Effects of step change of heating source on synthesis of zeolite 4A from coal fly ash

Effects of step change of heating sources on the crystallization of zeolite 4A from coal fly ash by hydrothermal reaction were investigated with emphasis on the change in the crystallinity of the synthesized zeolite 4A. Most of the Si and Al components were effectively transformed into zeolite 4A by step change of the first conventional heating and then the second microwave heating of synthesis mixture dissolved from coal fly ash, and maximum crystallinity of zeolite 4A obtained was 91%. The first conventional heating also plays an important role in enhancing the nuclei formation that Si and Al in synthesis mixture reacted to form ring-like structures for combining sodalites, and further to small zeolite 4A seeds. The second microwave heating increases the crystallization rates from small zeolite 4A nuclei to more zeolite 4A crystals.The cation exchange capacity (CEC) of the zeolite 4A crystallized by step change of heating source from the conventional to the microwave was 5.5 meq/g compared to 5.7 meq/g for commercial zeolite 4A. Test results showed that removal efficiency of heavy metals by zeolite 4A synthesized from fly ash was more than 98% and similar to commercial zeolite 4A.     

Preparation of Na‐P1‐Type Zeolite and its Composite Material with Nanosized Magnetite

The Na‐P1‐type zeolite having a high cation‐exchange capacity (CEC) was obtained using the waste coal fly ash from thermal power stations and a 2M NaOH solution at 100°C. The Na‐P1‐type zeolite was formed with the reaction time of 6 h at 100°C, and its CEC value increased with an increase in the reaction time. The addition of a suitable amount of NaAlO₂ to the fly ash was also effective for improving the CEC value. A new composite material consisting of the Na‐P1‐type zeolite and magnetite was synthesized from the fly ash and iron chlorides because the magnetic collection was possible using this composite material after radioactive Cs⁺ ion adsorption. The existence of nanosized magnetites in the polycrystalline zeolite (several micrometers) was confirmed by TEM observations. The CEC and magnetic property of these composite materials were characterized.     

Removal of Phosphate from Aqueous Solution Using Zeolite Synthesized from Fly Ash by Alkaline Fusion Followed by Hydrothermal Treatment

The removal of phosphate from aqueous solution by the adsorption process using zeolite synthesized from fly ash was investigated in this study. The XRD patterns revealed that the major crystalline phase of the synthesized zeolite was gismondine. The phosphate immobilization capacity (PIC) increased significantly from 52.7 mg/g of fly ash to 102.9 mg/g of synthesized zeolite after conversion. The batch experiments were conducted to investigate the effect of pH, initial phosphate concentration, and adsorbent amount. The maximum adsorption capacity was obtained at the pH value of 7.0. The adsorption process followed Ho' pseudo-second-order model, and both liquid film and intra-particle diffusion were the rate-controlling step for the process. The adsorption equilibrium data had been analyzed by Langmuir, Freundlich, Radlich-Peterson, Koble-Corrigan, Tempkin, Dubinin-Radushkevich, and Generalized models. The results showed that the Langmuir model gave the best fit. The process was also found to be endothermic. The maximum phosphate adsorption capacity obtained was 132.02 mg/g (30°C), 156.36 mg/g (40°C) and 184.17 mg/g (50°C), respectively, suggesting that the synthesized zeolite is a promising material and can be used to remove phosphate from wastewater.     

粉煤灰制备高纯度X型沸石及其对含铅废水处理的研究

采用经碱熔融-离心提取处理的粉煤灰为原料,经水热反应法研究合成高纯度X型沸石的过程,探讨了碱灰比、焙烧温度对硅铝熔出量的影响,研究了碱度、陈化时间、晶化时间与硅铝比对合成的影响以及其对含Pb2＋废水的吸附性能。结果表明：碱灰比为2．3∶1,焙烧温度为680℃时可获得最佳的硅铝熔出量;当SiO2／Na2 O＝1（摩尔比）,SiO2／Al2O3＝3．5（摩尔比）,陈化时间为5 h,晶化时间为16 h时可获得高纯度X型沸石。合成沸石表现出对含Pb2＋废水较强的吸附能力,在投加0．23 g／100 mL含Pb2＋500 mg／L溶液中,调节pH值为5,常温下30 min,Pb2＋去除率可达99．6％;吸附容量达到了216．8 mg／g。     

粉煤灰沸石的合成及其对Pb~（2＋）的吸附研究

以驻马店热电厂粉煤灰为原料,在水热条件下合成了沸石,利用FT-IR对合成沸石进行表征。利用正交试验法研究了所合成沸石吸附Pb2＋的性能,考察了粉煤灰预处理方法、吸附条件（pH值、吸附时间、沸石用量等）对吸附的影响。结果表明：采用加碱焙烧预处理合成的沸石,在pH=7、吸附时间45 min、投加量为1.2 g时,对Pb2＋有很好的吸附作用。该条件下Pb2＋的去除率在83.5%左右。     

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.     

