Conversion of coal fly ash into zeolite and heavy metal removal characteristics of the products

Fly ash obtained from a power generation plant was used for synthesizing zeolite. Zeolites could be readily synthesized from the glassy combustion residues and showed potential for the removal of heavy metal ions. By the use of different temperatures and NaOH concentration, five different zeolites were obtained: Na-P1, faujasite, hydroxy sodalite, analcime, and cancrinite. The synthesized zeolites had greater adsorption capabilities for heavy metals than the original fly ash and natural zeolites. Na-P1 exhibited the highest adsorption capacity with a maximum value of about 1.29 mmole Pb g^-1 and had a strong affinity for Pb²⁺ ion. The metal ion selectivity of Na-P1 was determined as: Pb²⁺> Cu²⁺> Cd²⁺> Zn²⁺, consistent with the decreasing order of the radius of hydrated metal ion. The adsorption isotherm for lead by Na-P1 fitted the Freundlich rather than the Langmuir isotherm.     

Geopolymeric materials prepared using Class F fly ash and elevated temperature curing

This paper reports the results of the study of the influence of elevated temperature curing on phase composition, microstructure and strength development in geopolymer materials prepared using Class F fly ash and sodium silicate and sodium hydroxide solutions. In particular, the effect of storage at room temperature before the application of heat on strength development and phase composition was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM were utilised in this study.Long precuring at room temperature before application of heat was beneficial for strength development in all studied materials, as strength comparable to 1 month of curing at elevated temperature can develop in this case only after 24 h of heat curing. The main product of reaction in the geopolymeric materials was amorphous alkali aluminosilicate gel. However, in the case of sodium hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1 (gismondine) zeolites and hydroxysodalite were also present. The type of zeolite present and composition of aluminosilicate gel were dependent on the curing history.     

铁尾矿在蒸压养护过程中的物相变化

以铁矿尾矿替代河砂或者粉煤灰作为主要原料,铝粉作为发气剂,研究制备出了蒸压加气混凝土砌块.在铁矿尾矿、石灰、水泥和脱硫石膏的配合比(质量比)为60∶25∶10∶5时,加气混凝土砌块的强度最优,约为4.43 MPa,此时体积密度为513 kg/m',比强度为8.34 MPa.由X射线衍射测试分析可知,成品中主要的矿物成分...     

Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: I, Tobermorite Formation and Reaction Behavior of Slag

The chemical reactions in the formation of autoclaved aerated concrete (AAC) block were investigated. The samples were prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. Autoclaving for 1 h yielded 1.1-nm tobermorite with higher Al substitution and lower Ca/(Al + Si) ratio than that made without slag, due to the high solubility of the slag during the initial stage of reaction. This suggests that the utilization of slag has an advantage of reducing processing time. On further reaction, the crystallinity of the tobermorite increases and its Ca/(Al + Si) ratio decreases, becoming constant after 64 h. After a long period of autoclaving. thick reaction rims are formed around unreacted slag particles, interrupting the diffusion of Ca from slag to matrix.     

Phase Evolution during Autoclaving Process of Aerated Concrete

The reactions were investigated that occur when lime, cement, and quartz sand are mixed together and molded, then treated at 180°C under saturated steam pressures to produce autoclaved aerated concrete. The hydrothermal treatment of mixtures gives Ca-rich C-S-H with varying Ca/Si ratios as an initial product, which reacts further with silica dissolved from quartz to form 1.1-nm tobermorite with increase of curing time. During autoclaving, the composition of C-S-H and tobermorite as a binder continues to change until after 8 h, when the Ca/(Al + Si) ratio becomes constant at 0.8. As the reaction proceeds, the number of micropores increases, and the strength also increases due to the binder effect of the tobermorite. However, the total pore volume does not change, remaining constant values.     

