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Thermal effects on arsenic emissions during coal combustion process
Abstract
In this study, the rate of emission of arsenic during the burning process of different kinds of coal is examined in order to study the volatile characteristics of arsenic during coal combustion which have negative effects on the ecological environment and human health. The results show that the emission rate of arsenic gradually increases with increased burning temperature, with a threshold of approximately 700°C to 800°C in the process of temperature increase. Then, the relationships among the arsenic emission rate and combustion environment, original arsenic content, combustion time, burning temperature, air flow and amount of arsenic fixing agent are discussed, and it is found that except for the original arsenic content, the rest of the factors have a nonlinear relationship with the emission rate of arsenic. That is, up to a certain level, they all contribute to the release of arsenic, and then their impact is minimal. The original arsenic content in coal is proportional to the arsenic emission rate. Therefore, taking into consideration the nonlinear relationships between factors that affect the arsenic emission rate can reduce contamination from arsenic.
... Arsenic association with calcareous minerals is in agreement with other fluidizedbed coal combustion results [47,[50][51][52][53][54]. Most researchers reported efficient As retention using CaO [52][53][54]; however, CaSO4 can also capture As [43,55]. ...
... Arsenic association with calcareous minerals is in agreement with other fluidizedbed coal combustion results [47,[50][51][52][53][54]. Most researchers reported efficient As retention using CaO [52][53][54]; however, CaSO4 can also capture As [43,55]. Since the correlation coefficient r(As-SO3) is very high as well (r = +0.906), the association of As to calcareous sulphates can be expected. ...
Separation of coal ash into magnetic and non-magnetic fractions facilitates their utilization when processed separately. Due to desulphurization additives added to coal during the fluidised-bed combustion, non-magnetic fractions often contain elevated CaO levels (while magnetic concentrates are typically rich in Fe2O3). Both CaO and Fe2O3 are known for their ability to bind As during the combustion, whose distribution is a crucial parameter in terms of proper utilization of these fractions. Therefore, the study deals with the As partitioning within magnetic and non-magnetic fractions of fluidized-bed coal combustion ashes. Two different (successive) procedures of dry magnetic separation were used to separate each ash into strongly magnetic, less magnetic, and a non-magnetic fraction. Due to their optimal utilization, the concentrations of As and other target elements in these fractions were evaluated and compared. Magnetic concentrates from the first separation step (in vibrofluidized state) contained 60–70% Fe2O3, magnetic concentrates separated manually out of the residues after the first separation contained 26–41% Fe2O3, and the non-magnetic residues contained 2.4–3.5% Fe2O3. Arsenic levels were the highest in the non-magnetic residues and gradually decreased with the increasing Fe2O3 content in the magnetic fractions. The dominant As association in the studied samples was to CaO (r = +0.909) and with SO3 (r = +0.906) whereas its joint occurrence with Fe2O3 was improbable (r = −0.834).
... The mining and smelting of arsenic-containing minerals and the use of arsenic-containing pesticides are the main reasons for the excessive arsenic content in water bodies (Yan et al., 2015). The World Health Organization (WHO) has regarded the removal of arsenic a priority because of its toxicity to humans (Zhang et al., 2018). ...
The removal of trivalent arsenic (As (III)) from water has received extensive attention from researchers. Iron electrocoagulation (Fe-EC) is an efficient technology for arsenic removal. However, electrode passivation hinders the development and application of Fe-EC. In this work, an innovative Fe-EC route was developed to remove As (III) through an electrochemical-siderite packed column (ESC). Ferrous ions were produced from siderite near the anode, and hydroxide was generated near the cathode during the electrochemical decomposition of siderite. As a result, an effect of Fe-EC-like was obtained. The results showed that an excellent removal performance of As (III) (>99%) was obtained by adjusting the parameters (As (III) concentration at 10 mg/L, pH at 7, Na2SO4 at 10 mM and the hydraulic retention time at 30 min) and the oxidation rate of As (III) reached 84.12%. The mechanism analysis indicated that As (III) was oxidized to As (Ⅴ) by the produced active oxide species and electrode, and then was removed by capturing on the iron oxide precipitates. As (III) was likely to be oxidized in two ways, one by the reactive oxygen species (possibly •OH, Fe(IV) and •O2⁻ species), and another directly by the anode. The long-term effectiveness of arsenic removal demonstrated that ESC process based on the electrochemical-siderite packed column was an appropriate candidate for treating As (III) pollution.
... Exceptionally, As abundance in Bac Giang and Hai Phong were 3.1 and 22.8-times higher than that of HCMC. Studies have considered As as a tracer for coal combustion especially in industrial sectors (Cheng et al., 2018;Zhang et al., 2018;Wu et al., 2020) which could imply more coal-burning activities (e.g., industrial zone or coal fire power plans) observed in northern Vietnam than southern regions. Besides, we also attempted to compare the HCMC PM10-HMs with results shown in a previous study (Hien et al., 2001). ...
Airborne particulate matter (PM) pollution is a global concern, in which partitioned heavy metals (HMs) could impose great risks to residents living in metropolitan areas. In this study, PM10 samples were collected in Ho Chi Minh City (HCMC) – a megacity in southern Vietnam – and analyzed for 11 HMs to investigate their concentration profiles, perform source apportionment and estimate their risk factors. Results showed that atmospheric HMs concentration decreased following the order of Al > Fe > Sr > Mn> Pb > Cu > Cr > V > Ni > Sb > As. Traffic activities were likely the major cause of rush-hour peaks for most HMs in which Cr, As, and Cu showed > 20% increases in their relative proportions. For seasonal variation, most HMs showed a dry > rainy pattern as a result of washout by higher rainfall in the rainy season while crustal elements (Al, Sr, Mn) showed a rainy > dry pattern and might be explained by the difference in air mass transport modulating by monsoon activities. The positive-matrix factorization (PMF) model revealed 5 primary sources for HMs, including traffic emission, shipping activity and combustion activity, fugitive dust re-suspension and waste incineration. Combustion activity might enrich As, Sb, Pb levels at HCMC, and As contributed half (50.8%) to the potential ecological risk (PER) in the city. Besides, the current Cr level could impose a carcinogenic effect towards children in HCMC (total carcinogenic index > 10-4) while Mn might impose intolerable non-carcinogenic risk (hazard index > 1). This study provides information on local air quality status for scientific and regulatory perspectives as well as helps fill the information gap and update the understanding of air pollution in South and Southeast Asia.
