Heavy Metals In Fly Ash Research Articles

"Evaluation of Health Status and Effects of Thermal Power Plant Pollutants on the Population's Health and the Environment around the Plant"

The quality of the soil, air, and water are significantly impacted by coal-fired thermal power plants (TPPs), which negatively affects the surrounding environment and human health. The current study's goals were to detect specific heavy metals in fly ash, air, water, and soil samples, as well as to evaluate the respiratory health of the community living close to the plant. Materials and Procedures In the current cross-sectional study, 3533 adult people from two strata within a 10-kilometer radius of the TPP in the Karnataka state's Udupi district participated. Semi-structured questionnaires, spirometry, environmental air monitoring with a DustTrak aerosol monitor, water samples, and soil samples were used to obtain the data. Results: The majority of the study's participants were over 45 years old (41.4 percent). There were 70.6 percent females and 0.39 percent transgender people. There were different respiratory issues in 4.3 percent of the population. According to bivariable logistic regression, participants aged 46–65 and >65 respectively had 2.91- and 4.42-times greater risks of respiratory disease than those aged 45 years. The results of multivariable logistic regression revealed a significant correlation between older age groups and subjects who had closed their windows while cooking (P 0.006). While the amounts of iron, manganese, and copper in the ground water samples were overly high, the levels of heavy metals in soil samples and particulate matter 2.5 were well within allowable limits. The results of this study have consequences for the formulation of policies that safeguard the environment and human health.

Co-stabilization/solidification of heavy metals in municipal solid waste incineration fly ash and electrolytic manganese residue based on self-bonding characteristics

Municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue (EMR) were classified as hazardous waste, must be harmlessly processed prior to subsequent treatment or disposal. The competition between massive free manganese ions of raw EMR and other heavy metals was found, thus raw EMR was pretreated by calcining to eliminate competition of manganese with other heavy metals for stabilizer complexation. MSWI fly ash was successfully solidified with 6% NaH2PO4, 6% H2NCSNH2 and 20% sintered EMR (800 °C). The addition of sintered EMR enhanced solidification/stabilization of heavy metals in fly ash and the resulting product had a higher compressive strength for further reutilization like trench backfilling, structural fill and void filling. The stabilization/solidification mechanism of heavy metals was attributed to the combined interaction of heavy metal precipitation in stabilizers and ion exchange or physical encapsulation in silicate compounds like calcium silicate, which is a feasible and valuable approach to co-disposal of MSWI fly ash and EMR.

Novel hydroxyapatite (HAP)-assisted hydrothermal solidification of heavy metals in fly ash from MSW incineration: Effect of HAP liquid-precursor and HAP seed crystal derived from eggshell waste

Novel hydroxyapatite (HAP)-assisted hydrothermal methods were applied to solidify heavy metals in fly ash (FA) from solid waste incineration to create hydrothermally-treated (HT) products that meet landfilling standards. The leaching behavior, speciation distribution of heavy metals, and characteristics of HT products were analyzed by XRD, FT-IR, SEM-EDX, and XPS to explore the solidification mechanism. Large amounts of Ca2+, HPO42−, and PO43− in the HAP liquid-precursor (LP-HAP) directly formed hydrothermally-synthesized HAP and reacted with heavy metal ions to form stable compounds. Adsorption and ion exchange occurred between HAP and metals (i.e., Pb2+, Cd2+, and Zn2+), in which heavy metals occupied the Ca2+ sites. For one-step hydrothermal method with LP-HAP, a lower temperature of 35 °C resulted in better solidification efficiency than a subcritical temperature of 140 °C. By adding hydroxyapatite seed crystal (C-HAP) during the second step of two-step hydrothermal method, solidification was improved because more HAP or metal-exchanged HAP was formed via seed-induced mechanism. Under hydrothermal conditions, LP-HAP and C-HAP additives reduced the leaching toxicity but also inhibited the transfer of heavy metals from FA to the liquid phase. The overall pollution toxicity index of HT products from the optimized two-step hydrothermal method with LP-HAP and C-HAP was reduced by 96.3%.

