD），考查了AQ007煤在弱还原性气氛下不同加热温度下煤灰熔融过程中的矿物演变过程，对煤灰的熔融机理进行了探讨，对Shell气化过程产生的大块渣和细渣的晶体矿物组成进行了对比研究。结果表明：AQ007煤中的主要晶体矿物有高岭石、石英、方解石、白云母等。在还原性气氛下，煤灰随着温度的升高，石英、硬石膏等结晶矿物含量逐渐减少，生成新的矿物质，莫来石的生成是导致AQ007煤灰熔点高的主要原因。大量钙长石的生成是导致安庆石化sheu气化炉产生大块熔渣和堵渣主要原因。     

贵州六盘水煤矸石的矿物特性

对贵州六盘水地区煤矸石的矿物特性进行了研究. 结果表明,以煤巷矸和岩巷矸混合矸为主的煤矸石固定碳含量和热值均较低,不适宜直接用于动力燃料发电,而富铝、高铁、高钙是其重要特征,SiO2, Al2O3和Fe2O3含量之和达70%~80%,所含V, Co, Ni, Cr, Ge的富集度高,均具有回收利用价值. 矿物组成以石英和高岭石为主,其次为菱铁矿、黄铁矿、蒙脱石、斜长石、伊利石、白云石、方解石、锐钛矿等;粉末状煤矸石由大小不一的不规则颗粒组成,粒径多为1~3 mm,部分粒径为0.2~1 mm;石英、菱铁矿、黄铁矿等晶体矿物多呈致密块状,结晶完整;高岭石、蒙脱石、伊利石等多呈片状、疏松团块状,结晶较石英差;而含碳有机质多呈片状,呈无定型.     

Mineral and trace element composition of the Lokpanta oil shales in the Lower Benue Trough, Nigeria

The concentrations of minerals and trace elements in the Lokpanta oil shale from the Lower Benue Trough, Nigeria have been determined by X-ray diffraction (XRD) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively. X-ray diffraction data were evaluated using the SIROQUANT™ interactive data processing system based on Rietveld interpretation methods. A new method of trace element determination in oil shale, involving LA-ICP-MS analysis of glass beads prepared by fusing oil shale ash on an iridium strip heater was used, and the accuracy of the method was assessed by including a standard shale reference material (SGR-1b) in the analysis program.The minerals in the raw oil shales are mainly quartz, calcite and clay minerals, with the latter being represented by kaolinite and interstratified illite/smectite. Ashes of the oil shale samples prepared at 815 °C have quartz and (in some cases) illite as the dominant mineral phases, along with a significant proportion of amorphous materials. The Lokpanta oil shales are highly enriched in some potentially hazardous trace elements, including V, Cr and Ni, when compared with oil shales from other deposits around the world. The results obtained for the trace elements in the reference material show that the LA-ICP-MS method described in this study is very accurate and precise for the determination of a wide range of trace elements in oil shales.     

准东煤燃烧中矿物质转化行为的CCSEM研究

在沉降炉中进行了准东煤的燃烧实验,利用计算机控制扫描电镜技术(computer controlled scanning electron microscopy,CCSEM)研究了煤中矿物质的转化行为。研究表明煤中主要矿物为方解石、高岭石、含铁类物质以及未分类矿物,燃烧后灰中石英、铁的氧化物、白云石的含量急剧增加,未分类矿物和方解石的含量下降。同时对3种重要致渣元素Na、Fe、Ca在燃烧前后的矿物转化行为及颗粒粒径分布进行了详细研究。     

Behaviour of inorganic matter during heating of Bulgarian coals: 2. Subbituminous and bituminous coals