... As a native special agricultural product, chili peppers are very popular in Guizhou; when dried over high-arsenic coal fires in rural kitchens, chili peppers can adsorb 550 ppm of arsenic on average, while the amount of arsenic in kitchen dust reaches 3000 ppm (Finkelman et al. 1999). Arsenic can be released to the environment during coal processing and combustion (Kang et al. 2011;Zhang et al. 2018), thus causing arsenicosis, leading to skin lesions, lung dysfunction, neuropathy, nephrotoxicity, cirrhosis, ascites, and even skin or liver cancer. This condition has been recognized since 1976, largely due to exposure to coal-burning arsenic in the air and/or on crops (Liu et al. 2002;Zhang et al. 2007). ...
Exposure to arsenic-contaminated air and food caused by the burning of coal in unventilated indoor stoves is a major environmental public health concern in Guizhou Province, China. The liver is one of the main target organs for coal-fired arsenic exposure; however, there is little information about the risk assessment between cumulative arsenic exposure and the prevalence of liver damage. This study first evaluated the chronic daily intake (CDI) for two exposure pathways (inhalation and ingestion) and five environmental media (i.e., indoor and outdoor air, drinking water, rice, corn, and chili peppers) in 1998, 2006, 2014, and 2017. Then, the dose-effect and dose-response relationship between hair arsenic (HA) and cumulative arsenic (CA) levels and liver damage was analyzed. The results clearly show that the CDI in 1998 was 34.9 μg·kg−1·d−1, 22.9 μg·kg−1·d−1 in 2006, 11.7 μg·kg−1·d−1 in 2014, and 6.7 μg·kg−1·d−1 in 2017 in the arsenic exposure area. All of these values were higher than the daily baseline level of 3.0 μg·kg−1·d−1 as recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), and the increased HA and CA can increase the risk of coal-fired arsenic-induced liver damage. In addition, we analyzed the possible maximum acceptable CA exposure level for coal-fired arsenic-induced liver damage using the Bayesian benchmark dose. The recommended maximum acceptable CA exposure level for liver damage caused by coal-burning arsenic is 7120 mg. This study provides scientific insight into understanding the dose-response relationship of liver damage caused by coal-burning arsenic exposure and the monitoring and prevention of arsenic poisoning.
... The mining and smelting of arsenic-containing minerals and the use of arsenic-containing pesticides are the main reasons for the excessive arsenic content in water bodies (Yan et al., 2015). The World Health Organization (WHO) has regarded the removal of arsenic a priority because of its toxicity to humans (Zhang et al., 2018). ...
The use of iron species to remove PO4³⁻ is widely used, and the fresh Fe³⁺ produced in situ demonstrate better effect on the removal of PO4³⁻ in many researches. Therefore, in order to develop a simpler and more efficient method for PO4³⁻ removal, we designed an easy operation by electrochemically dissolving siderite to produce fresh Fe³⁺ in situ for PO4³⁻ removal from wastewater. Results showed that current intensity at 20 mA, initial pH at 6, initial PO4³⁻ concentration at 6 mM and influent flow rate at 2.5 mL min⁻¹ were the best parameters for removing PO4³⁻, ensuring that the PO4³⁻ concentration of effluent can be kept below 1 mg L⁻¹ through the electrochemical system. Different from other studies, a large amount of Fe²⁺ can be dissolved from natural minerals without adding H⁺ to the system and Fe³⁺ species are generated in situ from the oxidation of the Fe²⁺ without using a specific oxidizer. This electrochemical treatment method with siderite as a packed column can be used as a new method of high efficiency, simple operation and low-cost for treating eutrophic water bodies.
... In China, As concentration in coal ranges from 0.24 to 71 µg/g, and the average concentration is 5.5 µg/g [13]. In addition, the As concentration level in coal from southwestern provinces is higher than that from other provinces [14,15]. ...
Arsenic emission from coal combustion power plants has attracted increasing attention due to its high toxicity. In this study, it was found that there was a close relationship between the ash fusion temperature (AFT) and arsenic distribution based on the thermodynamic equilibrium calculation. In addition to the AFT, coal characteristics and combustion temperature also considerably affected the distribution and morphology of arsenic during coal combustion. Thus, an arsenic volatilization model based on the AFT, coal type, and combustion temperature during coal combustion was developed. To test the accuracy of the model, blending coal combustion experiments were carried out. The experimental results and published data proved that the developed arsenic volatilization model can accurately predict arsenic emission during co-combustion, and the errors of the predicted value for bituminous and lignite were 2.3–9.8%, with the exception of JingLong (JL) coal when combusted at 1500 °C.
... In China, As concentration in coal ranges from 0.24 to 71 µg/g, and the average concentration is 5.5 µg/g [13]. In addition, the As concentration level in coal from southwestern provinces is higher than that from other provinces [14,15]. ...
