Field-tested innovation: Sustainable utilization of secondary alumina dross for flash setting admixtures production.

Secondary alumina dross (SAD) has emerged as an alternative to bauxite in the production of flash setting admixtures (FSA), a critical admixture in shotcrete. However, the presence of hazardous components has hampered its large-scale adoption. This study conducted field tests at an FSA factory, utilizing SAD as the primary raw material, to evaluate the feasibility and environmental risks. The results confirmed that SAD can effectively replace bauxite in FSA production without compromising quality, as it closely resembled the chemical properties of bauxite. Emissions of fluorides, heavy metals, dioxins in flue gases during production met the relevant Chinese standards. The analysis of hazardous component distribution revealed that more than 50% of volatile components, such as Cl, Cd, Pb, and Zn, were directed into fly ash, exhibiting a significant internal accumulation pattern. In contrast, more than 95% of low-volatility components, including Cu, Cr, Mn, and F, were transferred to the FSA, and the introduction of CaCO3 was confirmed to effectively immobilize F. Moreover, the leaching risk of heavy metals and fluorides in FSA applications slightly increased but remained minimal and within acceptable limits. This technology provides an environmentally sound solution for the disposal of SAD.

Characterization and stabilization of incineration fly ash from a new multi-source hazardous waste co-disposal system: field-scale study on solidification and stabilization.

The multi-source hazardous waste co-disposal system, a recent innovation in the industry, offers an efficient approach for hazardous waste disposal. The incineration fly ash (HFA) produced by this system exhibits characteristics distinct from those of typical incineration fly ash, necessitating the use of adjusted disposal methods. This study examined the physicochemical properties, heavy metal content, heavy metal leaching concentration, and dioxin content of HFA generated by the new co-disposal system and compared them with those of conventional municipal waste incineration fly ash. This study investigated the solidification and stabilization of HFA disposal using the organic agent sodium diethyl dithiocarbamate combined with cement on a field scale. The findings revealed significant differences in the structure, composition, and dioxin content of HFA and FA; HFA contained substantially lower levels of dioxins than FA did. Concerning the heavy metal content and leaching; HFA exhibited an unusually high concentration of zinc, surpassing the permitted emission limits, making zinc content a critical consideration in HFA disposal. After stabilization and disposal, the heavy metal leaching and dioxin content of HFA can meet landfill disposal emission standards when a 1% concentration of 10% sodium diethyldithiocarbamate (DDTC) and 150% silicate cement were employed. These results offer valuable insights into the disposal of fly ash resulting from incineration of mixed hazardous waste.

Removal of dioxins from municipal solid waste incineration fly ash by low-temperature thermal treatment: Laboratory simulation of degradation and ash discharge stages.

Dioxins in municipal solid waste incineration fly ash (MSWIFA) can cause significant risks to the environment and human health. In this study, the low-temperature thermal treatment of MSWIFA under industrial conditions was simulated in the laboratory to investigate the process parameters for dioxin degradation and ash discharge stages. Correlation analysis and dioxin fingerprint characterization were used to analyze the degradation and ash discharge processes. The degradation efficiency of low-temperature thermal treatment was influenced by multiple factors. At 400℃ for 90 min and 1% O2, the dioxin removal rate was 95.80%, the detoxification rate was 91.73%, and the residual dioxin toxicity in MSWIFA was 22.7 ± 17.8 ng I-TEQ/kg, which was in line with the limit value of 50 ng I-TEQ/kg in the "Technical specification for pollution control of fly-ash from municipal solid waste incineration" (HJ1134-2020). The increase in dioxins during ash discharge did not follow a linear relationship with the process parameters. This was assumed to be related to the MSWIFA composition, as some components containing P, Si, and Al at 150 °C may inhibit dioxin formation. The dioxin increased only by 0.79 ± 2.65 ng/kg, an increase in toxicity of 0.42 ± 0.10 ng I-TEQ/kg, when treated at 150 °C for 30 min and 10% O2.

Distributions of and environmental risks posed by Cr and Zn when co-treating solid waste in different kilns.

