Some aspects of characterisation,utilisation and environmental effects of fly ash

A review on fly ash, an important but problematic waste material is presented. The article deals with several aspects of the characterisation, extraction of metal values leaching and associated environmental pollution problems due to fly ash. Characterisation includes classification, physicochemical and mineralogical analysis, presence of organic carbon and the significance of cenospheres. Utilisation aspects are confined to extraction of metal values and discuss the elemental distribution in fly ash while also covering several aspects of leaching including the leaching of specific metals. Effect of fly ash on surroundings, including ground water pollution and associated problems during disposal, are considered while dealing with the environmental aspects. Some remedial measures are also suggested. © 2001 Society of Chemical Industry     

粉煤灰中战略金属锂的回收研究进展

随着锂电池行业的快速发展,中国锂原料对外进口的依赖程度逐年增加。从粉煤灰中回收锂,既可以缓解中国锂供应量严重不足的现状,又可以有效解决粉煤灰污染环境的问题。在分析比较锂矿石、盐湖卤水和粉煤灰的组成及其特点的基础上,从浸出和提取两个方面综述了目前粉煤灰回收锂的工艺技术。锂浸出工艺受粉煤灰浸出铝工艺的影响,目前已较为成熟,主要有酸法浸出和碱法浸出工艺。锂提取技术则受锂浸出工艺的影响,酸法浸出工艺的浸出液杂质元素比较多,提锂过程比较复杂,目前主要有溶剂萃取法、煅烧浸出法和吸附法;碱法浸出工艺的浸出液杂质元素简单,提锂相对容易,目前主要采用的是吸附法。由于粉煤灰浸出液与盐湖卤水的成分相似,因此借鉴盐湖卤水的提锂技术经验,开发适用于粉煤灰浸出液的提锂技术,是未来粉煤灰回收锂的主要研究方向。     

石煤发电飞灰碱浸提钒工艺

对我国某地石煤发电飞灰进行碱浸提钒实验研究,飞灰中的钒主要以V(V)形态弥散于硅、铝氧化物中. 结合钒的赋存形式,考察了反应时间、液固比、碱浓度及温度对钒浸出率的影响. 结果表明,钒浸出率与四因素均呈正比关系. 在搅拌转速500 r/min、180℃、浸出时间3 h、液固比5 mL/g及NaOH浓度200 g/L的最佳工艺条件下,钒浸出率可达85%以上. 浸出液中Al2O3, K, Fe含量分别小于500, 420与9 mg/L. 浸出液返回浸出体系,可充分利用浸出液中富余的碱进一步富集溶液中的钒.     

粉煤灰在稳定抗生素废水处理剩余污泥中的应用

进行了利用粉煤灰稳定抗生素废水处理过程中产生的剩余污泥的实验. 粉煤灰与剩余污泥按4种比例、3种搅拌时间混合后,采用毒性特性浸取实验、平衡渗漏实验和长期渗漏实验考察重金属离子的渗漏性能. 考虑混合物的重金属离子浓度和病原菌的含量,粉煤灰和污泥的混合物可以农田利用. 在粉煤灰对重金属离子的固定机制中,表面络合作用在较宽的pH值范围内,尤其是在较低pH值时起主要作用,氢氧化物沉淀作用在较高pH值时是主要的作用机制. 实验还发现,粉煤灰固定金属离子的能力随其负荷的增加而增加. 本实验中,粉煤灰能除掉至少92.6%的微生物,粉煤灰的强碱性是杀死剩余污泥中微生物的主要原因.     

Leaching of CCBs: observations from over 25 years of research

Leaching of coal combustion by-products (CCBs) using various batch laboratory methods has been ongoing at the Energy & Environmental Research Center for over 25 years. Early on in the various investigations involving leaching it became obvious that the methods being advocated and used were generating scientifically invalid and often misleading data. This realization came about because:

1.

The wrong leaching solutions were often being used. Methods such as the extraction procedure toxicity test and, later, the toxic characteristic leaching procedure used an acetic acid-containing solution that would be unlikely to contact CCBs under any conditions.

2.

It was found that the formation of secondary hydrated phases such as ettringite could have a profound influence on concentrations of certain trace elements that exist as oxyanions in aqueous solution.

Because of these realizations, a method that included long-term leaching (LTL) was developed called the synthetic groundwater leaching procedure, which addressed many of the problems with existing methods.Data collected over the last 25 years will be presented to demonstrate the need for the use of proper leaching solutions and LTL. Additionally, currently utilized and proposed methods will be discussed, including the new suite of leaching methods recently proposed by the US Environmental Protection Agency.     

