六盘水地区煤中汞含量的分布赋存状态研究

通过对六盘水地区93家204个煤层煤样进行汞含量测定,研究了六盘水地区煤中汞含量的分布特征,探究了特低硫煤、低硫煤、中硫煤、中高硫煤、高硫煤中汞含量与灰分、硫含量的关系。     

平顶山煤中汞的分布与释放

通过１２７个钻孔和矿井煤样分析，对平顶山煤田不同地质成煤期中汞的分布规律、煤中汞与硫的赋存状态、煤质与煤层中汞含量的关系、汞在煤层中的垂向变化等进行了分析研究。为防治汞对矿区的环境污染提供了可靠资料。     

活性焦制备过程中汞的迁移研究

为研究工业活性焦生产过程中汞的迁移情况,使用实验室设备模拟工业制备活性焦的工艺过程制备活性焦样品,并以冷原子吸收法为基本原理的测汞仪对制备活性焦的原料煤、炭化样品和活性焦样品的汞含量进行测定,计算制备过程中汞的迁移量。结果表明:制备活性焦的原料煤中汞含量为42. 4 ng/g,制备过程的中间产物炭化样品(TH)的汞含量仅为1. 0 ng/g,活性焦样品(HXJ)的汞含量仅为0. 8 ng/g。原料煤中汞的赋存形态主要以共价化合物的无机盐和一些腐植酸中的有机汞存在,这些汞化合物的分解温度在350℃左右,而炭化温度可达到650℃,此时原料煤中大部分汞的化合物都已分解并以零价汞蒸汽的形式逸散到大气中。炭化过程是活性焦制备过程中汞迁移逸散量最大的阶段,原料中97. 6%的汞在此阶段逸散到空气中。在工业化制备活性焦过程中,对炭化阶段产生的尾气进行脱汞处理十分必要。     

中国煤中硫的分布特征研究

以“中国煤种资源数据库”为基础,结合新采集煤样,对中国不同煤田2237个煤层煤样的硫含量数据进行了统计分析,分不同时代、不同地域和不同煤种讨论了中国煤中硫的分布特征,并总结了煤中硫的分布规律.认为中国煤中硫的含量分布与成煤时代、聚煤地区密切相关.引入“储量权重”概念,按聚煤区储量加权计算,中国煤中平均硫含量为1.02%,该数值比算术平均值(1.40%)更能准确地反映中国煤中硫的含量分布.     

潞安煤的微观结构性质研究

结合潞安煤的煤质特征,采用扫描电镜和红外光谱对煤样的微观结构性质进行了研究分析和测试;结果表明:潞安煤原煤为高灰、高硫、低热值的低品质煤,属特强黏结煤;煤中含有大量的黏土类矿物及含硫矿物,Al、Si、Ca、Fe、Mg、S等元素较多,表面无明显裂隙和孔;煤中含有部分杂原子基团和芳香族化合物。其小于1.4 g/cm~3的煤样为高硫、低中灰、特高热值煤。     

丙二醇-氢氧化钾脱除煤中有机硫的研究

以重庆万盛高硫煤作为研究对象,选用硝酸预处理去除无机硫,并采用单因子法考察了煤浆浓度、反应时间、反应温度、丙二醇与氢氧化钾的配比对煤中有机硫脱除率的影响.结果表明,对于粒径小于0.075 mm的煤样,丙二醇-氢氧化钾脱除煤中有机硫的适宜条件为:煤浆浓度0.05 g/mL,反应时间90 min,反应温度180℃,丙二醇与氢氧化钾的配比为1∶1.在此条件下,有机硫从0.72%降到0.35%,脱除率为51.4%.     