In order to dispose solid waste reasonably and provide reference data for solid waste co-treatment in industrial kilns, coal chemical products were co-treated in a pulverized coal furnace and refuse-derived fuel was co-treated in a gasifier-coupled pulverized coal furnace system. The distribution and environmental risks of Cr and Zn in different kilns were compared and analyzed. The Cr and Zn distributions in the solid products from the pulverized coal furnace tests were similar. Fly ash contained > 80% of the Cr and Zn. In the gasifier, cyclone dust and gasification gas contained only âˆ¼ 60% of the Cr and Zn, and gasification slag contained > 40% of the Cr and Zn. The gasification gas contained âˆ¼ 33% of the Cr and Zn volatilized. The pulverized coal furnace temperature was > 1,500 °C. Most of the Cr and Zn volatilized and then condensed, so became enriched in the fly ash. The gasifier temperature was âˆ¼ 750 °C, so less volatilization occurred and Cr and Zn became enriched in the gasification slag. The Cr and Zn concentrations in leachates of the solid products were lower than the limits of "GB 5085.3-2007". However, the Cr and Zn concentrations in the gasification slag and cyclone dust leachates were close to the limits and tens to hundreds of times higher than the concentrations in the pulverized coal furnace fly ash and slag leachates. The low temperatures and low-oxygen environments of gasifiers are not conducive to heavy metals being stable in the solid products, and the environmental risks posed by heavy metals in the solid products are high. The risks to the environment are less serious for co-treating solid waste in pulverized coal furnaces than gasifiers.

Emission characteristics of dioxin during solid waste co-processing in the Chinese cement industry.

Development of co-processing technology in the cement industry in China is important for environmentally sound disposal and recycling of waste, and contributes to sustainable development of the cement industry. However, dioxin pollution could negatively affect promotion of this technology. Therefore, it is necessary to study the emission characteristics of dioxins in cement kilns. In this study, the emission characteristics of dioxins and factors influencing their generation during co-processing solid wastes were studied in 14 new dry cement kilns. The dioxin concentrations were very similar regardless of whether solid wastes were fed into the kiln. In blank runs without co-processing, the average dioxin concentration was 0.0097 ng international toxic equivalents (I-TEQ)/Nm3. By comparison, that for co-processing solid wastes was 0.012 ng I-TEQ/Nm3. These values meet the relevant emission standards. The type of co-processed solid wastes had almost no effect on the dioxin concentration. At larger production scales, the concentration of dioxin emitted in the flue gas decreased. The dioxin concentrations in kiln dust were obviously higher than those in clinker and raw materials. The average emission factor of dioxin per ton of cement was 30 ng I-TEQ/t, which is equivalent to that in cement kilns in other countries.

Effects of increasing chlorine concentration in feedstock on the emission and distribution characteristic of dioxins in circular fluidized bed boiler.

Field studies were conducted to study the emission and distribution characteristics of dioxins by elevating the chlorine concentration in feedstock in a circular fluidized bed boiler. The concentration and total equivalent quantity of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in all flue gas, electrostatic ash, bag filter ash, and bottom ash samples under blank condition (i.e., feedstock was normal coal) and chlorine labeling condition (i.e., feedstock mixed with coal and chlorine-containing labeling agent) were analyzed. Results illustrated that the concentration of PCDD/Fs in all gaseous and ash samples increased with the addition of chlorine in feedstock, with the largest and least increment in dioxin concentration observed in electrostatic ash and flue gas. PCDDs were the predominate congeners in flue gas, accounted for 50.1-60.4% of the total PCDD/F concentration under chlorine labeling and blank conditions, while PCDD/F distribution changed from PCDD- to PCDF-predominate by increasing chlorine content in feedstock under all field test conditions: 46.6-92.9%, 34.0-76.1%, and 47.0-53.1% of PCDFs were distributed in electrostatic ash, bag filter ash, and bottom ash, respectively. Highly chlorinated PCDD/F congeners such as O8CDD/F and 1,2,3,4,6,7,8-H7CDD/F were the primary contributors to dioxin concentration in flue gas and bottom ash samples, whereas low-chlorinated 2,3,7,8-T4CDF and 1,2,3,7,8-P5CDF congeners became critically dominating in electrostatic and bag filter ash.

