Reclamation and revegetation of fly ash disposal sites - Challenges and research needs

Coal-fired power generation is a principal energy source throughout the world. Approximately, 70-75% of coal combustion residues are fly ash and its utilization worldwide is only slightly above 30%. The remainder is disposed of in landfills and fly ash basins. It is desirable to revegetate these sites for aesthetic purposes, to stabilize the surface ash against wind and water erosion and to reduce the quantity of water leaching through the deposit. Limitations to plant establishment and growth in fly ash can include a high pH (and consequent deficiencies of Fe, Mn, Cu, Zn and P), high soluble salts, toxic levels of elements such as B, pozzalanic properties of ash resulting in cemented/compacted layers and lack of microbial activity. An integrated organic/biotechnological approach to revegetation seems appropriate and should be investigated further. This would include incorporation of organic matter into the surface layer of ash, mycorrhizal inoculation of establishing vegetation and use of inoculated legumes to add N. Leaching losses from ash disposal sites are likely to be site-specific but a sparse number of studies have revealed enriched concentrations of elements such as Ca, Fe, Cd, Pb, and Sb in surrounding groundwater. This aspect deserves further study particularly in the longer-term. In addition, during weathering of the ash and deposition of organic matter during plant growth, a soil will form with properties vastly different to that of the parent ash. In turn, this will influence the effect that the disposal site has on the surrounding environment. Nevertheless, the effects of ash weathering and organic matter accumulation over time on the chemical, physical and biological properties of the developing ash-derived soil are not well understood and require further study.     

粉煤灰处理染料废水的研究

利用粉煤灰吸附性能较好、来源广泛及价格低廉等特点,对染料废水进行吸附试验研究。结果表明,粉煤灰的活化方式、粒度及用量对染料废水吸附性能有影响。160—200目30%硫酸活化粉煤灰吸附能力最强,且对染料废水的吸附过程符合Langmuir吸附等温曲线,最大吸附量为667mg/g。     

煤粉锅炉飞灰份额影响因素分析

通过对10个电厂22台机组36组实测数据的分析,论述了燃煤挥发分、灰分及过剩空气系数对煤粉锅炉飞灰份额的影响趋势。     

利用活化粉煤灰处理造纸废水的研究

通过正交试验,对粉煤灰处理造纸废水的影响因素进行了研究。研究结果表明：对粉煤灰进行活化,能增加其对造纸废水COD的去除效果;最佳的试验设计方案为：粉煤灰经40％硫酸活化、粒度160—200目、投加量为30g／100ml;影响COD去除率的大小顺序为：投加量影响最大,粒度次之,活化方式影响最小。     

垃圾焚烧飞灰处理处置研究进展

针对作为危险废物的垃圾焚烧飞灰,介绍了近年来国内外对其进行处理处置的研究情况.飞灰的固化/稳定化处理主要从水泥(沥青)固化、熔融固化及化学药剂固化几方面进行论述,飞灰中重金属的提取主要从酸碱浸提、生物浸提、螯合剂浸提及电渗析法提取几方面进行论述.     

垃圾焚烧飞灰处置与资源化利用研究进展

随着生活垃圾焚烧处理方式的不断推广,焚烧飞灰的产生量也不断增加。按照我国固体废物分类方法,焚烧飞灰属于危险废物,必须进一步处置才能进入填埋场或资源化利用。本文分析了飞灰物理化学特性,论述了常规处置技术（水泥固化、化学药剂稳定化、酸溶剂提取和熔融固化等）存在的问题。将原始飞灰直接应用于水泥、混凝土或路基材料,飞灰中高含量的重金属和盐类会产生新的环境问题。飞灰水洗可以高效去除其中的可溶性盐类,水洗飞灰在焙烧后重金属的浸出浓度远低于原始飞灰烧结后的相应浓度,飞灰水洗-焙烧技术具有很好的应用前景。     

Effect of unburned carbon on lead, zinc, and copper recovery from molten fly ash by chloride-induced volatilization

