煤燃烧中无机矿物向颗粒物的转化规律

为深入理解燃煤颗粒物的形成机理,利用计算机控制扫描电镜技术对煤及其颗粒物中的无机矿物进行了详细表征,研究了煤燃烧过程中主要矿物向颗粒物的转化规律.结果表明煤中粘土矿物由于含有K、Na、Ca、Mg和Fe等杂质元素,容易在较低温度下发生熔融和聚合,从而使颗粒粒径变大.黄铁矿在燃烧中易发生分解、破碎而使颗粒粒径减小,Fe氧化物与硅酸盐发生反应形成富Fe硅酸盐.方解石和铁白云石在高温条件下分解生成对应的氧化物,也可与硅酸盐发生反应形成富Ca或富Fe硅酸盐.石膏在燃烧过程中会经历脱水和分解反应,生成的CaO可与SO3和熔融硅酸盐发生竞争反应.     

褐煤热解与燃烧时矿物转化和细灰形成的CCSEM研究

在沉降炉中进行了一种典型中国褐煤的热解与燃烧实验,热解气氛为N2,燃烧气氛为O₂/N₂=21:79,采用CCSEM分析原煤、煤焦与煤灰。CCSEM分析结果表明,铁氧化物、石英、黄铁矿、伊利石和高岭土是煤中主要的矿物成分,同时也是主要的外在矿成分,褐煤中57.26%的矿物粒径小于10μm。在热解与燃烧过程中,煤中主要矿物发生了明显转化。富Si矿物和硅铝酸盐在热解和燃烧过程中可能发生了破碎;而富Fe矿物部分明显破碎生成细小矿物,部分外在矿直接转化,未发生明显破碎。细灰少量来自于细小富硅矿、石英和铁氧化物等矿物的直接转化,70%以上的细灰由Ca、Fe含量很高的混合硅铝酸盐组成。     

利用CCSEM对煤中矿物特性及其燃烧转化行为的研究

利用计算机控制扫描电镜技术(Computer Controlled Scanning Electron Microscopy,CCSEM)研究了煤中矿物特性及其在燃烧过程中的转化行为.结果表明原煤中矿物主要为粘土和黄铁矿,且主要以外在矿物的形式存在,粒径多在10 μm以上,而内在矿物绝大部分小于10 μm.不同矿物具有不同的粒径分布和内在/外在特性,显示煤中矿物分布的非均一性.煤灰主要由莫来石、铁、钙和钠的铝硅酸盐组成.通过K、Fe、Ca和Na在原煤及其产物所含矿物中的质量分布对比,揭示了它们在燃烧过程中的转化行为.煤灰粒径的变大是矿物颗粒熔融聚合的结果.     

西部低阶煤中铬赋存形态及燃烧排放特性研究

对典型西部低阶煤进行逐级提取、热解/燃烧实验及热力学计算,研究煤中重金属Cr的赋存形态、燃烧排放特性及金属氧化物对铬迁移转化的影响。结果表明,BCR逐级提取法相比常用的水铵-酸逐级提取法对研究低阶煤中Cr赋存形态有很大优势,四种西部低阶煤中Cr主要以有机态和残渣态形式存在,其中万向煤中有机Cr含量高达65.36%。与N_2相比,CO_2对煤中Cr的分解释放有一定的抑制作用,燃烧过程中O_2的加入对Cr的释放影响不大,燃烧温度对煤中Cr释放的影响与煤种有关。CaO和MgO对剧毒Cr(Ⅵ)的生成有一定的促进作用,而Fe基矿物对捕获Cr蒸汽同时抑制燃煤六价铬的生成有很大优势。     

低比重分煤中结渣相关矿物质分布的实验研究

对结渣特性差异大的神华煤和山西贫煤比重分离制取低比重分煤,使用ICP-AES、XRD和穆斯堡尔谱分析低比重分煤及其原煤盐酸分离前后的样品,对比研究低比重分煤及其原煤中结渣相关矿物质,特别是黏土矿物分布。结果表明神华煤低比重分煤中钙主要为有机钙,铁基本以黄铁矿存在,并且该黄铁矿大部分溶于盐酸。煤燃烧时这些含铁、钙物质和黏土矿物的作用产物应该对该煤种的易结渣性具有重要贡献。两种动力煤的低比重分煤中黏土矿物种类和相对分布均与原煤中相同,并且黏土矿物在低比重分煤成灰物质中的份额均高于在原煤中的份额,针对黏土矿物在煤粉燃烧过程中的热反应产物的研究将为理解飞灰中易熔融物质的形成机理提供更深入的认识。     

