Comparison of CaO’s effect on the fate of heavy metals during thermal treatment of two typical types of MSWI fly ashes in China

Both grate and fluidized bed incinerators are widely used for MSW incineration in China. CaO addition for removing hazardous emissions from MSWI flue gas changes the characteristics of fly ash and affects the thermal behavior of heavy metals when the ash is reheated. In the present work, two types of MSWI fly ashes, sampled from both grate and fluidized bed incinerators respectively, were thermal treated at 1023–1323 K and the fate of heavy metals was observed. The results show that both of the fly ashes were rich in Ca and Ca-compounds were the main alkaline matter which strongly affected the leaching behavior of heavy metals. Ca was mostly in the forms of Ca(OH)₂ and CaCO₃ in the fly ash from grate incinerator in which nascent fly ash particles were covered by Ca-compounds. In contrast, the content of Ca was lower in the fly ash from fluidized bed incinerator and Ca was mostly in the form of CaSO₄. Chemical reactions among Ca-compounds caused particle agglomeration in thermal treated fly ash from grate incinerator, restraining the heavy metals volatilization. In thermal treated fly ash from fluidized bed incinerator, Ca was converted into aluminosilicates especially at 1323 K which enhanced heavy metals immobilization, decreasing their volatile fractions as well as leaching concentrations. Particle agglomeration hardly affected the leaching behavior of heavy metals. However, it suppressed the leachable-CaCrO₄ formation and lowered Cr leaching concentration.     

Thermal removal of PCDD/Fs from medical waste incineration fly ash--effect of temperature and nitrogen flow rate

The fly ash used in this study was collected from a bag filter in a medical waste rotary kiln incineration system, using lime and activated carbon injection followed by their collection as mixed fly ash. Experiments were conducted on fly ash in a quartz tube, heated in a laboratory-scale horizontal tube furnace, in order to study the effect of temperature and nitrogen flow rate on the removal of PCDD/Fs. Results indicated that in this study PCDD/Fs in the fly ash mostly were removed and desorbed very little into the flue gas under thermal treatment especially when the heating temperature was higher than 350 °C, and dechlorination and destruction reactions took important part in the removal of PCDD/Fs. However, in terms of flow rate, when flow rate was higher than 4 cm s⁻¹, destruction efficiency of PCDD/Fs decreased dramatically and the main contributors were P₅CDF, H₆CDF and H₇CDF desorbed to flue gas, the PCDD/Fs in the fly ash decreased with enhanced flow rate.     

Influence of the operation conditions on CO2 capture by CaO-derived sorbents prepared from synthetic CaCO3

In this work, a statistical experimental design is performed in order to prepare CaCO₃ materials for use as CaO-based CO₂ sorbent precursors. The influence of different operational parameters such as synthesis temperature (ST), stirring rate (SR) and surfactant percent (SP) on CO₂ capture is studied by applying Response Surface Methodology (RSM). The samples were characterized using different analytical techniques including X-ray diffraction, N₂ adsorption isotherm analysis and Scanning Electron Microscopy–X-ray Energy Dispersive Spectroscopy (SEM-EDX). CO₂ capture capacity was determined by means of a thermogravimetric analyzer which recorded the mass uptake of the samples when these were exposed to a gas stream containing diluted (15%) CO₂. The statistical approach used in this work provides a rapid way of predicting and optimizing the main preparation variables of CaO-derived sorbents for CO₂ sorption. The results obtained clearly indicate that four parameters statistically influence CO₂ uptake: SR, the square of SR, its interaction with SP and the square of SP.     

