粉煤灰合成Na-X沸石去除废水中镍离子的研究

粉煤灰通过碱熔融 水热法合成了Na-X型沸石,研究了Na-X型沸石的用量、吸附时间、溶液pH值、初始镍离子浓度和温度对废水中镍离子去除效果的影响。结果表明,Na-X型粉煤灰沸石对镍离子的去除性能与化学原料合成的13X相当,明显优于粉煤灰。在20℃,pH值为6,沸石用量10g/L,吸附15min时,对初始浓度为20mg/L~150mg/L的镍离子去除率均可达90%以上。镍离子的吸附过程符合Langmiur吸附等温方程式,其单层吸附量为11.2×10^-3。粉煤灰沸石重复使用5次,对废水中镍离子的去除率仍高达95%,再生性能良好。     

Removal of phosphate from aqueous solution by zeolite synthesized from fly ash

Fifteen Chinese fly ashes were converted hydrothermally into zeolites, and phosphate immobilization capacity (PIC) of the synthesized zeolites and the corresponding raw fly ashes were determined using an initial phosphate concentration of 1000 mg/L. Results showed that there was a remarkable increase in PIC (from 1.2 to 7.6 times) following the synthesis process. Fractionation of immobilized phosphorus indicated that Fe+Al-P increased most significantly and consistently among all the phosphorus fractions following the conversion of fly ash to zeolite. The PIC and Ca+Mg-P were closely related to Ca content (with r values of 0.9683 and 0.9651, respectively) rather than Mg content (with r values of 0.3920 and 0.3212, respectively). The r values of PIC and Fe+Al-P with Fe content (with r values of 0.4686 and 0.6385, respectively) were higher than those with Al content (with r values of -0.7857 and -0.3770, respectively). Although calcium and iron components were mainly involved in phosphate immobilization, there was no significant change of Ca and Fe content following the conversion of fly ash to zeolite. Increase in dissociated Fe(2)O(3) and specific surface area probably accounted for the enhancement in PIC of synthesized zeolites compared with corresponding fly ashes. The PIC value of zeolites showed a significant correlation with dissociated Fe(2)O(3) (r=0.6186). The specific surface area increased 26.0-89.4 times as a result of the conversion of fly ash to zeolite. The maximum removal of phosphate occurred within different pH ranges for zeolites which were synthesized from high, medium and low calcium fly ashes and this behavior was explained by the reaction of phosphate with calcium and iron components.     

粉煤灰合成Na-P1沸石去除饮用水中氟的研究

采用水热法合成了Na-P1型粉煤灰沸石,改性后用于去除饮用水中的氟离子。研究了吸附时间、沸石用量、氟离子浓度对除氟率的影响,探讨了沸石除氟的吸附机理。研究表明,将粉煤灰沸石用1.0%的NaOH溶液浸泡12 h,然后用2.0%的硫酸铝钾溶液浸泡36 h活化,能够明显提高其吸附除氟能力。在考察的范围内,除氟率随吸附时间的延长和沸石用量增多而增加。吸附等温线拟合结果表明,吸附除氟过程符合Langmuir吸附等温式。     

Adsorption of indigo carmine from aqueous solution using coal fly ash and zeolite from fly ash

Coal fly ash, a waste generated at the Figueira coal-fired electric power plant located in Brazil, was used to synthesize zeolite by hydrothermal treatment with NaOH solution at 100 °C for 24 h. The fly ash (FA) and this synthesized zeolite (ZM) that was characterized predominantly as hydroxy-sodalite were used as adsorbents for anionic dye indigo carmine from aqueous solutions. The samples were analyzed by instrumental neutron activation analysis (INAA) for the determination of As, Co, Fe, La, Mo, Na, Sb, Sc, Sm, Th, U and Zn. Effects of contact time and initial dye concentration were evaluated in the adsorption processes. The kinetics studies indicated that the adsorption followed the pseudo-second order kinetics and that surface adsorption and intraparticle diffusion were involved in the adsorption mechanism for both the adsorbents. The Langmuir isotherm model provided the best correlation of the experimental data. The maximum adsorption capacity was found to be 1.48 mg L⁻¹ for FA and 1.23 mg L⁻¹ for ZM. Laboratory leaching and solubilization tests conducted to classify this ZM as if was a waste residue according to the Brazilian regulation classified it as a residue non-hazardous and non-inert.     

Simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash as influenced by salt treatment

To develop an effective technique for enhancing the removal efficiency of ammonium and phosphate at low concentrations without losing potential removal capacity, Na-ZFA (zeolite synthesized from fly ash) was converted into Ca-, Mg-, Al-, and Fe-ZFA by salt treatment and the simultaneous removal of ammonium and phosphate by ZFA saturated with different cations was investigated. It was shown that Al3+-ZFA had the highest removal efficiencies (80-98%) for ammonium, followed by Mg2+ (43-58%), Ca2+ (40-54%), Na+ (<20%), and Fe3+ (<1%). Both alkaline pH values (in the cases of Na+, Ca2+, Mg2+) and acidic pH value (in the case of Fe3+) inhibited the sequestration of ammonium. At low initial phosphate concentrations, the efficiency of phosphate removal by Al3+- and Fe3+-ZFA approached 100%, followed by Ca2+ (60-85%), Na+ (<25%), and Mg2+ (<5%). The difference in phosphate removal efficiency was explained by the adsorption mechanisms. It was concluded that ZFA could be used in simultaneous removal of NH4+ and phosphate at low concentrations with presaturation by an appropriate cation such as Al3+ through salt treatment.     

Speciation of chromium in Australian fly ash

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO₃ containing 0.5%-CH₃OH. When the column was operated at a flow rate of 1.2 ml min⁻¹ and samples were injected by use of a sample loop with a volume of 100 μl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3σ) were 5 ng for Cr(III) (0.050 mg l⁻¹) and 9 ng for Cr(VI) (0.090 mg l⁻¹), respectively. A relative standard deviation of 1.9% (n = 6) was obtained for the determination by IC-ICP-AES of 0.25 mg l⁻¹ Cr(III) and Cr(VI).     

Evaluation of Co and Zn competitive sorption by zeolitic material synthesized from fly ash using 60Co and 65Zn as radioindicators

Journal of Radioanalytical and Nuclear Chemistry - Zeolitic material prepared by hydrothermal treatment of brown coal fly ash was used for sorption separation of Co2+ and Zn2+ ions from single and...     

New ceramic microfiltration membranes from mineral coal fly ash

This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700 °C for about 3 h. The elaboration of the mesoporous layer was performed by the slip casting method using a suspension made of the mixture of fly ash powder, water and PVA. The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24 h then a sintering at 800 °C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macro defects (cracks, etc.). The average pore diameter of the active layer was 0.25 μm and the thickness was around 20 μm. The membrane permeability was 475 l/h m² bar.This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 l/h m²). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90%, respectively.     

Characterization of coal fly ash components by laser-induced breakdown spectroscopy

The high sensitivity of laser-induced breakdown spectroscopy (LIBS) for the detection of most of the fly ash components enables the analysis of these residues produced during the combustion of coal. Fly ash consists of oxides (SiO₂, Al₂O₃, Fe₂O₃, CaO…) and unburnt carbon which is the major determinant of combustion efficiency in coal fired boilers. For example, an excessive amount of residual carbon dispersed in the fly ash means a significant loss of energy (Styszko et al., 2004 [1]). Standard methods employed for the analysis of fly ash make not possible a control of boiler in real time. LIBS technique can significantly reduce the time of analysis, in some cases even an online detection can be performed. For this reason, some studies have been addressed in order to demonstrate the capability of the laser-induced breakdown spectroscopy technique for the detection of carbon content in high pressure conditions typical of thermal power plants (Noda et al., 2002 [2]) and for the monitoring of unburnt carbon for the boiler control in real time (Kurihara et al., 2003[3]).In particular, the content of unburnt carbon is a valuable indicator for the control of fly ash quality and for the boiler combustion. Depending on this unburnt carbon content, fly ash can be disposed as an industrial waste or as a raw material for the production of concrete in the construction sector. In this study, analyses were performed on specimens of various forms of preparation. Pressed pellets were prepared with two different binders. Presented results concern the nature and amount of the binder used to pelletize the powder, and the laser-induced breakdown spectroscopy parameters and procedure required to draw calibration curves of elements from the fly ash. Analysis “on tape” was performed in order to establish the experimental conditions for the future “online analysis”.     