铁系矿物对煤灰相变过程的内在影响规律研究

为深入研究煤燃烧与煤气化过程中煤中矿物的熔融变化行为对煤灰物理相变变化过程的内在影响规律,本文采用高温热显微镜、SEM-EDX等分析测试手段,实验研究了不同条件(煤燃烧与煤气化)下煤中矿物演变规律与煤灰物理相变变化行为间的内在联系和影响规律。研究结果表明:高铁含量的煤灰A在气化条件下发生初始熔融温度(T_(in))及快速熔融温度(T_(max))要比其在燃烧条件下对应的温度分别低144℃和113℃,而低铁含量的煤灰B则对应气化条件下的T_(in)和T_(max)分别比燃烧条件下的对应温度低25℃和62℃;不同气氛下灰中Fe的不同价态是导致这种差别的主要原因,高温下煤灰相变发生、发展过程中,灰中方铁石、铁铝榴石以及铁做榄石等铁系矿物是引发煤灰发生初始熔融的主要矿物。     

准东煤热解过程中钠的迁移规律研究

新疆准东煤中钠含量较高,在热转化利用过程中会造成设备的腐蚀、积灰和结渣等问题。本文通过煤的逐级萃取和热解实验,考察了准东煤热解过程中钠的迁移转化规律。初步实验结果表明准东煤中的钠以水溶钠为主,约占60%~70%。热解过程中钠的形态发生转变,温度低于700℃时钠主要是以有机钠的形式释放,温度升高,原煤和水洗煤中可溶钠向不溶钠转化。     

刚玉床料对高钠煤循环流化床气化中钠迁移转化的影响

选择刚玉作为床料,利用循环流化床对天池木垒煤进行了气化实验研究,研究了刚玉对失流的抑制作用、矿物元素在不同粒径颗粒中分布以及煤中Na经过气化反应后的迁移转化规律。研究结果表明,以刚玉作为床料会降低底渣表面包覆层黏性,避免颗粒聚团导致失流;在刚玉诱导下,煤中Al、Si、Ca、Fe、Na和Mg等绝大多数矿物质元素在底渣和循环灰中富集,并导致物料粒径不断增大;935℃床温下(以刚玉为床料),天池木垒煤中Na在底渣、飞灰和煤气中的分布率分别为39.6%、45.4%和15%,相对于以石英砂为床料的情形,刚玉有效抑制了Na的挥发,降低了尾部沾污发生的机率;在刚玉作用下,固留在底渣中的Na主要以NaAl_(11)17、NaAlSi_2O_6和NaAlSi_3O_8等形式存在,并且刚玉与煤中矿物质元素反应生成的物质具有较高的熔点,避免低温共熔现象发生。     

九江网纹红土中粘土矿物过渡相的矿物学特征及成因

为研究长江中下游网纹红土中粘土矿物过渡相的矿物学特征及成因,采用X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、以及高分辨透射电子显微分析(HRTEM)等现代测试技术方法,对江西九江红土剖面网纹红土中粘土矿物过渡相开展系统、深入的研究。X射线衍射及红外吸收光谱分析结果表明,九江剖面网纹红土中粘土矿物组成主要有伊利石和高岭石,少量蒙脱石和伊利石/蒙脱石及微量高岭石/蒙脱石混层矿物过渡相。在高分辨透射电子显微镜下,可观察到蒙脱石晶层向高岭石晶层转化的现象。伊利石/蒙脱石过渡相是伊利石向蒙脱石转化的过渡产物,而高岭石/蒙脱石过渡相则为蒙脱石向高岭石转化的过渡产物,网纹红土中这两种过渡相的出现说明了粘土矿物风化演化的过程,即：伊利石→伊利石/蒙脱石混层矿物→蒙脱石→高岭石/蒙脱石混层矿物→高岭石的演化,同时表明网纹红土形成于风化作用增强的温暖潮湿气候环境。     