利用粉煤灰制备分子筛及对水体中六价铬的吸附研究

以粉煤灰为原料,采用湿法加碱煅烧法合成了4A分子筛,研究了粉煤灰与烧碱配比、煅烧温度、煅烧时间对合成4A分子筛的影响,结果表明粉煤灰与烧碱配比1.0:0.8,煅烧温度700℃,煅烧时间1 h有利于4A分子筛的合成.利用合成的4A分子筛对水体中六价铬进行了吸附研究,实验确定的最佳吸附条件为:分子筛投加量为0.3 g,溶液pH值为6～7,吸附时间为30 min,吸附温度为10～25℃.最佳吸附条件下分子筛对六价铬有较好的去除效果.吸附以物理吸附为主,符合Freundlich等温吸附式.同时对4A分子筛的再生性进行了研究,2次循环使用后其吸附能力仍能保持初次吸附能力的90.0％以上.     

Effects of Ageing and Seeding on the Formation of Zeolite Y from Coal Fly Ash

Zeolite Y was selectively synthesised by treating Tarong fly ash in a hydrothermal system. The effects of ageing and seeding on the formation of the resultant phases, crystallisation kinetics, and gel chemistry of Si and Al were investigated. Most of the Si and Al components in the Tarong fly ash could be effectively transformed into zeolite Y in the presence of seeds but not the mineral phase, like mullite. The maximum crystallinity of zeolite Y obtained was 72%. The cation-exchange capacity (CEC) of the fly ash was 0.08 mmol/g but increased to 3.2 mmol/g after a proper treatment. Crystallisation of zeolite materials from fly ash is quite different from that of normal zeolite synthesis because the sources of Si and Al are relatively less reactive and other cation ions (e.g., K⁺, Mg²⁺) are present in fly ash. Zeolite P is a competitive phase present in the resulting products that could be eliminated by employing the seeding method. NMR study demonstrated that ageing plays an important role in enhancing the hydrothermal condition during which both Si and Al in fly ash dissolved into a basic solution and reacted to form ring-like structures, and further to zeolite materials. Seeding can selectively induce the formation of zeolite Y and eliminate the processes of induction and nucleation.     

不同钙含量粉煤灰合成沸石对污水中磷的去除

进行了以不同钙含量的粉煤灰为原料合成的3种沸石对污水中磷去除的试验,探讨了表面交换性阳离子种类、投加量以及磷浓度对除磷的影响。结果表明：最佳投加量为8g／L,磷去除率可达到70％以上合成沸石除磷能力均高于粉煤灰,钙饱和处理又可明显进一步提高粉煤灰合成沸石的除磷效果。粉煤灰合成沸石钙含量越高,对磷的去除率越高。因此,采用高钙粉煤灰为原料合成沸石并进行钙饱和处理,可以获得除磷能力强的合成沸石材料。     

Artificial neural network (ANN) approach for modeling of Cr(VI) adsorption from aqueous solution by zeolite prepared from raw fly ash (ZFA)

In this present work, artificial neural networks (ANN) are applied for prediction of percentage adsorption efficiency for the removal of Cr(VI) ions from aqueous solution by zeolite (ZFA) prepared from raw fly ash (RFA). The off operational parameters such as initial pH, adsorbent dosage, contact time and temperature is studied to optimize the conditions for maximum removal of Cr(VI) ions. Three equations, i.e. Morris–Weber, Lagergren, and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich, Redlich–Peterson, Temkin, and D-R are subjected to sorption data to estimate sorption capacity. Thermodynamic parameters showed that the adsorption of Cr(VI) onto ZFA was feasible, spontaneous and endothermic. Artificial neural networks are effective in modeling and simulation of highly non-liner multivariable relationships. The comparison of the removal efficiencies of Cr(VI) using ANN model and experimental results showed that ANN model can estimate the behavior of the Cr(VI) removal process under different conditions.     