Synthesis and properties of magnetic zeolite with good magnetic stability from fly ash

Magnetic fly ash-based zeolites (MFZ) with good magnetic stability were in situ synthesized from fly ash (FA) modified by Fe₃O₄ after alkali fusion, hydrothermal treatment, and followed by reduction. The effects of the synthesis parameters of MFZ, such as the loading amount of Fe₃O₄, NaOH/FA ratio, and SiO₂/Al₂O₃ molar ratio, were investigated as well as its adsorption capacity for Cu²⁺ ions. The results indicated that MFZ were composed of zeolite A and sodalite phases and possessed excellent magnetic property. Fe₃O₄ nanoparticles were encapsulated in or covered below the as-synthesized zeolites, resulting in a good magnetic stability of MFZ. The magnetic property and crystal type of MFZ could be adjusted by controlling the synthesis parameters. High loading amount of Fe₃O₄ hindered the leaching of active SiO₂ from FA and then limited the formation of zeolite A. MFZ exhibited a high adsorption capacity for Cu²⁺ ions and the latter increased with the amount and crystallinity of zeolite A in MFZ.

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Application of the Taguchi method to investigate the effects of experimental parameters in hydrothermal synthesis of Na-P1 zeolite from coal fly ash

Research on Chemical Intermediates - The aim of this study is to optimize the hydrothermal parameters to maximize Na-P1 (Na6Al6Si10O32·12H2O) zeolite crystallization from fly ash using the L9...     

Effect of quaternary ammonium cations on dye sorption to fly ash from aqueous media

The efficacy of the surface modification of fly ash by quarternary ammonium cations in the removal of dyes from aqueous solution is demonstrated. A series of organo-fly ash materials were synthesized by treating fly ash with quarternary ammonium cations such as tetraethylammonium, hexadecyltrimethylammonium, and benzyldimethyltetradecylammonium (TEA, HDTMA, and BDTDA). Two types of dyes were used for the investigation, disperse and anionic dyes. The effects of initial dye concentration, contact time, temperature, and the mechanism of dye sorption were investigated. The sorption was found to be affected by the structure and size of the quaternary ammonium cations as well as that of the dyes. Sorption of dyes was considerably enhanced by the surface modification. Thermodynamic parameters such as free energy (DeltaG0), enthalpy (DeltaH0), and entropy (DeltaS0) for the sorption process were also calculated.     

Transformation of South African coal fly ash into ZSM-5 zeolite and its application as an MTO catalyst

This study presents a way of using South African coal fly ash by extracting metals such as Al and Fe with concentrated sulphuric acid, and then using the solid residue as a feedstock for the synthesis of ZSM-5 zeolite. The percentage of aluminium and iron oxides decreased from 28.0 ± 0.2% and 5.0 ± 0.1% in coal fly ash to 24.6 ± 0.1% and 1.6 ± 0.01% in the acid treated coal fly ash respectively. The fly ash-based zeolite ZSM-5 sample synthesised from the solid residue after extraction of Al and Fe, contained 62% of ZSM-5 zeolite pure phase with a number of Brønsted acid site density of 0.61 mmol per g_zeolite.By properly treating the as-prepared coal fly ash-based ZSM-5 zeolite, an active and selective methanol-to-olefins acid catalyst could be designed, leading to full methanol conversion during 15 h on stream. The optimised catalyst exhibited a cumulative methanol conversion capacity of 71 g(MeOH_converted)/g(catalyst) and a light olefin productivity of 21 g(C₂₌–C₄₌)/g(catalyst).     