铁的氢氧化合物稳定相α, β-FeOOH的表征及光谱分析

铁的氢氧化合物稳定相针铁矿(α-FeOOH)及四方纤铁矿(β-FeOOH)的合成材料因具有纳米颗粒粒径、较高比表面积,在工业生产和环境治理中被广泛应用。α,β-FeOOH作为重金属等污染物的吸附材料尤受关注。但其合成过程中溶液pH值和反应条件(如不同温度下加热或室温磁力搅拌等)对α,β-FeOOH矿物材料晶型、颗粒形貌、尺寸和界面特性的影响及其与矿物环境功能的相关性报道较少。故本工作基于Fe(NO₃)₃和FeCl₃溶液在一定pH值范围内分别易于形成α-FeOOH和β-FeOOH稳定相,利用X射线衍射仪、透射/扫描电子显微镜和激光粒度分析仪对加热(40和70 ℃)和磁力搅拌(25 ℃)条件下形成的矿物α, β-FeOOH的晶型和颗粒形貌结构进行了鉴定与表征,同时利用红外光谱仪测定了矿物表面的特征结构基团。研究结果表明,40和70 ℃反应温度下形成的矿物Aka-T40, Aka-T70, Gth-T70具有颗粒均一、结晶型较好、比表面积较大等特性,是良好的去除环境污染物的吸附剂材料。     

Mössbauer Studies of Thermal Power Plant Coal and Fly Ash

Iron-57 Mössbauer spectroscopic studies were carried out at room temperature on samples of coal, slag (bottom ash) and mechanical ash collected from Bhatinda (India) thermal power plant. Hyperfine parameters such as isomer shift, quadrupole splitting and total internal magnetic field of ⁵⁷Fe nuclei were used to characterize various iron-bearing minerals. The observed parameters indicate the presence of pyrite, siderite and ankerite in coal sample while magnetic fractions of mechanical ash and slag samples show the formation of hematite and Al-substituted magnesio-ferrite. The non-magnetic fraction of slag ash shows the dominance of Fe²⁺ phases while that of mechanical ash demonstrates the formation of both Fe²⁺ and Fe³⁺ phases. These findings are compared with Mössbauer and magnetic susceptibility studies on fly ash samples of Panipat (India) thermal power plant reported earlier.     

Insight of arsenic transformation behavior during high-arsenic coal combustion

The release of arsenic vapors (As³⁺) during high-arsenic coal combustion not only raises serious environmental concerns, but also causes catalyst deactivation in selective catalytic reduction (SCR) systems. To illuminate the mechanisms involved in the transformation of arsenic vapors towards less troublesome arsenates (As⁵⁺) during coal combustion, the accessory minerals in the high-arsenic coal were identified and the association relationship of these compounds with arsenic in fly ash was estimated. The results showed that Si/Al were the main inorganic elements in high-arsenic coal while the content of Ca was quite low. Ca was mostly transformed into sulfates during coal combustion and the effect of Ca on the arsenic transformation was limited. Al/Fe played a more significant role in arsenic speciation transformation and arsenic in the fly ash was predominantly bound with Al/Fe-oxides as arsenates. It was further confirmed that Al in kaolin/metakaolin showed good capacity on arsenic capture. In addition, few arsenic vapors were captured through the physical adsorption mechanism and the large fraction of As³⁺ in some fine particles was mostly attributed to the chemical reactions between arsenic vapors and Al-compounds. Meanwhile, a certain amount of arsenic vapors were converted into As₂O₅(s) under the influence of SCR catalyst and then carried by flue gas to participate in fly ash. Besides, part of arsenic distributed in the fly ash was through the stabilization of ash matrix in high temperature conditions. The transformation of arsenic from vapors towards particulate arsenic favored arsenic emission control by particulate matter control devices.     