Synergistic effect of polyvinyl chloride and coal ash on thermal separation of heavy metals from MSWI fly ash through molten salt process.

Municipal solid waste incineration fly ash (FA) contains high contents of salts and high concentrations of heavy metals, which makes FA disposal extremely difficult. However, heavy metal elements could potentially be separated from FA during thermal treatment process to make it possible to be recycled. This work aims to study the volatilization of heavy metals in FA treated by molten salt method. The influence of polyvinyl chloride (PVC) and coal ash (CA) on volatilization of heavy metals was investigated. Within the scope of this study, the highest heavy metal removal rate can be under the condition: the calcium chloride/sodium chloride weight ratio 1:1, the FA/molten salt weight ratio 1:10, treatment temperature 1000°C for 2 hours in reducing atmosphere. The volatilization rates of lead, zinc, copper, chromium and manganese were 86.20, 67.53, 65.24, 50.07 and 39.45%, respectively. On the basis of molten salt treatment, adding PVC could promote the volatilization of heavy metals. The volatilization rate of lead was 96.71%, and the volatilization rates of chromium and manganese were higher than 60% when the content of PVC was 5 wt%. When adding 10 wt% CA and 1 wt% polyvinyl chloride, the volatilization rate of lead could reach 100%. The experiments and thermodynamic calculations showed that silicon dioxide and aluminium oxide in CA and hydrochloric acid decomposed from PVC could promote the chlorination and volatilization of heavy metals. The volatilized heavy metal chlorides provided the possibility of recovery and utilization of heavy metals in FA.

Reduced Utilization Process Leaching Toxicity by Stabilizing Heavy Metals in Fly Ash from MSW Incineration Based on Hydrothermal Oxidation.

Hydrothermal oxidation is an effective approach to reduce leaching toxicity of fly ash from municipal solid waste incineration during utilization process. Herein, the effects of temperature, time, pH and Ce-Mn catalyst dosage on the stabilization of heavy metals in fly ash during hydrothermal oxidation were studied. The temperature of hydrothermal oxidation was positively correlated to the stabilization effect. However, the reaction time and pH emerged unstable effect. The amount of Ce-Mn catalyst had a slightly positive effect on the stabilizing at low doses, but it can be inhibited by excessive dose. The leaching concentrations of all heavy metals accorded with National Wastewater Discharge Standard of China (GB 8978-1996) under the optimal parameters, especially for Pb, Ni and Cu. The heavy metals were transformed from unstable fractions to residue fractions during hydrothermal process, among which the proportion of Cu and Zn residue fractions significantly increased and further reduced leaching toxicity.

Stabilization of heavy metals in municipal solid waste incineration fly ash via hydrothermal treatment with coal fly ash

The environmental risk of heavy metals in hazardous municipal solid waste incineration fly ash (FA) is one of the most important concerns for its safely treating and disposing. This study investigated the stabilization behavior of heavy metals in FA using coal fly ash (CFA) as an additive via hydrothermal treatment. The effects of water washing pre-treatment and FA/CFA ratio on leaching behavior, speciation evolution, and risk assessment of heavy metals were studied. The results showed that 96.6–98.0 % of Cl can be effectively removed by water washing pre-treatment and hydrothermal treatment. Most heavy metals (Cr, Cu, Ni, Pb and Zn) (>91.5 %) were stabilized in the hydrothermal product, rather than transferred to liquid phase. Tobermorite can be synthesized by adjusting Ca/Si ratio with the addition of CFA. The heavy metals were transferred into more stable residue fractions with increasing CFA addition, which resulted in the significant reduction of leaching concentrations and risk assessment code (RAC) of heavy metals. Among, the product with 30% CFA exhibited the most superior performance with the lowest leaching concentrations of heavy metals and RAC was at no risk level (<1). In addition, the economic performance of hydrothermal treatment exhibited a potential advantage by comparing with FA-to-cement, FA-to-glass slags and FA-to-chelating agent & cement solidification/stabilization. Therefore, the hydrothermal treatment coupled with water washing pre-treatment would be a promising method for the detoxification of FA, as well as synergistic treatment of FA and CFA.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Supercritical CO2 coupled with mechanical force to enhance carbonation of fly ash and heavy metal solidification

