Mechanism study of Cu(Ⅱ) adsorption from acidic wastewater by ultrasonic-modified municipal solid waste incineration fly ash

High concentrations of copper ions(Cu(Ⅱ)) in water will pose health risks to humans and the ecological environment. Therefore, this study aims to utilize ultrasonic-cured modified municipal solid waste incineration(MSWI) fly ash for Cu(Ⅱ) adsorption to achieve the purpose of “treating waste by waste.” The effects of p H, adsorption time, initial concentration, and temperature on the modified MSWI fly ash’s adsorption efficiency were systematically studied in this article. The adsorption performance of the modified MSWI fly ash can be enhanced by the ultrasonic modification. At pH = 2, 3 and 4, the adsorption capacity of the modified MSWI fly ash for Cu(Ⅱ) increased by 2.7, 1.9 and 1.2 times, respectively. Furthermore, it was suggested that the adsorption process of the modified MSWI fly ash can be better simulated by the pseudo-second-order kinetic model, with a maximum adsorption capacity calculated by the Langmuir model of 24.196 mg.g-1. Additionally, the adsorption process is spontaneous,endothermic, and chemisorption-dominated from the thermodynamic studies(ΔH and ΔS > 0, ΔG < 0).Finally, the enhanced adsorption performance of the modified MSWI fly ash for Cu(Ⅱ) may be attributed to electrostatic interaction and chelation effects.

Degradation of PCDD/Fs in MSWI fly ash using a microwave-assisted hydrothermal process

In this work,microwave treatment was introduced to a hydrothermal treatment process to degrade PCDD/Fs(Polychlorinated dibenzo-p-dioxins and dibenzofurans)in municipal solid waste incineration(MSWI)fly ash.Three process additives(NaOH,Na2 HPO4,H2 O),temperatures(150℃,185℃,220℃)and reaction times(1 h,2 h,3 h)were investigated to identify their effect on the disposal of fly ash samples through orthogonal experiments.High-resolution gas chromatography–mass spectrometry(HRGC/MS)was applied to determine the PCDD/F concentrations in MSWI fly ash.The experimental results revealed that 83.7%of total PCDD/Fs was degraded.Reaction temperature was the most important factor for the degradation of the total PCDD/Fs.Both direct destruction and chlorination reactions(the chlorination degree of PCDFs increased)took part in the degradation of PCDD/Fs in fly ash,which was a new discovery.Several PCDD/F indexes determined by the concentration of indicative congeners were found to quantitatively characterize the dioxin toxicity of the fly ash.Furthermore,heavy metals in the fly ash sample were solidified using microwave-assisted hydrothermal treatment,which provided an experimental basis for the simultaneous disposal of dioxins and heavy metals.Thus,the microwave-assisted hydrothermal process should be considered for the future disposal of MSWI fly ash.

Effect of the MgO/SiO_(2) ratio on MgO–silica binders solidifying MSWI fly ash

To improve the effect of MgO–SiO_(2) binders solidifying municipal solid waste incineration fly ash(MSWI FA),MSWI FA solidified bodies with five MgO/SiO_(2) ratios(0.41~3.77)were investigated.The leaching behavior of solidified bodies was evaluated by leaching toxicity tests and pH-dependent experiments.In addition,hydration products in solidified bodies were analyzed by thermodynamic modeling and microstructure characterizations.The results showed that the variation in the MgO/SiO_(2) ratio had a significant effect on the leaching toxicity of the solidified bodies,because it affected the leachate pH and the composition of the hydration products of the solidified bodies.The acid and alkali resistance of the MSWI FA was enhanced through solidification with MgO–SiO_(2) binders.MgO can improve the alkalinity of the solidified bodies and facilitate the chemical precipitation of heavy metals.Moreover,silica fume,an industrial waste,can serve as a cost-effective measure.Overall,MgO–SiO_(2) binders demonstrated great potential as promising candidates for encapsulating MSWI FA.

Hazardous waste incineration in a rotary kiln:a review

Hazardous waste output in the world is increasing every year.To achieve higher efficiency and lower pollution,the incin-eration technology for hazardous waste needs to be studied further.This study mainly reviews the research progress in incineration,slagging,and pollutant emission in the rotary kiln in China and abroad in the last 10 years,and conducts a comprehensive analysis and evaluation of the research.Considering that there are many variables involved in the incineration process,the incineration law cannot be validated in a limited timeframe by experiments.Researchers often use computer simulations to predict and verify the incineration process through experiments and to provide reference opinions for com-mercial operations.Through the analysis of the research progress in rotary kilns,it is observed that the basic research in rotary kilns is becoming mature.The latest research trend in rotary kilns is interdisciplinary and mixed research.From a new perspective,further research should be focused on a comparative analysis of the rotary kiln and the cement kiln,full life cycle assessment of the impact factors of rotary kiln on the environment,the impact of the factory treatment process on the workers’health,etc.The research direction of rotary kiln in China and abroad for the future has been predicted reasonably.

Removal of PCDD/Fs and PCBs from flue gas using a pilot gas cleaning system

A 100 Nm3 /hr capacity pilot scale dual bag filter （DBF） system was tested on the flue gas from an actual hazardous waste incinerator （HWI）, the removal efficiency of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans （PCDD/Fs） and polychlorinated biphenyls （PCBs） was also studied. The first filter collected most of the fly ash and associated chlorinated organic; then activated carbon （AC） was injected and used to collect phase chlorinated organic from the gas. Concentrations of PCDD/Fs and PCBs after the DBF system were 0.07 and 0.01 ng TEQ/Nm3 , respectively, which were both far below the national emission standard. Comparing with the original single bag filter system, the PCDD/Fs concentration dropped a lot from 0.36 to 0.07 ng TEQ/Nm3 . Increasing AC feeding rate enhanced their collection efficiency, yet reduced the AC utilization efficiency, and it still needs further study to select an appropriate feeding rate in the system. These results will be useful for industrial application and assist in controlling emissions of PCDD/Fs and other persistent organic pollutions from stationary sources in China.

