Synthesis of mesoporous silica materials from municipal solid waste incinerator bottom ash

Incinerator bottom ash contains a large amount of silica and can hence be used as a silica source for the synthesis of mesoporous silica materials. In this study, the conditions for alkaline fusion to extract silica from incinerator bottom ash were investigated, and the resulting supernatant solution was used as the silica source for synthesizing mesoporous silica materials. The physical and chemical characteristics of the mesoporous silica materials were analyzed using BET, XRD, FTIR, SEM, and solid-state NMR. The results indicated that the BET surface area and pore size distribution of the synthesized silica materials were 992 m²/g and 2–3.8 nm, respectively. The XRD patterns showed that the synthesized materials exhibited a hexagonal pore structure with a smaller order. The NMR spectra of the synthesized materials exhibited three peaks, corresponding to Q² [Si(OSi)₂(OH)₂], Q³ [Si(OSi)₃(OH)], and Q⁴ [Si(OSi)₄]. The FTIR spectra confirmed the existence of a surface hydroxyl group and the occurrence of symmetric Si–O stretching. Thus, mesoporous silica was successfully synthesized from incinerator bottom ash. Finally, the effectiveness of the synthesized silica in removing heavy metals (Pb²⁺, Cu²⁺, Cd²⁺, and Cr²⁺) from aqueous solutions was also determined. The results showed that the silica materials synthesized from incinerator bottom ash have potential for use as an adsorbent for the removal of heavy metals from aqueous solutions.     

Degradation of Al/SiCp composites produced with rice-hull ash and aluminum cans

The use of recycling aluminum from beverage containers and rice-hull ash (RHA) offers to be an attractive alternative for the economic production of Al/SiCp composites. However, corrosion phenomena in the composites represent technological barriers yet to be resolved before they can be exploited to their full potential. A simple methodology involving characterization by XRD, SEM, EDX, FTIR and ICP was designed in order to investigate the causes of the rapid degradation in a humid environment of Al/SiCp composites produced with RHA and aluminum cans. Results reveal that the use of RHA was beneficial to avoid degradation through the formation and subsequent hydration of the Al4C3 phase. However with condensed moisture acting as an electrolyte, localized corrosion took place with aggressive damage manifested by the disintegration of the composite into a powdery mixture. The relevant corrosion mechanism was mainly attributed to microgalvanic coupling between the Mg2Si intermetallic compound and the matrix (although other phases such as SiC, Si, MgAl2O4 could also work as microcathodes).     

Stabilization of heavy metals in MSWI fly ash using silica fume

The objective of this work was to investigate the feasibility and effectiveness of silica fume on stabilizing heavy metals in municipal solid waste incineration (MSWI) fly ash. In addition to compressive strength measurements, hydrated pastes were characterized by X-ray diffraction (XRD), thermal-analyses (DTA/TG), and MAS NMR (²⁷Al and ²⁹Si) techniques. It was found that silica fume additions could effectively reduce the leaching of toxic heavy metals. At the addition of 20% silica fume, leaching concentrations for Cu, Pb and Zn of the hydrated paste cured for 7 days decreased from 0.32 mg/L to 0.05 mg/L, 40.99 mg/L to 4.40 mg/L, and 6.96 mg/L to 0.21 mg/L compared with the MSWI fly ash. After curing for 135 days, Cd and Pb in the leachates were not detected, while Cu and Zn concentrations decreased to 0.02 mg/L and 0.03 mg/L. The speciation of Pb and Cd by the modified version of the European Community Bureau of Reference (BCR) extractions showed that these metals converted into more stable state in hydrated pastes of MSWI fly ash in the presence of silica fume. Although exchangeable and weak-acid soluble fractions of Cu and Zn increased with hydration time, silica fume addition of 10% can satisfy the requirement of detoxification for heavy metals investigated in terms of the identification standard of hazardous waste of China.     

