Coal fly ash and synthetic coal fly ash aggregates as reactive media to remove zinc from aqueous solutions

Coal fly ash (CF) and synthetic coal fly ash aggregates (SCFAs) were evaluated as low-cost reactive media for the remediation of groundwater contaminated with Zn. The SCFAs were prepared by mixing CF, sodium silicate, and deionized (DI) water. Serial batch kinetic and static tests were conducted on both CF and SCFAs, under various conditions (i.e., pH, initial Zn concentration, reaction time, and solid dosage), using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on both CF and SCFAs. The final rather than the initial pH of the solution had a greater effect on the removal of Zn. At pH>7.0, the removal of Zn was due to precipitation, whereas at <7.0, the removal of Zn was due to adsorption onto the reactive media. The removal of Zn increased with increasing dosage of the reactive medium and decreasing initial Zn concentration. The results of the column and batch tests were comparable. Preferential flow paths were observed with CF, but not SCFA. The hydraulic conductivity of CF was more significantly decreased than that of SCFA with increasing dry density of the specimen.     

Removal mechanism of phosphate from aqueous solution by fly ash

This work studied the effectiveness of fly ash in removing phosphate from aqueous solution and its related removal mechanism. The adsorption and precipitation of phosphate by fly ash were investigated separately in order to evaluate their role in the removal of phosphate. Results showed that the removal of phosphate by fly ash was rapid. The removal percentage of phosphate in the first 5min reached 68-96% of the maximum removal of phosphate by fly ash. The removal processes of phosphate by fly ash included a fast and large removal representing precipitation, then a slower and longer removal due to adsorption. The adsorption of phosphate on fly ash could be described well by Freundlich isotherm equation. The pH and Ca2+ concentration of fly ash suspension were decreased with the addition of phosphate, which suggests that calcium phosphate precipitation is a major mechanism of the phosphate removal. Comparison of the relative contribution of the adsorption and precipitation to the total removal of phosphate by fly ash showed that the adsorption accounted for 30-34% of the total removal of phosphate, depending on the content of CaO in fly ash. XRD patterns of the fly ash before and after phosphate adsorption revealed that phosphate salt (CaHPO4 x 2H2O) was formed in the adsorption process. Therefore, the removal of phosphate by fly ash can be attributed to the formation of phosphate precipitation as a brushite and the adsorption on hydroxylated oxides. The results suggested that the use of fly ash could be a promising solution to the removal of phosphate in the wastewater treatment and pollution control.     

Electrodeposition of hard nanocrystalline chrome from aqueous sulfate trivalent chromium bath

A sulfate trivalent chromium bath is described which contains chromium(III) salt, sodium sulfate, aluminum sulfate, boric acid, formic acid, carbamide and surfactant. The bath is operated using either titanium-manganese dioxide anodes or platinized titanium anodes without separation of anodic and cathodic compartments. Effect of bath composition and electrolysis conditions on current efficiency of chromium electrodeposition was studied. At optimal bath composition and electrolysis conditions, the deposition rate does not practically change during electrolysis time; it is close to 0.8 μm min⁻¹. The nanocrystalline coatings with a thickness of several tens of micrometers are bright and smooth. The value of Cr-coatings hardness does not substantially differ from that observed in case of Cr(VI)-based baths. The possibility of continuous service of the proposed trivalent chromium bath was confirmed by means of a durational electroplating test (~ 2 months).     

Synthesis of zeolite Li-ABW from fly ash by fusion method

The zeolite Li-ABW was synthesized by fusion method using fly ash as raw material. It comprised alkaline fusion followed by hydrothermal treatment in LiOH·H₂O medium. Crystallinity of zeolite as high as 97.8% was attained under the following conditions: LiOH·H₂O concentration, 3 M; hydrothermal temperature, 180 °C; the corresponding aging time, 12 h. The content of Li-ABW increased at the expense of lithium aluminum silicate or quartz with an increase of LiOH·H₂O concentration. With increasing hydrothermal temperature and aging time, the soluble species re-crystallized and crystalline phase transformation between different zeolites was observed. Scanning electron microscopy (SEM) observation revealed that the obtained zeolite Li-ABW was a rod-like crystal. The pore size distribution curve indicated the presence of mesopores.     