Study on HCI removal for medical waste pyrolysis and combustion using a TG-FTIR analyzer

Under both pyrolysis and combustion condition, HCl removal efficiency for medical waste with Cabased additives was semi-quantitatively studied by means of TG-FTIR. Additionally, the difference of HCl removal efficiency for PVC and medical waste was compared. Experimental results showed that： 1） Thermal degradation of medical waste mainly took place in two steps under both pyrolysis and combustion condition; 2） HC1 emitted at both two steps and HCl concentration increased with the increased of Cl ratio in the medical waste; 3） for the same additive, HCI concentration decreased with the increased of additives amount, that is to say, HCI removal efficiency of medical waste increased as the increased of Ca/Cl molar ratio. Fourth, when Ca（OH）2 was used as additive, HCl removal efficiency for medical waste combustion was a little higher than that for medical waste pyrolysis, but either CaCO3 or CaO was used as additive, it was just opposite, more specifically, when CaCO3 was used as additive with Ca/CI= 1.3, HC1 removal efficiency was 5.49% under pyrolysis condition, but that was only 4.24% under combustion condition. Fifth, under the same Ca/CI molar ratio, HCl removal efficiency for PVC was higher than that for medical waste under both pyrolysis and combustion condition, more specifically, when Ca（OH）2 was used as additive with Ca/Cl-1, HCl removal efficiency was 64.51% for PVC, but that was only 27.66% for medical waste pyrolysis with 4% Cl under pyrolysis condition .

Stabilization of heavy metals in municipal solid waste circulating fluidized bed incineration fly ash by fusion-hydrothermal method

Municipal solid waste circulating fluidized bed incineration(MSWCFBI)fly ash was a hazardous waste,maintaining chal-lenges for disposal.One effective approach was stabilizing the toxic heavy metal ions in the fly ash structures in situ.This work proposed a fusion-hydrothermal method,including fusion pretreatment in nitrogen atmosphere and microwave-assisted hydrothermal process,to treat three MSWCFBI fly ash samples.Specifically,leaching tests were performed to demonstrate the heavy metal stabilization.Through the treatment of the fusion-hydrothermal process,the concentrations of Cd,Cu,Zn,Pb,Ni,and Cr ions leaching from the fly ashes were obviously less than those of the raw fly ash and the sample only treated by hydrothermal process.Meanwhile,the heavy metal ions migrating from the fly ash to the hydrothermal residual liquid were reduced.Importantly,lots of zeolites formed during the fusion-hydrothermal process,such as to bermorite and sodalite.The fusion pretreatment significantly facilitated the conversion of quartz into amorphous silicon and silicate salts.Then,the silicon dissolution was accelerated and zeolite formation was promoted.Eventually,the heavy metal ions could be trapped in zeolite frameworks,enhancing the stabilization of heavy metal.Moreover,the cation-exchange capability values of the three treated fly ash were 1.099,1.168,and 1.188 meq g−1,two-folder larger than those of the samples only treated by hydrothermal process.In summary,the fusion-hydrothermal method could facilitate the stabilization of heavy metal ions in the fly ash and the as-obtained solid product with high content of zeolite was promising for future applications.

Thermogravimetric coupled with Fourier transform infrared analysis study on thermal treatment of monopotassium phosphate residue

In China,safe disposal of hazardous waste is more and more a necessity,urged by rapid economic development.The pyrolysis and combustion characteristics of a residue from producing monopotassium phosphate(monopotassium phosphate residue),considered as a hazardous waste,were studied using a thermogravimetric,coupled with Fourier transform infrared analyzer(TGFTIR).Both pyrolysis and combustion runs can be subdivided into three stages:drying,thermal decomposition,and final devolatilization.The average weight loss rate during fast thermal decomposition stage in pyrolysis is higher than combustion.Acetic acid,methane,pentane,(acetyl)cyclopropane,2,4,6-trichlorophenol,CO,and CO_(2) were distinguished in the pyrolysis process,while CO_(2) was the dominant combustion product.

In-situ sampling investigation of deposition and corrosion of convective heating surfaces in a grate type municipal solid waste incineration plant:a case study

Metal corrosion and ash deposition are two common issues in municipal solid waste incineration(MSWI)plants.An in-situ sampling investigation was conducted in an MSWI plant in Jiangsu,China.The deposit samples were collected from 6 convective heating surfaces including the reheaters,superheaters,and economizer.The corrosion samples were obtained from a ruptured tube cut from the tertiary superheater.The element composition,crystal phases,and morphology of deposit and corrosion samples were characterized and analyzed.The results show that S contents of these deposits are 32-45 wt%,considerable Cl(10.63 wt%)was only detected in the deposits of the tertiary superheater.The composition of the deposits varies with the location because the flue gas temperature determines the thermodynamic trend of the sulfation reactions of different chlorides and the SO_(2)equilibrium partial pressure required in these reactions.Ca sulfates mainly exist in deposits at high temperatures(above approximately 500℃).Whereas alkali metal sulfates are the main component of deposits at low temperatures(below approximately 500℃).A multi-layer structure is exhibited on the cross-section of the corrosion samples.The discovery of Cl in the interface between the matrix and the oxide layer confirms that Cl can penetrate the outer oxide film.Besides,polysulfate components were observed inside the metal oxide layers,which indicates that a melt has occurred there.This study has provided a better understanding of ash deposition and corrosion phenomena in MSWI systems and more emphasis should be placed on the research of ash deposition and corrosion mechanisms.