Coal and coal byproducts:A large and developable unconventional resource for critical materials—Rare earth elements

Rare earth elements(REEs) are critical materials and provide significant values to national security,energy production, environmental protection and economic growth. The supply of REEs in U.S. solely relies on import as domestic production of REEs was ceased because of the environmental concerns during mining and lack of competitiveness. Nonetheless, unconventional REEs-containing resources,including produced water. acid mine drainage, and coal and coal byproducts(CCBs) contain significant amounts of REEs. However, the concentrations of REEs in these resources are several orders of magnitude lower than that of REEs ores. Thus, extraction of REEs from these materials is challenging. Here we report REEs extraction with environmentally friendly method that successfully concentrated REEs from312 ppm in fly ash to 99.4% in the final product. Especially, the five critically important REEs(Dy, Eu, Nd.Tb. and Y) account for up to ～63% of the total weight of all REEs in the final 99.4%-purity product. Coal fly ash is one of the major solid coal utilization byproducts, representing great potential resources for REEs extraction. Extraction of REEs from these unconventional resources could be the way to secure domestic supply of these critical materials.     

Estimating REY content of eastern Kentucky coal samples based on their associated ash elements

Coal and coal combustion byproducts can be considered as an alternative source of rare earth elements and yttrium (REY). The study of relationships between REY and other main coal properties could have several advantages such as estimating REY content of coal particles and designing beneficial extraction method. In this investigation, inter-correlations between REY content with coal parameters (proximate and ash elements) for a wide range of eastern Kentucky coal samples (708 records) were explored. Results demonstrate that zircon and monazite are the main source of heavy and light rare earth elements (HREE and LREE), respectively. Zr has the highest correlation with Y and Th has the strength relationship with Ce and La. In general, LREE have higher interaction with coal ash content in comparison with HREE. Results indicated that REY can be estimated quite satisfactorily by using their associated elements in coal ash.     

电感耦合等离子体质谱法分析粉煤灰漂珠中稀土元素

为研究粉煤灰漂珠中稀土元素对环境的影响,减少二次污染,建立了一种压力密闭消解-电感耦合等离子体质谱法测定粉煤灰漂珠中Sc,La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb和Lu等15种稀土元素的方法。方法用于分析国家标准物质(GBW07103)中稀土元素,结果与认定值一致;用于分析粉煤灰样品中稀土元素并做加标回收实验,加标回收率在93.9%~104.2%之间。     

微波消解-电感耦合等离子体质谱法测定粉煤灰中铀

粉煤灰是一种宝贵的铀资源,为了满足我国日益增长的核电对铀的需求,必须加大对粉煤灰中铀的综合回收利用,因此准确测定粉煤灰中铀含量意义重大。采用HNO₃-HF-HClO₄体系微波消解样品,选择¹⁸⁷Re为内标元素,²³⁸U为铀测定同位素,建立了微波消解-电感耦合等离子体质谱法(ICP-MS)准确快速测定粉煤灰中铀的分析方法。对溶样条件进行了优化,确定溶样酸用量为5.0mL HNO₃、3.0mL HF、0.50mL HClO₄,消解程序如下所示:消解功率为800W,15min从室温升到150℃,保温10min,15min从150℃升到200℃,保温30min。实验表明,当铀的质量浓度范围为0.5~20ng/mL时,铀的质量浓度与其对应的信号强度呈线性关系,线性相关系数为0.9999,方法检出限为0.05μg/g。将实验方法应用于粉煤灰实际样品分析,测定结果的相对标准偏差(RSD,n=6)为3.2%,加标回收率为95%~104%。选取来自不同地方燃煤电厂的粉煤灰,按照实验方法进行铀的测定,并与激光荧光法进行对比,两种方法测定结果基本一致。     

Partitioning of rare earth elements and yttrium (REY) in five coal-fired power plants in Guizhou,Southwest China

