The Cement Solidification of Municipal Solid Waste Incineration Fly Ash

The chemical composition, the content and the leachability of heavy metals in municipal solid waste incineration （ MSWI） fly ash were tested and analyzed. It is shown that the leachability of Pb and Cr exceeds the leaching toxicity standard, and so the MSWI fly ash is considered as hazardous waste and must be solidifled. The effect of solidifying the MSWI fly ash by cement was studied, and it is indicated that the heavy metals can be well immobilized if the mass fraction of the fly ash is appropriate. The heavy metals were immobilized within cement hydration products through either physical fixation, substhtaion, deposition or adsorption mechanisms.

MSWI Fly Ash Based Novel Solidification/Stabilization Matrices for Heavy Metals

The possibilities of MSWI fly ash as a major constituent of novel solidification/stabilization matrices for secure landfill were investigated by mixing MSWI fly ash with rich aluminum components, which was added as bauxite cement or metakaolinite instead, to form Friedel and Ettringite phases with high fixing capacities for heavy metals. The physical properties, heavy metals-fixing capacity, mineral phases and its vibration bands in the novel matrices were characterized by compressive strength, TCLP（toxic characteristic leaching procedure）, XRD （x-ray diffraction） , DTG （derivative thermogravimetry）, and FTIR （fourier transform infrared spectroscopy）, respectively. The Tessier＇s five-step sequential extraction procedure was used to analyze the fractions of chemical speciation for Pb, Cd and Zn ions. The experimental results indicate that Friedel-Ettringite based novel solidification/stabilization matrices can incorporate Pb, Cd and Zn ions effectively by physical encapsulation and chemical fixation, and it exhibits a great potential in co-landfill treatment of MSWI fly ash with some heavy metals-bearing hazardous wastes.

Low-carbon stabilization/solidification of municipal solid waste incineration fly ash

Municipal solid waste incineration(MSWI)fly ash(FA)is classified as hazardous waste,which requires additional treatment before disposal or further utilization.Stabilization/solidification(S/S)is regarded as a low-cost and high-efficient method for MSWI FA treatment.“Low-carbon S/S”has captured extensive interest in recent years,which could treat hazardous wastes and enable resource recycling in a sustainable way.This article introduced the state-of-art low-carbon S/S strategies for MSWI FA treatment.The immobilization mechanisms of pollutants in various matrices were also discussed.Prospects were raised to foster the actualization of sustainable management of MSWI FA.

Effects of sulfur on variations in the chemical speciation of heavy metals from fly ash glass

This work designed a new CaO-Al_(2)O_(3)-SiO_(2)-SO3 glass for the immobilization of multiple heavy metals found in dechlorinated fly ash having high amounts of calcium and sulfur. Increasing the (CaO + SO3)/SiO_(2) mass ratio (M(CS/S)) from 0.28 to 0.85 was found to lower the proportions of Mn, Ni and Zn in an unstable state, while an M(CS/S) ratio of 0.51 gave the lowest proportions of unstable Cr and Pb. Decreasing the degree of polymerization of the glassy network increased the proportions of Mn, Cr, Ni, Pb and Zn in the carbonate bound state. The leaching out of metals in this state was the primary cause of degradation of Q^(3) structural units in the glassy network. The amount of Mn in the iron-manganese oxide bound state was increased by increasing the number of Q^(2) units in the silicate network. Decreasing the CaO/SiO_(2) mass ratio (M(C/S)) raised the proportions of Mn, Ni and Zn in the unstable state. An M(C/S) value of 0.43 lowered the proportions of unstable Cr and Pb. A principal components analysis determined that the leaching of toxic heavy metals from the glass was primarily related to the proportions of these metals in the unstable state while there were no evident correlations between leaching and the proportions in stable states.

Cleaner geopolymer prepared by co-activation of gasification coal fly ash and steel slag:durability properties and economic assessment

Geopolymer is a material with high early strength.However,the insufficient durability properties,such as long-term strength,acid-base resistance,freeze-thaw resistance,leaching toxicity,thermal stability,sulfate resistance and carbonation resistance,restrain its practical application.Herein,a longterm stable geopolymer composite with high final strength(ASK1)was synthesized from shell coal gasification fly ash(SFA)and steel slag(SS).Additionally,a geopolymer composite with high early strength(ASK2)was also synthesized for comparison.The results showed that ASK1 exhibited better performance on freezing-thawing resistance,carbonization resistance and heavy metals stabilization compared to the ASK2 at long-term curing.Raising the curing temperature could accelerate the unconfined compressive strength(UCS)development at initial curing ages of 3 to 7 d.Both ASK1 and ASK2 exhibited excellent acid-base and sulfate corrosion resistance.An increase for UCS was seen under KOH solution and MgSO_(4)solution corrosion for ASK1.All leaching concentrations of heavy metals out of the two geopolymers were below the standard threshold,even after 50 freezingthawing cycles.Both ASK1 and ASK2 geopolymer concrete exhibited higher sustainability and economic efficiency than Portland cement concrete.The result of this study not only provides a suitable way for the utilization of industrial solid waste in civil and environmental engineering,but also opens a new approach to improve the long-term stabilities of the geopolymers.