Heavy metal and metalloid emissions during co-processing of waste in a sintering kiln: Migration characteristics in the kiln and long-term leaching from bricks.

Heavy metals (HMs) in mixed hazardous waste can be volatilized in the kiln for preparing sintered bricks, which greatly increases the environmental risk. In this study, the volatilization, transformation, and leaching of HMs from bricks were evaluated. Field tests and laboratory leaching experiments were carried out. HM-contaminated soil was used to prepare sintered bricks at high-temperature in a tunnel kiln. Release of HMs from brick under rainfall conditions was investigated in laboratory simulation experiments. The field tests showed that the total amount of Pb, Zn, Cd distributed to the gas phase were all less than 2%, but the amount of Hg entering the gas phase 40.1%-60.5% in the particulate forms. The As leaching rate increased after sintering of bricks in the kiln, which was attributed to the increased formation of soluble arsenate and the reduced availability of sorption sites. The tank leaching test indicated that the release mechanism of trance elements (Cr, As, Zn, Cd, Pb and Ni) was mainly controlled by diffusion. This study provides useful knowledge for decreasing the volatilization and leaching of HMs from sintered bricks prepared using hazardous waste.

Simulation of heavy metals behaviour during Co-processing of fly ash from municipal solid waste incineration with cement raw meal in a rotary kiln.

Fly ash produced from incineration of municipal solid wastes (MSW) contains heavy metals, such as Cd and Pb, that make this material difficult to manage and dispose of safely. Because the composition of fly ash is similar to cement raw meal, partial replacement of raw meal with fly ash may be a feasible way to reduce the health and environmental hazards of the ash, provided that the heavy metals can be effectively stabilized in the solid phase. This research employs proprietary thermochemical software to simulate the thermodynamic behavior and single-step fixation of Cd and Pb in industrial cement kilns. The effect of Cd, Pb and Cl loadings on the fixation and/or evaporation of Cd and Pb during the sintering process is analyzed using data from industrial cement kilns. A simplified model is created based on elemental mass balance to evaluate multi-step fixation of Cd and Pb with cement kiln dust recycle.The results indicate that Cd forms Cd(OH)2(g) in a highly alkaline environment, while nearly 90% Pb is volatilized as PbCl2(g). In the clinker, increased Cl-1 decreased the proportion of Pb and Cd, moreover, Pb and Cd increased in kiln dust with Cl-1 increased; Calculations using a kiln dust recycle model showed that, the concentrations of Pb and Cd in both kiln dust and clinker increased sharply after recycling of kiln dust in steady state. Under unstable conditions, the concentrations of Pb and Cd in kiln dust increased, as well as the heavy metals re-entering the cement kiln.

The fate of heavy metals in the co-processing of solid waste in converter steelmaking.

The improper disposal of large amounts of solid waste (SW) has led to serious ecological and environmental problems, especially heavy metal (HM) pollution. Converter steelmaking has the potential to co-process SW, but the distribution of heavy metals (HMs) during converter steelmaking is unclear. In this study, the effects of smelting temperature and slag alkalinity on the distribution of typical HMs in the SW of steel samples, steel slag, and the gas phase were investigated in a specially-made induction furnace. The results showed that upon increasing the smelting temperature, As (As2S3) was mainly distributed in the steel sample, and the HM-containing compounds Cr2O3, CrCl3, ZnCl2, ZnS, ZnO, PbCl2, PbS, and PbO were mainly distributed in the gas phase. Upon increasing the alkalinity within a certain range, the distribution of HMs in steel samples and steel slag increased gradually, while their distribution in the gas phase decreased. Thermodynamic calculations, Eh-pH diagrams, XRD patterns, and XPS spectra indicated that impurity elements in the hot metal and the CaO content affected the chemical reactions by which HM-containing compounds in the steel sample formed elemental HMs and those in steel slag existed as oxides; therefore, it is necessary to choose a suitable temperature and alkalinity for slag when disposing of different types of SW.

