Effect of occurrence mode of heavy metal elements in a low rank coal on volatility during pyrolysis

The harmful trace elements will be released during coal utilization, which can cause environment pollution and further endangering human health, especially for heavy metal elements. Compared to combustion, the release of heavy metal elements during coal pyrolysis process, as a critical initial reaction stage of combustion, has not received sufficient attention. In the present paper, a low rank coal, from Xinjiang province in China, was pyrolyzed in a fixed bed reactor from room temperature, at atmospheric pressure, with the heating rate of 10 °C/min, and the final pyrolysis temperature was from 400 to 800℃ with the interval of 100℃. The volatility of heavy metal elements (including As, Hg, Cd and Pb) during pyrolysis process was investigated. The results showed the volatility of all heavy metal elements increased obviously with increasing temperature, and followed the sequence as Hg > Cd > As > Pb, which was mainly caused by their thermodynamic property and occurrence modes in coal. The occurrence modes of heavy metals were studied by sink-andfloat test and sequential chemical extraction procedure, and it can be found that the heavy metal elements were mainly in the organic and residual states (clay minerals) in the raw coal. And most of the organic heavy metals escaped during the pyrolysis process, the remaining elements were mainly in the residual state, and the elements in Fe-Mn state also tended to remain in the char.

Distribution and occurrence of trace elements in the No.14 coal from the Huolinhe mine

Optical microscopy, and scanning electron microscopy in conjunction with energy dispersed X-ray spectrometry （SEM-EDX）, have been used to study the minerals and the concentrations of 12 trace elements in the No.14 coal from the Huolinhe mine, Inner Mongolia China. The distribution, affinity and removability of the trace elements were studied by float-sink experiments and petrological methods. A high mineral content, dominated by clay minerals, was found in the No.14 coal from the Huolinhe mine. The concentrations of As, Sb and Hg are relatively high compared to the average values for Chinese coals. As, Cr, Hg, Li, Mn, Pb are mainly associated with the minerals while Cd, Co, Ni, Sb, and Se are evenly distributed between the minerals and the organic matter. Be and Ba are mainly distributed in the minerals with a minor proportion in the organic matter. Most elements have a low organic affinity, although Sb, Se, Co, Cd, Ni are closely integrated with the organic matter. High theoretical removabilities are indicated for most trace elements. So it may be possible to lower the concentrations of trace elements during coal preparation.

Modes of occurrence and pre-concentration of rare earth elements in No.17 coal in Liupanshui coalfield,China

Rare earth elements(lanthanide and yttrium,abbreviated as REY) provide important support for national security,energy production,environmental protection and economic growth.In recent years,many studies have shown that the content of REY in some coal or coal by-products is close to or even higher than that in traditional REY ore,which makes coal a potential source of REY.This study took the No.17 coal of Panzhou mining area in Liupanshui coal field as the research object,and the content and occurrence modes of REY in raw coal and 7 density fraction samples were studied.The results show that the content of REY in the raw coal reaches 220.67 μg/g,which is significantly higher than the average REY content in the world coal and Chinese coal as reported in the literature.Gravity separation has a certain pre-enrichment effect on REY and the fraction sample> 1.8 g/cm~3 has the highest REY of 426.27 μg/g(equal to rare earth oxide 0.1%).Study on correlation between REY and ash yields reveals that the organic affinity of the light rare earth is higher than that of the medium rare earth and the heavy rare earth.As shown by X-ray diffraction(XRD) and X-ray flouresence spectroscopy(XRF),the major minerals in coal are kaolinite,quartz and calcite,and the content of REY in coal is significantly related to Al,Si and kaolinite,which implies that REY occur mainly in kaolinite.Laser ablation inductively coupled plasma mass spectroscopy(LA-ICP-MS) was adopted to determine chemical composition of micro-zone in kaolinite in coal and the results show that there is no obvious correlation between REY and the contents of Al and Si.This indicates that the REY occur probably in the form of adsorption.The research results provide a scientific reference for the potential extraction of the associated REY in the coal.

Geochemistry of rare earth elements and yttrium in Late Permian coals from the Zhongliangshan coalfield, southwestern China