水泥、粉煤灰及其硬化体中Cr(Ⅵ)溶出条件与其影响因素

分析了国内外现行的溶出试验方法,研究了不同溶出试验条件对水泥、粉煤灰及其硬化体中Cr(Ⅵ)溶出的影响,探讨了粉煤灰中可溶性Cr(Ⅵ)最大溶出量的测定方法.结果表明:静置时间、温度、液固比、颗粒细度、振荡频率及振荡容器尺寸对水泥和粉煤灰及其硬化体中Cr(Ⅵ)的溶出及测定都具有一定的影响,其中振荡时间和浸提液pH值的影响较为显著.粉煤灰中Cr(Ⅵ)的溶出是一个缓慢连续的过程,其可溶性Cr(Ⅵ)最大含量的测定以多级萃取溶出试验为宜.     

Production of glass from coal fly ash

The coal fly ash from a Chinese thermal power plant was vitrified after the addition of ∼10 wt% Na₂O. The glass products have suitable viscosity at 1200 °C and displayed a good chemical durability. The heavy metals of Pb, Zn, Cr and Mn were successfully immobilized into the glass as determined by the toxicity characteristic leaching procedure method. Results indicate an interesting potential for the coal fly ash recycling to produce useful materials.     

Assessment of metal mobility in MSW incineration ashes using water as the reagent

In this work, the methodology for quantification of water-soluble species in ash was evaluated by varying the parameters leaching time, liquid-to-solid ratio, and size reduction by grinding. The basis for the methodology is a modification of Tessier’s sequential extraction method. This work concentrated on fly ashes from combustion of MSW in a fluidised bed boiler, and generally the amounts of water-soluble forms of metals in the ashes were low. Longer leaching time generally reduced the amount of water-soluble metal detected, showing the importance of adsorption and re-precipitation processes. The effects of the L/S parameter and of grinding seem to be dependent on the characteristics of the ash matrix.     

粉煤灰中镓的浸出试验研究

研究了从粉煤灰中酸法预提取镓的方法;粉煤灰中无添加剂时,焙烧试验条件与浸出试验条件对镓浸出率的影响。对粉煤灰酸浸影响因素做了正交试验,分析了各因素对镓浸出率影响的主次。试验结果表明,浸出温度对镓浸出率影响最大,其次为盐酸浓度和浸出时间,影响因素最小的是固液比。粉煤灰中预提取镓的适宜条件为:焙烧温度1 050℃,焙烧时间1.5 h,酸浸条件为浸出温度80℃,8 mol/L盐酸溶液,浸出时间6.0 h,固液比为1:8的条件下浸出率最高,可达46.37%。     

含砷飞灰固化处理及浸出毒性试验研究

以含As飞灰作为研究对象,采用水泥固化对飞灰进行无害化处理,研究了pH值和液固比以及浸取时间对固化体中As浸出毒性的影响。结果表明：水泥固化体中As的浸出主要受pH值影响,在强酸OH〈2）和强碱（pH〉11）条件下的浸出质量浓度高,而在中性（pH值为5-11）条件下浸出质量浓度低。随着浸取剂与液固比的增加,As的浸出量逐渐增加,但As的浸出质量浓度受稀释作用影响逐渐降低。相对于去离子水体系,醋酸缓冲体系浸出结果较稳定。     

An investigation into physicochemical characteristics of ash produced from combustion of oil palm biomass wastein a boiler

Ash derived from combustion of Malaysian oil palm biomass (empty fruit bunches consisting of fibers) was physically and chemically characterized in order to provide a comprehensive understanding of its specific properties in terms of toxicity, compositions and reusability. Principal analyses conducted include particle size distribution, scanning electron microscopy, elemental dispersive X-ray, elemental analysis, toxicity characteristic leaching procedure (TCLP) as well as thermogravimetric, X-ray diffractometry and Fourier-transform infrared analyses. TCLP result indicated that the oil palm ash (OPA) should not be classified as toxic wastes in terms of heavy metal leachability since leachable copper, cadmium, lead and nickel concentrations were detected below the stipulated leachability limits. It was determined that the OPA contained high amount of potassium as well as presence of silica which implied its suitability to be reused as crude fertilizer or cement replacement material.     

