Effects of the type of sintering atmosphere on the chromium leachability of thermal-treated municipal solid waste incinerator fly ash

The sintering process offers an opportunity to combine detoxification and resource recovery for the treatment of municipal solid waste (MSW) incinerator fly ash. However, the chromium (Cr) in the sintered fly ash becomes more readily leachable with increasing sintering time and temperature, thus posing severe threats to the environment and human health when the sintered ash is recycled or reused. This study investigated the enhanced leachability of fly ash containing Cr, by heating the chromium (III) oxide (Cr2O3)-spiked fly ash to 800 degrees C in atmospheres containing air, nitrogen gas (N2), and 5% H2 + 95% N2, respectively. The results indicated that trivalent chromium was converted to its soluble hexavalent form during sintering in the air atmosphere; whereas sintering in a nitrogen atmosphere significantly reduced the leachability of Cr due to lack of oxygen (O2) to oxidize. The effects of the sintering temperature on the total chromium content and the leaching concentration in the toxicity characteristic leaching procedure (TCLP) extract are also discussed.     

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。     

碱激发粉煤灰对Cs~+的吸附行为

将粉煤灰进行碱激发改性,运用XRD和SEM技术对碱激发粉煤灰进行了表征,通过静态平衡吸附实验研究了碱激发粉煤灰对Cs+的吸附动力学和热力学特性,并对吸附前后的碱激发粉煤灰进行了FTIR分析。表征结果显示,碱激发处理后,粉煤灰的晶相发生了改变,且粉煤灰表面密实的硬壳层被破坏。实验结果表明:在初始Cs+质量浓度为200 mg/L、吸附温度为25℃、溶液pH为10、碱激发粉煤灰投加量为12.0 g/L的条件下,碱激发粉煤灰对Cs+的平衡吸附率可达80%以上,其吸附能力比碱激发前提高了3倍以上;吸附过程可用准二阶动力学方程来描述,并较好地符合Langmuir等温吸附模型;碱激发粉煤灰对Cs+的吸附是吸热过程,且能自发进行;该过程以物理吸附为主,并伴随化学吸附。     

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH-HCl); (4) oxidizable fraction (H2O2 + CH3COONH4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg(-1) (dry weight) in bottom ash and of 68.5 g kg(-1) (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg(-1) (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (approximately 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.     

REVEGETATION OF WASTE FLY ASH LAGOONS II. SEEDLING TRANSPLANTS AND PLANT NUTRITION

As an alternative or in addition to direct seeding, container-grown transplants provide a means of economically and rapidly revegetating waste fly ash lagoons through the expeditious establishment of vegetation islands. Survival and growth ofEnchylaena tomentosaandNitraria billardiereitransplants were largely dependent on the size of the root volume at transplanting. Growth response of both species in fly ash increased significantly as transplant container size increased from 110 ml to 800 ml. Fly ash incorporated into the potting mix during the containerised stage of growth generally reduced plant growth and survival following eventual transplantation. Gradual hardening ofEnchylaena tomentosaseedlings to increasing concentrations of fly ash in the potting mix (25 to 50 to 75% fly ash), however, improved immediate survival following transplantation, into pure ash. Nitrogen deficiency in Port Augusta fly ash was a major nutritional limitation to growth of these two species. Growth and dry matter production responded optimally to application of N fertiliser (NH₄NO₃) at 100–150 kg N ha⁻¹. Although bicarbonate-extractable P levels in fly ash were high (over 250 mg kg⁻¹), a response ofEnchylaena tomentosato supplementary P application [Ca(H₂PO₄)₂.H₂O] at 100–200 kg P ha⁻¹was observed.N. billardiereidid not respond to supplementary P, and it was suggested that fly ash P may be selectively available to plants on a species dependent basis. No growth responses to K application (KCl) at rates of up to 400 kg K ha⁻¹were found.     