Rare earth elements and yttrium(REY)in coal deposits are considered promising alternative sources for these resources owing to their increasing global demand.This paper reports the geochemical characteristics of REY in the Late Permian coals from an underground K1a seam section of the Zhongliangshan coalfield in Chongqing,southwestern China.The mineralogy,degree of enrichment,distribution patterns,modes of occurrence,and sediment origin of REY were investigated.Compared with the average of world coals,the concentration of REY in the K1a coals were normal,dominated by light REY(LREY),with less medium and heavy REY(MREY,HREY).The fractionation degree of the MREY and HREY are higher than that of LREY in most K1a coal samples,deduced from the mixed enrichment type of REY,mainly including M-H-type,and a few L-M type and H-type.In addition,the combination of anomalies of Ce,Eu,Gd,and Al_(2)O_(3)/TiO_(2) parameters,the terrigenous materials in the K1a coal were derived from the felsic-intermediate rocks at the top of the Emeishan basalt sequence,and the samples were affected by seawater intrusion during early peat accumulation.Although the minerals primarily consist of kaolinite,illite,pyrite,and small amounts of quartz,calcite and anatase,REY are correlated with ash yield,SiO2,and Al_(2)O_(3),revealing that the REY mainly occur in aluminosilicate minerals,especially kaolinite and illite.Meanwhile,REY positively relate to P_(2)O_(5) and Zr,which may exist in phosphate-containing minerals or zircon.Furthermore,most samples in the K1a coal or ash do not reach the cut-off grade for the beneficial recovery of REY.With the exception of central Guizhou,southwestern Chongqing,and the junction of western Guizhou and northeastern Yunnan,the REY content in coals from southwestern China are high,and its by-products are suitable as potential REY sources.

Rare earth elements in flotation products of coals from East Kootenay coalfields,British Columbia

With the identification of coal deposits that are enriched in rare earth elements(REEs)across the world,coal and coal by-products are considered as an alternative source for REEs due to the combined supply and demand restrictions for these elements.Studies are being conducted to recover these elements from various coal sources.In this study,coal samples from the East Kootenay coalfields in British Columbia,Canada were examined for the presence of REEs in run-of-mine coal samples and flotation products.Results reveal that on an ash basis,the concentration of REEs varies from 174 to 1038 mg/kg in the samples.To understand the REE as sociation,which is essential for extraction purposes,a three-step sequential extraction process along with a mineralogical evaluation using scanning electron microscopy(SEM)with energy dispersive X-ray spectroscopy(EDX)and quantitative X-ray diffraction(XRD)data was used.It is found that a significant portion of REEs in the feed samples were reported to middling and tailings streams.The mineralogical analyses reveal REE association with aluminosilicate mineral in the samples.

中国煤中砷的含量分布、赋存状态、富集及环境意义

砷是煤中有害微量元素之一,在煤加工利用过程中,砷会以各种形式释放出来,进入环境。本文在全面分析现有资料和文献的基础上,结合作者对中国煤中砷的研究成果,分析了中国煤中砷的含量与分布、赋存状态、富集因素以及环境意义。通过研究和分析可知,中国煤中砷的平均值约为5μg/g,但在不同地区、不同时代以及不同类型的煤中有较大的差异,除中国西南地区含量异常高外,一般含量均在10μg/g以内;煤中砷的赋存状态多种多样,主要以无机态的硫化物结合为主,并常与黄铁矿等矿物伴生,也存在有机态结合的砷;中国煤中砷的来源和富集主要是以陆源母岩、成煤植物、沉积环境和构造裂隙—热液作用等为主的多种因素综合控制的结果;在煤燃烧过程中,煤中的砷释放出来,并对长期生活在燃煤地区的环境和人体产生影响。本文还提出今后煤中砷研究的主要方向,以为煤中砷的研究提供参考资料。

河北峰峰矿区煤中微量有害元素的赋存与分布

运用仪器中子活化分析、电离耦合等离子体原子发射光谱、带能谱仪的高分辨率扫描电镜以及逐级化学提取对河北峰峰矿区不同煤阶的煤中微量有害元素进行了测定,发现该矿区煤中微量有害元素含量均值与华北地台晚古生代煤的均值相比,As(3.21μg/g),Br(13.01μg/g),Co(6.21μg/g),Cu(31.29μg/g),Mo(3.63μg/g),Rb(7.73μg/g),Sn(9.60μg/g),W(1.62μg/g)等元素的含量偏高;该矿区不同变质程度煤中微量有害元素的含量不同,在明显受岩浆热液影响的无烟煤中As,Co,Cu,F,Fe,Mo,Ni,U,Zn含量较高;岩浆热液形成的方解石和黄铁矿脉是峰峰矿区无烟煤中Zn,As,Mo,Cu,Ni,Co等微量有害元素富集的主要载体。燃煤产物特别是飞灰中As(9.10μg/g),Co(10.55μg/g),Cr(58.18μg/g),Mo(13.95μg/g),Se(4.25μg/g),Th(34.50μg/g),U(7.65μg/g)的含量和原煤相比普遍较高,对它们的赋存状态及其对环境和人体健康的危害值得深入研究。