Utilization of coal fly ash in the glass-ceramic production

Manufacturing the glass-ceramic has been proposed as a useful choice to recycle coal fly ash from power plants. In this work, a glass-ceramic of SiO2-Al2O3-Fe2O3-CaO family was synthesized by mixing 90 wt% of coal fly ash, from a power plant in west of China, with Na2O, and then melted at 1350 degrees C. The ceramization of the obtained glass was carried out at 770 degrees C for 2h. Esseneite and nepheline were found present as major crystal phases. The produced glass-ceramic exhibited good chemical durability as well as good mechanical properties. The toxicity characteristic leaching procedure (TCLP) method found that the glass-ceramic was non-hazardous.     

Synthesis of MCM-41 from coal fly ash by a green approach: influence of synthesis pH

The present study reports a green synthesis method for preparing pure (free of fly ash) and ordered MCM-41 materials from coal fly ash at room temperature (25 degrees C) during 24 h of reaction. It was shown that the impurities in the coal fly ash were not detrimental to the formation of MCM-41 at the tested conditions. The influence of initial synthesis pH on material properties of calcined MCM-41 samples was investigated by various techniques such as XRF, XPS, XRD, FTIR, DR-UV-vis, solid state NMR, N2 physisorption, TG-DTA, SEM and TEM. The experimental results showed that the amount of trace elements such as Al, Na, Ti and Fe incorporated into the sample increased with synthesis pH value. More aluminum species were incorporated with tetrahedral coordination in the framework under a high pH value. The particle size of the sample decreased with the synthesis pH value. Samples synthesized at high pH values had a larger pore size and were more hydrothermally stable than those at low pH values. From thermal analysis, it was observed that the synthesized MCM-41 samples showed a high thermal stability. These properties made the synthesized MCM-41 suitable for further processing into more useful materials in a wide range of applications.     

Removal of chlorophenols from aqueous solution by fly ash

Fly ash from coal-fired thermal power plants can be used for the removal of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) with enthalpy changes of about -3 kcal/mol. The amounts of 2-CP and 2,4-DCP removed are affected by the pH value of the solution. The efficiency of removal improves when the pH value is less than the pK(a) values of 2-CP and 2,4-DCP, respectively. The adsorbed amount of chlorophenol by fly ash is also affected by particle diameter, carbon content, and the specific surface area of the ash used in this study. As expected, more adsorption takes place with fly ash of higher carbon content and larger specific surface area. Moreover, the adsorbed amount of chlorophenol is not influenced by the matrix in the wastewater, as shown by studying the removal of 2-CP and 2, 4-DCP in wastewater from a synthetic fiber plant. Chlorophenols in the wastewater were also removed efficiently through a fly ash column, with breakthrough times being inversely proportional to flow rates.     

Heavy metal accumulation from coal fly ash by cyanobacterial biofertilizers

Bioleaching of heavy metals (Cu, Zn, Cr and Pb) from coal fly ash by cyanobacterial strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis and Aulosira fertilissimia), that are commonly used as biofertilizers in rice cultivation was studied to assess utilization of fly ash while mitigating its environmental metal toxicity. Cyanobacteria were grown at different concentration of fly ash at 0, 5, 10, and 20% was treated with different blue green algal strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis, and Aulosira fertilissimia) in suitable growth medium (BG-11) and distilled water to observe their growth and metal accumulation. Nostoc muscorum (ARM 442?mg?g^?1) showed maximum uptake of Cr (3.65?mg?g^?1), Pb (2.12?mg?g^?1) at BG 11(-N) medium amended with 10% fly ash, respectively. Anabaena variabilis (ARM 441) showed maximum uptake of Cu (0.313?mg?g^?1) and Pb (2.01?mg?g^?1) in BG 11 (–N) medium amended with 5% fly ash whereas Cr uptake (1.21?mg?g^?1) at 10% fly ash and Zn uptake (0.697?mg?g^?1) at 20% fly ash grown in BG 11(-N) medium. Increased accumulation of metals in blue green algae biomass grown in BG 11(-N) medium amended fly ash confirms that metal concentration was balanced between the algal strains.     