Utilization of amorphous rice husk ash for the synthesis of ZSM-5 zeolite under low temperature

The present study deals with the production and characterization of ZSM-5 zeolite under low temperature using amorphous rice husk ash as an alternative cheap silica source. Rice husk was combusted at various temperatures for the production of amorphous silica. The resulted amorphous silica ash was then utilized without any other treatment as a starting material for the synthesis of ZSM-5 zeolite using low temperature and under atmospheric pressure. For comparison, the high-temperature synthetic approach, the hydrothermal treatment under high temperature and autogenous pressure with the autoclave process, was also applied for the synthesis of ZSM-5 zeolite. The low-temperature method led successfully to the synthesis of highly siliceous zeolite of type ZSM-5. The produced materials were characterized using a variety of analytical techniques, including X-ray diffraction, Fourier transformation infrared spectroscopy, thermogravimetry–differential thermogravimetry analyses, scanning electron microscopy, electron dispersion X-ray analysis and nitrogen porosimetry. The results show that the utilization of an industrial by-product in abundance as a starting material can lead through a simple inexpensive technique to the synthesis of a high value added microporous material with many potential applications.     

Synthesis of zeolite from Italian coal fly ash: Differences in crystallization temperature using seawater instead of distilled water

In this study Italian coal fly ash was converted into several types of zeolite in laboratory experiments with temperatures of crystallization ranging from 35 up to 90 °C. Distilled and seawater were used during the hydrothermal synthesis process in separate experiments, after a pre-treatment fusion with NaOH.The results indicate that zeolites could be formed from different kind of Italian coal fly ash at low temperature of crystallization using both distilled and seawater. SEM data and the powder patterns of X-ray diffraction analysis show that faujasite, zeolite ZK-5 and sodalite were synthesized when using both distilled and seawater; zeolite A crystallized only using distilled water. In particular the experiments indicate that the synthesis of zeolite X and zeolite ZK-5 takes place at lower temperatures when using seawater (35 and 45 °C, respectively). The formation of sodalite is always competitive with zeolite X which shows a metastable behaviour at higher temperatures (70–90 °C).The chemical composition of the fly ash source could be responsible of the differences on the starting time of synthesized zeolite with distilled water, in any case our data show that the formation of specific zeolites takes place always at lower temperatures when using seawater.     

碱熔融—微波晶化法合成粉煤灰沸石及其对Cd2+的吸附

以粉煤灰为主要原料，采用碱熔融—微波晶化法合成粉煤灰沸石。采用XRD，SEM，TEM等技术表征了粉煤灰沸石的微观结构，并对其吸附Cd²⁺的性能进行了研究。表征结果显示，粉煤灰沸石主要由X型沸石、P型沸石和铝组成，粉煤灰沸石中有排列规则、呈蜂窝状的孔穴和孔道存在，其孔穴和孔道大小分布均匀，致密。粉煤灰沸石的比表面积为108.49 m²/g，平均孔径为3.779 nm，孔体积为0.221 mL/g。实验结果表明，在溶液pH为7、吸附时间30 min的最佳吸附条件下，Cd²⁺去除率均大于94%。粉煤灰沸石对Cd²⁺的吸附可很好地用二级动力学方程进行拟合，相关系数为0.999 99。可用Langmuir等温吸附模型描述该吸附过程，该吸附过程是单分子层吸附，主要是化学吸附，粉煤灰沸石对Cd²⁺的饱和吸附量为49.261 mg/g。     

Fabrication of bulk materials with zeolite from coal fly ash

After packing a compact of coal fly ash mixed with 3.5?M (mol/L) sodium hydroxide solution into a cylindrical plastic mold at 80?°C and 50?% relative humidity for 24?h, the plastic mold was released and the compact was immersed in 3.5?M sodium hydroxide solution at 80?°C for 48?h. When the resultant compact was removed from the solution and cured at 80?°C and 50?% relative humidity for 7?days, a bulk material with zeolite was formed. The strength of the resultant bulk material was a result of the formation of geopolymer (alkali-activated cement). The specific surface area and the compressive strength of the bulk body sample were 21.4?m²/g and 29.0?MPa, respectively. According to a quantitative analysis conducted using the X-ray diffraction (XRD) technique, the content of the formed Na-P type zeolite was estimated to be approximately 28.2?% in mass ratio. The pore size of the resultant bulk materials with zeolite ranges from sub-nanometer to several tens of nanometers, so the resultant bulk material with zeolite exhibited excellent water vapor retention characteristics.     