煤中部分潜在毒害微量元素在表生条件下的化学活动性

利用连续化学浸取实验方法，对采自贵州省二叠纪龙潭组的３２ 个煤样中的１０ 种潜在毒害微量元素的化学活动性进行了研究．结果表明：煤中Ｈｇ、Ａｓ、Ｓｅ、Ｃｄ、Ｃｕ、Ｐｂ 等元素具有极强的化学活动性，其中平均８３－８％ 的Ｈｇ 、９３．５％ 的Ａｓ、８０－３ ％ 的Ｓｅ、６３ ．３ ％ 的Ｃｄ、７１ ．１ ％ 的Ｃｕ 和８６－８ ％ 的Ｐｂ 可以被带出煤中而进入表生环境；煤中Ｚｎ 的化学活动性次之，只有平均４６－６ ％ 的Ｚｎ 可能迁移进入环境中；Ｔｌ、Ｃｒ、Ｎｉ 的化学活动性最差，平均可浸取比例分别是２２－９％ 、１９－７ ％ 和２５－７％ ．煤中潜在毒害微量元素的化学活动性取决于其在煤中的赋存状态．存在于硫酸盐、碳酸盐、硫化物和部分有机相中的元素在风化过程中很容易被带出，而存在于硅酸盐矿物相中的元素在表生条件下是非常稳定的．

煤中微量元素赋存状态研究方法

简要介绍了煤中微量元素赋存状态的主要研究方法：（１）间接方法。ａ．浮沉实验；ｂ．单组分分析；ｃ．逐级化学提取；ｄ．低温灰化＋Ｘ射线衍射；ｅ．数理统计分析。（２）直接方法。ａ．显微分析；ｂ．光谱分析。并指出了其应用范围。

煤中常量元素的赋存特征与研究意义

煤中常量元素(包括Na、Mg、Al、Si、K、Ca、Ti、P和Fe)是煤的重要无机组成,也是影响煤物理化学性质及加工利用的主要影响因素。本文结合华北鄂尔多斯盆地、开滦矿区和峰峰矿区晚古生代煤、贵州西部晚二叠世煤的具体实例,对煤中常量元素的赋存状态、地质成因和指相意义进行了总结,并对煤中常量元素在煤加工利用过程中的影响做了简要陈述。

义马煤中几种微量污染元素的赋存形态研究

微量元素在煤转化过程中的变迁行为和其向环境的释放能力主要取决于它们的原始赋存形态。由于微量元素赋存形态的多样性和煤本身的复杂性,煤中微量元素赋存形态的研究尚没有十分成熟的方法。采用密度分离、脱灰处理、逐级化学提取等间接方法研究了义马煤中As、Pb、Cd、Cr等几种微量污染元素的宏观赋存形态。研究表明,义马煤中As、Pb、Cd主要与矿物质伴生,Cr主要赋存在有机质当中。As主要与黄铁矿相伴生;Cd部分与黄铁矿类矿物质伴生,部分与其它难溶矿物质伴生;Pb在硫酸盐、硫化物、硅酸盐等矿物质中均有分布。

煤中潜在毒害元素分布的多元分析及其地球化学意义

在对贵州省二叠纪龙潭组煤层中 S、Fe、As、Cd、Hg、Pb、Se、Sb、Tl和 Zn分布规律进行讨论的基础上 ,作者运用多元分析方法研究了这些潜在毒害元素的相关关系 ,并结合元素地球化学知识给出了这些元素在煤中赋存状态的信息。煤层中 As、Hg、Sb主要赋存于次生黄铁矿中 ;Zn和 Se主要赋存于闪锌矿中 ;Pb以方铅矿形式存在于煤中 ;从元素地球化学性质上讲 Cd应赋存于闪锌矿中 ,但由于其在煤中的含量较低 ,造成分析数据的误差较大 ,从而掩盖了它与 Zn之间的相关关系 ;煤中 Tl的赋存状态较为复杂。运用多元分析方法讨论煤中微量元素赋存状态时 ,一方面要保证所选样品具有代表性 ;另一方面 。

晋北-宁北煤中痕量元素的地球化学特征

应用仪器中子活化(INAA)、电感耦合等离子体原子发射光谱(ICP-AES)和原子吸收光谱(AAS)等方法测定了晋北-宁北一线5对矿井、2个露天矿、5个电厂和3个洗煤厂煤中环境敏感性痕量元素的含量;通过与中国土壤、其他地区煤以及世界范围煤中痕量元素含量进行对比,总结了研究区痕量元素的分布、富集特征,得知部分地区煤中Hg、Cd和Se的含量较高,在燃烧利用过程中可能对环境造成影响。通过分析痕量元素与灰分、挥发分的相关性以及痕量元素间、痕量元素与Al、Fe和Sp的相关、聚类特性,探讨了痕量元素间及其与矿物质间的亲合性及赋存特征。