Bulgarian subbituminous (Pernik, Bobov Dol) and bituminous (Balkan) coals were gradually heated under air from 100 °C to their fluid ash-fusion temperatures (1400–1600 °C) via 100 °C intervals and the behaviour of their inorganic matter (IM) was studied. The original minerals and newly formed inorganic phases in the oxidation and combustion products (OCPs) of these coals were identified and the behaviour of 33 minerals and phases was described. The coals studied reveal high detrital abundance and low authigenic mineralization with sulphide–sulphate, carbonate or mixed sulphide–sulphate and carbonate tendencies. The IM of coals is composed mainly of quartz, kaolinite, illite + muscovite, feldspars, pyrite, and calcite, while the other minerals identified have subordinate occurrence. The IM of OCPs includes various pre-existing minerals and newly formed phases. The latter phases are glass, quartz–cristobalite–tridymite, mullite, amorphous clay material, hematite–magnetite, anhydrite, and others originating from the heating of these coals or storage of their OCPs. The physico-chemical processes and temperatures that result in the formation of new phases in OCPs are described. The relationships between the ash-fusion behaviour and chemical and mineral composition of the coals are also discussed. A systematization of the physico-chemical transformations and some comparative characterizations, as well as prediction of certain technological and environmental problems related to the behaviour of IM during heating of Bulgarian lignites, subbituminous and bituminous coals are also described and summarized.     

Minerals in some Australian oil shales

The mineral composition of oil shales from three widely different ateas within Australia has been examined by X-ray diffractometry after low-temperature ashing. Quartz is more abundant than calcite. Feldspar is prominent in the Permian oil-rich shale from Glen Davis, New South Wales. Clay minerals are represented by smectite, illite, kaolinite and mixed-layer minerals (mostly mica-smectite). The content of clay minerals is generally low, except in the Tertiary oil shale from Rundle, Queensland.     

The inorganic geochemistry of coal,petroleum, and their gasification/combustion products

The inorganic makeup of coal and petroleum differ in several crucial ways. The origins of these differences include the disparate geologic environments of formation, the contrasting parent materials (plant versus planktonic) and hence distinct organic species, and the physical state of the fuels (solid versus liquid). The inorganic chemistry of petroleum is usually controlled by the type and abundance of its organic compounds (i.e., V, Ni, ± Fe-bearing porphyrins and S-bearing thiols, sulfides, disulfides, thiophenic derivatives, resins, and asphaltenes), with significant, though often smaller contributions from entrained mineral phases. This near balance of inorganic compositional control causes petroleum to form combustion/gasification (pyrochemical) slag and ash with a large number of elements (i.e., V, Ni, S, Fe, Ca, Na, K, Mg, Si, and Al) in significant relative concentrations. This balance provides also opportunities for large departures from any given “norm”. The inorganic chemistry of coal, on the other hand, is dominantly controlled by its contained detrital and authigenic mineral matter, with relatively small contributions from organically carried elements other than sulfur. Detrital minerals are those that survive the geological processes of weathering and transport, and hence are a small group of physically resistant and chemically stable minerals including quartz, clay minerals, and oxides of Fe and Ti. The most abundant authigenic minerals in coal include clay minerals, pyrite/marcasite, carbonates, Ca- and Fe-sulfates, and Fe-oxides and hydroxides. Pyrochemical slag and ash from coal are therefore primarily enriched in Si, Al, Ca, Fe, and S. From a processing standpoint, the behavior of slag and fly ash is largely a function of the complexity of the fuel's inorganic chemistry (including the original mode of occurrence of the various elements), and the observed oxygen fugacity. Pyrochemical environments vary from reducing to oxidizing as a result of proximity to the flame and operational mode (combustion versus gasification). Consequently, multivalent elements further contribute to the complexity of slag/ash behavior by essentially behaving as separately unique elements when in their various valence states. In coal, the two abundant, multivalent inorganic elements are Fe (0, + 2, and +3) and S (−2, 0, +2, +4, and +6). In petroleum there are four abundant, multivalent inorganic elements: Ni (0 or +2), Fe (0, +2, and +3), V (+2, +3, +4, and +5), and S (−2, 0, +2, +4, and +6). The larger number of abundant inorganic elements in petroleum than coal, as well as the broader range of associated valence states, leads to more diverse slag/ash species formed during petroleum combustion/gasification, and consequently less predictable slag/ash behavior. A phase characterization of slags produced by the gasification of petroleum coke (a petroleum refining byproduct) illustrates their increased complexity with respect to typical coal slags.     