Accelerated carbonation of fly ash is a potential way to achieve CO2 emission reduction and heavy metal solidification. Slow conversion in the diffusion control stage is the bottleneck of the carbonation technical route. Based on the strong diffusion and permeability of supercritical CO2, and the modification of mechanical force to produce more fresh surfaces and pores, a method consisting of supercritical CO2 coupled with mechanical force was carried out to strengthen the carbonation of fly ash. Research results show that the carbonation efficiency of fly ash under supercritical CO2 is generally higher than under low-pressure conditions, and carbonation under supercritical CO2 can effectively stabilize heavy metals in fly ash. In this work, the optimal amount of carbon sequestration under low-pressure was found to be 42.3 g-CO2/kg-fly ash (g/kg), with a carbonation efficiency of 18.65%. Under the supercritical condition of 8 MPa, the maximum carbon sequestration by fly ash is 54.9 g/kg, and the carbonation efficiency is 24.20%. In experiments with mechanical ball milling modification, the order of carbonation efficiency is: wet milling modified ashes > dry milling modified ashes > raw ashes. Additionally, carbonation has an obvious inhibitory effect on the leaching of Pb, Cr and Cd from fly ash.

Review on the Progress of Treatment Methods of Heavy Metals in Municipal Solid Waste Incineration Fly Ash

Municipal solid waste incineration is an important method of solid waste management, though this method reduces a great portion of the waste volume, it also produces fly ash which is rich in dioxins, heavy metals, soluble salts and other harmful substances that can be detrimental to the environment if not well treated. The disposal of incineration residues especially fly ash has been of great concern, due to the wide range of heavy metals and soluble salt which are harmful to the environment and groundwater This paper aims to evaluate the advantages and disadvantages of the different treatment techniques (land fill, chemical stabilization, acid extraction, cement solidification etc.,) of heavy metals in Municipal Solid Waste Incineration Fly Ash (MSWIFA) which have been used. Over the years scientist have experimented better ways to either eliminate, utilize or consolidate heavy metals in fly ash. Therefore, a systematic and structural review of both ancient and recent treatment methods of heavy metals in MSWIFA for different geographical locations is done following three principal criteria’s; (i) treatment efficiency, (ii) cost, and (iii) operability. The study depicts that the cement solidification method was mostly used because it is cheap and easy to operate, whereas vitrification method is expensive due to high energy consumption. On the other hand, methods such as; chemical stabilization, melting process, geopolymer and acid extraction are very costly. This review provides some guidance; on the selection of the best treatment methods of heavy metals in MSWIFA, useful for the application of a zero-waste concept which goes beyond traditional composting and recycling.

Assessment of health status and impact of pollution from thermal power plant on health of population and environment around the plant in Udupi District, Karnataka.

Coal-fired thermal power plants (TPPs) have a serious impact on soil, air, and water quality resulting in deterioration of health and environment around the plant. The present study was undertaken with the objectives of assessing the respiratory health status of the population around the plant and to measure selected heavy metals in fly ash, air, water, and soil samples. The current cross-sectional study was conducted among 3533 adult residents living in two strata within 10 km radius around the TPP in Udupi district of Karnataka state. Data were collected by using semi-structured questionnaire and spirometry and environmental air monitoring by DustTrak aerosol monitor, water, and soil samples were collected for analysis. Majority of the study participants were in the age group of >45 years (41.4%). 70.6% were females and 0.39% were trans-genders. 4.3% were suffering from various respiratory problems. Bivariable logistic regression showed subjects aged 46-65 years and >65 years have 2.91 times and 4.42 times higher odds of respiratory disease as compared to those with age ≤45 years. Multivariable logistic regression showed significant association between higher age group (P < 0.0001) and in subjects who had closed window during cooking (P < 0.006). Levels of heavy metals in soil samples and particulate matter 2.5 were well within permissible limits whereas the ground water samples had excess levels of iron, manganese, and copper. The present study has implications for policymaking to protect the environment and health of vulnerable populations in industrial clusters and the vicinity of power plants.