Emissions of BTEXs, NMHC, PAHs, and PCDD/Fs from Co-processing of Oil-based Drilling Cuttings in Brick Kilns.

Oil-based drilling cuttings (OBDC) produced from shale gas development is a hazardous waste that have high calorific values and should be disposed of properly. Burning bricks with OBDC is a promising co-disposal method; however, organic pollutants emitted during this process have not received sufficient attention. In this study, the composition and combustion characteristics of OBDC were determined, and the emissions of typical organic pollutants when burning bricks with the addition of OBDC were investigated; these included benzene series compounds (BTEXs), non-methane total hydrocarbons (NMHC), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The results showed that OBDC comprised large amounts of alkanes and aromatic hydrocarbons, and combusted mainly in the temperature range of 145-450 °C with an ignition temperature of 145 °C. The co-processing 10% OBDC increased the concentrations of toluene, NMHC, and PAHs in the flue gases by ∼1000%, ∼500%, and 200%, respectively, compared to the control experiment; however, their emission concentrations were within the limits set by the Integrated emission standards of air pollutants of Chongqing. It is worth noting that 26.443 ng/Nm3 PCDD/Fs with a total toxicity of 0.709 ng I-TEQ/Nm3 was generated from the co-processing 10% OBDC, which was ascribed to the high content of chlorine and aromatic hydrocarbons in the OBDC-promoted PCDD/Fs formed during the burning and cooling processes. Though PCDD/Fs in flue gas exceeded the 0.5 ng I-TEQ/Nm3 limit prescribed in the Pollution control standard for hazardous wastes incineration of China, the realistic emission of PCDD/Fs is expected to meet with this emission limit after desulfurization treatment as PCDD/Fs can be absorbed by gypsum. It is recommended that a lower amount of OBDC is added to reduce PCDD/F formation at the source and to take more efficient air pollution control system in order to reach a stricter emission limit of 0.1 ng I-TEQ/Nm3 in EU and USA. Cycling flue gas may also be an effective method to reduce other organic pollutants. Under these conditions, co-processing OBDC in brick kilns can be achieved without serious environmental pollution, making it a potential method for disposal and utilization.

A field study of dioxins during co-processing of hazardous waste in multicomponent slurry gasifier.

A field test was conducted to study the emission and distribution characteristics of dioxins during co-processing of hazardous waste in a multicomponent slurry gasifier (MCSG). The toxicity equivalent concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in all exhaust gas, waste water, and solid waste under both blank condition (i.e., feedstock was normal coal-water slurry) and test condition (i.e., feedstock mixed with hazardous waste and labeling reagents) were analyzed. Results showed that organic matter was fully degraded in the MCSG. The dioxin amount in the black water flash steam increased with the addition of hazardous waste and chlorine in the feedstock, and octachlorodibenzo-p-dioxins (OCDD) with the largest increase is the most easily formed monomer in dioxins. The dioxin amount in all samples was far below the standard limit in China and other countries. This indicates the low environmental risk from dioxins during the co-processing process. The dioxin distribution trend in solid, liquid, and gas phase during co-processing did not change: 86.63%-94.18%, 0.02%-0.13%, and 5.8%-13.23% of PCDDs were distributed in the exhaust gas, waste water, and solid waste, respectively, while 6.10%-22.95%, 0.59%-0.80%, and 76.45%-93.10% of PCDFs were distributed in the exhaust gas, waste water, and solid waste, respectively.

Characteristics of migration and speciation of trace elements during co-processing of antibiotic residues in a circulating fluidized bed.