优化煤中汞含量测定样品消解条件的试验研究

燃煤所引起的汞污染问题,已越来越受到人们的广泛关注,而准确测定煤中汞含量是研究汞污染的前提。本论文结合实际的试验条件,在分析试验数据的基础上,对比研究了氧弹燃烧法消解煤样和《GBT 16659-2008煤中汞的测定方法》中规定的汞蒸气发生瓶消解煤样的测试结果,优化了煤中汞含量测定样品消解的条件。研究结果表明,氧弹燃烧法消解煤样不仅具有较好的重复性和准确度,而且具有简便快速、减少化学试剂用量、能有效地测定煤中痕量汞等优点。     

硝酸预处理对正丙醇脱除煤中有机硫的影响

用1:4硝酸脱除无机硫后,通过正交实验确定了1:1正丙醇水溶液脱除涪陵高有机硫煤的最佳条件.分析了煤样的粒径、溶浆浓度、萃取时间及萃取温度对有机硫脱除率的影响.结果表明:用1:4硝酸脱除无机硫后,1 : 1正丙醇水溶液对高硫煤中有机硫的脱除率高,反应条件温和,容易实现.最佳脱硫条件为:煤样粒径0.12 mm,煤浆浓度0.083 g/mL,萃取时间90 min,萃取温度87 ℃,煤样的有机硫脱除率最高可达52.29%.     

乌鲁木齐市煤矿商品燃煤中汞释放研究

利用两个乌鲁木齐市汞含量较高的煤矿商品煤样开展释放试验,结果表明释放温度≥700℃、释放时间≥30 min时,其中汞释放完全,释放规律与国内其他地区高汞燃煤相似。乌鲁木齐市11个煤矿商品燃煤最大总汞释放率研究表明,在一定温度、时间下,汞基本全部释放;最大总汞释放率与煤中汞含量无必然联系;最大总汞释放强度与煤样汞含量呈高度正相关,高汞煤即高汞释放煤。     

渭北煤中硫的赋存特性研究

对渭北煤中硫的赋存特性进行了较为系统的研究,经对煤样进行工业分析,全硫、形态硫、煤灰成分的测定,渭北煤呈现出灰分含量高、水分含量较低、中高挥发分、高硫含量等特征。对原煤样进行XPS测试,煤中硫的存在形态较为复杂,其中有机硫所占比例非常大,样品表面的有机硫含量达到80%。而在有机硫中,主要是噻吩类和硫醇硫醚型硫,共占到有机硫含量的96%。由此可见在研究渭北煤中的硫脱出迁移特性必须着重考虑有机硫的脱出迁移特性。研究煤中硫的赋存特性,为煤的脱硫提供具有应用价值的数据和脱硫方法,对于减少二氧化硫的排放具有重要意义,符合国家可持续发展战略的要求。     

煤在富氧流化床燃烧条件下汞的析出及形态分布

目前有关于富氧气氛下流化床燃烧汞的形态转化特性的报道还不是很多,因此本文开展了富氧气氛下煤种对汞形态转化特性的影响的实验研究。采用流化床作为实验设备,选用徐州烟煤和淮北烟煤作为实验燃料,研究了空气气氛下不同温度和不同煤种对汞析出规律的影响,富氧气氛下煤种对汞形态转化规律的影响,并深入分析了相应的汞氧化机理。研究结果表明：在空气气氛下,温度的增加会促进汞的氧化,煤中的含硫量对汞的氧化也有影响;在富氧气氛下,徐州烟煤燃烧产生的气态总汞浓度高于淮北烟煤燃烧产生的气态总汞浓度,徐州烟煤的Hg²⁺（g）的分布率也比淮北烟煤的Hg²⁺（g）的分布率高出16%左右,因为徐州烟煤中高含硫量会影响Hg²⁺（g）的分布率;富氧气氛下徐州烟煤的Hg²⁺的分布率低于空气气氛下的,而淮北烟煤的Hg²⁺（g）分布率则与之相反,这与两种煤中硫含量的不同有关。     