Kinetic,isotherm, and thermodynamic studies of Cr(VI) removal from aqueous solution using mesoporous silica materials prepared by fly ash

A series of mesoporous silica materials (FMD, FMT, and FMC were synthesized with DTAB, TTAB, and CTAB as template, respectively) have been prepared using fly ash as a silica resource. The as-synthesized materials were characterized by BET, XRF, FTIR, and XPS. The results confirmed the mesoporous structure and nitrogen content to act as potential adsorbents. The adsorption properties of these materials were also investigated by batch adsorption experiments. The FMC exhibited the highest effective removal of Cr(VI) (99%). The Cr(VI) adsorption process over FMC follows the pseudo-second-order kinetic and Langmuir model. Thermodynamic studies revealed that the Cr(VI) adsorption by FMC was spontaneous and endothermic. The study of the adsorption mechanism showed that the removal of Cr (VI) by FMC is through electrostatic attraction and chemical reduction. The coexisting ions experiment showed that FMC had high selectivity for Cr(VI). After three regeneration cycles, the Cr(VI) removal rate of FMC adsorbent still remained about 80%. Thus, this inexpensive adsorbent (FMC) is suitable for removing Cr(VI) from discharged industrial water.     

Using Coal Fly Ash and Wastewater for Microwave Synthesis of LTA Zeolite

The reuse of industrial wastes from a coal‐fired power plant and a plasma electrolytic oxidation process was attempted to realize a zero discharge. The batch composition was adjusted by adding sodium hydroxide and sodium aluminate. A single‐mode microwave oven equipped with reflux condenser was used for crystallization under atmospheric pressure. The synthesized samples were characterized by X‐ray diffraction, scanning electron microscopy, BET, thermogravimetric analysis, and cation‐exchange capacity (CEC) measurement. Analytical results indicated that Na‐A zeolite with a defined maximum crystallinity could be successfully synthesized by hydrothermal treatment of fly ash with wastewater. Due to the high CEC, the product can be applied for gas purification and soil remediation processes.     

粉煤灰合成沸石对Cr3＋的吸附性能研究

利用粉煤灰合成沸石吸附重金属Cr3＋,探讨吸附剂量、初始pH值以及反应温度对Cr3＋吸附效果的影响,同时进行吸附等温线和吸附动力学的数据模拟。结果表明：沸石投加量、初始pH值以及反应温度均对Cr3＋的去除效果影响显著。随着吸附剂投加量的不断增大,Cr3＋去除效果不断提高,饱和吸附量逐渐减小。初始pH值为4时沸石吸附Cr3＋的去除率为100％。反应温度的上升不利于沸石对Cr3＋吸附,沸石对Cr3＋的吸附效果随着反应温度的升高逐渐降低。沸石吸附Cr3＋的过程符合Freundlich吸附等温式;准二级反应动力学方程能较好描述沸石对Cr3＋的吸附行为。     

Low cost adsorbents obtained from ash for copper removal

We investigated the utilization of ash and modified ash as a low-cost adsorbent to remove copper ions from aqueous solutions such as wastewater. Batch experiments were conducted to determine the factors affecting adsorption of copper. The influence of pH, adsorbent dose, initial Cu²⁺ concentration, type of adsorbent and contact time on the adsorption capacity of Cu²⁺ from aqueous solution by the batch adsorption technique using ash and modified ash as a low-cost adsorbent were investigated. The optimum pH required for maximum adsorption was found to be 5. The results from the sorption process showed that the maximum adsorption rate was obtained at 300 mg/L when a different dosage of fly ash was added into the solution, and it can be concluded that decreasing the initial concentration of copper ion is beneficial to the adsorption capacity of the adsorbent. With the increase of pH value, the removal rate increased. When the pH was 5, the removal rate reached the maximum of over 99%. When initial copper content was 300 mg/L and the pH value was 5, the adsorption capacity of the zeolite Z 4 sample reached 27.904 mg/g. The main removal mechanisms were assumed to be the adsorption at the surface of the fly ash together with the precipitation from the solution. The adsorption equilibrium was achieved at pH 5 between 1 and 4 hours in function of type of adsorbent. A dose of 1: 25 g/mL of adsorbent was sufficient for the optimum removal of copper ions. For all synthesized adsorbents the predominant mechanism can be described by pseudo-second order kinetics.     

热改性粉煤灰对水中Cr(Ⅵ)的吸附性能

将粉煤灰与助熔剂混合进行高温焙烧制得热改性粉煤灰(TFA),对其进行表征并考察其对水中Cr(Ⅵ)的吸附性能。与原粉煤灰相比,TFA疏松多孔,比表面积显著提高。20℃下的吸附实验结果表明:当初始废水p H为6.7、Cr(Ⅵ)质量浓度为10.00 mg/L、TFA加入量为4.0 g/L、吸附时间为90 min时,Cr(Ⅵ)去除率可达98.98%,吸附量为2.39 mg/g。用拟二级动力学模型可较准确地描述TFA对Cr(Ⅵ)的吸附过程;吸附实验数据与采用Freundlich等温吸附模型得出的计算值吻合很好;降低温度有利于吸附反应的发生。     