In order to study the emission characteristics of the products during the blending of antibiotic residues in coal-fired power plants, blending tests were performed on a 140 t/h circulating fluidized bed boiler. It was found that during combustion, 64 to 87.6% of Cr, As, and Pb are concentrated in the fly ash, and 11.4 to 35% are concentrated in the bottom ash. Only a small amount of these elements are captured by the desulfurization system or enter the environment. During the material distribution of the desulfurization system, trace elements are mostly concentrated in gypsum. In the desulfurization system, the proportion of Cr, As, Pb, Be, Mn, Co, Ni, Se, and Mo in the gypsum range from 82.8 to 99.9%, and the content has reached the level of ppm. When the blending ratio is controlled within 7%, the blending of antibiotic residues has little effect on the elemental composition of coal. The contents of Cr, Ni, Cu, Zn, and Ba in the products increased by 9.5 to 22.3%. This may mean when the blending ratio is increased, it will be harmful to the environment.

Field-scale study of co-processing dichlorodiphenyltrichloroethane-contaminated soil in a cement kiln.

Persistent organic pollutants in soil are not readily degraded in the short term. The utilization of co-processing solid waste in cement kilns has received increasing attention in recent years. Co-processing may be a good way of disposing of dichlorodiphenyltrichloroethane-contaminated soil (CS). The feasibility of co-processing CS pretreated to desorb dichlorodiphenyltrichloroethane, was assessed by performing an industrial-scale trial, focusing on the risks posed by emissions to the environment. Samples of the input and output in cement kiln were collected for determining clinker quality, production operation, pollutant emissions, cement kiln system destruction efficiency, and distribution profiles of persistent organic pollutants unintentionally produced from kiln. The destruction efficiency and destruction removal efficiency both were > 99.99% in cement kiln system at the appropriate CS feeding rate. Emissions of stack gases produced by cement kilns co-processing CS were within the reasonable range set in China. Dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs) concentrations and distribution profiles in flue gases and particulate samples from two tests showed PCBs mainly formed at the same sites as PCDD/Fs, indicating they are may formed in a similar way in cement kiln. A comparison with the processing parameters in the clinker, cement kiln dust, and flue gas under baseline and co-processing conditions, manifested that co-processing had no effect on the operation or cement quality of the cement kiln. Thus co-processing CS at a rate of 20 t/h with pretreatment process, is an environmentally sound and highly efficient treatment for CS.

The potential oxidation characteristics of CaCr2O4 during coal combustion with solid waste in a fluidized bed boiler: A thermogravimetric analysis.

CaCr2O4 (Cr (III)), mainly generated through the decomposition of CaCrO4 (Cr (VI)), is a significant intermediate for toxic Cr (VI) formation during solid fuel combustion. In this study, the formation, oxidation and sulfation kinetics of CaCr2O4 were analyzed to forecast the potential of CaCr2O4 oxidation during co-firing of coal and solid waste in a circulating fluidized bed boiler. The results indicated that the formation and oxidation of CaCr2O4 were fitted to a single step nucleation and growth model while CaCr2O4 sulfation was fitted to a shrinking core model. CaCr2O4 formation through CaCrO4 decomposition was favored in oxygen-lean atmosphere and considerably suppressed in the presence of oxygen. In contrast, CaCr2O4 oxidation was mainly determined by the contacts between CaCr2O4 and CaSO4/CaO, which influenced not only oxidation rates but also the product species. Moreover, the oxidation reactivity of CaCr2O4 was higher in the presence of CaO than that of CaSO4. On the other hand, CaCr2O4 sulfation can occur more easily than CaCr2O4 oxidation, the reaction rate of which was deeply affected by sulfate product layer. Findings in this study suggested that spraying calcium in furnace for desulphurization may increase the risk of CaCr2O4 oxidation. Measures including the adjustment of Ca/S ratio in blended fuel (with added limestone) and operating conditions (such as temperature and local atmosphere) in co-firing system could be taken to control CaCr2O4 formation and oxidation.

Industrial disposal processes for treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans in municipal solid waste incineration fly ash.