A comparative study of two methods for the synthesis of fly ash-based sodium and potassium type zeolites

Fly ash (FA) from the Rugeley Power Station, West Midlands (England) was used in a study on synthesis at laboratory scale of zeolitic materials under various conditions by two different routes. Zeolitic materials were synthesized from FA by hydrothermal treatment in NaOH (Na-phillipsite, hydroxysodalite, hydroxycancrinite, tobermorite, analcime and herschelite) and KOH (hydroxysodalite, zeolite Barrer-KF, K-chabazite and zeolite Linde Type F) solutions. By fusion with NaOH followed by hydrothermal reaction, FA was converted into faujasite and hydroxysodalite. No zeolitic materials were obtained by this method using KOH as alkali activator. The process of synthesis was optimised by applying a wide range of experimental conditions with a wide range of reaction temperature, time, alkali hydroxide concentration and solid/solution ratio. The efficiency FA-based zeolites (FAZs) for heavy metal and ammonium uptake from synthetic solutions at laboratory scale have been investigated by the authors, revealing that these FAZs may reach appropriate cation exchange capacities for their application in industrial wastewater treatment.     

Chemical factors that influence the performance of mine sulphidic paste backfill

Sulphide-rich tailings from four Canadian mines were sampled (Mines A1, A2, B and C) to prepare several different paste backfill mixtures. The sulphur grade within these tailings samples range from 5 to 32 wt.%. The binders used were Portland-cement-based binders, fly-ash-based binders and slag-based binders with proportions ranging from 3 to 6 wt.%. The study was carried out in two stages. Stage I allowed us to understand the effects of binder type, binder proportion and tailings properties on compressive strength development of paste backfill during the course of curing time. It was pointed out that for high sulphide tailings, neither the slag-based binders nor the fly-ash-based binders were effective, whereas the sulphate-resistant-based binder (mix of Type I [TI] and Type V [TV] Portland cements) gave good long-term strength. However, the slag-based binders gave the best strength for low and medium sulphide-bearing tailings for which the Portland- and the fly-ash-based mixtures have a relatively low strength. Stage II allowed us to study the early stage strength acquisition of the various mixtures. It was found that the chemical composition of the mixing water plays a role on the mechanical behavior of certain cemented backfills.     

Influence of air-cooled slag on physicochemical properties of autoclaved aerated concrete

Lime and sand in autoclaved aerated concrete (AAC) were replaced by air-cooled slag (AS). The compressive strength and the type and nature of the hydration products were studied for samples autoclaved at 8 bar for different periods of times: 2, 6, 12 and 24 h. The hydration reactions were monitored by determining free-lime contents and combined water. The types of the hydration products were investigated using XRD and SEM/EDX. Slag substitutions for sand and lime up to 50% enhance the compressive strength, especially at short curing times (2 and 6 h). The optimum strength is obtained by 50% AS substitution for low-lime mixes (10% CaO) and 30% AS substitution for high-lime mixes (25% CaO). In high-lime mixes containing up to 30% AS, the initially formed fibrous calcium-rich CSH was changed to needle-like and lath-like 1.1 nm tobermorite. In low-lime mixes with AS-substitution, tobermorite appears at 2 h processing time with grass-like silica-rich CSH around quartz particles.     

Production of silver‐doped analcime by isomorphous substitution technique

BACKGROUND: Metal‐exchanged zeolites have been reported to have significant limitations on cayalytic activity, such as counterbalancing the negative framework charges and limitation of active space. Alternative methods of incorporating silver ions into the framework of zeolites are therefore necessary. This paper reports on a technique for producing silver doped analcime by isomorphous substitution of silver ion into the framework of analcime. The amount of aluminium in the gel composition was reduced by a factor of 5%, 10% and 20% and an equivalent amount of silver was added to the gel and treated in a conventional manner for zeolite crystallisation. Some of the aluminium in the reaction gel was replaced with the silver. The silver‐doped analcime samples where characterised by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐rays (EDX), Fourier transform infrared (FTIR) spectroscopy and inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES) analysis. RESULTS: The amount of silver ions loaded for each reduction of aluminium as determined by EDX were found to be (w/w) 0.29%, 1.41% and 2.10%, respectively. XRD pattern SEM images of the silver‐doped analcime showed the presence of zeolite P in addition to analcime. CONCLUSION: Silver‐doped analcime was successfully produced with different silver loadings and may exhibit higher anti‐microbial activities than silver‐exchanged counterparts. Copyright © 2008 Society of Chemical Industry     

Al-substituted tobermorite: shows cation exchange

It has been found that the tobermorite family--fundamental to cement chemistry can exhibit base exchange behavior. Several Al-substituted tobermorites were synthesized and these 11Å type tobermorites were discovered to have cation exchange as well as selective cation adsorption properties. For example, Al-substituted tobermorite (synthesized from a mixture of clinoptilolite and mortar) has a cation exchange capacity of 56 meq/100g and a selective Cs adsorption K_d of 3400 (ml/g). The cation exchange and selective properties of Al-substituted tobermorite are analogous to those of zeolites because of its rigid structure but unlike those of smectites or vermiculites where the basal spacing varies with the nature of the interlayer cation.     