Coal blending has been extensively applied in coal-fired power plant. The emission of trace elements was greatly affected by the change of combustion characteristic in the blended coal. Based on thermodynamic calculation and combustion experiments, the distribution of arsenic and selenium in the process of SH bituminous and HLH lignite co-combustion were investigated at a wide temperature range (500–1500 °C). The result of thermodynamic calculation displayed that the main existing forms of arsenic were considered as Ca3(AsO4)2(s), As4O6(g), and As2O3(g). At temperatures below 1000 °C, As4O6 was deemed the dominant gas-phase species of arsenic. Moreover, the form of selenium was predicted to be SeO2(g) which accounted for almost 100% of the selenium species at 500–1100 °C. When the temperature was increased to 1200 °C, gaseous-phase SeO begun to appear. The result of co-combustion experiments suggested that the retention ratio of arsenic and selenium in ash was decreased obviously at 500–900 °C with the increasing of temperature, which was consistent with the result of the calculation. SH coal had more effective arsenic and selenium retention capacity than HLH coal at 500–900 °C. The retention ratio of arsenic in 3SH:1HLH coal was fluctuated between 6.20 and 18.04%, and that of 1SH:3HLH coal was 3.29–7.08%. The retention ratio of selenium in the ash of mixed coals combusted at different temperature was lower than 7%, especially at 800 and 900 °C; nearly all of the selenium species were volatilized.
... EPA (2016) reported that coal mining accounted for 8% of total global anthropogenic emissions in 2010 and is estimated to increase by 33% in 2030. Zhang et al. (2018a) presented that negative degree of coal combustion process and its impact factors. Most of existing studies concentrate on subsystems or the whole electric-coal supply chain. ...
CO2 emissions from electric-coal combustion remain dominant in aggregate CO2 emissions of China. Few of existing studies explore the systemic interactions among the whole life cycle of green electric-coal supply chain. This study proposes a CO2 emission estimation model from the perspective of direct costing, and then develops a system dynamics (SD) model to simulate the scenarios on CO2 emission mitigation in the whole life cycle of green electric-coal supply chain. System dynamics model contains four sub-systems, including production subsystem, transportation subsystem, storage subsystem and consumption subsystem. Major sources and key impact factors of CO2 emissions changes as well as mitigation scenarios for electric-coal supply chain greening are discussed. Results show that 1) the developed SD model in electric-coal supply chain is tested to be robust; 2) the potential for CO2 emission mitigation in transportation system is larger than the other systems; 3) the effective scenario for emission mitigation is to increase the proportion of railway transportation during transportation, expand gas extraction during production and increase technological investment of gas extraction during transportation. The framework of scenario simulation using developed SD model could be a reference to the greening of other energy-intensive supply chains, such as iron and steel supply chain etc.
... The temperature can reach 1000 C and more. Such temperatures are peculiar to solid fuel combustion processes taking place in boiler furnaces (Zhang et al., 2018). Under intensive heating of a fuel droplet, an increase in the oxidizer temperature over 1000 C will have lesser effect on the ignition delay time; thus, 1000 C has been taken as the limiting value of the temperature variation range. ...
The paper outlines the results of the experimental research into the ignition and combustion of composite liquid fuel with fine-grained particles of municipal solid wastes (MSW) added as a solid fuel component: wood, rubber, plastic, and cardboard. A relatively low concentration (about 10 wt%) of these components in the fuel intensifies the ignition process, given that all other conditions are the same. The experimental research has been performed using two experimental setups. The first setup allows for researching the conditions of radiant heating of motionless fuel droplets (about 1 mm in size) in a muffle furnace when the temperature is in the range of 400–1000 °C. The second setup allows for implementing the conditions of convective heating of motionless fuel droplets (about 1 mm in size) in the flow of pre-heated air (at the rate of 3 m/s and the temperature in the range of 400–700 °C). The research findings include minimum temperatures required for the stable ignition of composite liquid fuel with added MSW. They also include the dependencies of ignition delay times on the temperature under different heating conditions. It has also been determined that fuels with MSW are notable for lower nitrogen oxide and sulfur oxide concentrations in gaseous combustion products as compared to fuels without municipal wastes. Maximum difference in the concentrations of NOx and SOx for such fuels reaches 70% and 45% (in absolute units, 125 ppm and 50 ppm, respectively). The results of analytical calculations of relative fuel performance coefficients provide good reasons for the prospective use of such compositions in thermal power engineering. These relative coefficients took values in the range of 1–3. The results obtained provide ground for developing a disposal technology for MSW that cannot be processed or recycled. The technology must be power-efficient as well as economically efficient and environmentally friendly.
... Burning of a substantial amount of natural gas during this process can be perceived as a significant factor generating greenhouse gas emissions and damaging the ozone layer. Taking into account the previous studies of various authors, the combustion of fossil fuels is also accompanied with other negative externalities, such as production of formaldehyde, benzene, and other substances (Jiaqiang et al., 2017;Zhang et al., 2018). ...
Sustainable development efforts aimed at substantial reduction of carbon dioxide emissions focused research activities in this field, among others, on a partial or full replacement of Portland cement by environmental more friendly alternatives. Calcined gypsum can be considered as one of possible options in that respect. However, although the environmental impact is an important issue, gypsum was analyzed only rarely and sufficiently accurate data are still missing. In this paper, a carbon footprint analysis of two types of gypsum ranging from cradle to gate according to ISO 14067 is presented. The inventory data based on primary data obtained from the producers of natural gypsum and flue gas desulfurization gypsum in the Czech Republic are completed by the emission factors obtained from the literature survey. The results of the carbon footprint analysis show that the carbon dioxide emissions related to the manufacturing of calcined gypsum from flue gas desulfurization gypsum are 105.3 kg of carbon dioxide/t, i.e., 25.2% lower than for the application of natural gypsum. Calcination is identified as the most harmful process from the point of view of carbon dioxide generation for both raw materials; it is responsible for 55% and 72% of total carbon dioxide emissions for natural gypsum and flue gas desulfurization gypsum, respectively. The obtained information is essential for further design and development of new types of composites meeting the requirements of sustainable development better than today’s mainstream solutions.