粉煤灰合成沸石及其处理焦化废水A/O出水的试验

以NaOH作碱源,采用水热晶化法将粉煤灰转化成沸石.通过改变灼烧温度、NaOH浓度、液固比、晶化时间,考察合成条件对合成沸石阳离子交换容量的影响,并应用于焦化废水A/O出水的处理.结果表明:在灼烧温度为700℃、NaOH浓度为1 mol/L、液固比为5:1 mL/g、晶化时间为36 h条件下,合成沸石的阳离子交换容量最高为167 mmol/100g,是原粉煤灰的12.8倍,高于天然沸石的160 mmol/100 g;合成沸石处理焦化废水A/O出水的最佳条件是反应时间为1 h,沸石投加量为2g/100mL,pH值为6.0～9.0,此时NH3-N、COD去除率及出水质量浓度分别为46.7%、17.6%和62.6、197.8 mg/L,合成沸石对NH广N的吸附符合Freundlich吸附等温式.     

粉煤灰合成沸石除磷机理研究

利用粉煤灰合成沸石，考察了其对模拟废水中磷酸盐的去除效果，并着重研究了其除磷机理。结果表明，粉煤灰合成沸石有优良的除磷效果，其磷酸吸收系数几乎是原料粉煤灰的4倍，比原料粉煤灰有更高的吸附磷的潜力。粉煤灰合成沸石对磷酸盐的去除机理包括化学沉淀作用和吸附作用，且吸附作用随着平衡溶液的pH值的增大而减弱。粉煤灰合成沸石中沸石成分的骨架结构没有磷吸附作用，粉煤灰只能通过化学沉淀作用去除磷酸盐，粉煤灰合成沸石对磷的吸附作用主要来源于粉煤灰合成沸石过程中产生的无定型非晶体的中间体物质。     

粉煤灰碱熔-水热合成沸石用于水溶液中汞的吸附

汞被认为是危害最为严重的重金属之一。目前虽已有大量水处理技术可用于水中汞的去除,但由于成本较高等原因均未实现大面积的工业化应用。以工业固废粉煤灰为原料通过碱熔-水热法合成了沸石,可将其应用于水溶液中汞的吸附。结果表明:碱熔活化可以使得粉煤灰中稳定的莫来石、石英及非晶相矿物转变为钠铝硅酸盐、硅酸钠和钠霞石等矿物;这些矿物可溶于氢氧化钠溶液中,形成富含钠、铝、硅的碱性溶液;在适宜的水热条件下,通过调配铝硅比,可合成纯度较高的NaA型沸石;该法合成的粉煤灰基沸石可有效吸附水溶液中的Hg(II),去除率可达95%左右,吸附过程符合拟二级吸附动力学模型,反应速率同时受到内外扩散影响。     

Pb~(2+)在粉煤灰基方钠石上的吸附特性

以电厂粉煤灰为原料,在传统碱熔-水热法中引入脱硅工艺制备粉煤灰基方钠石,运用XRD和SEM对其进行物相和形貌表征,并通过研究不同因素条件下Pb~(2+)的吸附行为来考察Pb~(2+)在粉煤灰基方钠石上的吸附特性。结果表明:在碱度4.5 mol/L、晶化时间12 h、晶化温度100℃条件下能够合成出较高纯度的粉煤灰基方钠石;合成的方钠石相比原状粉煤灰吸附能力显著提高,对Pb~(2+)具有显著的去除效果,可作为重金属处置的高效吸附剂。     

煤粉炉和循环流化床锅炉飞灰特性对其汞吸附能力的影响

通过分析两台容量相近的循环流化床锅炉和煤粉锅炉飞灰样品的粒径分布、表面结构特性、未燃尽碳含量、反应性和汞含量，探究两种类型锅炉飞灰特性差异及其与飞灰汞吸附能力的关系。结果表明：循环流化床和煤粉锅炉尾端除尘设备排灰口飞灰汞的含量分别为1584.0 ng/g和503.7 ng/g，其原因与飞灰粒径、未燃尽碳含量和表面特性相关。对于循环流化床锅炉，飞灰中汞含量随其粒径和反应性温度的减小而增加，随未燃尽碳含量增加而增加，且与比表面积和吸附量呈正相关关系。对于煤粉锅炉，粒径为75～53 μm的飞灰对汞吸附能力较强，未燃尽碳含量明显小于循环流化床所产生飞灰的含量，飞灰比表面积随粒径变化不大，由此导致煤粉锅炉除尘设备排灰口所取样品对汞的吸附能力远低于循环流化床锅炉相对应位置飞灰对汞的吸附能力。