Mechanochemical stabilization of heavy metals in fly ash from coal-fired power plants via dry milling and wet milling.

Fly ash from coal-fired power plants has become the world's largest solid waste pollutant. The mechanochemical (MC) method used as a non-thermal method shows good stability to heavy metals in soil and municipal solid waste incineration (MSWI) fly ash. It is first uesd to stabilize the heavy metals in fly ash from coal-fired power plants. In this paper, dry milling and wet milling MC methods were carried out on fly ash from a 300MW supercritical circulating fluidized bed (CFB) boiler. The relative leaching rate (RLR) is defined to indicate the degree of leaching. Experimental results show that after mechanochemical treatment for 10h, the RLRs of Cu, Cr, Pb, Zn, Cd, and Ni by dry milling decrease by 52.10%, 70.16%, 89.80%, 22.97%, 3.15%, and 23.49% respectively, and the RLRs of Cu, Cr, Pb, Zn, Cd and Ni by wet milling decrease by 58.11%, 70.92%, 89.64%, 23.26%, 10.59%, and 30.77% respectively. Compared with dry milling, the fly ash particle size is smaller after wet milling, indicating that the presence of water will weaken the agglomeration of fine particles. A continuous extraction experiment shows that the water-and acid-soluble fraction of the six heavy metals in fly ash can be reduced by dry or wet milling, and the residual fraction can be increased.

Geopolymer hybrid fly ash concrete for construction and conservation in peat environment: A review

Fly ash is industrial residue from the coal combustion in electric and steam generating plants and recognized as an environmental pollutant. Fly ash contains a high concentration of silica and alumina and can be used as geopolymer concrete. Studies the use of fly ash as a geopolymer concrete mixture has been developing in recent decades. This review focuses on the characteristics of fly ash as hybrid geopolymer concrete, and its resistance is peat environment. The hybrid geopolymer is made by activating fly ash using an alkaline activator and Portland cement. The addition of fly ash geopolymer concrete with Portland cement forms N-A-S-H bond structure from fly ash, and C-S-H hydration bond from Portland cement forms C-A-S-H, which is more solid and stronger against aggressive environment such as peat. In addition, the geopolymer concrete is proven to be able to mobilize heavy metals in fly ash so the concrete has low leaching rate and not harmful to the peat ecosystem. This review proves that hybrid geopolymer concrete using fly ash is a potentially innovative and promising material in the future. The geopolymer hybrid not only has its resistance to peat and acts as conservative material in an environmentally friendly peat environment.

Coal beneficiation technology to reduce hazardous heavy metals in fly ash

Fly ash emitted from the coal-fired power plant is the major contributor of the outdoor airborne particulate matters (PMs). Coal beneficiation, an industrial process to improve the quality of raw coal by removing ash-bearing components, can be a cost-effective sustainable and clean technology to reduce the emission of hazardous trace metals. As the removal efficiency of mineral matters and heavy metals within the coal is depend highly on the raw coal and the employed beneficiation process, a wide range of case studies at laboratory- and industrial-scale, published in the last 20 years, are reviewed in this study. Our review indicates that the coal beneficiation processes can effectively reduce content of heavy metals of fly ash, encouraging the use of clean coal to reduce pollutants emission.

Experimental study on the stabilization of heavy metals in fly ash from municipal solid waste incineration by N-30 alkaline silica sol

The disposal of municipal solid waste incineration fly ash is a key environmental issue in China. The high content of heavy metals in fly ash makes ash disposal extremely difficult. A new method which binds N-30 alkaline silica sol and temperature was proposed for the first time in this study. The crystal composition and the patterns of heavy metal leaching concentration and speciation in fly ash were obtained via experiments. The results showed that adsorption of the self-made curing agent and the formation of metal silicate and phosphate promotes the migration of heavy metals from an unstable acid state to a stable residue state, thus improves the stability of heavy metals. The optimum temperature of self-made N-30 alkaline silica sol during treating process is about 700℃. Moreover, the risk assessment of heavy metal emission has proved that, the leaching amount of heavy metals after treatment reaches a risk-free level.