用XPS研究高灰熔融温度煤灰的矿物结构转化

高灰熔点X煤通过添加钙镁复配(W_CaO/W_MgO=1)助熔剂降低灰熔点,在模拟煤气化过程中制备灰渣,用X射线光电子能谱(XPS)分析不同温度点灰渣中O,Si,Al,Ca,Mg的存在形态及演化过程。认为钙镁复配助熔剂降低灰熔点主要是作用在硅、铝、氧结构变化上,表现为铝元素结构中铝氧配位方式的变化,即四配位的铝氧四面体[AlO₄]和六配位的铝氧八面体[AlO₆]随温度的变化而变化;硅元素结构中SiO₂链的破坏,Ca2+和Mg2+加入会破坏SiO₂链,使得桥氧硅变为非桥氧硅;以及氧元素结构中桥氧键断裂和非桥氧键形成。结合Factsage热力学分析软件,分析了添加钙镁复配助熔剂后,煤灰渣的高温相平衡组成,从矿物的结构变化研究助熔剂的助熔机理。结果表明,添加钙镁复配助熔剂后,Ca2+和Mg2+易与硅氧和铝氧四面体以及铝氧八面体中非桥氧键结合,生成低熔点的长石类矿物和镁质矿物,从而降低煤灰熔融温度。     

Mössbauer mineralogy on the Moon: The lunar regolith

A first-order requirement for spacecraft missions that land on solid planetary objects is instrumentation for mineralogical analyses. For purposes of providing diagnostic information about naturally-occurring materials, the element iron is particularly important because it is abundant and multivalent. Knowledge of the oxidation state of iron and its distribution among iron-bearing mineralogies tightly constrains the types of materials present and provides information about formation and modification (weathering) processes. Because Mössbauer spectroscopy is sensitive to both the valence of iron and its local chemical environment, the technique is unique in providing information about both the relative abundance of iron-bearing phases and oxidation state of the iron. The Mössbauer mineralogy of lunar regolith samples (primarily soils from the Apollo 16 and 17 missions to the Moon) were measured in the laboratory to demonstrate the strength of the technique for in-situ mineralogical exploration of the Moon. The regolith samples were modeled as mixtures of five iron-bearing phases: olivine, pyroxene, glass, ilmenite, and metal. Based on differences in relative proportions of iron associated with these phases, volcanic-ash regolith can be distinguished from impact-derived regolith, impact-derived soils of different geologic affinity (e.g., highlands and maria) can be distinguished on the basis of their constituent minerals, and soil maturity can be estimated. The total resonant absorption area of the Mössbauer spectrum can be used to estimate total FeO concentrations.     

Mössbauer and magnetic studies of nanocomposites containing iron oxides and humic acids

A sample of volcanic ashes emanated from the Osorno volcano, southern Chile, was characterized with X-ray fluorescence, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy, in an attempt to identify the iron-bearing minerals of that geologically recent magmatic deposit. X-ray patterns indicated that the sample is mainly constituted of anorthite, Fe-diopside-type and Ca-magnetite. The crystallographic structures of these dominant iron minerals are proposed on basis of their chemical composition and corresponding Mössbauer data to support models refined by fitting powder X-ray diffraction data with the Rietveld algorithm.     

Investigation of iron mineral formation by dissimilatory alcalophilic bacterium Geoalkalibacter ferrihydriticus using M?ssbauer spectroscopy

Formation of iron-bearing minerals by the dissimilatory alcalophilic bacterium Geoalkalibacter ferrihydriticus (strain Z-0531) under controlled laboratory conditions was studied using M?ssbauer spectroscopy. Strain Z-0531 was isolated from bottom sediments of Lake Khadyn (Tyva, Russia), a soda lake. The effect of the concentration of amorphous iron hydroxide (AFH) and anthraquinone-2,6-disulfonate (quinone) added to the medium was studied along with the effect of the incubation time on iron reduction.     