The present work focuses on investigation of the effective recovery of heavy metals from molten fly ash by applying chloride-induced volatilization. In particular, the effect of unburned carbon on the chloride-induced volatilization of lead, zinc, and copper from model and real molten fly ashes was investigated in the temperature range 873–1173 K under a N₂ atmosphere. As a result, almost 100% of lead and a significant proportion of zinc were volatilized from the real molten fly ash samples at 1173 K. In contrast, for the model fly ash, volatilization ratios of lead and zinc at 1173 K were only 85% and 25%, respectively. Further, the results of X-ray diffraction analysis suggested that PbO in molten fly ash was converted either to Pb₂OCl₂ or Pb by respective chlorination and reduction reactions. Meanwhile ZnO and CuO in the molten fly ash were reduced to Zn and Cu by reaction with unburned carbon. Subsequently, Pb, Zn, and Pb₂OCl₂ were volatilized, but Cu remained in the solid residue. Finally, the volatilization ratio of zinc increased with the addition of carbon, and more than 98% of zinc was volatilized at 1173 K from a fly ash with a carbon content of 20%.     

Leaching behavior of heavy metals from municipal solid waste incineration bottom ash and its geochemical modeling

With the increase in the number of municipal solid waste incineration (MSWI) plants constructed in China recently, great attention has been paid to the heavy metal leaching toxicity of MSWI residues. In this study, the effects of various parameters, including extractant, leaching time, liquid-to-solid ratio, leachate pH, and heavy metal content, on the release properties of Cd, Cr, Cu, Ni, Pb, and Zn from MSWI bottom ash were investigated. Partial least-squares analysis was employed to highlight the interrelationships between the factors and response variables. Both experimental research and geochemical modeling using Visual MINTEQ software were conducted to study the pH-dependent leaching behavior of these metals in fresh and weathered bottom ash, considering precipitation/dissolution and surface complexation reactions (adsorption by hydrous ferric oxide and amorphous aluminum oxide/hydroxide). The results showed that leachate pH was the predominant factor influencing heavy metal leachability. The leaching of Cu, Pb, and Zn was mainly controlled by precipitation/dissolution reactions, whereas surface complexation had some effect on the leaching of Cr, Cd, and Ni for certain pH ranges. The modeling results aggreed well with the experimental results. Part of this work was presented at the Fourth International Conference on Combustion, Incineration/Pyrolysis and Emission Control (i-CIPEC)     

Adsorption of basic dye from aqueous solution onto fly ash

The fly ash treated by H₂SO₄ was used as a low-cost adsorbent for the removal of a typical dye, methylene blue, from aqueous solution. An increase in the specific surface area and dye-adsorption capacity was observed after the acid treatment. The adsorption isotherm and kinetics of the treated fly ash were studied. The experimental results were fitted using Langmuir and Freundlich isotherms. It shows that the Freundlich isotherm is better in describing the adsorption process. Two kinetic models, pseudo-first order and pseudo-second order, were employed to analyze the kinetic data. It was found that the pseudo-second-order model is the better choice to describe the adsorption behavior. The thermodynamic study reveals that the enthalpy (ΔH⁰) value is positive (5.63 kJ/mol), suggesting an endothermic nature of the adsorption.     

碱熔融法合成NaA和NaX型粉煤灰沸石的品质表征

以粉煤灰为原料采用碱熔融法合成了2种单一沸石矿物种的NaA和NaX型沸石,并对产物的结构、性能和应用指标进行了详细表征.经x射线衍射和IR光谱分析,表明合成产物是无杂晶生成的NaA和NaX型沸石相;在扫描电镜观察下,产物分别具有NaA和NaX型沸石的立方体和八面体晶体骨架结构.DTA分析表明了合成产物中沸石水的存在,且产物热稳定性较好.通过对比,粉煤灰合成的NaA和NaX型沸石的比表面积达到了相应商品沸石的66.9%和83.6%;孔容为41.1%和70.2%;阳离子交换容量(CEC,cation exchange capacity)为82.93%和84.31%.通过比较化学组成表明,大规模应用合成产物不会对环境造成危害.