Demineralization mechanism and influence of parameters on high ash Indian coal by chemical leaching of acid and alkali solution

The current research was investigated the mechanism of coal demineralization and the effect of leaching parameters on high ash coal and study the characterization of pre and post-treated coal. The two high ash Indian coal selected from Mahanadi Coalfield Limited, Odisha, pulverized to 375, 230 and 180 gm particle size were undergone simultaneous acid and alkali treatment at a different concentration, temperature and time. The percent demineralization was increased with decrease the size of the particle and rises with leaching parameters. The investigation suggested 180 μm particle size offers efficient demineralization for both coals at 30% NaOH and 30% H2SO4 concentration. The alkali leaching leads to obtaining the demineralization 46% and 42% whereas acid treatment resulted in 34% and 32% of the original coal samples. The extent of demineralization was improved the calorific value of coal. Besides, the degree of demineralization was proved from the FTIR, XRF and FESEM-EDX analysis results. FTIR analysis result showed that the peak intensity of mineral band decreased by the leaching effect and the degree of demineralization was significantly obtained to large extent by the X-ray Fluorescence spectrometer; which elucidates major minerals removed from coal by the leaching effect of acid and alkali solution.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part Two: Durability

This work investigates durability of cement-free mortars with a binder comprised of ground granulated blast furnace slag (GGBFS) activated by high-calcium fly ash (HCFA) and sodium carbonate (Na2CO3): the soundness, sulfate resistance, alkali-silica reactivity and efflorescence factors are considered. Results of tests show that such mortars are resistant to alkali-silica expansion. Mortars are also sulfate-resistant when the amount of HCFA in the complex binder is within a limit of 10 wt%. The fineness of fly ash determines its’ ability to activate GGBFS hydration, and influence soundness of the binder, early strength development, sulfate resistance and efflorescence behavior. The present article is a continuation of authors’ work, previously published in MSA, Vol. 14, 240-254.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part One: Hydration and Mechanical Properties

High-calcium fly ash (HCFA)—a residue of high-temperature coal combustion at thermal power plants, in combination with sodium carbonate presents an effective hardening activator of ground granulated blast-furnace slag (GGBFS). Substitution of 10% - 30% of GGBFS by HCFA and premixing of 1% - 3% Na2CO3 to this dry binary binder was discovered to give mortar compression strength of 10 - 30 to 30 - 45 MPa at 7 and 28 days when moist cured at ambient temperature. High-calcium fly ash produced from low-temperature combustion of fuel, like in circulating fluidized bed technology, reacts with water readily and is itself a good hardening activator for GGBFS, so introduction of Na2CO3 into such mix has no noticeable effect on the mortar strength. However, low-temperature HCFA has higher water demand, and the strength of mortar is compromised by this factor. As of today, our research is still ongoing, and we expect to publish more data on different aspects of durability of proposed GGBFS-HCFA binder later.

Reaction behaviour of Al_2O_3 and SiO_2 in high alumina coal fly ash during alkali hydrothermal process

The reaction behaviours of A1203 and SiO2 in high alumina coal fly ash under various alkali hydrothermal conditions were studied. The means of XRD, XRF, FTIR and SEM were used to measure the mineral phase and morphology of the solid samples obtained by different alkali hydrothermal treatments as well as the leaching ratio of SiO2 to A1203 in alkali solution. The results showed that with the increase of the hydrothermal treating temperature from 75 to 160 ~C, phillipsite-Na, zeolite A, zeolite P, and hydroxysodalite were produced sequentially while the mullite and corundum phase still remained. Zeolite P was massively formed at low-alkali concentration and the hydroxysodalite was predominantly obtained at high-alkali concentration. By the dissolution of aluminosilicate glass and the formation of zeolites together, the leaching efficiency of SiO2 can reach 42.13% with the mass ratio of A1203/SIO2 up to 2.19：1.

Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

Lowering ash slagging and fouling tendency of high-alkali coal by hydrothermal pretreatment

High-alkali species in coal are notorious for causing ash slagging and fouling incidents.In this paper,four high-alkali coals were individually subject to hydrothermal pretreatment(HTP),within a batch-type autoclave at 300 -C for 1 h,and the treated coals were analyzed,along with the oxygen-containing functional groups determined by Fourier transform infrared spectrometer(FT-IR).Then the alkali species and other components in the coal ash were quantified by X-ray fluorescence(XRF)for evaluating the ash slagging and fouling tendency.Apart from this,FactSage was adopted to simulate the occurrence and transformation of alkali species during coal thermal conversion ending at various temperatures.The findings indicate that the treated coals are superior to the parent ones in terms of certain remarkable changes via HTP.The moisture,oxygen and sulfur of the hydrothermally treated coals decline obviously,while the calorific value rises sharply.HTP could reduce the alkali species to less than 2%(%,by weight,equivalent to Na2O in dry ash),with a maximum removal ratio of 88.9%,lowering the ash slagging and fouling tendency.The proposed mechanism of HTP was that the alkali species in coal matrix became released due to the breakage of the coal functional groups and micropores during HTP.

Synthesis of Mullite from High-alumina Fly Ash:a Case from the Jungar Power Plant in Inner Mongolia, Northern China

In this paper, an experimental study was conducted in order to test the feasibility of sintering mullite directly from the high-alumina fly ash, without adding any extra material. The results show that the mullite contents in most sintered samples are over 70%. The samples sintered from the beneficiated fly ash have a higher content of mullite than those from the as-received fly ash under the same synthetic conditions. To obtain an equal amount of mullite, a higher sintering temperature is needed for the beneficiated fly ash than for the as-received fly ash. Considering the physical properties of sintered mullite, the favorable sintering temperature is 1400℃ for the as-received fly ash and 1500℃ for the beneficiated fly ash. A higher sintering temperature and a shorter holding time are profitable to sintering mullite. The orthogonal test confirmed that the dominant factor affecting mullite synthesis is sintering temperature, and that the most profitable matching conditions are 200 MPa-1500℃-3 h for the as-received fly ash and 200 MPa-1500 ℃-4 h for the beneficiated fly ash.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

Properties of High Volume Fly Ash Concrete Compensated by Metakaolin or Silica Fume

The compressive strength and dynamic modulus of high volume fly ash concrete with incorporation of either metakaolin or silica fume were investigated. The water to cementitious materials ratio was kept at 0.4 for all mixtures. The use of high volume fly ash in concrete greatly reduces the strength and dynamic modulus during the first 28 days. The decreased properties during the short term of high volume fly ash concrete is effectively compensated by the incorporation of metakaolin or silica fume. The DTA results confirmed that metakaolin or silica fume increase the amount of the hydration products. An empirical relationship between dynamic modulus and compressive strength of concrete has been obtained. This relation provides a nondestructive evaluation for estimating the strength of concrete by use of the dynamic modulus.

Research on Preparation and Influencing Fctors of High Calcium High Sulfate Ash to Autoclaved Aerated Concrete

In this paper, a high calcium high sulfate ash as the main material, adding fly ash, lime, cement, gypsum and some modifiers to prepare autoclaved aerated concrete. The products complies with the technical requirements of GB/T11968-2006. This paper also studies the influence of the physical methods and water ratio on autoclaved aerated concrete by high calcium high sulfate ash aerated concrete. The best ratio of water and Grinding time were found in practice study.

硅灰及矿渣粉对大掺量粉煤灰砂浆力学性能的影响及机理研究

以硅灰和矿渣粉(GGBS)为辅助胶凝材料,使用聚羧酸高性能减水剂,分别研究了硅灰和GGBS对大掺量粉煤灰砂浆抗压强度的影响。通过压汞测试(MIP)、扫描电子显微镜(SEM)以及X射线衍射(XRD)等方法对制备试件的孔结构、微观产物、物相组成进行分析,得到了硅灰和GGBS影响大掺量粉煤灰砂浆强度的机理。结果表明:单掺硅灰的大掺量粉煤灰砂浆的抗压强度随着硅灰含量增加先增大后减小,单掺GGBS的规律与硅灰类似;复掺硅灰和矿渣时,砂浆的强度较其他同龄期组均有一定的提高,二者表现出良好的协同作用;无论是单掺还是复掺,硅灰和GGBS都对大掺量粉煤灰砂浆强度有良好的提升作用。砂浆试件总孔隙率和大孔占比与抗压强度总体呈负相关,强度越高的砂浆试件微观结构越致密,但相比于总孔隙率,毛细孔和大孔占比表现出与抗压强度更好的相关性。当硅灰和GGBS质量分数分别为8%和6%时,砂浆28 d强度最大,为88.05 MPa。