150 mm×150 mm小方坯结晶器内流场及凝固行为模拟

结晶器是整个连铸过程的核心环节,其内钢液流动、传热及初始凝固行为直接影响着铸坯质量,而拉速和过热度等工艺条件是影响结晶器冶金行为的关键参数。以某厂150 mm×150 mm小方坯结晶器为研究对象,建立耦合数学模型,分析过热度及拉速对结晶器内钢液流动与传热行为的影响。结果表明,当拉速由2.4 m/min增至3.0 m/min时,结晶器出口处铸坯角部温度与面部温度分别由960 K、1 050 K增至1 040 K、1 200 K;结晶器出口处坯壳厚度由11.21 mm降至8.71 mm,计算域出口处坯壳由16 mm降至14 mm;当过热度由15 K增至35 K时,铸坯表面和中心温度相应升高,幅度大致为5~10 K,结晶器出口坯壳厚度由10.45 mm降至9.01 mm,计算域出口处坯壳厚度由15 mm降至13 mm。研究结果可为冷镦钢小方坯连铸结晶器制定合理的工艺参数提供理论指导。

Production of glass-ceramics using Municipal solid waste incineration fly ash

Municipal solid waste incineration(MSWI) fly ash is a by-product from municipal waste incineration.According to incomplete statistics, each year more than one million tons MSWI fly ash was produced in China. Owing to high heavy elements content, widely used disposal methods of landfill are not suitable for MSWI fly ash treatment. In this study, by using MSWI fly ash as raw materials, glassceramics was synthesized for the solidification of heavy metals and waste recycle. Process parameters, including composition, heat treatment temperature and time, were studied and optimized. Under optimizing conditions, the product has good properties of density of 3.42 g·cm^(-3) and Vickers hardness of 6.91 GPa. Moreover, the leaching concentration of heavy metal elements meets allowable values of toxicity characteristic leaching procedure(TCLP).This study offers an alternative for MSWI fly ash recycle.

Review of harmless treatment of municipal solid waste incineration fly ash

Incineration is widely adopted in municipal solid waste management,which produces large amounts of municipal solid waste incineration(MSWI)fly ash.The harmless treatment of MSWI fly ash requires the appropriate disposal of heavy metals and dioxins that are enriched in fly ash.This review summarizes recently developed harmless disposal methods for MSWI fly ash including solidification/stabilization,thermal treatment,and separation/extraction.In addition,we discuss heavy metal and dioxin fixation,and the removal capacity of fly ash via solidification/stabilization(including cement solidification,chemical stabilization,hydrothermal processes,and mechano-chemical methods),thermal treatment(including sintering,fuel-burning,or electric melting/vitrification),and separation/extraction(including water-washing,chemical reagent leaching,biological leaching,electrodialysis separation,chemical reagent extraction,and nanomaterials extraction).The advantages and disadvantages of different harmless treatment methods are compared and future research prospects and suggestions are summarized.This review provides general guidelines for the harmless treatment of MSWI fly ash in the future.

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper.The stabilization of heavy metals such as Cd,Pb,Cu,and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors:additive quantity of cement and Na_(2)S,curing time,and pH of leaching liquor.The results showed that as more additives were used,less heavy metals were leached except for Pb,which is sensitive to pH of the leachate,and the worse effect was observed for Cd.The mass ratio of cement to fly ash=10% is the most appropriate parameter according to the national standard method.When the hydration of cement was basically finished,stabilization of heavy metals did not vary after curing for 1 d.The mixtures of cement and fly ash had excellent adaptability to environmental pH.The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.

Mechanism of MSWI Fly Ash Solidified by Microbe Cement

Microbe cement,a new type of gelling material,has attracted wide attention due to the increasing awareness of environmental protection.In this paper,the microbe cement in solidifying municipal solid waste incineration(MSWI)fly ash is investigated and the effect of the microbial induction method in solidifying MSWI fly ash is compared with the traditional chemical reaction strategy by characterizing the resulted calcite and the solidification productions with electronic universal testing machine,X-ray diffractometer(XRD),Fourier transform infrared spectrometer(FTIR),scanning electron microscope(SEM)and atomic absorption spectrometer.The results show that the MSWI fly ash solidified by microbe cement has the highest compressive strength while that of the chemical CaCO3 products is the lowest.The XRD results show that a new hydration gelling substance(Ca2SiO4·0.30H2O)is generated in the MSWI fly ash products.The FTIR results show that the frequency of Si-O bonds and C-O bonds in the products solidified by microbe cement has shifted,while there is no change occurred in the chemical CaCO3 products.The SEM results show that the microstructure of the products solidified by microbe cement is denser than that of chemical CaCO3 products.The test results of heavy metals show that the microbe cement could reduce the leaching concentration of heavy metals in MSWI fly ash.Ultimately,the leaching concentration of Pb meets the standard requirements,while that of Cd is still slightly higher than the standard requirement.

REMEDIATION OF POLLUTED SOILS BY UTILIZING HYDROTHERMALLY TREATED CALCAREOUS FLY ASHES

This paper investigates a treated fly ash to act as a synthetic zeolite to remediate soils polluted with heavy metals and metalloids （As, Pb, Cu, Zn, Fe, Cd and Mn）. Four types of such ＇zeolites＇ were synthesized by hydrothermal treatment of a calcareous fly ash derived from Greek lignite-fired power plants： two with excess of sodium hydroxide in a solid/liquid ratio of 50 g·L^-1, and two with excess of fly ash in a solid/liquid ratio of 100g·L^-1. Soil samples were obtained from a former mining site at Lavrion, Greece. Mobilization and transfer of metals to the retention agents was effected by using HCI aq 1M, with satisfactory results with respect to As, Pb, Cu, Mn and Cd. The great variety of metal complexes in soil was found to be of major importance for the effectiveness of the overall process. The final products were solidified either on their own, or by using additives such as lime and cement.