An aerosol flow tube study of the interaction of N2O5 with calcite, Arizona dust and quartz

The interaction of N₂O₅ with dispersed samples of Arizona Test Dust (ATD), Calcite (CaCO₃) and quartz (SiO₂) was investigated at varying relative humidity using an aerosol flow reactor. Reactive uptake coefficients, γ, obtained at close to zero relative humidity were (4.8 ± 0.7) × 10⁻³ for CaCO₃, (8.6 ± 0.6) × 10⁻³ for Quartz and (9.8 ± 1.0) × 10⁻³ for ATD. In the case of calcite, evidence was obtained for an enhanced rate of uptake at relative humidities above ≈ 50%. The results are compared to literature values obtained using bulk substrates and to previous aerosol uptake data on Saharan dust.     

Purification of carbonic anhydrase from bovine erythrocytes and its application in the enzymic capture of carbon dioxide

This work presents a study of industrially applicable techniques to obtain a biologically supported carbon dioxide capture system, based on the extraction of carbonic anhydrase from bovine blood. Carbonic anhydrase is a metalloenzyme which catalyzes the reversible hydration of carbon dioxide. The objective of this study was to establish conditions to obtain carbonic anhydrase from bovine erythrocytes and apply it in the capture of carbon dioxide. To achieve this, two different purification techniques were evaluated: one by extraction with the organic solvents chloroform and ethanol, where different solvent proportions were studied; and the other by ammonium sulfate precipitation, testing percent saturations between 10% and 80%. Carbon dioxide was enzymatically captured by its precipitation as calcium carbonate with the enzyme obtained by both techniques. The enzyme extracted by ethanol and chloroform showed an activity of 2623 U mL⁻¹, recovery of 98% and purification factor of 104-fold. That precipitated by ammonium sulfate showed an activity of 2162 U mL⁻¹, recovery of 66% and purification factor of 1.4-fold using 60% ammonium sulfate saturation. The results obtained in the carbon dioxide capture experiments showed that the carbonic anhydrase extracted in this study not only enhanced the hydration of CO₂, but also promoted the formation of CaCO₃.     

An assessment of indoor air quality in recent Mexican immigrant housing in Commerce City, Colorado

An indoor air quality assessment was conducted on 100 homes of recent Mexican immigrants in Commerce City, Colorado, an urban industrial community north of Denver. Head of households were administered a family health survey, filled out an activity diary, and participated in a home inspection. Carbon monoxide (CO) and carbon dioxide (CO₂) were measured for 24 h inside the main living area and outside of the homes. Harvard Impactors were used to collect 24-h samples of PM_2.5 at the same locations for gravimetric analysis. Dust samples were collected by vacuuming carpeting and flooring at four locations within the home and analyzed by ELISA for seven allergens. Mean indoor and outdoor PM_2.5 levels were 27.2 and 8.5 μg m⁻³, respectively. Indoor PM_2.5 and CO₂ were elevated in homes for which the number of hours with door/window open was zero compared to homes in which the number of hours was high (>15 h). Indoor PM_2.5 levels did not correlate with outdoor levels and tended to increase with number of inhabitants, and results indicate that the source of indoor particles were occupants and their activities, excluding smoking and cooking. Mean indoor CO₂ and CO levels were 1170 and 2.4 ppm, respectively. Carbon monoxide was higher than the 24-h National Ambient Air Quality Standard in 3 of the homes. The predominant allergens were cat (Fel d 1) and mouse (Mus m 1) allergens, found in 20 and 34 homes, respectively.     

A Study on the Treatment of CO2, SO2, Nox,and Fly Ash by Pulse Activation

ABSTRACT

This paper presents a technique for the complete, simultaneous decomposition of CO₂, SO₂, and NO_x, as well as the simultaneous removal of fly ash by ultra-high voltage pulse activation. Ultra-high voltage narrow pulse is used to make the gases in the reactor become active molecules, which are then dissociated into nonpoisonous gas molecules and solid particles under the control of a directional reaction model. By using a sufficient charge and a strong electric field, the fly ash can be removed. It becomes the carrier of C and S, and its efficiency is 99.5%. Owing to the action of catalyst B (using Ni as the mother's body), the activation energy of CO₂, SO₂, and NO_x gases is reduced in great magnitude, and their removal efficiency can reach 75~90% at normal pressure and 180 °C.     