As indispensable strategic materials for high-tech industries, rare earth elements and yttrium (REY) have become particularly important in recent years, raising the demand of developing new approaches for reclamation of REY from REY-rich materials such as coal combustion products (CCPs). In this study, five coal-fired power plants (CFPPs) in Guizhou of southwest China were selected for investigating REY concentrations of solid samples, atmospheric emissions, and recovery potentials. REY concentrations of feed fuels are higher in this study (147.2–468.6 mg/kg) than what have been reported previously for coals in China and the world. REY atmospheric emissions are extremely low (38.70–180.11 mg REY/t coal). REY are enriched in bottom ash and fly ash, with average of 658 ± 296 mg/kg and maximum of 1257 mg/kg from the five CFPPs. Relative enrichment factors (REF) of REY in bottom ash and fly ash compared with the feed fuel are 0.86–1.02 and 0.91–1.04, respectively. REY concentrations in desulfurized gypsum are very low (6–17 mg/kg), and that is mostly inherited from limestone. Critical REY (Nd, Eu, Tb, Dy, Y, and Er) in bottom/fly ash account for 34%–39% of the total REY and the outlook coefficients (C_outl) are in the range of 0.89–1.11. This study indicates a promising prospect to reclaim REY from REY-rich CCPs (bottom and fly ash) in CFPPs in Guizhou, especially in the central-north Guizhou, although such practices require further technology advancement.     

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.     

微生物技术在稀土资源利用中的研究进展

主要介绍了稀土资源的重要作用及利用现状,对我国的稀土矿分布及特征进行概述,并提出稀土开采存在的问题及微生物采矿的优势。回顾利用微生物进行稀土矿开采的发展进程,总结其研究进展,介绍微生物采矿作用机理的研究,主要包括微生物浸出、吸附和积累稀土元素机理的相关研究,以及稀土矿采矿微生物的分离方法及种属分布等。以中国白云鄂博矿床和澳大利亚Mount Weld矿床中的矿石为例,说明微生物对矿石中稀土元素的提取作用。简述微生物对废弃物中稀土元素的回收作用,及微生物利用稀土元素技术将面临的挑战,并对其未来进行了展望。      

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 occu...     

粉煤灰中有价元素的提取

粉煤灰的综合利用是目前我国煤炭工业的一件大事,而从粉煤灰中提取有价元素是提高粉煤灰综合利用价值的重要途径之一。文章对其回收方法进行了咩细的综述,发现虽然在这方面也进行了大量的工作,但大都处于实验研究阶段,实现产业化的不多。因此,加强从粉煤灰中提取有价元素的研究,并有效地实现产业化是每个科学技术工作者的重要任务。     

Surface Runoff from Full-Scale Coal Combustion Product Pavements during Accelerated Loading

In this study, the release of metals and metalloids from full-scale portland cement concrete pavements containing coal combustion products (CCPs) was evaluated by laboratory leaching tests and accelerated loading of full-scale pavement sections under well-controlled conditions. An equivalent of 20 years of highway traffic loading was simulated at the OSU/OU Accelerated Pavement Load Facility (APLF). Three types of portland cement concrete driving surface layers were tested, including a control section [i.e., ordinary portland cement (PC) concrete] containing no fly ash and two sections in which fly ash was substituted for a fraction of the cement; i.e., 30% fly ash (FA30) and 50% fly ash (FA50). In general, the concentrations of minor and trace elements were higher in the toxicity characteristic leaching procedure (TCLP) leachates than in the leachates obtained from synthetic precipitation leaching procedure and ASTM leaching procedures. Importantly, none of the leachate concentrations exceeded the TCLP limits or primary drinking water standards. Surface runoff monitoring results showed the highest release rates of inorganic elements from the FA50 concrete pavement, whereas there were little differences in release rates between PC and FA30 concretes. The release of elements generally decreased with increasing pavement loading. Except for Cr, elements were released as particulates (>0.45?μm) rather than dissolved constituents. The incorporation of fly ash in the PC cement concrete pavements examined in this study resulted in little or no deleterious environmental impact from the leaching of inorganic elements over the lifetime of the pavement system.     

垃圾焚烧飞灰预处理后水泥固化实验研究

为实现焚烧飞灰的无害化和资源化,采用对飞灰进行预处理后再与水泥混合固化的方法来处理飞灰,并比较了不同方式的处理效果:(1)用去离子水润湿飞灰再厌氧堆放24h后用水泥固化;(2)用绿矾溶液处理后再用水泥固化;(3)飞灰直接与水泥混合固化。研究3种方式所得水泥固化砌块试件强度的发展和控制重金属浸出的效果与直接固化物的对比,研究结果表明:在飞灰与水泥的质量比相同的条件下,采用先用绿矾处理飞灰再进行固化的处理方式,不但稳定重金属的效果好,而且试件强度最高,有望加以应用。     

Mobilization of iron from coal fly ash was dependent upon the particle size and the source of coal