Kinetics and thermodynamic studies of Cr(VI) adsorption using environmental friendly multifunctional zeolites synthesized from coal fly ash under mild conditions

Abstract

The Na-P1 zeolite was produced from coal fly ash and modified with different environmental friendly surfactants. The potential of these green modified zeolites was investigated as adsorbents for Cr(VI) ions in a batch system. XRD, SEM, XRF, and ICP-AES analyses were used for the characterization of raw materials and zeolite samples. The environmental friendly modified zeolites successfully immobilized different toxic elements in their framework inhibiting the transfer of these toxic elements to the surrounding liquid phase. The effects of various operational parameters on Cr(VI) removal were studied. The Hexamethylenediamine (HDTMA) and Ammonyx KP (KP) modified zeolites had larger chromium removal potential than the other samples at all temperatures. The effectiveness of Cr(VI) ions elimination became greater as the pH decreased and the adsorbent dose increased. The Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were fitted to the equilibrium data. The Dubinin–Radushkevich and Langmuir models gave a better fitness to equilibrium data of HDTMA-Na-P1 and KP-Na-P1, respectively. The positive and high ΔH° values showed the endothermic nature of the total Cr(VI) sorption procedure and indicated that Cr(VI) adsorption onto HDTMA-Na-P1 and KP-Na-P1 is a chemisorption. The negative ΔS° values also showed that chromium ions were stable on the surface of adsorbents. The adsorption potential of the developed eco-friendly KP-Na-P1 was higher than those of other adsorbents reported in the literature.     

热固性树脂微波固化研究进展

综述了近年来热固性树脂及其复合材料的微波固化研究进展,重点讨论了热固性树脂微波固化与加热固化的比较,热固性树脂微波固化工艺,颗粒、纤维增强树脂基复合材料的微波固化研究。研究发现微波固化和热固化在本质上是相同的,然而,微波极大地加速了固化进程,对体系性能无损害;加入无机、金属填料以及纤维可以改变体系介电性能,控制微波工艺对材料进行精加工。最后介绍了微波热效应原理,并展望了微波热固化技术发展与应用。     

Paragenesis of 11 Å tobermorite and poorly crystalline hydrated magnesium silicate

Poorly crystalline talc-like material and highly crystalline 11 Å tobermorite occurred as small veins in a basic tuff. These are the first assemblages of this type to be recorded in nature. The 11 Å tobermorite was rich in Al and very poor in Mg, and it showed anomalous thermal behaviour similar to that of the Loch Eynort specimen. These results suggest that Mg cannot enter into the tobermorite structure but forms poorly crystallized hydrated magnesium silicates, when the hydrothermal treatment is carried out at low temperature from Mg-bearing raw materials such as Portland cement, high-magnesia cement, slag, etc.     

Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: II, Fracture Toughness and Microstructure

The mechanical properties were investigated for autociaved aerated concrete (AAC) block samples, prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. The mechanical properties of AAC made using slag are comparable to those made without slag. With increased autoclaving time, the compressive strength increases due to the binder effect of the 1.1-nm tobermorite. In contrast, the fracture energy G _F. and resistance to crack growth decrease with increase of autoclaving time. This dependency is caused by the formation of voids around unreacted slag particles.     

Novel hydrothermal synthesis of tobermorite fibers using Ca(II)-EDTA complex precursor

A novel method for synthesizing large size tobermorite fibers without special instruments, high temperature and long time was developed. Tobermorite fibers with 40–100 μm in length and 0.1–1 μm in diameter were hydrothermally synthesized at 200 °C for 5 h using a Ca (II)-EDTA complex precursor. And the effect of experiment conditions on the phase, morphology and composition of final products were investigated.     