Studies on sorption properties of zeolite derived from Indian fly ash

Indian fly ash has been completely converted to crystalline porous 13X zeolite by NaOH fusion at 600 degrees C followed by hydrothermal treatment at 105 degrees C for 20 h. Obtained materials were characterized by XRD, SEM and surface area measurement. Prepared material was used for the sorption study of different metal ions (Cu(2+), Co(2+) and Ni(2+)) at different pH, temperature. Thermodynamic data (DeltaS, DeltaH and DeltaG) corresponding to different metal ion uptake were evaluated from Langmuir equation. In all the experiment sorption capacity of prepared zeolite was found to be quite high than that of fly ash at acidic pH. However, the uptake selectivity order for both the materials is Cu(2+)>Co(2+)>Ni(2+).     

Sorption properties of the activated carbon-zeolite composite prepared from coal fly ash for Ni(2+), Cu(2+), Cd(2+) and Pb(2+)

Composite materials of activated carbon and zeolite have been prepared successfully by activating coal fly ash (CFA) by fusion with NaOH at 750 degrees C in N(2) followed by hydrothermal treatments under various conditions. Uptake experiments for Ni(2+), Cu(2+), Cd(2+) and Pb(2+) were performed with the materials thus obtained from CFA. Of the various composite materials, that were obtained by hydrothermal treatment with NaOH solution (ca. 4M) at 80 degrees C (a composite of activated carbon and zeolite X/faujasite) proved to be the most suitable for the uptake of toxic metal ions. The relative selectivity of the present sorbents for the various ions was Pb(2+)>Cu(2+)>Cd(2+)>Ni(2+), with equilibrium uptake capacities of 2.65, 1.72, 1.44 and 1.20mmol/g, respectively. The sorption isotherm was a good fit to the Langmuir isotherm and the sorption is thought to progress mainly by ion exchange with Na(+). The overall reaction is pseudo-second order with rate constants of 0.14, 0.17, 0.21 and 0.20Lg/mmol min for the uptake of Pb(2+), Cu(2+), Cd(2+) and Ni(2+), respectively.     

Adsorption of herbicides on coal fly ash from aqueous solutions

Development of low cost adsorbent for pesticide retention is an important area of research in environmental sciences. The present study reports the sorption potential of coal fly ash, a waste from power stations, for removal of metribuzin, metolachlor and atrazine from water. Batch sorption method was used to study the sorption of herbicides from water. The amount of herbicides sorbed increased with increase in the amount of fly ash in the suspension. The maximum capacity of the fly ash to adsorb metribuzin, metolachlor and atrazine was found to be 0.20, 0.28 and 0.38 mg/g by Freundlich equation and 0.56, 1.0 and 3.33 mg/g by Langmuir equation. Freundlich adsorption equation better explained the results of herbicides sorption in fly ash as regression coefficient (R²) values were higher from Freundlich equation than the Langmuir equation. Adsorption isotherms were L-type suggesting that the herbicide sorption efficiency of fly ash depend on the initial concentration of herbicide in the solution and maximum removal of herbicide was observed at concentrations less than 10 μg/ml. The results of this study have implications in using the fly ash for removal of these herbicides from industrial and agricultural waste water and can find use as a material in the preparation of biobeds to minimize environmental contamination from pesticide use.     

Synthesis of Na-X zeolite from low aluminum coal fly ash: Characterization and high efficient As(V) removal

Na-X zeolite was successfully prepared from low aluminum coal fly ash (LACFA) via fusion-hydrothermal treatment. The influence of various synthesis parameters was investigated, including aluminum additives (AlCl₃·6H₂O, Al(NO₃)₃·9H₂O, AlF₃·3H₂O and NaAlO₂), dosages of NaAlO₂, weight ratio of LACFA/NaOH, crystallization temperature and time. The results indicated that the addition of Al species played a key role in the synthesis process of purity Na-X zeolite, and the corresponding relative crystallinity of the obtained samples was in the order of Na-X zeolite_(Al)???Na-X zeolite_(Cl)?>?Na-X zeolite_(N)?>?Na-X zeolite_(F) (Here, “Al”, “Cl”, “N” and “F” represent NaAlO₂, AlCl₃·6H₂O, Al(NO₃)₃·9H₂O and AlF₃·3H₂O, respectively). And the optimal operating conditions were: the weight ratio of LACFA/NaOH?=?0.83, short crystallization time 360?min, low crystallization temperature 90?°C and 0.038?mol NaAlO₂. Additionally, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), Fourier Transforms Infrared (FT-IR) and Scanning Electron Microscopy (SEM) were employed to determine the resultant samples. Based on the results of As(V) adsorption experiment, the experimental data was suitable fitted by Freundlich adsorption isotherm model, and the theoretical maximum adsorption capacity was 27.79?mg/g at pH?=?2.14. The kinetics studies suggested that “surface reaction” was the rate-determining step of adsorption process, and the thermodynamics studies indicated that the adsorption process was spontaneous and endothermic. These results deemed that the LACFA was suitable for preparing Na-X zeolite_(Al), and the obtained Na-X zeolite_(Al) was served as a promising adsorbent to remove As(V) from acid wastewater.     