Particulate air pollution, including coal fly ash, contains iron, and some of the pathological effects after inhalation may be due to reactive oxygen species produced by iron-catalyzed reactions. The objective of this study was to determine whether iron, present in coal fly ash, was mobilized, leading to ferritin induction in human airway epithelial cells, and whether the size of the particles affected the amount of iron mobilized. Three types of coal were used to generate the three size fractions of fly ash collected. The Utah coal fly ash was generated from a bituminous b coal, the Illinois coal fly ash from a bituminous c coal, and the North Dakota coal fly ash from a lignite a coal. Three size fractions were studied to compare the amount of iron mobilized in human airway epithelial (A549) cells and by citrate in cell-free suspensions. The size fractions selected were fine (<2.5 microm) and coarse (2.5-10 microm) components of PM10, airborne particulate matter <10 microm in diameter, and the fraction greater than 10 microm. Coal fly ash samples were incubated with 1 mM citrate to determine if iron associated with coal fly ash could be mobilized. Iron was mobilized by citrate from all three size fractions of all three coal types to levels as high as 56.7 nmol of Fe/mg of coal fly ash after 24 h. With all three coal types, more iron was mobilized by citrate from the <2.5 microm fraction than from the >2.5 microm fractions. Further, the mobilized iron was in the Fe(III) form. To determine if iron associated with the coal fly ash could be mobilized by A549 cells, cells were treated with coal fly ash, and the amount of the iron storage protein ferritin was determined after 24 h. Ferritin levels were increased by as much as 11.9-fold in cells treated with coal fly ash. With two of the three types of coal studied, more ferritin was induced in cells treated with the <2.5 microm fraction than with the >2.5 microm fractions. Further, inhibition of the endocytosis of the coal fly ash by the cells resulted in ferritin levels that were near that of the untreated cells, suggesting that iron was mobilized intracellularly, not in the culture medium. The results of this study suggest that differences in particle size and speciation of iron may affect the release of iron in human airway epithelial cells.     

Time Effect on Shear Strength and Permeability of Fly Ash

This paper investigates the effect of time on the shear strength and the permeability of fly ash, a major solid by-product of thermoelectric power plants. Direct shear tests using Mikasa's apparatus, conventional permeability tests, and consolidation tests were conducted on two silt-size fly ashes, with low free lime contents, obtained from two different power plants. The results show that the immediate settling of both fly ashes takes place in a short period of time during consolidation and does not change with time. The rate of increase in shear strength with time is different depending on the pozzolanic reactions taking place for the two ashes. The permeability tests under constant stresses of 49 and 98 kPa for 12 days show that the coefficient of permeability for the tested ashes is between 10?6 and 10?7 m∕s. During this period the coefficient of permeability either remains constant (for the case of the ash with a lower free lime content) or is slightly reduced (for the ash with a higher free lime content). The practical implications and the limitations of using low lime silt-size fly ash in vertical drains in the stabilization of soft ground are also discussed.     

稀土资源税费改革与资源地的可持续发展——以赣州市为例

在对可持续发展问题的探索中,如何利用税收手段促进资源所在地的可持续发展是一个持久的关注焦点.文中以南方离子型稀土主产区赣州为例,分析其财政状况及稀土产业发展现状,通过对现行稀土资源税费制度的梳理,发现存在资源税税制设计不合理、矿产资源补偿费和环境补偿成本标准过低、税费关系不协调、矿产资源收益分配不合理等问题,这在一定程度上制约了稀土资源地的可持续发展.在此基础上,提出“改革资源税征收方式和依据、提高矿产资源补偿费征收标准、开征环境税、收益分配向资源地倾斜、加大财政转移支付力度”等促进资源型地区可持续发展的策略,并探讨了稀土产业可持续发展风险准备金制度的建立.      

Research on the Solubility of Radioactive Elements in the Ashes from the Soma in Turkey

Coal combustion results in wastes such as fly ash, slag, and flue gases. In Turkey, approximately 45 million tons of coals are fired annually and consequently around 20 million tons of fly ashes are produced. Such large volumes of ash pose a significant problem both for society and the environment. Furthermore, significant amounts of uranium and thorium are often encountered in these ashes. These concentrations are relatively higher for ashes from younger age lignites. Within the scope of this study, a series of characterization tests were performed on samples taken from Soma thermal power plant, one of the largest in Turkey. Characterization studies include particle size analysis, moisture analysis, density determination, pH profile measurements, chemical analyses, and mineralogical analyses. Leach tests with sulfuric acid (H₂SO₄) were then performed. The leaching of the radioactive minerals (uranium and thorium) with the help of sulfuric acid in the ashes was examined and the optimum leaching parameters were investigated. The recovery opportunities of uranium and thorium metals in the ashes were addressed. The results indicated that under optimum conditions, 94.71% uranium dissolution efficiency and 93.21% thorium dissolution efficiency were obtained.     