Particulate-bound mercury (PBM) is a global environmental concern owing to its large dry deposition velocities and scavenging coefficients, both of which drive Hg into terrestrial and marine ecosystems. PBM observation studies have been widely conducted over East Asia, but comparable studies in Peninsular Southeast Asia (PSEA) remain scarce. This is the first study reporting PBM concentrations for Ho Chi Minh City (HCMC), the biggest metropolitan area in Vietnam. A total of 222 samples were collected in 2018 and contained an average PBM 10 (particulate matter-PM with diameter ≤10 μm) concentration and Hg mass fraction (i.e. PBM/PM) of 67.3 ± 45.9 pg m −3 and 1.18 ± 1.12 μg g −1 , respectively. Although PBM concentration was lower than those reported in Chinese megacities, the Hg mass fraction was similar to those in China, suggesting strong enrichment from anthropogenic Hg emissions in HCMC. Traffic-induced particulate emission and deposition processes were major factors governing PBM temporal variation at our site. In addition, the prevailing southwest monsoon winds brought air masses that passed through industrial areas and were associated with a higher Hg mass fraction. Statistically significant positive correlations (R 2 = 0.11-0.52, p < 0.01) were observed for PBM with PM and the Hg mass fraction, indicating similar PM and Hg sources or oxidized Hg adsorption onto PM via gas-particle partitioning. Moreover, PCA results revealed a higher contribution of primary sources than secondary sources to PBM concentration variability in HCMC. A health risk assessment indicated that the PBM concentrations at HCMC posed minimal non-carcinogenic risks (HI < 1) for children and adults, but dermal contact may act as an important exposure route since lightweight clothing is common among residents. This PBM dataset over PSEA, a region with high atmospheric Hg emissions, provides a valuable resource for the Hg scientific community to improve our understanding of Hg biogeochemical cycle.
As the typical hazardous arsenic pollutants, copper smelting flue dust (CSFD) and arsenic sulfide residue (ASR) are produced extensively during copper smelting process, which pose significant pressure on environmental protection and green development of the copper industry. This work proposed an economic, efficient, and applicable approach to treat waste with waste, in which the simultaneous removal and recovery of As from CSFD and ASR were realized by a roasting process, with adding sulfuric acid, at a relatively low temperature (300~350℃). The thermodynamic analysis and experiments confirmed that the main phases of As2S3 and S0 in the ASR were used as a reductant for reducing As(Ⅴ) in the CSFD, and the introduction of sulfuric acid favorably enhanced the thermodynamic driving force and greatly lowered the reaction temperature. The results indicated that removal and behavior of As were highly dependent on the mass ratio of ASR to CSFD, roasting temperature, and H2SO4 dosage. By regulating the parameters, the species As2S3, As2O5, and arsenate were all converted to volatile As2O3, which could be captured and deposited in cold water. In the optimized co-treatment, a satisfied As removal efficiency of 96.12% was achieved, while getting the 97.03% pure As2O3.
Arsenic emissions from coal-fired power plants has been given increasing attention due to its harmful effect on the environment and human health. The vaporization behavior of arsenic in high temperature flame zones is critical for understanding arsenic partitioning in downstream flue gas. However, the gaseous arsenic concentration in furnaces are hard to measure due to limitations in sampling technology. In this work, a novel vaporization model for arsenic was established to simulate the release behavior of arsenic during single-particle coal combustion. The temporal-spatial vaporization ratio and concentration of arsenic could also be obtained. The effects of temperature, O2 concentration, particle size as well as the content and occurrence mode of arsenic in coal are discussed in detail. Simulation results indicate that with increase in temperature or O2 concentration, or decrease in particle size, the vaporization rate of arsenic accelerated gradually with a higher As2O3(g) concentration peak. Meanwhile, the As2O3(g) concentration curves changed from one single peak to multiple peaks mainly due to the oxidation delay of sulfide-bound arsenic (simplified as FeAsS) in the inner shells of a single coal particle. Compared to anthracite, bituminous or lignite coal tended to have a larger vaporization ratio of arsenic with a more pronounced As2O3(g) peak. Further, the peak concentration of As2O3(g) was found to be correlated linearly to the arsenic content in the feed coal. Furthermore, model results were compared with both on-line and off-line experimental data for validation. The comparisons showed that the proposed single-particle model predicted well the vaporization kinetics of arsenic for the combustion temperatures analyzed, indicating the adaptability of the model as a potential tool for determining arsenic vaporization as well as gaseous arsenic concentration prediction.
To explore the effect of CO on the transformation of arsenic species, the reaction mechanism of homogeneous and heterogeneous reactions for arsenic oxides (AsO2 and As2O3) with CO were investigated via density functional theory (DFT). The geometries of reactants, intermediates, transition states and products for each reaction were optimized by using the B3LYP method in conjunction with the 6-31G(d) basis set, and the single-point energy of each structure was calculated at the B2PLYP/Def2-TZVP level. Also, thermodynamic and kinetic analyses were conducted to determine the reaction process. The results showed that the homogeneous reaction of AsO2 and CO has two channels and a transition state is found in each case. The homogeneous reaction process of As2O3 and CO undergoes two transition states and, finally, As2O3 is reduced to sub-oxides by CO. Char has a strong adsorption affinity for AsO2 and As2O3 in the presence of CO, and the adsorption mode of the AsO2 molecule on the char surface has a great influence on its reduction. The activation energy of the homogeneous reduction of As2O3 (75.9 kJ mol⁻¹) is lower than the heterogeneous reduction (94.2 kJ mol⁻¹), which suggests that As2O3 is more likely to react with CO in the flue gas. The calculation results revealed the mechanism for the influence of CO on arsenic behavior by density functional theory. These results are helpful for a molecular-level understanding of the transformation of arsenic species, which in turn provides a theoretical foundation for the emission and control of arsenic.