含锗烟尘的硫酸浸出工艺研究

为简化含锗烟尘浸出过程,提出一段硫酸浸出工艺。浸出工艺条件为：浸出温度90℃,初始硫酸质量浓度120g／L,液固比8mL／g,浸出时间2．5h,搅拌转速120r／min。在该条件下,锌、锗浸出率分别为99．1％和87．61％左右,最终硫酸质量浓度约34．80g／L。去除不溶性锗后,锗浸出率可达到97．21％。     

Leaching of elements from coal fly ash: Assessment of its potential for use in filling abandoned coal mines

Leaching of ten elements - namely, Fe, Mn, Ca, Na, K, Cu, Cr, Zn, As and Pb - from four fly ash samples collected from four different coal-fired thermal power plants in West Bengal, India, has been reported. The leaching conditions were selected to broadly simulate that of surface coal mines in order to estimate the usefulness of the materials for back-filling of abandoned mines and to assess the possibility of contamination of the sites by release of heavy metal ions. Sequential batch leaching consisted of four cycles each of seven days duration; the long-term leaching continued over a period of 180 days. The starting pH of the leaching solutions ranged from strongly acidic to strongly basic. The leaching pattern and its dependence on the pH as well as the solid-liquid ratio have been critically analyzed. A much higher mobility of the elements have been expectedly observed at a low pH. Less leaching is found at a high pH except for arsenic. The mobilization pattern is strongly governed by the well-known phenomenon of dissolution and re-precipitation of iron with co-precipitation of a series of elements depending upon the pH of the medium. Extraction equilibrium was reached for Ca, Fe, Na and Zn at certain pH values. A monotonic trend of release for the elements Mn, K, Cu, Pb, Cr and As persisted over the long-term leaching period of 180 days. The alkalinity or the calcium content of an ash sample greatly determines the leaching pattern if the solution pH is neutral or mildly acidic. It appears that the risk pollution of ground water as well as of surface water may not be avoidable if fly ash alone is used for mine back-filling in an environment where acid mine drainage is prominent. Nevertheless blending with lime to enhance the alkalinity appears to offer a practical solution to the problem.     

Extraction of Alumina from Coal Fly Ash with Sulfuric Acid Leaching Method

Coarse g-Al2O3 powder was prepared through acid leaching, solid-liquid separation, crystallizing and aluminum sulfate decomposing processes using coal fly ash and concentrated sulfuric acid as raw materials. The metallurgy level Al2O3 can be obtained by disposing coarse g-Al2O3 powder with Bayer process. The optimum conditions of acid leaching process were determined by experiments. The extraction rate of Al2O3 can be stabilized at about 87% under these conditions. The thermodynamics and kinetics of sulfuric acid leaching process were studied with irreversible thermodynamics.     

循环流化床灰中铝的浸出行为及动力学研究

以煤矸石电厂循环流化床粉煤灰(CFB灰)为原料,研究了CFB灰中Al2O3酸浸出行为的影响因素及其酸浸出过程动力学。试验结果表明:盐酸浓度6 mol/L、酸浸温度110℃、酸浸时间180 min、液固比为4:1,KF加入量为15%,Al2O3的浸出率为68.46%。CFB灰中Al2O3的浸出过程受扩散和化学反应控制,符合典型的"未反应核收缩模型"。其反应动力学方程可用1-(1-α)1/3=k’t来描述,反应表观级数为1.0875,反应活化能为21.186 kJ/mol。     

辽宁某钒钛磁铁矿酸浸提钒浸出动力学研究

辽宁某钒钛磁铁矿精矿在初始硫酸浓度为2.5 mol/L、氢氟酸浓度为2.5 mol/L、浸出温度为90℃、液固比为5、浸出时间为2 h、搅拌速率控制在100～200 r/min的条件下,钒的浸出率高达95.68％.试验主要考查了温度与浸出动力学的关系,主要研究内容包括:温度对钒浸出率的影响,通过试验数据处理及拟合分析求...     

Separation and recovery of neodymium and praseodymium from permanent magnet scrap through the hydrometallurgical route