Accelerated carbonation of wood combustion ash for CO<Subscript>2</Subscript> removal from gaseous streams and storage in solid form

In this work, ash generated by the combustion of wood in a central heating plant was used to remove and permanently store by accelerated carbonation CO₂ contained in a gas mixture simulating biogas. The process was studied as an alternative treatment to the ones currently available on the market for biogas upgrading. The process was investigated at laboratory scale by setting up a facility for directly contacting the wood ash and the synthetic biogas in a fixed bed reactor. The process was able to completely remove CO₂ during its initial phase. After about 30 h, CO₂ started to appear again in the outlet stream and its concentration rapidly increased. The specific CO₂ uptake achieved in solid carbonate form was of about 200 g/kg of dry wood ash. This value is an order of magnitude higher than the ones found for waste incineration bottom ash carrying out similar experiments. The difference was ascribed to the physicochemical properties of the ash, characterized by a fine particle size (d₅₀ <?0.2 mm) and high content of reactive phases with CO₂ (e.g., Ca hydroxides). The leaching behavior of the wood ash was examined before and after the accelerated carbonation process showing that the release of several elements was lower after the treatment; Ba leaching in particular decreased by over two orders of magnitude. However, the release of the critical elements for the management of this type of residues (especially Cr and sulfates) appeared not to be significantly affected, while V leaching increased.     

Potassium-based sorbents from fly ash for high-temperature CO<Subscript>2</Subscript> capture

Potassium-fly ash (K-FA) sorbents were investigated for high-temperature CO₂ sorption. K-FAs were synthesised using coal fly ash as source of silica and aluminium. The synthesised materials were also mixed with Li₂CO₃ and Ca(OH)₂ to evaluate their effect on CO₂ capture. Temperature strongly affected the performance of the K-FA sorbents, resulting in a CO₂ uptake of 1.45 mmol CO₂/g sorbent for K-FA 1:1 at 700 °C. The CO₂ sorption was enhanced by the presence of Li₂CO₃ (10 wt%), with the K-FA 1:1 capturing 2.38 mmol CO₂/g sorbent at 700 °C in 5 min. This sorption was found to be similar to previously developed Li-Na-FA (2.54 mmol/g) and Li-FA (2.4 mmol/g) sorbents. The presence of 10 % Li₂CO₃ also accelerated sorption and desorption. The results suggest that the increased uptake of CO₂ and faster reaction rates in presence of K-FA can be ascribed to the formation of K-Li eutectic phase, which favours the diffusion of potassium and CO₂ in the material matrix. The cyclic experiments showed that the K-FA materials maintained stable CO₂ uptake and reaction rates over 10 cycles.     

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

This study was conducted to examine the synthesis and application of novel nano-size calcium/iron-based composite material as an immobilizing and separation treatment of the heavy metals in fly ash from municipal solid waste incineration. After grinding with nano-Fe/Ca/CaO and with nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash). Heavy metals in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized, respectively. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) observations indicate that the main fraction of enclosed/bound materials on treated fly ash includes Ca/PO₄-associated crystalline complexes. After nano-Fe/Ca/CaO/[PO₄] treatment, the heavy metal concentrations in the fly ash leachate were much lower than the Japan standard regulatory limit for hazardous waste landfills. These results appear to be extremely promising. The addition of a nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique is potentially applicable for the remediation and volume reduction of fly ash contaminated by heavy metals.

Implications: After grinding with nano-Fe/Ca/CaO and nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash), whereas heavy metals either in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized. These results appear to be very promising, and the addition of nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique may be considered potentially applicable for the remediation and volume reduction of contaminated fly ash by heavy metals.     