Hazardous waste disposal is a serious environmental concern in China. Therefore, in this study, industrial trials were conducted in a low-temperature thermal degradation facility, a tunnel kiln, and a shaft kiln to effectively treat dioxins in municipal solid waste incineration (MSWI) fly ash. The results indicated that the low-temperature thermal degradation facility efficiently decomposed polychlorinated dibenzo-p-dioxins and dibenzofurans in the MSWI fly ash. Additionally, the concentrations of dioxins in the treated fly ash and exhaust gas were lower than the suggested standard limits and the degradation ratio of dioxins was ∼99%. Therefore, treated fly ash characterized by acceptable dioxin risks could be utilized for the production of non-fired building materials. The results from the tunnel kiln indicated complete decomposition of the dioxins in the firing and insulating sections. However, the addition of fly ash in the tunnel kiln increased the concentration of dioxins in the flue gas. This can be primarily attributed to the heterogeneous catalytic synthesis reaction in the low-temperature section of the tunnel kiln. The results from the shaft kiln indicated degradation of at least 22% of the dioxins in the ash. The dioxin concentration in the flue gas was lower than the national standard while that in the clinker was within a reasonable limit. Furthermore, the environmental risks were significantly reduced at fly ash addition ratios lower than 3%.

Arsenic migration during co-processing of secondary residues from ammonium paratungstate production in cement kiln.

To reduce the environmental pollution caused by ammonium paratungstate (APT) production in the Ganzhou area in China, simulated experiments in laboratory and field experiments in cement kilns were performed. The migration characteristics of As in secondary residues (thermometallurgy and hydrometallurgy residues) from APT production in cement kilns were similar, and As in the residues existed in the form of sulfides. When the residues were fed at the kiln inlet, the As in the residues was completely distributed in the clinker after a new mass balance of As was reestablished in a very short time. When the residues were fed at the raw mill, the total input rate of As was far higher than the total output rate. Therefore, a part of As was circulated in the cement kiln, and only a small part of As was distributed in the clinker. In addition, the As concentration in the flue gas and the leaching concentration of As in the clinker were far below the limit value in the Chinese standard. For feeding rates below that are used in the field experiment, co-processing of secondary residues in a cement kiln fed at the kiln inlet is environmentally safe. However, if the secondary residues are consistently fed at the raw mill, the As concentration in the flue gas may gradually increase.

Destruction and formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during pretreatment and co-processing of municipal solid waste incineration fly ash in a cement kiln.

During a three-day industrial trial, municipal solid waste incineration fly ash (FA) was co-processed in a cement kiln after water-washing pretreatment for waste-to-resource conversion. All inputs and outputs were sampled to obtain the dioxin fingerprints. During washing, the relative contents of polychlorinated dibenzo-p-dioxins and dibenzofurans in FA, washed FA and sludge were basically the same and only a simple physical migration resulted. During drying, only physical processes resulted, which included volatilization and migration. Minimal dioxins residue remained in the clinker, cement kiln dust and flue gas, and the dioxins degraded completely. Through co-processing, the dioxins degraded obviously. The main compounds synthesized include 1,2,3,4,7,8-hepta-chlorodibenzo-p-dioxin, 2,3,7,8-tetra- chlorodibenzofuran and octa-chlorodibenzofuran. A comparison of dioxins fingerprints in the clinker, cement kiln dust and flue gas under baseline and co-processing conditions showed that co-processing had no effect on the cement kiln production. The baseline sample also contained a certain amount of dioxins, possibly because of the 'memory effect' and heterogeneous formations. The dioxins concentrations in the clinker and FA were far lower than the national standards. Thus, no environmental risk results during co-processing.

Characterization of heavy metals and PCDD/Fs from water-washing pretreatment and a cement kiln co-processing municipal solid waste incinerator fly ash.