Modeling the mechanism involved during the sorption of methylene blue onto fly ash

Batch sorption experiments were carried out to remove methylene blue from its aqueous solutions using fly ash as an adsorbent. Operating variables studied were initial dye concentration, fly ash mass, pH, and contact time. Maximum color removal was observed at a basic pH of 8. Equilibrium data were represented well by a Langmuir isotherm equation with a monolayer sorption capacity of 5.718 mg/g. Sorption data were fitted to both Lagergren first-order and pseudo-second-order kinetic models and the data were found to follow pseudo-second-order kinetics. Rate constants at different initial concentrations were estimated. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D(i) values were estimated at different initial concentrations and the average value was determined to be 2.063 x 10(-9)cm2/s. Analysis of sorption data using a Boyd plot confirms the particle diffusion as the rate-limiting step for the dye concentration ranges studied in the present investigation (20 to 60 mg/L).     

Floating cultivation of marine cyanobacteria using coal fly ash

The aim of this study was to develop improved methodologies for bulk culturing of biotechnologically useful marine cyanobacteria in the open ocean. We have investigated the viability of using coal fly ash (CFA) blocks as the support medium in a novel floating culture system for marine microalgae. The marine cyanobacterium Synechococcus sp. NKBG 040607 was found to adhere to floating CFA blocks in liquid culture medium. Maximum density of attached cells of 2.0×10⁸ cells/cm² was achieved using sea water. The marine cyanobacterium Synechococcus sp. NKBG 042902 weaklyadhered to floating CFA blocks in BG-11 medium. Increasing the concentration of calcium ion in the culture medium enhanced adherence to CFA blocks.     

Chemical characterization of density separated submicrometer coal fly ash

A new geometrical particle size separation method in the range of submicrometer has been developed for coal fly ash. Coal fly ash particles prefractionated less than 5m in geometrical diameter were fractionated with a coupling of supersonical dispersion in methyl alcohol and filtration through antistatic Nucleopore filter into >1.0, 1.0–0.8, 0.8–0.6m.Submicrometer (1.0–0.6m) and micrometer coal fly ash (25–20m) were separated into six density fractions and their compositions measured by SEM-EDX were compared. For the both size fractions, for the low density fractions (<2.8 g/cm³) consisted mainly of aluminosilicates and the fractions of 2.8–3.2 g/cm³ consisted of oxides of aluminum, silicon and calcium, and in the fraction above 3.2 g/cm³ iron was rich. In submicrometer fly ash, phosphor and sulfur concentrated to the particles rich in calcium. In the heaviest fraction, the particles containing over 30 wt% titanium as oxide observed among the particles rich in iron. These fractions were revealed not as a single component, but as mixtures of several components.     

Effect of exopolymeric substances on the kinetics of sorption and desorption of trivalent chromium in soil

Laboratory batch sorption-desorption and column experiments were performed to better understand the effects of microbial exopolymeric substances (EPS) on Cr(III) sorption/desorption rates in the soil-water system. The experiments were carried out in two different modes: one mode (sorption) in which Cr(III) and EPS were applied simultaneously, and the other (desorption) included the sequential application of Cr(III) and EPS to the soil-water system. The batch sorption and desorption experiments showed that, while chromium(III) desorption was significantly enhanced in the presence of EPS relative to non-EPS-containing systems, the desorption rates were much smaller than the sorption rates, and the fraction dissolved by EPS accounted for only a small portion of the total chromium initially sorbed onto soil minerals. Similarly, the column experiments suggested that, while the microbial EPS led to an increase in Cr dissolution relative to non-EPS-containing systems, only a small portion of the total chromium initially added to the soil was mobilised. The differences observed in Cr sorption and desorption rates can be explained through the very low solubility and strong interactions of chromium species with soil minerals as well as the mass transfer effects associated with low diffusion rates. The overall results suggest that, while microbial EPS may play an important role in microbial Cr(VI) treatment in sub-surface systems due to the formation of soluble Cr-EPS complexes, the extent and degree of Cr mobilisation are highly dependent on the type of initial Cr sorption.     