Influence of NaOH concentrations on synthesis of pure-form zeolite A from fly ash using two-stage method

Synthesis of pure-form zeolite A were investigated using four concentrations of NaOH solution to dissolve Si source form fly ash, and with the addition of Al source, to prepare initial gel. Experimental results demonstrated, for two-stage method, that NaOH concentrations in initial gel played an important role in synthesis of pure-form zeolite A using fly ash as raw materials. Generally, pure-form zeolite A could be synthesized when following conditions were used: NaOH concentrations, 1.67, 5 and 6.67 M; the synthesis temperature, 100 °C; the corresponding crystallization time, 340, 250 and 190 min. However, a mixture phases of zeolites A and X were obtained at the condition of 3.33 M NaOH solution during various crystallization times. It was found that the higher NaOH concentration was used, the shorter crystallization time of zeolite A was required and the narrower particle size distribution of zeolite A was achieved. In addition, zeolite A submicron-crystals were first synthesized from fly ash using two-stage method in our study.     

Green activating silica-alumina insoluble phase of fly ash to synthesize zeolite P with high adsorption capacity for Pb(II) in solution

Using fly ash as a raw material to synthesize zeolite is an effective way to obtain cheap adsorbent. However, the high energy consumption of activating the insoluble silica-alumina phase of fly ash limits its practical application. In this study, a low-energy, wet-grinding hydrothermal method was used to activate the insoluble phase of fly ash to synthesize zeolite P, and the adsorption capacity of zeolite for lead ion in solution was studied. Wet-grinding can reduce fly ash particle size to nanometer scale and break long-chain Q⁴(Al) into short-chain low-polymer. Without aging, the activated material could directly synthesize zeolite P with a relative crystallinity of 89.37 %. Compared with the common alkali-fusion method, the wet-grinding method reduced energy consumption by 45.93 % and increased synthetic zeolite relative crystallinity by 7.51 %. The synthesized zeolite P could effectively remove Pb²⁺ ions from solution through ion exchange and hydroxyl reaction, and the adsorption capacity reached 497.01 mg/g.     

Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents

Single phase chamfered-edge zeolite 4A samples in pure form with a high crystallinity were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash. The calcium binding capacity of these zeolite 4A samples (prepared from coal fly ash) and the commercial detergent grade zeolite 4A were tested for usage as a detergent builder. The results show that these zeolite 4A samples behaved similarly as the commercial one in removing calcium ions during the washing cycle. Moreover, from the leaching tests (evaluation of toxicological safety), the results show that these zeolite 4A samples leached the same elements (Sb, As, Se and Tl) as the commercial one with the concentrations in the same order of magnitude. This shows that the toxicological effect of the coal fly ash converted zeolite 4A was not worse than that of the commercial sample. Finally, economic and environmental aspects of converting coal fly ash to useful products were discussed.     

Effect of microwave irradiation on crystal growth of zeolitized coal fly ash with different solid/liquid ratios

In the present work, coal fly ash (CFA) was converted to zeolite (CFAZP) experimentally at atmospheric pressure via a conventional hydrothermal heating for 6 h at low temperature (90 ± 3 °C) followed by microwave irradiation for 30 min. The synthesized products were characterized using XRD, TGA/DTA, SEM, PSD, BET, and cation-exchange capacity (CEC) techniques. The effect of microwave on the crystal growth of nucleated CFAZP at different solid/liquid ratios (suspended CFA mass to NaOH solution volume, g/mL) was studied. A three-variable, three level central composite statistical experimental design was applied to investigate the effect of the independent variables on the response function defined as the ratio of the characteristic peak intensity at 2θ: 28° of a sample to that of the same peak of a sample run for 24 h with conventional heating. The relative peak intensity of CFAZP as high as 97% was achieved under optimum experimental conditions with 1 M of NaOH concentration, 6 h of conventional heating followed by 30 min microwave irradiation with a solid/liquid ratio of 0.40 g/mL. Under constant microwave energy, higher solid/liquid ratios led to higher relative peak intensity of the product.     