A disposal method for fly ash from a municipal solid waste incinerator (MSWI-FA) that involved a water washing pretreatment and co-processing in a cement kiln was tested. The mass flows of toxic heavy metals (HMs), including volatile HM (Hg), semi-volatile HMs (Pb, Cd, Tl, and As), and low-volatility HMs, and polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran (PCDD/Fs) in the input, intermediate, and output materials were characterized. The flue gas Hg concentrations from tests 0, 1, and 2, fed with 0, 3.1, and 1.7 t/h of dried-washed FA (DWFA), were 28.60, 61.95, and 35.40 µg N m-3, respectively. Co-processing of DWFA did not significantly affect the metal concentration in clinker as most of the major input metals, with the exception of Cd, Pb, and Sb (which came from DWFA), were from raw materials and coal. Co-processing of DWFA did not influence on the release of PCDD/Fs; baseline and co-processing values ranged from 0.022 to 0.039 ng-TEQ/N m3, and from 0.01 to 0.031 ng-TEQ/N m3, respectively. The total destruction efficiency for PCDD/Fs in MSWI fly was 82.6%. This technology seems to be an environmentally sound option for the disposal of MSWI-FA.

A full-scale study on thermal degradation of polychlorinated dibenzo- p-dioxins and dibenzofurans in municipal solid waste incinerator fly ash and its secondary air pollution control in China.

Degradation of polychlorinated dibenzo- p-dioxins and dibenzofurans in municipal solid waste incinerator fly ash is beneficial to its risk control. Fly ash was treated in a full-scale thermal degradation system (capacity 1 t d-1) to remove polychlorinated dibenzo- p-dioxins and dibenzofurans. Apart from the confirmation of the polychlorinated dibenzo- p-dioxin and dibenzofuran decomposition efficiency, we focused on two major issues that are the major obstacles for commercialising this decomposition technology in China, desorption and regeneration of dioxins and control of secondary air pollution. The toxic equivalent quantity values of polychlorinated dibenzo- p-dioxins and dibenzofurans decreased to <6 ng kg-1 and the detoxification rate was ⩾97% after treatment for 1 h at 400 °C under oxygen-deficient conditions. About 8.49% of the polychlorinated dibenzo- p-dioxins and dibenzofurans in toxic equivalent quantity (TEQ) of the original fly ash were desorbed or regenerated. The extreme high polychlorinated dibenzo- p-dioxin and dibenzofuran levels and dibenzo- p-dioxin and dibenzofuran congener profiles in the dust of the flue gas showed that desorption was the main reason, rather than de novo synthesis of polychlorinated dibenzo- p-dioxins and dibenzofurans in the exhaust pipe. Degradation furnace flue gas was introduced to the municipal solid waste incinerator economiser, and then co-processed in the air pollution control system. The degradation furnace released relatively large amounts of cadmium, lead and polychlorinated dibenzo- p-dioxins and dibenzofurans compared with the municipal solid waste incinerator, but the amounts emitted to the atmosphere did not exceed the Chinese national emission limits. Thermal degradation can therefore be used as a polychlorinated dibenzo- p-dioxin and dibenzofuran abatement method for municipal solid waste incinerator source in China.

Distribution of Hg, As and Se in material and flue gas streams from preheater-precalciner cement kilns and vertical shaft cement kilns in China.

The aim of this study was to evaluate the behavior of Hg, As, and Se in cement production. Two types of cement plants were studied, including the vertical shaft kiln (VSK) and preheater-precalciner kiln (PPK) processes. Determination of Hg, As, and Se in the main material and gas streams were performed. It was found that recycling of particulate matter captured by an air pollution control device caused a significant enrichment of Hg and As inside both processes. The total quantity of Hg entering the process and the quantity emitted to the atmosphere were found to be 10-109 and 6.3-38 mg, respectively, per ton of clinker produced. The average Hg emission was calculated to be around 41% of the total mercury input. The emissions found complied with the European Union (EU) limit and exceeded partly the U.S. limit. Furthermore, it was found that oxidized mercury was the dominant species in the PPK process, whereas the reduced form was dominant in the VSK process, due to the oxidizing and reducing gas conditions, respectively. Regarding the distribution of As and Se, the major amounts were bound to the solid materials, that is, cement clinker and particulate matter. Based on cement production data in China in 2013, the annual emissions of Hg and As were estimated to be in the range of 8.6-52 and 4.1-9.5 tons, respectively.