Pyrolysis of low-density polyethylene using synthetic catalysts produced from fly ash

Catalytic pyrolysis of low-density polyethylene (LDPE) was investigated using various fly ash-derived silica–alumina catalysts (FSAs). FSAs were prepared by a simple activation method that basically includes NaOH treatment of fly ash by a fusion method, followed by an aging process. A series of LDPE pyrolysis experiments was conducted and the catalytic performance of FSAs was assessed in terms of the degradation temperature and the simulated boiling point distribution of the liquid products. The effects of synthesis conditions such as NaOH/fly ash weight ratio and aging time were examined by X-ray diffractometer (XRD), Brunauer-Emmett-Teller (BET) surface area analyzer, and scanning electron microscope to clarify the controlling factors affecting the catalytic activity. To obtain catalyst with high activity, it is necessary to produce sufficient silica and alumina species that can be easily co-precipitated into solid acid catalyst by destruction of the fly ash structure and to optimize the activation time for catalyst synthesis to prevent the transformation into inactive phases. The catalytic performance of FSA obtained from optimal conditions was equivalent to that of commercial catalysts, demonstrating the effectiveness of the catalyst.     

无黏结剂ZSM-5分子筛的制备及其对甲苯的吸附性能

以硅溶胶为黏结剂，将粗孔硅胶、聚乙二醇、拟薄水铝石、ZSM-5晶种导向剂捏条成型，采用干胶转化法制备得到了无黏结剂ZSM-5分子筛。XRD和SEM等表征方法的结果显示，采用干胶转化法制备得到的ZSM-5分子筛的相对结晶度较高，具有200nm左右的小晶粒构成的自支撑结构。采用无黏结剂ZSM-5分子筛吸附剂进行甲苯吸附-脱附实验，该吸附剂表现出良好的吸附性能，对甲苯的脱附性能优于活性炭。     

钛硅分子筛催化双氧水氧化水中间甲酚

探索催化双氧水氧化去除间甲酚对开发炼油厂碱渣废水处理新技术意义重大。采用钛硅分子筛催化双氧水氧化水中间甲酚,考察了反应时间、反应温度、双氧水加入量、催化剂加入量和初始溶液pH对间甲酚去除率的影响。实验结果表明：钛硅分子筛对双氧水氧化间甲酚具有显著的催化作用;在反应时间为90 min、反应温度为80 ℃、n（H₂O₂）∶n（间甲酚）为4、催化剂加入量为1.5 g/L、初始溶液pH为1.0~11.0的条件下,间甲酚去除率约为94%,间甲酚溶液的BOD₅/COD从氧化前的0.26提高到氧化后的0.38,可生化性显著提高。     

粉煤灰的改性及对刚果红的吸附

分别采用沸水浸泡、酸浸、碱浸和加热的方法对粉煤灰进行改性处理，利用FTIR仪和XRD仪对改性粉煤灰的成分和官能团进行了分析，并利用改性粉煤灰对模拟刚果红废水进行脱色。实验结果表明：碱改性粉煤灰中含有大量官能团，以及NaPl型沸石类物质，能够明显提高粉煤灰对刚果红的吸附性能；与活性炭相比，碱改性粉煤灰具有更高的性价比；在初始刚果红质量浓度为20mg/L、碱改性粉煤灰加入量为50g/L的条件下，废水的脱色率可达87.52%；碱改性粉煤灰对刚果红的吸附过程遵循二级反应动力学，较好地符合Langmuir等温式和Freundlich等温式。     

Performance of industrial by-products in controlled low-strength materials (CLSM)

As the construction industry continues to recognise the importance of sustainable development, technologies such as controlled low-strength material (CLSM) have come to the forefront as viable means of safely and efficiently using by-product and waste materials in infrastructure applications. CLSM, also known as flowable fill, can be defined as an engineered backfill material containing fine aggregates, Portland cement, water and a by-product material. CLSM can provide an economically and technically feasible alternative to conventional fill materials because of potential cost savings related to its unique and often superior technical properties. In this present experimental study, three industrial by-products, namely fly ash (FA), rice husk ash (RHA) and quarry dust (QD), were used as constituent materials in CLSM. Mixture proportions were developed for CLSM containing these industrial by-products and were tested in the laboratory for various properties, such as flowability, unconfined compressive strength (UCS), stress-strain behaviour, density, water absorption and volume changes. Comparison between the two pozzolanic materials, namely FA and RHA, for their potential to produce an effective CLSM has been made. It can be observed from the results that by-product materials such as FA, RHA and QD can be successfully used in CLSM. This successful utilization of by-product materials is important to sustainable development and is the focus of this research.     