Traffic generated non-exhaust particulate emissions from concrete pavement: A mass and particle size study for two-wheelers and small cars

This study aimed to understand the non-exhaust (NE) emission of particles from wear of summer tire and concrete pavement, especially for two wheelers and small cars. A fully enclosed laboratory-scale model was fabricated to simulate road tire interaction with a facility to collect particles in different sizes. A road was cast using the M-45 concrete mixture and the centrifugal casting method. It was observed that emission of large particle non exhaust emission (LPNE) as well as PM₁₀ and PM_2.5 increased with increasing load. The LPNE was 3.5 mg tire⁻¹ km⁻¹ for a two wheeler and 6.4 mg tire⁻¹ km⁻¹ for a small car. The LPNE can lead to water pollution through water run-off from the roads. The contribution of the PM₁₀ and PM_2.5 was smaller compared to the LPNE particles (less than 0.1%). About 32 percent of particle mass of PM₁₀ was present below 1 μm. The number as well as mass size distribution for PM₁₀ was observed to be bi-modal with peaks at 0.3 μm and 4–5 μm. The NE emissions did not show any significant trend with change in tire pressure.     

粉煤灰制备混凝剂及其对黄河水的处理效果

以粉煤灰和铁泥为原料、加入一定量NaCl作助溶剂室温下制备粉煤灰混凝剂,考察酸灰比与酸浓度对Fe3+、Al3+溶出率及混凝剂对黄河水处理效果的影响。结果表明,Fe3+、Al3+的最佳溶出条件为酸灰比3 mL/g、HCl浓度4 mol/L,此时Fe3+溶出率为28.1%,浓度为11.81 g/L;Al3+溶出率为5.2%,浓度为1.86 g/L。粉煤灰混凝剂对黄河水的处理效果在投加量2.38 mL/L、沉降时间30 min、pH 6.2～7.5时最佳,对浊度、SS和CODMn平均去除率分别为89.7%、83.6%和62.3%,优于传统市售混凝剂PAC和FC,Fe3+、Al3+同时存在有利于各自优势的发挥从而提高混凝效果。     

空速和二氧化碳对沼气脱硫剂硫容确定的影响

为了弄清空速与二氧化碳含量对氧化铁脱硫剂硫容确定的影响,分别在实验气源为纯硫化氢,空速为40、80、120和160 h-1以及实验气源为二氧化碳含量分别在0%、20%、40%和80%,其余为硫化氢,空速为80 h-1条件下,对T502(粗脱硫剂)和HXT-2(精脱硫剂)2种氧化铁脱硫剂进行了不同测试条件对氧化铁硫容确定影响的研究。研究结果表明,T502和HXT-2氧化铁脱硫剂硫容测试结果随着空速和二氧化碳含量增加而减少,结果显示了在空速较低条件下(120h-1),二氧化碳含量在40%以下时对氧化铁脱硫剂硫容测试结果影响不大,但二氧化碳含量在40%以上时,对氧化铁脱硫剂硫容测试结果影响显著。     

水泥窑协同处置生活垃圾焚烧飞灰过程中Pb和Zn的迁移转化特性

对某水泥窑协同处置生活垃圾焚烧飞灰系统进行采样分析,研究飞灰中的Pb、Zn在水洗脱氯预处理及水泥窑协同处置过程中的迁移转化特性。结果表明,水洗预处理过程中,飞灰中0.15%Pb和0.015%Zn进入结晶盐,94.05%的Pb和93.17%的Zn留存在水洗灰中,且赋存形态基本不变。水泥窑协同处置飞灰过程中,进入窑内的Pb和Zn少部分在窑内和预热器系统形成内循环,93.84%Pb和81.38%的Zn进入水泥熟料,0.002 7%的Pb进入窑尾烟气,0.001 4%的Pb和0.001 1%的Zn进入窑灰。热力学平衡计算表明,水泥熟料中Pb的主要存在形态是PbO、PbSiO₃,Zn的主要存在形态是ZnO、ZnFe₂O₄、ZnAl₂O₄。窑尾烟气排放指标和水泥熟料性能指标均满足相关规范要求,这说明Pb和Zn在水泥窑中实现了良好的固化,环境风险可接受。本研究结果可为水泥窑协同处置飞灰工艺系统设计优化提供参考。     