Residual and ecological risk assessment of heavy metals in fly ash from co-combustion of excess sludge and coal

Co-combustion of municipal excess sludge (ES) and coal provides an alternative method for disposing ES. The present study aims to investigate the residual and ecological risk of heavy metals in fly ash from co-combustion of ES and coal. The total concentration and speciation distribution of heavy metals, characterization of SEM, EDX, XRD and leaching test were carried out to assess the fly ash in this study. The results showed that the total concentrations of Cu, Zn and Mn were higher than others in fly ash, and most heavy metals were concentrated in fine particles. For Cd, Cr and Pb, the percentages of speciation of F4 and F5 were all over 90%, suggesting the relatively lower leaching toxicity. The leaching percent of all heavy metals was lower than 5% by two diluted HNO3 solutions for fly ash. The potential ecological risks increased with the decrease of particle size of fly ash, and Cd accounted for the main fraction for ecological risk despite of lower concentration in comparison to other measured heavy metals.

Assessment of heavy metals mobility and correlative recovery and decontamination from MSWI fly ash: Mechanism and hydrometallurgical process evaluation

Fly ash from municipal solid waste incineration (MSWI) enriches many leachable toxic metals which readily migrate into the environment, posing serious risks to the ecosystem and human. In this study, the elements mobility, leaching availability as well as the potential maximum amounts of heavy metals in fly ash were thoroughly evaluated. To decontaminate the toxic elements from resulting fly ash leachates, The aqueous zinc (Zn) was recovered using Cyanex 572, cadmium (Cd) and copper (Cu) were effectively removed through adsorption process by a self-assembled hierarchical hydroxyapatite (HAP) nanostructure. The removal mechanism of Cd, Cu and Zn by leaching, extraction and adsorption was revealed with the results from XRD, ICP-MS and SEM. The results showed that fly ash has a high mobility under maximum availability leaching test (95% of fly ash was dissolved), a recovery rate of 91% for Zn can be obtained using Cyanex 572, and a high adsorption rate (> 95% for both Cu and Cd) was reached using HAP for the pristine fly ash leachate. The outcomes from isothermal and kinetic study revealed that Langmuir isotherm and pseudo-second order model can well describe the Cd and Cu adsorption behavior. Economic assessment suggested that the application of HAP for the removal of Cd and Cu is a technically sound and economically feasible approach. The findings of this study demonstrated that this comprehensive process integrated leaching, solvent extraction and consequential decontamination can be a practical strategy for MSWI fly ash treatment.

Formation Characteristics of PCDD/Fs in the Co-combustion and Pyrolysis Process of Coal and Sewage Sludge

ABSTRACT Co-combustion technology of coal and sewage sludge (SS) was encouraged and recommended in China. Previous studies most focused on its influence on combustion characteristics, migration characteristics of heavy metals in fly ash, and emission of conventional pollutants, etc., but less reported the formation characteristics of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs). To well reveal it, this study carried out five parallel experiments, including the pyrolysis of SS, the combustion of SS, the co-combustion of coal and SS with the proportion of 0%, 2.5% and 5%, respectively. The emission concentration of PCDD/Fs respectively increased from 0.42 ng g–1 (0.0022 ng I-TEQ g–1) to 0.54 ng g–1 (0.0030 ng I-TEQ g–1) and 1.70 ng g–1 (0.0305 ng I-TEQ g–1) with increasing blending proportion of SS. The dominant part was also changed from PCDF (0.32 ng g–1 in M-0%, 0.38 ng g–1 in M-2.5%) to PCDD (1.11 ng g–1 in M-5%). The formation concentration of PCDD/Fs in the combustion process of SS was about 0.34 ng g–1 (0.0019 ng I-TEQ g–1). In the pyrolysis process of SS, the concentration of PCDD/Fs was 0.59 ng g–1 (0.0037 ng I-TEQ g–1). The de novo synthesis should be the major formation pathway of PCDD/Fs in the co-combustion process of coal and SS. On the basis of sufficient carbon sources, the PCA analysis revealed the chlorine source (Cl) and metal catalyst (Fe) should contribute a lot on the formation of PCDD/Fs. The results paved the way for further optimization on the operation of co-combustion of coal and SS and assist in controlling the PCDD/F emission from co-combustion process.