The leaching of neodymium (Nd) and praseodymium from scrap permanent magnet bearing 64.37% Fe, 30.57% Nd and 0.42% Pr and 0.71% B was carried out using HCl solution. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses study ensured the elements of the above metals as Nd-Fe-B in the solid phase . The leaching parameters – HCl concentration, time, temperature, particle size, pulp density (S/L) – were investigated to obtain the suitable leaching condition for the effective dissolution of both Nd and Pr. At the conditions of 0.2 M HCl, temperature 90°C, leaching time 240 min, particle size 76–105 µm, agitation speed 800 rpm and pulp density (PD) 1%, the leaching efficiencies of Nd and Fe were 99.99% and 61.36%, respectively. The optimum leaching condition was established by minimizing iron co-extraction vis-à-vis the quantitative recovery of Nd and Pr. The iron content of the leach liquor was removed by the precipitation method using lime (Ca(OH)₂) at pH 4.0. After the removal of iron, the solvent extraction (SX) parameters were optimized and the McCabe–Thiele diagram for extraction and stripping was developed. The McCabe–Thiele plot for extraction with 0.8 M NaD2EHPA (30% neutralized) and stripping with 8% H₂SO₄ showed two stages at A:O = 2:1 and O: A = 4:1, respectively, for the quantitative recovery of Nd and Pr. The final strip solution bearing 72 g/L Nd and 1.088 g/L Pr was crystallized to produce (Nd) ₂(SO₄)₃ and (Pr) ₂(SO₄)₃, respectively.     

低温中和-加压酸浸提取煤矸石中铝铁

以贵州盘县煤矸石为研究对象,为解决其工业生产提取铝铁时酸耗量大、酸利用率低及后续铝铁产品分离困难等问题,根据其矿物组成特点,本文首次采用低温中和-加压酸浸工艺对铝铁提取进行了详细研究。室温下中和最优工艺条件为20%理论酸耗、浸出时间120min、液固比3∶1（硫酸溶液与固体的质量比,以g/g计）;以中和渣为原料,煤矸石理论酸耗为基础,加压酸浸最优工艺条件为浸出时间120min、浸出温度150℃、液固比3.5∶1（硫酸溶液与固体的质量比,以g/g计）。在此条件下,氧化铁浸出率为98.37%,氧化铝浸出率为95.77%,酸浸渣灰分中氧化硅质量分数为90.2%,氧化钛质量分数为9.18%。以最优工艺条件下的酸浸液循环中和新鲜煤矸石,得到的铝铁提取液中氧化铁浓度为57.95g/L,氧化铝浓度为62.20g/L。相比常规酸浸工艺具有酸耗低、酸利用率高等优点。借助X射线衍射仪（XRD）、傅里叶红外光谱仪（FTIR）和扫描电子显微镜（SEM）等分析手段,初步对两步溶出过程进行了机理分析,为煤矸石工业生产提取铝铁提供了新路线和理论支撑。     

高硅高铁含铜渣氧压酸浸过程

对火法炼铅产高硅高铁含铜渣进行了氧压硫酸浸出过程研究. 结果表明,浸出时间、氧分压、酸量、浸出温度和搅拌速度对Cu的浸出率和浸出液中Fe含量有显著影响,溶液初始含Cu2+量对Cu浸出率影响不明显. 最佳工艺条件为：时间2 h,氧分压0.8 MPa,硫酸浓度46.6 g/L,温度(150±2)℃,搅拌速度600 r/min,复合絮凝剂A用量30~100 g/m3. 在该条件下,Cu浸出率>95%,浸出液中Fe<5 g/L,硫转化率20%~30%,料浆过滤速度约0.8 m3/(m2×h).     

Recovery of nickel from spent catalysts using ultrasonication‐assisted leaching

BACKGROUND: Solid catalysts containing metals or metal oxides play a key role in the chemical process industries to produce valuable products and fuels and consequently are left as solid wastes after a certain period of use. Disposal of these spent catalysts requires compliance with stringent environmental regulations because of their hazardous nature and content of toxic chemicals. Therefore recovery of the metals by various methods has been explored. In the present study recovery of nickel from spent nickel catalysts using ultrasonication‐assisted leaching has been investigated. RESULT: The effect on nickel recovery of acid concentration, temperature, solid to liquid (S:L) ratio, and time of digestion were studied in detail and optimized for the ultrasonication route. The results obtained are compared with the chelation route and conventional acid leaching technique. Using ultrasonication‐assisted leaching 95% extraction of nickel was achieved at 90 °C, 40% nitric acid concentration and S:L ratio 1:10 (g:mL) in 50 min from the spent nickel–alumina catalysts. CONCLUSION: Using an ultrasonication technique 95% recovery of nickel was significantly faster (50 min) than the chelation route (7 h), while with conventional acid leaching a maximum of 93% nickel recovery was obtained in 9 h. Compared with conventional acid leaching the purity of leached nickel salts was good and they could be recycled for the preparation of fresh catalysts after removing Al impurities. Copyright © 2011 Society of Chemical Industry