Effects of field-applied composted cattle manure and chemical fertilizer on ammonia and particulate ammonium exchanges at an upland field

The present study aimed to investigate the NH₃ volatilization loss from field-applied compost and chemical fertilizer and evaluate the atmosphere–land exchange of NH₃ and particulate NH₄⁺ (pNH₄) at an upland field with volcanic ash soil (Andosol) in Hokkaido, northern Japan. Two-step basal fertilization was conducted on the bare soil surface. First, a moderately fermented compost of cattle manure was applied by surface incorporation (mixing depth, 0–15 cm) at a rate of 117 kg N ha⁻¹ as total nitrogen (T-N) corresponding to 9.9 kg N ha⁻¹ as ammoniacal nitrogen (NH₄–N). Twelve days later, a chemical fertilizer containing 10% (w/w) of NH₄–N as a mixture of ammonium sulfate and ammonium phosphates was applied by row placement (cover depth, 3 cm) at a rate of 100 kg N ha⁻¹ as NH₄–N. The study period was divided into the first-half, beginning after the compost application (CCM period), and the second-half, beginning after the chemical fertilizer application (CF period). The mean air concentrations of NH₃ and pNH₄ (1.5 m height) were 7.6 and 3.0 μg N m⁻³, respectively, in the CCM period; the values were 3.7 and 3.9 μg N m⁻³, respectively, in the CF period. The composition ratios of NH₃ to the sum of NH₃ and pNH₄ (1.5 m height) were 72% and 49% in the CCM and CF periods, respectively. The NH₃ volatilization loss from the compost was 0.8% of the applied T-N (or 9.3% of the applied NH₄–N) and that from the chemical fertilizer was near zero. Excluding the period immediately after the compost application, the upland field acted as a net sink for NH₃ and pNH₄.     

Spatial gradients and source apportionment of volatile organic compounds near roadways

Concentrations of 55 volatile organic compounds (VOCs) (C₂–C₁₂) are reported near a highway in Raleigh, NC. Thirty-minute samples were collected at eight locations, ranging from approximately 10–100 m perpendicular from the roadway. The highest concentrations of VOCs were generally measured closest to the roadway, and concentrations decreased exponentially with increasing distance from the roadway. The highest mean concentration for individual VOCs were for ethylene (3.10 ppbv) (mean concentration at x = 13 m), propane (2.27 ppbv), ethane (1.91 ppbv), isopentane (1.54 ppbv), toluene (0.95 ppbv), and n-butane (0.89 ppbv). Concentrations at the nearest roadway location (x = 13 m) were generally between 2.0 and 1.5 times those from the farthest roadway location (x = 92 m). The data were apportioned into four source categories using the EPA Chemical Mass Balance Model (CMB8.2): motor vehicle exhaust, compressed natural gas, propane gas, and evaporative gasoline. The majority of the VOCs resulted from motor vehicle exhaust (67 ± 12%) (% of total VOC at x = 13 m ± S.D.). Compressed natural gas, propane gas, and evaporative gasoline accounted for approximately 15%, 7% and 1% of the total VOC emissions, respectively, at x = 13 m.     

Inhibition of PCDD/F by adding sulphur compounds to the feed of a hazardous waste incinerator

Sulphur compounds, including (NH₄)₂SO₄ and pyrite, were tested as suppressants in a hazardous waste incineration facility. The test results suggested that adding sulphur compounds only slightly reduced PCDD/F stack emissions; this restricted effect was attributed to the release of fly ash in large amounts during the sulphur adding experiments, i.e., it was due to a malfunctioning of the baghouse filter. Nevertheless, for the combined flow of flue gas + fly ash a reduction of more than 50% was achieved for the total PCDD/F concentrations and the total toxic concentrations, and an even higher inhibition capability was observed for PCDD. Also, a simulation of the thermodynamic equilibrium conditions by sulphur dioxide was conducted in the domain of experimental interest. Deactivation of catalysts, which promote PCDD/F formation, was found to be the dominant inhibition mechanism in low temperature PCDD/F formation. SO₂ could also inhibit the formation of molecular Cl₂ via the Deacon reaction, but that was not the main reason for inhibition.     