Optimization of Eisenia fetida stocking density for the bioconversion of rock phosphate enriched cow dung–waste paper mixtures

Vermitechnology is gaining recognition as an environmental friendly waste management strategy. Its successful implementation requires that the key operational parameters like earthworm stocking density be established for each target waste/waste mixture. One target waste mixture in South Africa is waste paper mixed with cow dung and rock phosphate (RP) for P enrichment. This study sought to establish optimal Eisenia fetida stocking density for maximum P release and rapid bioconversion of RP enriched cow dung–paper waste mixtures. E. fetida stocking densities of 0, 7.5, 12.5, 17.5 and 22.5 g-worms kg^?1 dry weight of cow dung–waste paper mixtures were evaluated. The stocking density of 12.5 g-worms kg^?1 resulted in the highest earthworm growth rate and humification of the RP enriched waste mixture as reflected by a C:N ratio of <12 and a humic acid/fulvic acid ratio of >1.9 in final vermicomposts. A germination test revealed that the resultant vermicompost had no inhibitory effect on the germination of tomato, carrot, and radish. Extractable P increased with stocking density up to 22.5 g-worm kg^?1 feedstock suggesting that for maximum P release from RP enriched wastes a high stocking density should be considered.     

粉煤灰基吸附剂对模拟废水中Cd2+的吸附性能

以粉煤灰为原料、Na2CO3为助熔剂,采用盐熔融—水浴结晶法制备粉煤灰基吸附剂。探讨了吸附剂的最佳制备条件及其对模拟废水中Cd2+的最佳吸附条件、吸附动力学和吸附机理。实验结果表明:制备吸附剂的最佳工艺条件为m(粉煤灰)∶m(Na2CO3)为1∶2,焙烧温度为450℃;采用最佳制备工艺条件下制备的吸附剂(记作2-450℃-FA吸附剂),在初始Cd2+质量浓度为300 mg/L、初始溶液pH为7.7、振荡时间为120 min的条件下,对模拟废水中Cd2+的去除率为98.0%。2-450℃-FA吸附剂对Cd2+的吸附主要受颗粒内扩散控制,吸附过程可用准二级吸附动力学方程很好地描述。Ea为77.22 kJ/mol,吸附过程主要为化学吸附。     

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM-fly ash-lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM-fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.     

Concentrations of heavy metals in fly ash from a coal-fired power plant with respect to the new Finnish limit values

In Finland, the new limit values for heavy metals in fertilizers used in agriculture and in forestry came into force in March 2007, and for materials used as earth construction agents, in June 2006. From the utilization point of view, it was notable that the total heavy metal concentrations (Cd, Cu, Pb, Cr, Mo, Zn, As, Ni, Ba, and Hg) in fly ash from a coal-fired power plant were lower than those limit values. The concentrations of the easily soluble elements Ca, Mg, Na, P, and Zn in the fly ash were between 3.5 and 35 times higher than those found in the coarse mineral soils of Finland. Fly ash is a potential agent for soil remediation and for improving soil fertility. If inorganic materials and by-products are utilized in earthworks, the content of harmful compounds must be low and the harmful components must be tightly bound to the matrix. Therefore, a five-stage sequential extraction procedure was used to evaluate the extractability of different elements in fly ash into the following fractions: (1) the water-soluble fraction, (2) the exchangeable fraction (CH₃COOH), (3) the easily reduced fraction (NH₂OH-HCl), (4) the oxidizable fraction (H₂O₂ + CH₃COONH₄), and (5) the residual fraction (HF + HNO₃ + HCl).     

Semi-technical demonstration of the 3R process

The 3R Process: (1) recovers fly ash and HCl from the flue gases; (2) removes heavy metals from the fly ash by extraction with HCl; (3) and returns a pelletized fly ash to the incinerator. Recoveries of about 90% of the Cd, 65% of the Zn and 20% of the Pb and Cu have been achieved in pilot tests. Full scale experiments proved the thermal decomposition of PCDD/PCDF. The 3R products meet the Swiss elution requirements.     

Improvements of nano-SiO2 on sludge/fly ash mortar

Sewage sludge ash has been widely applied to cementitious materials. In this study, in order to determine effects of nano-SiO(2) additives on properties of sludge/fly ash mortar, different amounts of nano-SiO(2) were added to sludge/fly ash mortar specimens to investigate their physical properties and micro-structures. A water-binding ratio of 0.7 was assigned to the mix. Substitution amounts of 0%, 10%, 20%, and 30% of sludge/fly ash (1:1 ratio) were proposed. Moreover, 0%, 1%, 2%, and 3% of nano-SiO(2) was added to the mix. Tests, including SEM and compressive strength, were carried out on mortar specimens cured at 3, 7, and 28 days. Results showed that sludge/fly ash can make the crystals of cement hydration product finer. Moreover, crystals increased after nano-SiO(2) was added. Hence, nano-SiO(2) can improve the effects of sludge/fly ash on the hydration of mortar. Further, due to the low pozzolanic reaction active index of sludge ash, early compressive strengths of sludge/fly ash mortar were decreased. Yet, nano-SiO(2) could help produce hydration crystals, which implies that the addition of nano-SiO(2) to mortar can improve the influence of sludge/fly ash on the development of the early strength of the mortar.     