粉煤灰酸法制氧化铝中溶出罐内料浆的温度测量方法研究

由于高温有压,强酸腐蚀等特殊性,目前尚未有对粉煤灰酸法制氧化铝中溶出罐内矿浆实时温度测量的好方法,本文提出了一种新方法,使溶出罐内料浆温度的实时检测得以实现,并且兼顾高精度和低成本的优点。     

Arsenate removal from water by an alumina-modified zeolite recovered from fly ash

A cancrinite-type zeolite was synthesized from Class C fly ash by molten-salt method. The product (ZFA) was used as the adsorbent for the arsenate removal from water. The adsorption equilibriums of arsenate are investigated on various adsorbents. ZFA showed a higher adsorption capacity (5.1 mg g(-1)) than activated carbon (4.0 mg g(-1)), silica gel (0.46 mg g(-1)), zeolite NaY (1.4 mg g(-1)), and zeolite 5A (4.1 mg g(-1)). The relatively higher adsorption capacity of ZFA than zeolite NaY and 5A was attributed to the low Si/Al ratio and the mesoporous secondary pore structure of ZFA. However, it was found that the adsorption capacity of zeolites were generally lower than activated alumina (16.6 mg g(-1)), which is ascribed to the small pores in zeolite frameworks. The adsorption capacity of ZFA was significantly improved after loaded by alumina via a wet-impregnation method. The modified ZFA (ZFA-Al(50)) with the optimum alumina loading showed an adsorption capacity of 34.5 mg g(-1), which was 2.1 times higher than activated alumina. The Toxicity Characteristic Leaching Procedure (TCLP) leachability tests indicated that the spent ZFA and alumina-modified ZFA complied with the EPA regulations for safe disposal.     

Synthesis and characterization of low-cost zeolite NaA from coal gangue by hydrothermal method

Through this investigation, we have demonstrated a low-cost preparation method of zeolite NaA from coal gangue. The well-developed zeolite NaA of 87.56% crystallinity was successfully prepared by hydrothermal alkali activation method, which required low alkali concentration (1.8 mol/L) compared to other researches (3–6 mol/L). The characterization results of product prepared at different conditions suggest that the purity and crystallinity of zeolite NaA are high at low alkali concentration and longer crystallization time. The Ca²⁺ exchange value of synthesized zeolite attained 265 mg CaCO₃/g compared to commercial zeolite, which is typically 340 mg CaCO₃/g. The basic structure parameters and thermal stability have also been studied. The results suggest that the obtained zeolite has a potential to be used as hard water softening agent. Moreover, the result of Rietveld quantitative phase analysis and Box-Behnken's response surface methodology showed that the weight fraction of zeolite NaA in product can reach 71.9%, and the crystallinity can attain 88.14% at the optimal condition of n(SiO2)/n(Al2O3) of 2.60, NaOH(aq) concentration of 1.86 mol/L at 95 °C for 10.08 h.     

Sintering of MSWI fly ash by microwave energy

This study presents the sintering of municipal solid waste incineration (MSWI) fly ash assisted by microwave energy. The composition of fly ash was investigated by chemical sequential extraction and modified microwave digestion method. Effects of process time, container materials, aging time and salt contents were also discussed. The major elements of fly ash are Ca, Cl, Na, Si, K, Al, Mg, and Zn, and the metal species, Zn, Cr, Pb, Ca, and Cu, are mainly in the oxide phase. Under microwave processing, the fly ash was sintered into a glass-ceramics and the leaching concentrations of heavy metals were restrained. The stabilization efficiency increased with an increase in processing time in most of the cases. Better stabilization efficiency of fly ash was discovered by using the SiO(2) or Al(2)O(3) container than by using the graphite plate/SiC plate. The presence of salt in the fly ash could enhance the sintering and stabilization of fly ash. During the aging time of 0-30 days, negligible Pb in the sintered fly ash was leached out, and the leaching concentration was lower than the criterion.