煤中有害物质及其对环境的影响研究进展

综述了煤中有害物质的种类、分布赋存特征及对环境的影响研究进展。探讨了煤中黄铁矿的形态、世代交替、有机硫的结构及煤中硫的地质成因。阐述了煤中微量元素的种类、地质分布、赋存状态、迁移聚集机制及其环境危害。并对煤及燃煤产物中多环芳烃的种类、赋存规律及对环境和人类健康的危害进行了详细阐述。最后指出了煤中有害物质研究中存在的问题与发展趋势。

贵州织金煤矿区晚二叠世煤地球化学性质变异的硅质低温热液流体效应

运用仪器中子活化分析、电离耦合等离子体原子发射光谱、X射线荧光光谱、X射线衍射分析、带能谱仪的扫描电镜和逐级化学提取试验研究了贵州织金煤矿区上二叠统含煤岩系30号煤层中伴生元素的含量、赋存状态和矿物特征。结果表明,煤层中有高含量的脉状石英(9.4％),其δ30Si、δ18O值分别为0.6‰和15.4‰,表明脉状石英来源于硅质低温热液流体;脉状石英是煤中高含量Fe(2.31％)、Cu(356μg／g)、U(8μg／g)、Pd(2.1μg／g)、Pt(2.43μg／g)和Ir(0.006μg／g)的主要载体。

黔西南高砷煤热解过程中微量元素释放规律研究

采用高温箱式电阻炉对黔西南海子地区煤样进行热解,研究了在300～1200℃下慢速热解过程中,热解温度、元素赋存状态和灰分对微量元素释放规律的影响.结果表明,热解温度是影响煤失重和微量元素挥发的主要原因.As、Mo在900℃以上挥发较快;Pb热解前期挥发较快,450℃以上挥发缓慢;Sb随热解温度的升高缓慢增大.微量元素的挥发性还与赋存状态关系密切,有机态最为活泼;硫化物态和碳酸盐态在热解后期由于矿物的分解而逐步释放;硅酸盐态最稳定,基本残留在灰分中.灰分越高微量元素越不易挥发.

煤中次要元素的赋存方式

对煤中次要元素的赋存方式进行了分析，讨论了元素赋存方式的研究方法，指出采用草取方法和沉／浮方法结合将更有益于确定煤中次要元素的赋存方式．根据元素的矿物学类别详细讨论了煤中各次要元素的赋存方式．结果表明，次要元素在煤中的赋存方式远较其在矿物中的复杂．

凯里高硫煤中某些微量元素的富集及成因分析

用电感耦合等离子体质谱(ICP-MS)等方法,对贵州省凯里下二叠统梁山组高硫煤中Be、P、Sc、Mn、Co、Ni、Cu、Mo、Tl、Pb、Th和U等12种有害微量元素进行了测定。结果表明,凯里煤中多数有害微量元素含量明显高于中国煤中微量元素含量平均值。根据数理统计结果,将凯里煤中22种微量元素划分为5个群和4个旋转主因子,其中群5元素Be和Y对4个主因子均无贡献,暗示其成因来源可能具有特殊性。认为凯里煤中相当一部分Be、Co、Cu和Pb起源于成煤植物生长期间的同生阶段;受海水影响强烈的还原偏碱性沼泽环境有利于Be、Co和Cu的相对富集,受海水影响微弱的弱还原性和弱碱性环境条件更有利于Mn、Mo、Ni、P、Pb、Th、Tl和U的富集。

煤中环境敏感性痕量元素的挥发性研究

对我国西北部4个电厂原煤在实验室不同温度下进行燃烧实验,应用原子吸收光谱(AAS)、电感耦合等离子体原子发射光谱(ICP-AES)和仪器中子活化(INAA)等方法对煤和灰样中As,Pb,Hg,Cd,Co,Se,Mn,U,Th,Be,Mo,Sb,Br和V等14种环境敏感性痕量元素的质量分数进行了测定,通过对比痕量元素在煤与灰样中质量分数的差异以及不同温度下痕量元素的挥发率,研究了在实验室不同温度下痕量元素的转化、分配规律,结合元素的赋存状态和物理化学特性,揭示了影响痕量元素燃烧迁移、分配规律的主要因素.

煤及其燃烧产物中无机组分分析方法比较

从三个方面对煤及其燃烧产物中无机组分的分析方法进行了比较和评价 :1 )比较和评价了煤及其燃烧产物中矿物分析方法 ,其中主要讨论了 XRD法和 CCSEM法 ;2 )比较和评价了煤及其燃烧产物中元素含量的分析方法 ,主要包括 X-射线和 v-射线技术 ;原子吸收或发射技术( AAS/ AES)和质谱法 ( MS) ;3)比较和评价了煤及其燃烧产物中微量元素的赋存形态分析方法 ,主要包括直接分析方法和间接分析方法 .