Synthesis of zeolites from coal fly ash: application of a statistical experimental design

With the intention of decreasing the experimental test runs during the optimization of synthesis of zeolites from fly ash, a 2⁴ full-factorial experimental design was applied in this study. The preparation parameters that had showed significant influence on the synthesis of pure phase zeolite Na-P1 using one-step-at-a-time experimental approach were included, but extended also to those parameters of importance identified in the literature. At the same time, it was important that the levels of variation of parameters not be restricted to the conditions where a pure phase of zeolite Na-P1 was formed. The four synthesis variables investigated were; NaOH concentration (NaOH:SiO₂ molar ratio ranged between 0.35 and 0.71), ageing temperature (35?C55°C), hydrothermal treatment time (36?C60?h) and temperature (130?C150°C). The results obtained were assessed by the improvement in the cation exchange capacity (CEC) of the obtained zeolite, which showed that the phase purity is strictly controlled by the synthesis conditions. In the end, this approach provided sufficient understanding of the relationship between product properties and the four synthesis parameters, which took into account the individual effects as well as linear and nonlinear interacting phenomena. From the analysis, it was found that the main effects were ageing temperature and hydrothermal treatment time and temperature, which showed some interactions among each other.     

准东煤流化床气化飞灰的理化特性研究

采用灰熔点测定仪、X射线荧光光谱仪、扫描电镜和热重分析仪等方法,研究了准东煤流化床气化飞灰的灰熔融特性、物理结构和化学组成及气化反应活性。结果表明,准东煤与其流化床气化飞灰中Si O2、Fe2O3、Na2O和Ca O等矿物质含量存在显著的差异,但飞灰的灰熔点与原煤无明显差异。准东煤气化飞灰具有较宽的粒径范围,呈现双峰分布特征,且不同粒径区间飞灰的元素含量存在显著差异。提高气化温度,有利于提高飞灰的气化反应活性。准东煤流化床气化飞灰石墨化程度比煤焦要高,但其孔隙结构更为发达,含有丰富的中孔和中大孔,使得飞灰的气化反应活性高于煤焦。可通过提高气化温度、循环再气化的方法提高气化效率。     

Leachability and analytical speciation of antimony in coal fly ash

A new procedure was described with multiwalled carbon nanotubes as solid phase extraction packing material for the trace analysis of nicosulfuron, thifensulfuron and metsulfuron-methyl in water samples. The possible parameters influencing the enrichment were optimized and the optimal conditions were as followed: eluent, sample pH, flow rate and sample volume were acetonitrile containing 1% acetic acid, pH 3, 8 mL min⁻¹ and 500 mL, respectively. Under the optimal chromatographic separation and SPE conditions, the linear range, detection limit (S/N = 3) and precision (R.S.D., n = 6) were 0.04-40 ng mL⁻¹, 6.8 ng L⁻¹ and 2.5% for nicosulfuron, 0.04-40 ng mL⁻¹, 11.2 ng L⁻¹ and 5.4% for thifensulfuron, 0.02-20 ng mL⁻¹, 5.9 ng L⁻¹, 2.1% for metsulfuron-methyl, respectively. The established method was well employed to determine nicosulfuron, thifensulfuron and metsulfuron-methyl in tap water, seawater, reservoir water and well water samples, and satisfactory results were obtained, the spiked recoveries in the range of 87.2-100.7%, 96.5-105.6% and 83.7-111.1% for them each, respectively.