硅钙基固废原料配比及蒸养条件对硅酸钙板力学性能的影响

研究协同利用硅钙渣、粉煤灰、水泥和脱硫石膏制备硅酸钙板时,原料配比、蒸养条件对硅酸钙板力学性能、水化产物的影响,并利用XRD、IR和SEM表征了原料的协同水化历程和水化产物的微观结构和表面形貌.试验结果表明:最佳原料配比为硅钙渣60%、粉煤灰24%、水泥10%和脱硫石膏6%;最佳蒸压养护条件为蒸养温度180℃,恒温蒸养时间8 h,硅酸钙板抗折强度满足国家标准强度的D1.3的Ⅱ级要求;随着蒸养温度升高,原料水化依次生成C-S-H凝胶、托贝莫来石和针状硬硅钙石,大量托贝莫来石和硬硅钙石的生成使得硅酸钙板的强度得以提升.     

Solid-state nuclear magnetic resonance (NMR): Application to precursors of ceramics—Polycarbosilane

The chemical structures of oxidation- and electron irradiation-cured polycarbosilane fibers has been studied by IR and chemical analysis, but its structure has not been identified in detail. In this work, the chemical structure and curing mechanism was examined by solid-state high-resolution NMR spectroscopy. From the analysis of NMR spectra, it is explained that (i) in oxidation curing of PCS fibers, oxygen attacks first the SiC₃H bond and forms the SiC₃O bond and, next, the SiC₄ backbone bond and forms the SiC₂O₂ units; (ii) in electron irradiation curing, the signal intensity of SiC₃H units decreases with the increase in dose, the increase in the signal being due to the formation of SiC₄ units; (iii) solid-state²⁹Si high-resolution (CP/MAS) NMR spectroscopy is a powerful tool for investigating the chemical structure and curing mechanism of PCS fibers complementing infrared and solid-state¹³C high-resolution NMR spectroscopy; and (iv)¹H CRAMPS NMR spectroscopy is very useful for investigating the chemical structure and curing mechanism of PCS fibers.     

Influence of additions of coal fly ash and quartz on hydrothermal solidification of blast furnace slag

Blast furnace water-cooled slag (BFWS) has been solidified hydrothermally with tobermorite formation. The experimental results showed that the addition of fly ash and quartz was favorable to the formation of tobermorite, and the strength development of solidified body depended on both of the tobermorite formation and filling degree of formed tobermorite in the spaces between BFWS particles. The fly ash added appeared to have a higher reactivity than the quartz used during the initial hydrothermal processing due to the higher solubility of glassy phase in fly ash. The tobermorite formation seemed to be very sensitive to the fly ash content, e.g., the addition of fly ash 10-20 mass% was favorable to tobermorite formation, while the excessive addition of fly ash (> 20 mass%) appeared to impede the tobermorite formation. The excessive addition of quartz was also shown to exert a negative effect on the tobermorite formation, which causes strength deduction.     

斜发沸石水热固化机理的探讨

采用水热法对斜发沸石进行固化,研究了水热固化时间及加水量等因素对沸石性能的影响。利用X射线衍射分析和傅里叶变换红外分析手段,探讨了斜发沸石的水热固化机理。结果表明成型压强30 MPa、钙硅比为0.8、加水量为10%、200 ℃水热固化12 h时,斜发沸石抗折强度达到最大,机理分析表明斜发沸石水热固化强度的增大是源于托勃莫来石晶相的逐渐结晶长大。     

Microstructural investigations of naturally and artificially weathered autoclaved aerated concrete

The microstructural changes in autoclaved aerated concrete (AAC), particularly due to chemical degradation, have been investigated. The carbonation process has been studied on naturally and artificially weathered AAC by spectrographic and microscopic analysis. Visual inspections of unexposed and aged AAC were made by means of light optical microscopy and scanning electron microscopy (SEM), while chemical and structural analysis were based on X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The results obtained from two different experimental exposure set-ups, i.e., natural and artificial weathering, are presented. Thin-section images clearly indicate leaching out of the surface layer resulting in open larger air voids. Both naturally and artificially weathered samples displayed similar ageing characteristics in terms of mineralogical changes. The XRD patterns confirm that tobermorite were gradually transforming into calcium carbonate with exposure time. Calcite and gypsum were the two main crystal structures growing during weathering as detected in the SEM+EDS examinations.