The exploitation of thallium (Tl) resources through mining poses a significant threat to ecological systems and human health due to its high toxicity and ready assimilation by human body. We report the first assessment of the pollution, spatial distribution, source, and ecological-health risks of potentially toxic elements (PTEs) in Tl mining area of southwest Guizhou, China. Spatial distribution maps for PTEs were visualized by ArcGIS to identify their distribution trends. We use the enrichment factor (EF), correlation analysis, and principal component analysis to identify likely sources of seven PTEs mining area. The wider risk assessment was evaluated using the geoaccumulation index (Igeo), potential ecological risk index (RI), human non-carcinogenic risk (HI), and carcinogenic risk (CR). The results revealed the PTEs content in the study area identifies direct mining, metal production, and domestic pollution sources. In addition, the distribution of PTEs was also affected by the topography, rain water leaching, and river dispersals. The main elements of concern are Tl and As, while Cd, Cr, Cu, Pb, and Zn do not show significant enrichment in the area despite associations with the ore deposit. Risk assessment identifies strong pollution and ecological risks and poses unacceptable human health risks to local residents, especially for children. The ecological risk in the study is identified to be predominantly from Tl (74.32%), followed by As (8.57%) and Cd (7.32%). The contribution of PTEs to the non-carcinogenic risk of humans in the study area is exclusively from As and Tl, while the carcinogenic risk is dominated by As, and the other elements pose no significant risk to human health.
This text contrapose on the contradiction between price of alumina powder material and performance of alumina ceramic manufacture at present. Abundant natural bauxite mineral in China as main raw materials was used through the favorable craft course and a small amount of other auxiliary additive to produce grinding medium which have the character of color white, higher performances, lower sintered temperature, fewer consume of resources, cheaper production cost, etc. And the problem of producing high-level grinding medium only using expensive industrial alumina powder was solved and pollution in production of alumina powder was avoided. So the environmental pollution and energy consuming can be reduced and high added value of bauxite can be achieved through this method. The experimental design continued to use the industrial production route and apt to realize industrialization, once it is put into production, enormous social effect will be achieved.
The release characteristics of arsenic in coal and coal gangue was discussed in this paper. At firsrt, Coal and coal gangue were sampled in the study area, determination of the arsenic content and sulfur content in the coal. Then the occurrence of the arsenic was analyzed in coal by chemical extraction experiment , the characteristics of mineral distribution was analyzed by X-ray diffraction (XRD) method in the coal sample. At last, the release law of arsenic in coal and coal gangue was analyzed by coal combustion experiment and leaching experiment. The results showed that, with the combustion temperature increasing during the coal combustion process, the release rate of arsenic in coal increase the arsenic content in coal residue ash decrease gradually. In different temperature combustion process, the arsenic content in coal residue ash almostly no change, however, the release of arsenic rate had a significant difference between them. The release of calcium carbonate mineral composition of arsenic in coal had inhibitory effect The influence of the pH value of leaching liquor on the leaching amount of arsenic in coal gangue is great, the higher the acidity of leaching liquor, the greater the precipitation amount of arsenic in coal gangue. The arsenic content precipitated from coal gangue is relatively large in the initial leaching, while the arsenic content decreased with the leaching amount increasing.
Hazardous Trace elements (HTEs) emitted from coal combustion has raised widespread concern. Studies on the emission characteristics of five HTEs, namely arsenic (As), chromium (Cr), barium (Ba), manganese (Mn), lead (Pb) at three different loads (100%, 83%, 71% output) and different coal types were performed on a 350 MW coal-fired power plant equipped with SCR, ESP + FF, and WFGD. HTEs in the flue gas at the inlet/outlet of each air pollution control device (APCD) were sampled simultaneously based on US EPA Method 29. During flue gas HTEs sampling, coal, bottom ash, fly ash captured by ESP + FF, fresh desulfurization slurry, desulfurization wastewater were also collected. Results show that mass balance rate for the system and each APCD is in an acceptable range. The five studied HTEs mainly distribute in bottom and ESP + FF ash. ESP + FF have high removal efficiency of 99.75–99.95%. WFGD can remove part of HTEs further. Total removal rate across the APCDs ranges from 99.84 to 99.99%. Concentration of HTEs emitted to atmosphere is within the extremely low scope of 0.11–4.93 μg/m³. Emission factor of the five studied HTEs is 0.04–1.54 g/10¹²J. Content of As, Pb, Ba, Cr in solid samples follows the order of ESP + FF ash > bottom ash > gypsum. More focus should be placed on Mn in desulfuration wastewater, content of which is more than the standard value. This work is meaningful for the prediction and removal of HTEs emitted from coal-fired power plants.
Arsenic volatilization characteristics during co-combustion of high arsenic lignite and low arsenic bituminous coal were carried out on an isothermal experiment system from 600℃ to 1100℃ at different blending ratios (3:1, 1:1, 1:3). The results showed that with increasing temperature, the arsenic volatilization in single and mixed coals increased gradually. The volatilization ratios of arsenic in mixed coals at various blending ratios were between two single coals, while they were larger than the weighted average values. Combined with isothermal coal combustion curves, it was found that high volatile content in lignite affected the char combustion properties in blended coals, which in turn promoted the volatilization of arsenic. Considering the effects of temperature, coal blending and the difference of coal rank, the arsenic volatilization model during mixed coal combustion was proposed. The model results fit the experimental curves well, which provided a reference for the prediction of arsenic volatility characteristics of blended coals.