Coffee husk composting: An investigation of the process using molecular and non-molecular tools

Various parameters were measured during a 90-day composting process of coffee husk with cow dung (Pile 1), with fruit/vegetable wastes (Pile 2) and coffee husk alone (Pile 3). Samples were collected on days 0, 32 and 90 for chemical and microbiological analyses. C/N ratios of Piles 1 and 2 decreased significantly over the 90 days. The highest bacterial counts at the start of the process and highest actinobacterial counts at the end of the process (Piles 1 and 2) indicated microbial succession with concomitant production of compost relevant enzymes. Denaturing gradient gel electrophoresis of rDNA and COMPOCHIP microarray analysis indicated distinctive community shifts during the composting process, with day 0 samples clustering separately from the 32 and 90-day samples. This study, using a multi-parameter approach, has revealed differences in quality and species diversity of the three composts.     

Some limitations of sluiced fly ash as a liming material for acidic soils

Innovative methods are currently being sought to safely utilize and reduce the amount of sluiced fly ash stored in on-site facilities at thermal electric power facilities in Ontario, Canada. The objective of this study was to investigate the possibility of utilizing sluiced fly ash as a liming material on acidic soils. A greenhouse experiment was established to examine the influence of the ash on soil pH values and the yield and chemical composition of corn, soybeans, wheat and alfalfa grown on amended soil.The sluiced ash had an initial pH value of 9.1 (1:1 H₂O) and contained an equivalent CaCO₃ content of 11.5% (±0.2%) based on total content of Ca and Mg in the ash. Fly ash was applied at rates of up to 167 tonnes ha⁻¹ to samples of the surface horizon (0–15 cm) of an acidic clay textured soil found local to the power plant. Application of fly ash increased soil pH values but a high concentration of boron in the added ash limited plant growth. Results indicated that the sluiced ash could be used as a liming material at application rates of up to 110 tonnes ha⁻¹, on acidic, clay textured soils provided boron tolerant crops such as alfalfa were grown. Further research is required to establish the potential for leaching of boron to ground water and to determine the potential for plant uptake of other trace elements such as As and Se.     

Thermal and hydrometallurgical recovery methods of heavy metals from municipal solid waste fly ash

Heavy metals in fly ash from municipal solid waste incinerators are present in high concentrations. Therefore fly ash must be treated as a hazardous material. On the other hand, it may be a potential source of heavy metals. Zinc, lead, cadmium, and copper can be relatively easily removed during the thermal treatment of fly ash, e.g. in the form of chlorides. In return, wet extraction methods could provide promising results for these elements including chromium and nickel. The aim of this study was to investigate and compare thermal and hydrometallurgical treatment of municipal solid waste fly ash. Thermal treatment of fly ash was performed in a rotary reactor at temperatures between 950 and 1050 °C and in a muffle oven at temperatures from 500 to 1200 °C. The removal more than 90% was reached by easy volatile heavy metals such as cadmium and lead and also by copper, however at higher temperature in the muffle oven. The alkaline (sodium hydroxide) and acid (sulphuric acid) leaching of the fly ash was carried out while the influence of temperature, time, concentration, and liquid/solid ratio were investigated. The combination of alkaline-acidic leaching enhanced the removal of, namely, zinc, chromium and nickel.     

Investigation of MSWI fly ash melting characteristic by DSC-DTA

The melting process of MSWI (Municipal Solid Waste Incineration) fly ash has been studied by high-temperature DSC-DTA experiments. The experiments were performed at a temperature range of 20-1450 degrees C, and the considerable variables included atmosphere (O(2) and N(2)), heating rates (5 degrees C/min, 10 degrees C/min, 20 degrees C/min) and CaO addition. Three main transitions were observed during the melting process of fly ash: dehydration, polymorphic transition and fusion, occurring in the temperature range of 100-200 degrees C, 480-670 degrees C and 1101-1244 degrees C, respectively. The apparent heat capacity and heat requirement for melting of MSWI fly ash were obtained by DSC (Differential Scanning Calorimeter). A thermodynamic modeling to predict the heat requirements for melting process has been presented, and it agrees well with the experimental data. Finally, a zero-order kinetic model of fly ash melting transition was established. The apparent activation energy of MSWI fly ash melting transition was obtained.     