拉曼Mapping研究白云鄂博萤石型稀土矿物赋存特征及分布规律

白云鄂博矿以资源丰富、储量巨大而闻名。其中独居石矿物是主要稀土原料之一,在冶金、军事、化工材料等领域都有广泛的应用。前人已经对白云鄂博矿物学特征进行了充分的研究,随着开采深度的增加,原生矿物增多,对现阶段稀土矿物赋存状态有待深入了解。利用拉曼Mapping成像技术结合扫描电子显微镜(scanning electron microscope, SEM)与能谱议（energy dispersive spectrometer, EDS）方法,能够对白云鄂博共伴生矿物赋存特征进行更深的研究。EDS与能谱结果显示：矿物扫描区由萤石、重晶石、独居石、磷灰石和铁矿物构成。拉曼Mapping分析显示：显微共聚焦图下扫描基底为萤石矿物（CaF₂）,拉曼特征峰普遍出现在220～650 cm-1,与已知文献报道的萤石拉曼峰略有不同。较大颗粒为重晶石矿物（BaSO₄）,为典型的硫酸盐矿物。中等颗粒大小为独居石矿物（Ce,La,Nd）PO₄,细小颗粒集中区为磷灰石矿物（Ca₅[PO₄]₃F）。虽然独居石与磷灰石都为典型的磷酸盐矿物且具有相同磷酸根结构,但由于外部金属阳离子的结合种类不同,其拉曼峰位也不相同。拉曼Mapping结合EDS分析矿物的赋存特征及分布规律关系为：独居石呈板状或块状分布在重晶石与磷灰石中间或磷灰石与萤石矿物之间,粒度约为50～120 μm。重晶石矿物颗粒较粗呈块状集合体分布,颗粒大小为50～200 μm,常与独居石共生,矿物颗粒紧密生长。磷灰石呈细粒状或块状,星散分布在独居石与重晶石周围,类似侵染分布在萤石中。少量磷灰石颗粒与独居石相互交代成不规则共生体,大部分磷灰石呈单体分布在矿物之间。萤石矿物中富集最多,占比约55%,与独居石、重晶石、磷灰石、铁矿物伴生。从赋存状态上判断形成时期应早于其他伴生矿物。对矿物成因复杂,共伴生矿物极多白云鄂博矿床。EDS虽能分析矿物学基本关系,但独居石与重晶石矿物中的能谱图部分重合。是由于能谱扫描Ba,S与稀土元素Ce,La,Nd时激发能量线系太相近以及能谱分辨率较低。利用Mapping成像技术对于矿物鉴定上具有简单、可靠的优点,可以弥补EDS分析误判拉曼Mapping为矿物学分析提供一种新的鉴别思路,同时也为白云鄂博矿物的鉴定提供了参考性的拉曼光谱。     

Nanophase mixed-valence iron minerals in meteorites identified by cryogenic Mössbauer spectroscopy

Determination of oxidation states and the crystal chemistry of iron-bearing minerals in carbonaceous chondrites by Mössbauer spectroscopy is complicated by thermally-induced electron-hopping in cronstedtite, superparamagnetism of hydrous ferric oxides and ill-defined contributions from an incommensurate layered iron sulfide phase believed to be tochilinite. Mössbauer spectra measurements at 30 K of several terrestrial cronstedtite and tochilinite specimens have enables modal proportions of these minerals, as well as Fe³⁺/Fe²⁺ ratios, to be determined quantitatively in a suite of CM-type meteorites.     

Clay fraction mineralogy of a Cambisol in Brazil

Clay minerals having a 2:1 (tetrahedral:octahedral sheet) structure may be found in strongly weathering soils only if the local pedo-climatic environment prevents them from further weathering to other minerals such as iron oxides. The clay minerals impart important chemical properties to soils, in part by virtue of changes in the redox state of iron in their crystal structures. Knowing the chemical nature of soil clays is a first step in evaluating their potential reactivity with other soil constituents and processes, such as the chemical decomposition of organic substrates to be potentially used in environmental remediation. The purpose of this work was to characterize the iron oxides and iron-bearing clay minerals from a B horizon of a Cambisol developed on tuffite in the State of Minas Gerais, Brazil, using chemical analysis, powder X-ray diffraction, Mössbauer spectroscopy, and thermal analysis. The iron oxides of this NaOH-treated clay-fraction were found to contain mainly maghemite (γFe₂O₃) and superparamagnetic goethite (αFeOOH). Kaolinite (Al₂Si₂O₅(OH)₄), smectite, and minor portions of anatase (TiO₂) were identified in the CBD-treated sample.