不同密度准东高铁煤熔融特性

研究不同密度准东高铁煤灰熔融特性,可探究准东高铁煤灰不均匀熔融规律。用有机重液浮沉法分离准东高铁煤不同密度组分,测定各煤样低温灰化后矿物组成及煤灰化学组成、熔融温度,经XRD和SEM-EDS分析熔融灰矿物组成、微观形貌和元素分布。发现准东高铁煤分离出不同密度组分主要分布于1.40~1.50 g/cm^(3),占51.79%,煤中铁赋存形态主要为硫铁矿及少量菱铁矿;煤灰中元素不同,分离出组分密度也不同,且随Fe元素含量增加煤样组分密度增大,在密度组分>1.50 g/cm^(3)的制备煤灰中Fe元素质量分数达67.50%;各组分灰成分差异大,煤中Fe是影响熔点主要因素之一,可显著降低整体煤灰熔融温度;结合高温灰样XRD与SEM-EDS分析,不同密度组分中钙铝黄长石含量增加是导致灰熔融温度增加的原因;Fe、Mg主要富集于轮廓较明显块状灰颗粒,Si和Ca主要富集于熔融区域,且随密度增大块状颗粒含量增多;块状灰颗粒矿物主要为镁铁氧化物和赤铁矿,熔融区域矿物主要为钙铝黄长石,在1300℃煤灰中熔融区域与块状颗粒并未熔合,可知高铁煤中Fe主要存在于煤中外来矿物,且含钠矿物与钙铝黄长石发生低温共熔,熔融区域熔点降低。

粉煤灰基催化材料提升电子迁移率的制备机理

固体表面催化材料提升电子迁移率的制备机理目前缺少系统研究。以粉煤灰为研究对象,采用湿式磁选、高能球磨法和等离子体放电改性等方法联合改性以提升材料电子迁移率,并探讨其制备机理。实验结果表明,最佳实验参数组合为用1.2 T磁棒磁选3次,然后在转速550 r/min下球磨30 h,最后在放电间隙3 mm、放电长度200 mm、放电功率130 W和改性时间20 min条件下等离子体放电改性。得到的粉煤灰样品电阻率下降到27.92 MΩ·cm,比原始粉煤灰的电阻率提高四个数量级。该研究表明构筑完善且连续的导电网络是提升材料导电性能与电子迁移率的前提。

超高韧性磷酸镁水泥基复合材料压缩力学性能研究

磷酸镁水泥(Magnesium phosphate cement,MPC)是一种具有凝结时间短、早期强度高、粘结性能好等诸多优点的新型无机胶凝材料,但材料本身具有脆性性质,应变能力低。工程水泥基复合材料(Engineered cementitious composites,ECC)是通过在水泥基复合材料中添加高性能纤维制备而成。通过纤维增韧技术,可以制备出同时具备MPC和ECC优良特性的超高韧性磷酸镁水泥基复合材料(Ultra-high toughness magnesium phosphate cement-based composites,UHTMC)。本工作通过拉伸试验证实了UHTMC具有优异的拉伸力学性能、应变硬化和多缝开裂特征。通过试件的轴心抗压强度、极限压应变、受压弹性模量和泊松比分析了粉煤灰(Fly ash,FA)替代量(0%、15%、30%和45%)和养护龄期(14 d和28 d)对UHTMC压缩力学性能的影响规律。结果表明,UHTMC试件表现出良好的压缩韧性,随着粉煤灰替代量的增加和养护龄期的延长,试件的轴心抗压强度和受压弹性模量升高,但极限压应变降低,泊松比变化较小。通过对UHTMC的轴心受压应力-应变全曲线进行分析,提出和建立了轴心受压本构关系模型。最后,从微观层面上分析了粉煤灰替代量和养护龄期影响UHTMC宏观压缩力学性能的机理。

含生活垃圾焚烧炉渣的碱矿渣水泥耐高温机理

为探究生活垃圾焚烧炉渣(MSWI-BA)对碱矿渣净浆耐高温性能的影响机理,将6%的矿渣等质量替换为MSWI-BA,制备碱矿渣水泥净浆(AASBp),研究不同温度对AASBp的质量损失率、干燥收缩率和强度的影响.以普通硅酸盐水泥净浆作为对照组,结合多种微观手段,揭示AASBp的耐高温机理,并与未掺MSWI-BA的碱矿渣水泥(AASp)进行对比.结果表明:随着温度的升高,AASBp中水化硅铝酸钙的钙硅比(C/S)先降低后升高;在400℃时,水化硅铝酸钙的聚合度最高,C/S最低;Al—O键在600℃断裂,而Si—O键在1000℃断裂;MSWI-BA可提高基体孔隙的连通性,高温处理后孔隙压力得到释放,因此AASBp比AASp具有更高的归一化抗压强度和耐高温性能.