Adsorption of rare earth elements on organic matter in coal

The occurrence modes of rare earth elements(lanthanide and yttrium,abbreviated as REY) in coal are impo rtant both for coal geochemistry studies and the application potential of REY as a by-product of coalbased resources.In this study,the adsorption behaviors of REY on organic matter in coal were investigated by leaching tests using REY solution and ultra-low ash coal samples.On this basis,the adsorption mechanism of REY on organic matter in coal was also studied by molecular simulation calculat...     

粉煤灰中铝资源回收技术研究进展

粉煤灰是火力发电厂燃煤产生的大宗工业固体废弃物,富含丰富的铝资源。基于生态环境效益及我国铝土矿资源匮乏的双重驱动,从粉煤灰中回收铝资源具有重要意义。主要综述了酸法、碱法和其他方法等粉煤灰中回收铝资源的方法,比较了氧化铝提取率、反应温度和酸碱浓度等主要技术指标,总结和讨论了现有技术的优缺点,指出上下游产业链的构建是粉煤灰中铝资源回收产业化的迫切问题,提出紧密结合地方区域循环经济发展,研发绿色、温和、副产品综合利用的新技术是未来粉煤灰综合利用产业发展的必由之路。     

Naphthalene and o-Xylene Adsorption onto High Carbon Fly Ash

Adsorption is an effective remediation technique for petroleum hydrocarbons because of its ease of use and high efficiency. The utilization of high-carbon content industrial by-products in such applications can present significant economic and environmental advantages. In this study, batch adsorption tests and petrographic analyses were used to investigate the adsorption of two nonpolar petroleum contaminants, naphthalene and o-xylene, onto seven fly ashes with varying carbon contents, with powdered activated carbon (PAC) as a control. Six equilibrium isotherm models were used to evaluate the batch data. The results yielded nonlinear sorption isotherms characterized by high sorption capacity at low concentrations. The naphthalene and o-xylene adsorption capacity of the fly ashes was correlated with the unburned carbon content, specific surface area of the sorbent, and the percentage of the anisotropic and isotropic carbon content of the ash. On the basis of the Polanyi-Dubinin-Manes model, a pore-filling mechanism is the dominant mechanism for the adsorption of the nonpolar organic chemicals onto PAC, whereas the adsorption onto fly ash is likely to be governed by the unburned carbon content and the specific surface area of the ash.     

Feasibility of Using Coal Fly Ash for Mine Waste Containment

This study investigates the feasibility of using coal fly ash and fly ash-bentonite mixtures as a barrier material for mine waste. The hydraulic conductivity of the coal fly ash was measured to be in the order of 2×10?9?m/s when it was permeated with deionized water, and this value decreased significantly when the permeant was switched to acid mine drainage (AMD). The addition of bentonite to coal fly ash lowered the hydraulic conductivity during water permeation but no further significant change was observed upon switching the permeant to AMD. Chemical analyses on the effluent from the hydraulic conductivity tests indicated that heavy metals present in AMD were attenuated and were well below the leachate criteria set by the Ontario Government. X-ray diffraction and scanning electron microscopy analyses results of postpermeation samples showed significant structural differences and formation of secondary minerals after AMD permeation. The results of this study suggest that the addition of 10% bentonite to coal fly ash reduced the hydraulic conductivity of the coal fly ash to less than 1×10?9?m/s and improved the chemical compatibility for mine waste containment.     

钕铁硼废料资源化回收利用研究进展

中国每年会产生很多钕铁硼废料,这些废料中含有大量的稀土等有价元素。对钕铁硼废料进行资源化回收利用有助于改善中国稀土资源短缺、环境污染和资源浪费的问题。钕铁硼废料的绿色回收前景广阔,因此有必要对钕铁硼废料的资源化回收利用做更加全面和系统的研究。文中对一些传统钕铁硼废料回收工艺和钕铁硼废料回收的新方法进行了综述,并总结了这些方法的特点,以期在高效回收钕铁硼废料工艺的研究上提供指导和帮助。