循环流化床中烟气飞灰汞迁移规律

在小型热态循环流化床试验台上进行褐煤、烟煤、无烟煤燃烧试验,研究3种典型煤的烟气气态汞和飞灰颗粒汞迁移规律。试验结果表明：褐煤、烟煤、无烟煤在燃烧过程中,炉膛温度、空截面风速、给煤量以及煤颗粒大小变化时,汞元素在烟气和飞灰之间的迁移规律相似;降低炉膛密相区温度和增大炉膛空截面风速可促进烟气气态总汞Hg^T（g）迁移到飞灰颗粒汞Hg（p）中,同时也促进烟气气态零价汞Hg⁰（g）向烟气气态二价汞Hg²⁺（g）和Hg（p）转化;增加给煤量,烟气气态总汞Hg^T（g）和烟气气态零价汞Hg⁰（g）减少,飞灰颗粒汞Hg（p）含量增加,并且影响Hg⁰（g）的转化;选择合适的煤颗粒粒度可以促进Hg⁰（g）的转化以及Hg^T（g）向Hg（p）迁移。随燃烧工况的变化,3种煤Hg^T（g）、Hg（p）和Hg⁰（g）含量变化趋势相似,但含量相差较大,Hg⁰（g）占Hg^T（g）的比例y值也不同,其中无烟煤的y值高于烟煤和褐煤的y值。     

Development of a method for the determination of ultra-trace level mercury in adipose tissue by cold vapour atomic fluorescence spectrometry

A method for the determination of total mercury in rat adipose tissue by cold vapour atomic fluorescence spectrometry (CVAFS) has been developed. Adipose samples were initially subjected to a lyophilization procedure in order to facilitate the homogenization and accurate weighing of small tissue aliquots (~50 mg). A closed vessel microwave digestion procedure using a mixture of sulphuric and nitric acids was used to liberate mercury from the adipose matrix. All mercury species were quantitatively oxidized to Hg(II) by a potassium bromate/bromide oxidation, then reduced to Hg(0) vapour by stannous chloride prior to fluorescence detection. The CVAFS exhibited a linear range of 10 pg Hg/ml to 120 pg Hg/ml. The method detection limit in solution was 2 pg Hg/ml, or 1 ng Hg/g adipose tissue, based on a nominal 50 mg sample and a final volume of 25 ml. A reference material from the National Research Council of Canada (DOLT-2, trace metals in dogfish liver) was prepared in quadruplicate in order to assess the accuracy and precision of the method. Mercury in this material was recovered at 2.22 +/- 0.08 mu g/g, which is 104% of the certified level (2.14 +/- 0.10 mu g/g).     

Experimental study on mercury transformation and removal in coal-fired boiler flue gases

This paper reported mercury speciation and emissions from five coal-fired power stations in China. The standard Ontario Hydro Method (OHM) was used into the flue gas mercury sampling before and after fabric filter (FF)/electrostatic precipitator (ESP) locations in these coal-fired power stations, and then various mercury speciation such as Hg⁰, Hg²⁺ and Hg^P in flue gas, was analyzed by using EPA method. The solid samples such as coal, bottom ash and ESP ash, were analyzed by DMA 80 based on EPA Method 7473. Through analysis the mercury speciation varied greatly when flue gas went through FF/ESP. Of the total mercury in flue gas, the concentration of Hg²⁺ is in the range of 0.11–14.76 μg/N m³ before FF/ESP and 0.02–21.20 μg/N m³ after FF/ESP; the concentration of Hg⁰ ranges in 1.18–33.63 μg/N m³ before FF/ESP and 0.77–13.57 μg/N m³ after FF/ESP, and that of Hg^P is in the scope of 0–12.11 μg/N m³ before FF/ESP and 0–0.54 μg/N m³ after FF/ESP. The proportion of Hg²⁺ ranges from 4.87%–50.93% before FF/ESP and 2.02%–75.55% after FF/ESP, while that of Hg⁰ is between 13.81% – 94.79% before FF/ESP and 15.69%–98% after FF/ESP, with that of Hg^P is in the range of 0%–45.13% before FF/ESP and 0%–11.03% after FF/ESP. The mercury in flue gas mainly existed in the forms of Hg⁰ and Hg²⁺. The concentrations of chlorine and sulfur in coal and flue gas influence the species of Hg that are formed in the flue gas entering air pollution control devices. The concentrations of chlorine, sulfur and mercury in coal and the compositions of fly ash had significant effects on mercury emissions.     