The co-combustion experiments of a high arsenic lignite(GX coal from Guizhou) and three low arsenic bituminous coals were conducted on an isothermal system at 600°C∼1100°C with different blending ratios. The mass loss and mass loss rate of arsenic were studied and compared with the weighted average values. Results show that the arsenic content in blended coal has additive property. The volatilization characteristics of arsenic in blended coals are between two single coals and decrease with increasing blending ratio of bituminous coal. While due to the larger volatile matter in lignite, the mass loss ratio and mass loss peak of arsenic in mixed coals are both higher than the weighted average values. Considering the effects of temperature, coal blending and coal type, the volatilization model of arsenic during co-combustion of one high-arsenic lignite(coal A, blending mass ratio x) and one bituminous coal(coal B) at 600∼1100°C was established. The expression is . The larger difference between bituminous and lignite coal, the greater value of η. Model calculations fit the experimental results well, which provides a reference for the prediction of arsenic volatilization in blended coals.
A combination of thermogravimetric analysis (TG) and laboratory-scale circulated fluidized bed combustion experiment was conducted to investigate the thermochemical, kinetic and arsenic retention behavior during co-combustion bituminous coal with typical agricultural biomass. Results shown that ignition performance and thermal reactivity of coal could be enhanced by adding biomass in suitable proportion. Arsenic was enriched in fly ash and associated with fine particles during combustion of coal/biomass blends. The emission of arsenic decreased with increasing proportion of biomass in blends. The retention of arsenic may be attributed to the interaction between arsenic and fly ash components. The positive correlation between calcium content and arsenic concentration in ash suggesting that the arsenic-calcium interaction may be regarded as the primary mechanism for arsenic retention.
Arsenic is one of the most widespread and most hazardous carcinogenic substances. Coal combustion is the major source of arsenic in the atmosphere. In this paper, it has been identified that lime can restrain the volatility of arsenic. In fixed bed combustion of coal, the restraining rates of arsenic volatility are between 3.05% and 37.35% by using lime. In circulating fluidized bed (CFB) combustion of coal, partitioning of arsenic changes markedly in ash with different size fraction between both with and without lime. By using lime the content of arsenic in ash with particle size <0.0308mm decreases from 172.8 mg.kg-1 to 17.67 mg.kg-1 and that in ash from chimney decreases 4-5.4 times, too. Restraining of arsenic volatility using lime is effective in coal combustion under certain temperature.
Coal, slag and fly ashes were sampled from a 300 MW utility boiler. The concentration of mercury, arsenic in these samples and the particle size distribution of the fly ash were determined. Results indicate that the arsenic concentration in fly ash is relatively dependent on the particle size. We suggest that gas-solid reactions are happened between arsenic vapors with other compounds. The mercury concentration in fly ash is independent on the particle size. Mercury has been found to concentrate in the carbon-rich fraction of fly ash.
Arsenic emission characteristics during coal combustion were studied by means of fluidized-bed tube furnaces. And the modes of arsenic occurrence in coal were discussed by float-and-sink test of coal. The results indicated that arsenic emission tends to increase with increasing combustion temperature, the effect of combustion temperature on arsenic emission is weak at 600 - 700°C, 700 - 900°C is the main arsenic emission temperature range and at which the effect of combustion temperature on arsenic emission is obvious. Arsenic emission increases with increasing combustion time, the initial 10 min is the main arsenic emission period. Arsenic in coal exists by means of organic and inorganic association and the arsenic emission percent increases with increase of the ratio of organic arsenic to inorganic arsenic in coal during coal combustion.
In order to be more specific research the dearsenic characteristics of calcium-based desulfurizing absorbents during coal combustion.The influence on the dearsenic rate of different factors are investigated including the type, Ca/S, particle of calcium-based desulfurizing absorbents and the combustion temperature. The result shows that the amount of calcium-based desulfurizing absorbents is 2.0, the particle size of calcium-based desulfurizing absorbents top 200 mesh, dolomite has the best dearsenic ability and it's dearsenic rate still could reach 65.71% in 1200°C high temperatures. Therefore the calcium-based desulfurizing absorbents not only can captue suifur but also was good to inhibit the volatile of arsenic during coal combustion.
Concentrations of heavy metals, e. g. arsenic, cadmium, antimony, lead and mercury, in lignite and combustion products of Xiaolongtan mine in Yunnan were analyzed. Based on the laboratory experiment, the distribution characteristics of these five heavy metals in combustion product were identified and their environmental impacts were estimated. It was found that the volatility of mercury was the strongest. It showed extremely high volatile rate in 300°C, and can volatile completely in 500°C. The order of volatility was Hg>As>Cd>Sb>Pb, and the mode of occurrences of heavy metals had a significant impact on their volatility. Through the environmental impact assessment of the five heavy metals during coal combustion, heavy pollution was recorded in the laboratory combustion while only light pollution was recorded in power plant combustion. This indicated that emissions of trace metals were controlled by the combustion modes and combustion conditions.
Four typical coals in southwestern Guizhou were selected as the research object. The test apparatus for arsenic and sulfur emission during coal combustion were established. Moreover, the main factors of arsenic and sulfur emission rate were researched. The kinetics parameters of arsenic and sulfur emission were obtained preliminly during the coal combustion. The results showed that arsenic and sulfur emission rate of four kinds of coal increased with increasing combustion temperature. The arsenic activation energy is higher than that of the sulfur in coal, indicating that the arsenic forming temperature is higher than that of the sulfur in coal. The experimental results arc also consistent with the dynamics data.
Combustion of three coal samples of different types and origins has been conducted in a lab-scale drop-tube furnace (DTF) to examine the speciation and emission of As during air and oxy-fuel combustion. The synchrotron XANES has been used to quantify the contents of toxic As3+ and less toxic As5+ in char and fly ash samples. Irrespective of coal type and the original mode of occurrence of As, the substitution of N2 by CO2 for oxy-fuel combustion caused little changes to the emission and speciation of As at the initial step of coal combustion, pyrolysis. The reduction of original As5+–O and/or oxidation of the As(g) derived from the decomposition of As–S association favoured the retention of approximately 20% of As as As3+ in char, which remained unchanged with the progress of the bituminous coal char oxidation, but was further vaporised during the combustion of lignites. For the oxy-fuel mode with no less than 27% oxygen to match air in terms of adiabatic flame temperature, the fraction of toxic As3+–O in the final fly ash of the bituminous coal and high-ash lignite is much lower than in air, due to the higher oxygen partial pressure in the system. However, for the As-doped low-ash brown coal, its high CO2-gasification reactivity slightly promoted the fraction of As3+–O in oxy-fuel mode that decreased with increasing oxygen content. In addition, the amount of inherent Ca and/or Fe in coal has been proven insignificant in affecting the stabilisation of As vapours, instead relying more on the availability of Ca and/or Fe active sites for As capture. For the addition of external free lime (CaO), its capture capability is also lower in oxy-fuel mode than in air, probably due to the preferential carbonation caused by vast CO2 in the reactor.