Role of aluminous component of fly ash on the durability of Portland cement-fly ash pastes in marine environment

The durability, of mixtures of two kinds of Spanish fly ashes from coal combustion (ASTM class F) with 0, 15 and 35% replacement of Portland cement by fly ash, in a simulated marine environment (Na(2)SO(4)+NaCl solution of equivalent concentration to that of sea water: 0.03 and 0.45 M for sulphate and chloride, respectively), has been studied for a period of 90 days. The resistance of the different mixtures to the attack was evaluated by means of the Koch-Steinegger test. The results showed that all the mixtures were resistant, in spite of the great amount of Al(2)O(3) content of the fly ash. The diffusion of SO(4)(2-), Na+ and Cl- ions through the pore solution activated the pozzolanic reactivity of the fly ashes causing the corresponding microstructure changes, which were characterized by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). As a result, the flexural strength of the mixtures increased, principally for the fly ash of a lower particle size and 35% of addition.     

粉煤灰-粉煤灰合成沸石对Cs~+的固化

以电厂废弃物粉煤灰为原料、采用碱熔-水热法制备了粉煤灰合成A型沸石(以下简称沸石),再以沸石对溶液中的Cs+进行分离富集,最后在碱激发剂的作用下以粉煤灰和吸附后的沸石制得地聚合物固化体。对固化体的性能进行了评价,并探讨了固化机理。实验结果表明:在吸附温度25℃、初始Cs+质量浓度100 mg/L、固液比10.0 g/L的条件下,沸石对的Cs+的吸附率达98%,比粉煤灰提高了2倍以上;沸石掺量为20%~30%(w)时,固化体的抗压强度符合GB 14569.1—2011要求,固化体中Cs+的42 d浸出率和累计浸出分数均远优于GB 14569.1—2011限值,表现出优异的抗浸出性能。     

Accelerated carbonation of municipal solid waste incineration fly ashes

As a result of the EU Landfill Directive, the disposal of municipal solid waste incineration (MSWI) fly ash is restricted to only a few landfill sites in the UK. Alternative options for the management of fly ash, such as sintering, vitrification or stabilization/solidification, are either costly or not fully developed. In this paper an accelerated carbonation step is investigated for use with fly ash. The carbonation reaction involving fly ash was found to be optimum at a water/solid ratio of 0.3 under ambient temperature conditions. The study of ash mineralogy showed the disappearance of lime/portlandite/calcium chloride hydroxide and the formation of calcite as carbonation proceeded. The leaching properties of carbonated ash were examined. Release of soluble salts, such as SO4, Cl, was reduced after carbonation, but is still higher than the landfill acceptance limits for hazardous waste. It was also found that carbonation had a significant influence on lead leachability. The lead release from carbonated ash, with the exception of one of the fly ashes studied, was reduced by 2-3 orders of magnitude.     

Effects of fly ash addition on physical properties of porous clay-fly ash composites via polymeric replica technique

The porous composites of clay and fly ash have the potential to be used in many fields, such as catalyst support and gas adsorbents. In this study, various ratios of fly ash (1–2) with different percentage of suspension (50–70 wt%) were applied to produce porous clay-fly ash composites via polymeric replica technique. Fabrication process starts by mixing clay and fly ash in distilled water to form slurry. The process is followed by fully immersing polymer sponge in slurry. The excess slurry is then removed through squeezing. Finally, the sponge coated with slurry is sintered at 500 and 1250 °C for 1 h. It is found that the compressive strength of porous composites improves significantly (0.178–1.28 MPa) when the amount of clay-fly ash suspension mixture (50–70 wt%) increases. The compressive strength of porous composites is mainly attributed to the mullite, quartz and amorphous phase formations. These results are supported by X-ray diffraction analysis. On the other hand, increase in the amount of suspension reduces the apparent density (from 2.44 to 2.32 g/cm³) and porosity (from 97 to 85 %). The reduction in apparent density is believed to be caused by the presence of high fly ash content in porous composites. The melted fly ash cenospheres have closed the internal pores and increased density of samples. Higher suspension level not only reduces porosity, but also increases close pores of the porous composites. The results are justified through the observation from the structures of porous clay-fly ash composites.