国内高铝粉煤灰提取氧化铝主要技术进展及发展建议

粉煤灰已成为我国排放量最大的工业固废,目前堆存量估计在 30 亿吨以上,如果不及时处理或处理不当,将会对环境造成严重危害。由于其具有高含量的氧化铝,特别是高铝粉煤灰,含量超过38%,被认为是取代铝土矿,生产氧化铝的理想原料之一。近几十年来,高铝粉煤生产氧化铝是一项热门的研究课题,各企业及科研院校均投入了大量的人力和物力,并且取得了一定的成就,提出了不同的工艺路线,部分工艺已经进行了中试试验或者工业化生产。目前,初步形成了三种主要的工艺路线:预脱硅-碱石灰石烧结法、石灰石烧结法、一步酸溶法。文章主要综述了以上三种技术的原理、工艺流程及技术进展,分析其发展难点,同时提出评价和建议。

防漏堵漏低密度水泥浆技术

跃进3-3XC井完钻井深达9432 m,水平钻进距离超过3400 m,刷新了亚洲最深和超深水平大位移井的纪录。该井地质结构复杂,施工难度大,对水泥浆性能要求高,除了高温、高压外,地层承压能力低,极易发生漏失。针对此类问题,通过研发新型功能性材料,构建了C-Lo PSD(1.30 g/cm^(3))、C-Lite STONE(1.60 g/cm^(3))与C-Hi PSD(1.40 g/cm^(3))三套低密度水泥浆体系,涵盖了中低温、高温等应用条件,并在跃进3-3XC井中成功应用,水泥浆性能满足固井需求。与之前用水泥浆体系相比,混浆效率、流变性、悬浮稳定性、水泥石抗压强度等明显提升。其中,C-Lite STONE(T_(BHC)=75℃/T_(TOC)=30℃)与C-Hi PSD(T_(BHC)=145℃/T_(TOC)=105℃)水泥浆体系在温差分别为45℃和40℃下,顶部48 h抗压强度达到8.1 MPa和14.3 MPa。跃进3-3XC井在施工期间多次遭遇漏失,通过使用自研的新型堵漏材料C-B62和C-B66,成功封堵裂缝,保证了固井施工的顺利进行。

改性淀粉对垃圾焚烧飞灰中Pb和Cd稳定化研究

垃圾焚烧飞灰中Pb和Cd对人体及环境危害极大且浸出质量浓度严重超标。为稳定飞灰中的Pb和Cd,合成了一种以玉米淀粉为主体的有机螯合剂,用于处理飞灰中的Pb和Cd。通过改变螯合剂投加质量分数、养护时间、液固比(mL∶g)和pH值来研究螯合剂稳定效果并进行表征。X射线衍射(X-ray Diffraction,XRD)结果显示,改性处理未改变玉米淀粉的结晶结构类型。通过对结晶度计算,表明改性过程发生在淀粉结晶区。扫描电镜(Scanning Electron Microscope,SEM)结果显示,处理前飞灰比表面积较大,飞灰经过改性玉米淀粉处理后粒径明显增大,降低了飞灰比表面积。通过傅里叶变换红外(Fourier Transform Infrared,FT-IR)光谱表征,显示飞灰处理前后主要存在碳酸盐、硫酸盐和硅铝酸盐。采用单因素试验确定改性淀粉螯合飞灰Pb和Cd的最佳条件为:改性淀粉投加质量分数为3%、养护时间为24 h、液固比(mL∶g)为2∶5、pH值为7~9。该条件下,Pb和Cd浸出质量浓度最低分别为0.162 mg/L、0.087 mg/L,对Pb和Cd稳定化率均大于93%,浸出质量浓度远低于《生活垃圾填埋场控制标准》限值。淋溶试验显示,淋溶速率较慢及酸雨条件下,螯合体中Pb和Cd的溶解程度较高。