粉煤灰两步水热法制备人工沸石

以粉煤灰为原料，采用两步水热法制备人工沸石。SEM、XRD、X射线荧光光谱分析结果表明:制得的人工沸石纯度较高，主要为Na-A型沸石和少量13X型沸石，主要化学成分为SiO2和Al2O3。说明采用两步法制备人工沸石克服了传统水热法杂质含量高的缺陷。采用人工沸石处理初始Mn2+质量浓度为50.00mg/L的模拟含锰废水，吸附125min后，Mn2+去除率达98.19%，模拟废水中剩余Mn2+质量浓度为0.90mg/L。     

Hydrothermal solidification of municipal solid waste incineration bottom ash with slag addition

Hydrothermal solidification of municipal solid waste incineration (MSWI) bottom ash has been carried out under saturated steam pressure (1.56 MPa) at 200 °C for up to 24 h by mixing quartz, slaked lime and water-cooled blast furnace slag (WBFS). The strength enhancement for the WBFS addition was best. The strength development was shown to be due mainly to tobermorite formation, and the tobermorite formation densified matrix, thus promoting the strength development. WBFS seemed to have a higher reactivity than the quartz during the initial hydrothermal process, which provided more silica available to harden the solidified specimens. However, a longer curing time (24 h) was favorable to the quartz dissolution for tobermorite formation, which in turn, enhanced the strength for quartz addition. Curing time affected the crystal morphology evolution, and the stubby plate of tobermorite seemed to result in a high strength enhancement in this study. Laboratory leaching tests were conducted to determine the amount of heavy metals dissolved from the final solidified specimens, and the leaching results showed that after hydrothermal processing the heavy metals dissolved from the solidified specimens were reduced effectively. As such, the hydrothermal processing may have a high potential for recycling/reusing MSWI ash on a large scale.     

粉煤灰及其制备沸石对高浓度氨氮的去除比较

以粉煤灰为原料,采用改进的水热合成法制备了粉煤灰沸石,并将粉煤灰和粉煤灰沸石用于高浓度氨氮的吸附去除。实验结果表明:在粉煤灰和粉煤灰沸石的投加量分别为0.10 g/m L和0.04 g/m L、反应体系p H为5~7、初始氨氮质量浓度为500 mg/L的条件下,分别吸附660 min和60 min,粉煤灰和粉煤灰沸石对氨氮的去除率分别约为20.1%和50.7%左右,粉煤灰沸石对高浓度氨氮的去除效果明显优于粉煤灰;粉煤灰和粉煤灰沸石对氨氮的吸附动力学行为符合准二级动力学方程;Langmuir和Freundlich等温吸附模型能较好地描述粉煤灰对氨氮的等温吸附过程,而粉煤灰沸石对氨氮的等温吸附过程则更适宜用线性模型和Freundlich模型描述。     

Solidification and recycling of incinerator bottom ash through the addition of colloidal silica (SiO2) solution

The possibility of using incinerator bottom ash as a substitute for natural aggregates was investigated. Rough, porous surface of bottom ash, which diminishes the strength of solidified products, was improved by colloidal silica solution. As a result, a significant increase of mechanical strength was accomplished by a slight amount of silica (<1 wt% to total). Moreover, pozzolanic reaction was induced in initial cement hydration due to the nano-particle size of about 20 nm in colloidal silica solution. Cylindrical specimens and bricks were prepared from bottom ash added to a colloidal silica (SiO2) solution and cement, and then their compressive strengths were evaluated. Cylindrical specimens showed an increase of approximately 60% in compressive strength when colloidal solution containing 4 wt% silica particles was sprayed onto the bottom ash. The strength of bricks containing colloidal silica was in excess of 20 MPa, which meets the requirement of construction materials. Results of leaching tests based on Toxicity Characteristic Leaching Procedure (TCLP) proved that the solidified bottom ash possessed good chemical stability.     

Utilization of gold tailings as an additive in Portland cement.