The leaching characteristics of arsenic (As) in fly ash collected from lab-scale fluidized bed reactor have been systematically investigated through the combustion of two bituminous coals (A and B) and their mixture with different blending ratio. Leaching tests were conducted according to Japanese Industrial Standard (JIS).The results indicate that, the fly ash derived from the combustion of coal B, which contains abundant calcium, shows a larger capture ability for arsenic vapor than that from coal A, due to the chemical reaction of arsenic with CaO. This reaction is however competed by the sulfation of CaO at coal combustion temperature, therefore, a nonlinear increase was observed with increasing the blending ratios of high-calcium coal B with coal A. Leaching performance of arsenic from fly ash is largely dependent on the finally pH of the leachate. CaO in fly ash preferentially generates a high-pH leachate during leaching test and subsequently promotes the combination of calcium with arsenic to form precipitate. Improving Ca/S ratio through the combustion of blending coal is a promising method to prevent the emission of arsenic into ambient and reduce its leachability from fly ash.
Fly ash samples were collected from a Chinese power station and divided according to particle size. The solid fly ash samples were digested according to ASTM methods. The arsenic contents of samples with different particle sizes were analyzed using atomic fluorescence spectroscopy after digestion. Other metals were analyzed using inductively coupled plasma-atomic emission spectrometer after digestion, and the carbon content was analyzed by a CHN elemental analyzer. The results show that the arsenic components are enriched in smaller fly ash particles. The arsenic contents have a positive relationship with calcium, magnesium, and iron contents, which indicate that stable compounds are formed between these components. Thermogravimetric experiments of fly ash samples with different particle sizes were conducted, and the results indicate the combination of calcium hydroxide with arsenic form stable compounds.
The concentrations of mineral-forming elements and trace elements in coal and coal ashes from Balingian
coalfield, Sarawak, Malaysia were assayed and their modes of occurrence, enrichment origin, and partitioning behaviour during coal combustion were studied as well. Balingian coal is high in As, Cu, Pb, Sb, Th and Zn. Of particular concern are As (as high as 181 ppm), Pb (325 ppm) and Sb (96 ppm), all of which are highly enriched in Balingian coal relative to their respective coal Clarke values. Arsenic, Pb and Sb in the coal are mostly organic, and to a lesser extent, they are bound to discrete minerals in the form of aluminosilicates. During coal combustion in the power plant, a substantial portion of organically associated As, Pb and Sb in the coal vaporize and are released into the atmosphere, whereas Ba and Mn are highly enriched in the coal ashes as compared to the raw coal. The As, Pb and Sb anomalies observed in Balingian coal may be related to a large Sb–As, and probably Pb mineralization in the vicinity of the coalfield, with some localised epigenetic infiltration of these elements from the surrounding rocks by circulating groundwaters.
Vapor-phase arsenic in coal combustion flue gas causes deactivation of the catalysts used in selective catalytic reduction (SCR) systems for NOx control. A one-dimensional model has been developed to predict the behavior of arsenic in the postcombustion region of a coal-fired boiler as a function of gas residence time. The purpose of the model is to calculate the partitioning of arsenic between the vapor phase from volatilization and arsenic on the ash particles due to surface reaction and/or condensation at temperatures characteristic of SCR systems. The model accounts for heterogeneous condensation of arsenic on the fly ash, as well as surface reaction for two regimes: (1) the free molecular regime (submicrometer ash particles) and (2) the continuum regime (supermicrometer ash particles). All gas properties are computed as functions of gas temperature, pressure, and composition, which are allowed to vary. The arsenic model can be used to calculate the impact of coal composition on vapor-phase arsenic at SCR inlet temperatures, which will help utilities better manage coal quality and increase catalyst lifetimes on units operating with SCR. The arsenic model has been developed and implemented and was tested against experimental data for several coals.
Pilot experiments were carried out to reduce the fluorine (F) and arsenic (As) pollution of roasted corn dried by open ovens in "coal-burning" fluorosis area Yunnan, China. The results indicated that the average emission amount of F and As in briquettes in experimental group were 29.20mg/kg and 0.76 mg/kg in Xiaolongdong, and 46.8 mg/kg and 0.54 mg/kg in Mangbu respectively. The results also indicated that the fixing rate of F and As in briquettes in experimental group was more than 4 times and 1.2 times of that in control group respectively. The average concentration of F and As in roasted corn in experimental group were 3.86 mg/kg and 13.23 μg/kg in Xiaolongdong, and 4.77 mg/kg and 122.96 μg/kg in Mangbu respectively, which reduced by more than 65% and 75% respectively compared with that in control group. Adding local natural calcium-based materials in briquettes can reduce the emission of F and As and their pollution on roasted corn largely, and thus will reduce the risk of fluorosis for residents greatly in "coal-burning" fluorosis area of southwestern China.