Utilization of oxygen flask combustion method for the determination of mercury and sulfur in coal

By use of oxygen flask combustion (OFC), a rapid and convenient determination method for mercury (Hg) and sulfur (S) in coal was developed. For the determination of Hg in coal, the OFC method with a KMnO₄ solution as an absorbent was carried out, and the resulting solution was analyzed by cold vapor atomic fluorescence spectrometry (CVAFS). For six certified reference material coals, the Hg concentrations obtained by this method were in good accordance with the certified or reference values. In addition, nine brands of Japanese standard coals (SS coals) were analyzed by the present method, and the data were compared to those from the authentic microwave-acid digestion (MW-AD) method. For the determination of total S in coal, the OFC method with H₂O₂ solution as an absorbent followed by ICP-AES or precipitation titration was successfully applied.     

煤粉炉和循环流化床锅炉飞灰特性对其汞吸附能力的影响

通过分析两台容量相近的循环流化床锅炉和煤粉锅炉飞灰样品的粒径分布、表面结构特性、未燃尽碳含量、反应性和汞含量，探究两种类型锅炉飞灰特性差异及其与飞灰汞吸附能力的关系。结果表明：循环流化床和煤粉锅炉尾端除尘设备排灰口飞灰汞的含量分别为1584.0 ng/g和503.7 ng/g，其原因与飞灰粒径、未燃尽碳含量和表面特性相关。对于循环流化床锅炉，飞灰中汞含量随其粒径和反应性温度的减小而增加，随未燃尽碳含量增加而增加，且与比表面积和吸附量呈正相关关系。对于煤粉锅炉，粒径为75～53 μm的飞灰对汞吸附能力较强，未燃尽碳含量明显小于循环流化床所产生飞灰的含量，飞灰比表面积随粒径变化不大，由此导致煤粉锅炉除尘设备排灰口所取样品对汞的吸附能力远低于循环流化床锅炉相对应位置飞灰对汞的吸附能力。     

Laboratory study of air-water-coal combustion product (fly ash and FGD solid) mercury exchange

Recent laboratory research has indicated that coal fly ash derived from subbituminous and bituminous type coals is a sink for atmospheric mercury (Hg), however lignite-based ash was found to emit Hg to the air. Solids collected from systems with components that enhance Hg removal (i.e. activated carbon injection (ACI), flue gas desulfurization (FGD), and selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR)) may have higher Hg concentrations and therefore a higher potential for Hg release. For this study we investigated the potential for Hg release to the air and water from coal combustion products (CCPs) collected from coal-fired units with FGD equipment, SCR and SNCR equipment, and sorbent injection for Hg removal. In the laboratory study, most dry samples acted as sinks for atmospheric Hg in the dark at 25 °C. When exposed to light or increased temperature (45 °C), deposition of Hg to the fly ash substrates in most cases continued but decreased. Wet FGD samples emitted Hg. However, they became a sink for atmospheric Hg or exhibited low Hg emission rates when dried. Mercury flux in the dark at 25 °C was correlated with fly ash carbon content (LOI). Most liquid extracts derived using the synthetic precipitation leaching procedure (SPLP EPA method 1312) had very low Hg concentrations (<13 ng/l).     

Sulfurization of a carbon surface for vapor phase mercury removal - II: Sulfur forms and mercury uptake

Sulfur forms deposited on carbonaceous surfaces after exposure to hydrogen sulfide were analyzed using XPS and XANES. Higher temperatures promote the formation of organic sulfur and the presence of H₂S during the cooling process increased elemental sulfur content. Temperatures between 400-600 °C were found to be optimal for producing effective mercury uptake sorbents. The increased amount of sulfur deposited during the cooling process in the presence of H₂S was very effective towards Hg uptake in nitrogen. Correlation of mercury uptake capacity and the content of each sulfur form indicated that elemental sulfur, thiophene, and sulfate are likely responsible for mercury uptake, with elemental sulfur species being the most effective.     