Efficiency of burning sediments of waste water in a boiling layer

It has been experimentally shown that the Metso HYBEX steam boiler installed at CHP-1 of JSC APPM and designed to burn a mixture of bark and wood waste and sewage sludge ensures their efficient utilization without highlighting fuel oil. At boiler loads close to the nominal efficiency, the gross value was 85.22–85.24%. The environmental indicators of the boiler unit fully and even with a margin meet the requirements established by directive 2010/75 / EC and GOST R 50831-95. The operation of the boiler ensured the complete utilization of sewage sludge generated at the sewage treatment plant. The annual savings of fossil fuels amounted to more than 80 thousand tons of fuel equivalent. The total content of heavy metals in fly ash emitted into the atmospheric air by a recycling and energy boiler with a bubbling fluidized bed when burning high-moisture biofuels is many times lower than when burning coal, even in low-emission furnaces.

순환유동층 연소로에서 하수슬러지/목질계 바이오매스 혼합펠릿의 연소: 오염물질 저감을 위한 산화제 변화 영향

Combustion experiment for pellets of sewage sludge and woody biomass blend was conducted in a pilot-scale circulating fluidized bed combustor (CFBC) consisting of the riser, two hot cyclones and a loop-seal to reduce pollutant emission in exhausted flue gas. To achieve them, the effect of the oxidant variations, such as superficial velocity, equivalence ratio(ER: 1.2, 1.3, 1.4) and combustion atmosphere (air-fired and oxy-fired) was evaluated. As pollutant emissions in flue gas, SO₂, NO, CO, CO₂, HCl, odor contaminants and leaching behavior of heavy metals were analyzed. As a result, to stably operate combustion of pellet mixed with sewage sludge and woody biomass as alternative renewable fuel in a CFBC system, the superficial velocity in the riser had to be kept under 6 m/s and the equivalence ratio was proper around 1.3-1.4. All odor contaminants formed at these operating conditions met the domestic air pollutant standards. Heavy metals in fly ash met the environment ministry’s standard. Additionally, compared to air-firing, SO₂, NO and CO as precursors of fine particles during oxy-firing were reduced by 70.8, 77.1 and 38.2%, respectively.

The poisoning mechanisms of different zinc species on a ceria-based NH3-SCR catalyst and the co-effects of zinc and gas-phase sulfur/chlorine species

Low-medium temperature NH3-SCR technology has been applied for years in municipal solid wastes incineration (MSWI) to control the emissions of nitrogen oxides. Unlike coal-fired flue gases, the tail gas from MSWI contains high levels of heavy metals in fly ash, especially the zinc species, which may harm SCR catalysts. As such, in this paper, the deactivation mechanism of different zinc species (ZnO, ZnSO4 and ZnCl2) on the Sb-CeZr2Ox catalysts and the co-effects of zinc species and gas-phase pollutants (including SO2 and HCl) were investigated. The experimental results indicated that the deactivation rate of various poisoning zinc species was in the order of ZnCl2 > ZnSO4 > ZnO. Moreover, the interactions between zinc and antimony species would disrupt the structure of the Sb-Ce mixed oxides to decrease the redox ability, consequently suppressing the ammonia activation and NO adsorption. Furthermore, such damaging effects on catalyst structures would promote the formation of bulk-like sulfate species in the presence of SO2, resulting in a decreased mobility of surface oxygen species, which significantly decrease the sulfur resistance. However, the presence of HCl did not show an evident co-effect on the Zn poisoned sample owing to the limited coverage of the chlorine deposition.