Mine tailings are formed as an industrial waste during coal and ore mining and processing. In the investigated process, following the extraction of gold from the ore, the remaining tailings are subjected to a two-stage chemical treatment in order to destroy the free cyanide and to stabilize and coagulate heavy metals prior to discharge into the tailings pond. The aim of this study was the investigation of the feasibility of utilization of the tailings as an additive material in Portland cement production. For this purpose, the effects of the tailings on the compressive strength properties of the ordinary Portland cement were investigated. Chemical and physical properties, mineralogical composition, particle size distribution and microstructure of the tailings were determined by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), particle size analyzer (Mastersizer) and scanning electron microscope (SEM). Following the characterization of the tailings, cement mortars were prepared by intergrinding Portland cement with dried tailings. Composition of the cement clinkers were adjusted to contain 5, 15, 25% (wt/wt) dried tailings and also silica fume and fly ash samples (C and F type) were added to clinker in different ratios. The mortars produced with different amounts of tailings, silica fume, fly ashes and also mixtures of them were tested for compressive strength values after 2, 7, 28 and 56 days according to the European Standard (EN 196-1). The results indicated that gold tailings up to 25% in clinker could be beneficially used as an additive in Portland cement production. It is suggested that the gold tailings used in the cement are blended with silica fume and C-type fly ash to obtain higher compressive strength values.     

Modelling of long-term dynamic leaching tests applied to solidified/stabilised waste

The paper aims at simulating the closed-system dynamic leaching of a cement-based monolith containing lead with the numerical reactive transport code HYTEC in a 3D-cylindrical geometry. The model considers, simultaneously, the chemical evolution of pore water, the progression of mineralogical alteration fronts, and the concomitant release of elements from the S/S waste. In good agreement with the experiment, element releases were found to be mainly controlled by either diffusion (Na, K, and, to a lesser extent, Cl), by surface dissolution (Ca, Si) or by a mixed evolution (Pb, SO4). All of the calculated mineralogical transformations take place in a thin layer beyond the monolith surface. Consequently, modelling of Ca, Si and SO4 releases was quite sensitive to the node size of the simulation grid and was improved by taking into account the increase of porosity and effective diffusion coefficient due to mineral dissolution in the leached layer. In agreement with experimental results, the deepest front corresponds under closed-system conditions to portlandite dissolution and calcium silicate hydrates CSH 1.8 transformation into CSH of lower Ca/Si ratio. A second, distinct and intermediate, front is made by ettringite dissolution. The network of CSH is globally preserved in the leached layer, complete dissolution occurring over a very small thickness only. Finally, hydrotalcite precipitation in the leached layer is expected by modelling due to pH drop.     

Effect of the milling solution on lead stabilization in municipal solid waste incinerator fly ash during the milling processes

The wet milling process had been found to effectively stabilize lead in fly ash. This study adopts this method and looks at the effect of different milling solutions to improve the efficiency of lead stabilization. Different milling solutions (water, phosphoric acid and ethanol) and different milling times (1, 24, 48 and 96 h) were selected as parameters. Since lead oxide can be identified by XRD in this experiment’s samples, 5% lead oxide was added to the extracted mixed fly ash to make instrumental analysis easier. The experimental results indicate that the effect of stabilization of lead after milling could exceed 96%. During milling with water, considerable lead leached into the water in the initial stage (1 h) of the process, but a stable level was reached as the milling time increased. After milling with ethanol and 0.2 M phosphoric acids, the efficiency could exceed 93% after 1 h of milling time. The results of the sequential extraction procedure (SEP) results show that the residual fraction could be increased from 8.93% to 56.16% when a 0.2 M phosphoric acid solution was used. Clearly the choice of an appropriate milling solution can enhance lead stabilization in the fly ash.     

粉煤灰制聚合氯化铝铁和白碳黑新工艺

采用粉煤灰制备聚合氯化铝铁和白碳黑.该法共分一次酸浸、碱溶、焙烧、二次酸浸4个阶段.实验确定的最佳工艺条件为:一次酸浸阶段酸溶温度100℃,碱溶阶段m(氢氧化钠):m(活化高硅渣)=0.6,二次酸浸阶段m(碳酸钠):m(灰渣A)=0.8、盐酸质量分数20%.在此条件下Fe~(3+)和Al~(3+)的总浸出率分别为96.54%和86.67%.主要产品聚合氯化铝铁的质量符合GB15892-2003<水处理剂聚氯化铝>的标准;产品白碳黑的质量符合GBl0517-89<沉淀二氧化硅>的标准.