Characteristics and composition of fly ash from Canadian coal-fired power plants

Fly ashes were collected from the electrostatic precipitator (ESPs) and/or the baghouse of seven coal-fired power plants. The fly ashes were sampled from power plants that use pulverized subbituminous and bituminous feed coals. Fly ash from bituminous coals and limestone feed coals from fluidized-bed power plant were also sampled. The fly ashes were examined for their mineralogies and elemental compositions. The fly ashes from pulverized low sulfur coals are ferrocalsialic, those from high sulfur coals are ferrosialic and the fly ashes from the fluidized bed coals are ferrocalcic. The concentrations of As, Cd, Hg, Mo, Ni, and Pb in fly ash are related to the S content of the coal. Generally, those feed coals with a high S content contain higher concentrations of these elements. The concentrations of these elements are also greater for baghouse fly ash compared to ESP fly ash for the same station. The S content of fly ash from high S coal is 0.1% for pulverized ESP fly ash and 7% for baghouse fly ash from the fluidized bed, indicating that most of the S is captured by fly ash in the fluidized bed. The baghouse fly ash from the fluidized bed has the highest content of Cd, Hg, Mo, Pb, and Se, indicating that CaO, for the most part, captures them. Arsenic is captured by calcium-bearing minerals and hematite, and forms a stable complex of calcium or a transition metal of iron hydroxy arsenate hydrate [(M²⁺)₂Fe₃(AsO₄)₃(OH)₄·10H₂O] in the fly ash. Most elements in fly ash have enrichment indices of greater than 0.7 indicating that they are more enriched in the fly ash than in the feed coal, except for Hg in all ESP ashes. Mercury is an exception; it is more enriched in baghouse fly ash compared to ESP. Fly ash collected from a station equipped with hot side ESP has a lower concentration of Hg compared to stations equipped with cold side ESP using feed coals of similar rank and mercury content. Fly ash particles from fluidized bed coal are angular and subangular with cores of quartz and calcite. The quartz core is encased in layer(s) of calcium-rich aluminosilicates, and/or calcium/iron oxides. The calcite core is usually encased in an anhydrite shell.     

Effects of Methylmercury Contained in a Diet Mimicking the Wayana Amerindians Contamination through Fish Consumption: Mercury Accumulation, Metallothionein Induction, Gene Expression Variations, and Role of the Chemokine CCL2

Methylmercury (MeHg) is a potent neurotoxin, and human beings are mainly exposed to this pollutant through fish consumption. We addressed the question of whether a diet mimicking the fish consumption of Wayanas Amerindians from French Guiana could result in observable adverse effects in mice. Wayanas adult men are subjected to a mean mercurial dose of 7 g Hg/week/kg of body weight. We decided to supplement a vegetarian-based mice diet with 0.1% of lyophilized Hoplias aimara fish, which Wayanas are fond of and equivalent to the same dose as that afflicting the Wayanas Amerindians. Total mercury contents were 1.4 ± 0.2 and 5.4 ± 0.5 ng Hg/g of food pellets for the control and aimara diets, respectively. After 14 months of exposure, the body parts and tissues displaying the highest mercury concentration on a dry weight (dw) basis were hair (733 ng/g) and kidney (511 ng/g), followed by the liver (77 ng/g). Surprisingly, despite the fact that MeHg is a neurotoxic compound, the brain accumulated low levels of mercury (35 ng/g in the cortex). The metallothionein (MT) protein concentration only increased in those tissues (kidney, muscles) in which MeHg demethylation had occurred. This can be taken as a molecular sign of divalent mercurial contamination since only Hg(2+) has been reported yet to induce MT accumulation in contaminated tissues. The suppression of the synthesis of the chemokine CCL2 in the corresponding knockout (KO) mice resulted in important changes in gene expression patterns in the liver and brain. After three months of exposure to an aimara-containing diet, eight of 10 genes selected (Sdhb, Cytb, Cox1, Sod1, Sod2, Mt2, Mdr1a and Bax) were repressed in wild-type mice liver whereas none presented a differential expression in KO Ccl2(-/-) mice. In the wild-type mice brain, six of 12 genes selected (Cytb, Cox1, Sod1, Sod2, Mdr1a and Bax) presented a stimulated expression, whereas all remained at the basal level of expression in KO Ccl2(-/-) mice. In the liver of aimara-fed mice, histological alterations were observed for an accumulated mercury concentration as low as 32 ng/g, dw, and metal deposits were observed within the cytoplasm of hepatic cells.