SGA对垃圾焚烧飞灰中重金属的固化性能研究简

根据EPA 1311、HJ/T 299-2007、HJ/T 300-2007和HJ 557-2009等国内外不同标准,研究了深圳某垃圾焚烧发电厂垃圾焚烧飞灰的浸出毒性,探讨了六硫代胍基甲酸（sixthio guanidine acid,SGA）、二甲基二硫代氨基甲酸盐（sodium dimethyl dithio carbamate,SDD）和Ca（OH）₂浓度对垃圾焚烧飞灰中重金属的固定性能的影响。研究结果表明,随着浸提液pH的降低,该厂焚烧飞灰中大部分金属元素的浸出量增大,焚烧飞灰浸出液中的Cd、Ni、Pb和Zn浓度分别超过国家危险废物鉴别标准（GB5085.3-2007）规定值的4.75倍、1.47倍、6.72倍和2.20倍,属于危险废弃物,必须进行稳定化处理。当固化剂SGA加入量为0.1 mol/kg时,稳定化后的重金属浸出浓度已经低于危险废物鉴别标准,且对Cd、Cr、Cu和Pb的固化性能优于SDD和Ca（OH）₂;当固化剂SGA、SDD和Ca（OH）₂加入量为0.5 mol/kg时,稳定化后的焚烧飞灰重金属浸出浓度均低于国家危险废物鉴别标准（GB 5085.3-2007）中的规定值。与SDD和Ca（OH）₂相比,SGA对垃圾焚烧飞灰中重金属的固化处理更具有优势。     

The growth response of Alternanthera philoxeroides in a simulated post-combustion emission with ultrahigh [CO2] and acidic pollutants

Although post-combustion emissions from power plants are a major source of air pollution, they contain excess CO₂ that could be used to fertilize commercial greenhouses and stimulate plant growth. We addressed the combined effects of ultrahigh [CO₂] and acidic pollutants in flue gas on the growth of Alternanthera philoxeroides. When acidic pollutants were excluded, the biomass yield of A. philoxeroides saturated near 2000 μmol mol⁻¹ [CO₂] with doubled biomass accumulation relative to the ambient control. The growth enhancement was maintained at 5000 μmol mol⁻¹ [CO₂], but declined when [CO₂] rose above 1%, in association with a strong photosynthetic inhibition. Although acidic components (SO₂ and NO₂) significantly offset the CO₂ enhancement, the aboveground yield increased considerably when the concentration of pollutants was moderate (200 times dilution). Our results indicate that using excess CO₂ from the power plant emissions to optimize growth in commercial green house could be viable.     

The Capture of Heavy Metals from Incineration Using a Spray Dryer Integrated with a Fabric Filter Using Various Additives

ABSTRACT

This study investigated the effects of feedstock additives [polyvinyl chloride (PVC) and NaCl] and spray dryer additives (SiO₂, CaCl₂, NaHCO₃) on heavy metal and fly ash removal efficiencies, and on particle size distribution of heavy metals. A spray dryer with an integrated fabric filter was used as an air pollution control device (APCD). Removal efficiencies for fly ash and heavy metals were greater than 95 and 90%, respectively. When additives of PVC or NaCl were used, the concentration of heavy metals distributed in fly ash apparently varied when the particle diameter was <1 μm. Although the effects of the additives SiO₂, CaCl₂, and NaHCO₃ on the elemental size distribution of Cr were insignificant, these additives did slightly increase concentrations of Cd, Zn, and Pb partitioning in coarser particles (>1μm).