硅灰石原料及硅灰石质釉面砖坯焙烧过程物相变化的X射线研究

本文采用XRD分析对生坯和素坯进行系统地物相鉴定,发现南平硅灰石焙烧过程物相变化的显著特点是:1Tr型 β-CaSiO_3 1150℃开始 1200℃完成 α-CaSiO_3。而以硅灰石40%,福州高岭土35％,大湖白粘土25％为配方的生坯焙烧过程物相变化的特点是:1000℃以下时主要表现为原料矿物高岭石、伊利石、方解石的分解,1000℃——1100℃时,主要表现为新生物相钙长石和熔体的生成及1Tr型β-CaSiO_31075℃左右 2M型β-CaSiO_3;1100℃——1130℃时,主要表现为钙长石、2M型β-CaSiO_3和石英的部分熔解。     

Coal and coal ash characteristics to understand mineral transformations and slag formation

A knowledge of the composition and structure of minerals in coal is necessary in order to understand the mineral transformations and agglomerate or slag formation during combustion or gasification. Coal ash fusibility characteristics are difficult to determine precisely, partly because the ash contains many components with different chemical behaviours, and may vary from coal source to coal source.The first objective of this study was to determine if the most relevant characteristics of coal were representative of the typical coal from the South African Highveld region. Secondly, a detailed understanding of the coal and coal ash are needed in order to explain slag formation and mineral transformations.Based on standard coal properties, such as the ash content, volatile content, carbon content and maceral composition, it can be concluded that the coal sample used for this study was representative and comparable with the coal from the Highveld region.From the results obtained and the analysis done on the coal samples, it was observed that the mineral grains showed a wide range of types that ranged from pure coal to pure minerals. The types of mineral particles within the coal range from large irregular minerals to small irregular minerals on the edge of coal particles. Kaolinite and quartz can occur as fine inclusions in carbon rich particles or associated with mudstone, siltstone or sandstone, together with kaolinite infillings. The main minerals present in the coal feed are kaolinite, quartz, dolomite, calcite, muscovite, pyrite and microline. An abundance of calcium-rich particles, which are probably calcite and dolomite, were observed. These minerals are present throughout the coal structure and are not specific to one type of mineral grain or structure. An increase in Si and Al abundance in three different prepared coal fractions with increasing particle size distribution was observed the high density fractions are mainly situated in the coarser particles.After combustion or gasification, the major source of glass is derived from included minerals in carbon rich particles. It is clear that focus on the modification of the unclassified/amorphous phase, to increase viscosity (decrease slag formation or have a higher concentration of crystalline phases) at a certain temperature, or in general terms the ash fusion temperature of the coal, is important. Altering the ash chemistry involves the addition of a material to the coal to increase the viscosity.     

不同粘土矿物与聚羧酸减水剂相互作用机理研究

通过X射线衍射(XRD)、红外光谱(IR)、有机碳吸附(TOC)、饱和吸水率以及净浆流动性等试验方法,研究了不同粘土矿物与聚羧酸减水剂的相互作用机理.结果表明:聚羧酸减水剂的侧链可进入粘土矿物蒙脱石的层间,发生插层反应,即层间吸附,而其侧链结构不进入伊利石、高岭土、海泡石等粘土矿物的层间,仅发生表面吸附,且吸附量大小为蒙脱石>高岭土>海泡石>伊利石;饱和吸水率试验显示,粘土矿物的饱和吸水率大小为蒙脱石>高岭土>海泡石>伊利石;流动度试验表明,粘土矿物对水泥-减水剂体系净浆流动度均有不同程度的影响,且蒙脱石影响程度最大.由此可知,粘土矿物对自由水和聚羧酸减水剂的吸附是造成流动度损失的主要原因.