We used a suite of techniques to characterize the mineralogy, geochemistry, and arsenic speciation in fresh combustion waste (ash) from burning of this coal and ash buried under agricultural soil since 1965 when a dam of one of the ash ponds failed. Coal seams from Nováky (Slovakia) contain low-temperature hydrothermal mineralization with orpiment (As2S3). The fresh ash has 1000-1400 ppm As and consists of vesicular and compact glasses (86.29 % of the ash with an average of 0.13 wt% As2O5), spheroidal glasses (2.53; 1.35), unburned coal particles (7.76; 0.10) with calcite veins (0.27; 1.60), as well as quartz, plagioclase, and traces of poorly crystalline mullite (3.15; 0.01). The major As carriers are the glasses and electron microprobe analyses document high affinity of As towards Ca-rich material in the glasses. Sequential extractions show massive release of Ca during the mildest leaching (water or MgCl2 solution); As is released especially under reducing conditions. The soil-ash mixtures from 1965 have 1078-1381 ppm As, almost the same As concentration as the fresh ash. In addition to the constituents identified in the fresh combustion waste, they contain an omnipresent fine-grained matrix (0.05 wt% As2O5) between the grains, most likely made of poorly crystalline clays and iron oxides. More than 90 % of the As in the fresh ash and soil-ash mixtures occurs as As5+. Our results allow us to track the fate of As: during combustion, As is incorporated into glasses, especially in those rich in Ca; in the ash impoundment, calcium arsenates form (assumption based on literature data) and are slowly replaced by calcite with a concomitant release of As. In the ashes buried in soils, part of this As is retained on pre-existing or newly-formed iron oxides and clays.
The fate of several trace elements in the thermal conversion of coal has been investigated, assuming global equilibrium and using an in-house database and a Fortran-77 computer code for the calculations. The format and content of the database DGFDBASE, containing reduced data on ΔG°fi(T) for approximately 800 chemical species of the elements Al, As, B, Be, Br, C, Ca, Cd, Cl, Co, Cr, F, Fe, Ga, Ge, H, Hg, K, Mg, N, Na, Ni, O, P, Pb, S, Sb, Se, Si, Sn, Ti, V and Zn are described. Results of thermodynamic equilibrium calculations performed using ‘the total Gibbs free energy minimization’ program MINGTSYS on simple systems containing one of the trace elements As, B, Be, Cd, Co, Cr, Ga, Ge, Hg, Ni, P, Pb, Sb, Se, Sn, Ti, V and Zn are presented and compared with results from the literature. Combustion as well as gasification conditions have been considered.At oxidizing conditions all the trace elements considered form at least one stable condensed phase in the temperature range from 300–2000 K. Regarding the condensed phase being stable at the lowest temperatures, the trace elements can be divided into two groups, the first of sulfate forming elements (this group includes the elements Be, Cd, Co, Cr, Hg, Ni, Pb, Sb, Sn, V, and Zn) and the latter of oxide-hydroxide forming elements (this group includes the elements: As, B, Ga, Ge, P, Se and Ti).At reducing conditions, the behavior of the trace elements considered is complex, and no simple classification of the elements is possible.
The review presented covers: (a) historical introduction; (b) some analytical comments; (c) some peculiarities of the As geochemistry in environment; (d) an estimation of coal Clarke value of As; (e) some coals enriched in As; (f) mode of As occurrence in coal; (g) factors influencing the As distribution in coal matter and coal bed; (h) genetic topics; (i) some topics related to environmental impact of As by the coal combustion.The World average As content in coals (coal Clarke of As) for the bituminous coals and lignites are, respectively, 9.0±0.8 and 7.4±1.4 ppm. On an ash basis, these contents are higher: 50±5 and 49±8 ppm, respectively. Therefore, As is a very coalphile element: it has strong affinity to coal matter — organic and (or) inorganic but obligatory authigenic. The coalphile affinity of As is like that for Ge or S.There is strong regional variability of As distribution due to geologic variability of the individual coal basins. For example, bituminous coals in Eastern Germany, Czech Republic and SE China are enriched in As, whereas the coals in South Africa or Australia are very depleted compared to coal Clarke of As. In general, some relationship exists between As content and its mode of occurrence in coals. Typically, at high As content, sulphide sites dominate (pyrite and other more rare sulphides), whereas at low As content, Asorg dominates, both being authigenic. A contribution of the terrigenic As (in silicates) is usually minor and of the biogenic Asbio (derived from coal-forming plants) is poorly known.Both organic and inorganic As can exist not only as chemically bound form but also in the sorbed (acid leacheable) arsenate form. With increasing coal rank, sorbed exchangeable arsenate content decreases, with a minimum in the coking coals (German data: the Ruhr coals).Relations of As content in coal to ash yield (or its partitioning in sink–float fractions) and to coal petrographic composition are usually complicated. In most cases, these relations are controlled by main site (form) of As — Aspyr or Asorg. If Aspyr dominates, an As accumulation in heavy fractions (or in high-ash coals) is observed, and if Asorg dominates, it is enriched in medium-density fractions (or low- and medium-ash coals). Arsenic is in part accumulated in the inertinite vs. vitrinite (Asorg ?).There are four genetic types of As accumulation on coal: two epigenetic and two syngenetic: (1) Chinese type—hydrothermal As enrichment, sometimes similar to known Carlin type of As-bearing telethermal gold deposits; (2) Dakota type—hypergene enrichment from ground waters draining As-bearing tufa host rocks; (3) Bulgarian type—As enrichment resulting from As-bearing waters entered coal-forming peat bogs from sulphide deposit aureoles; (4) Turkish type—volcanic input of As in coal-forming peat bog as exhalations, brines and volcanic ash.During coal combustion at power plants, most of the initial As in coal volatilizes into the gaseous phase. At the widely used combustion of pulverized coal, most of Asorg, Aspyr and “shielded” As-bearing micromineral phases escape into gaseous and particulate phase and only minor part of Asclay remains in bottom ash. The dominant fraction of escaping As is in fly ash. Because 97–99% of the fly ash is collected by electrostatic precipitators, the atmospheric emission of As (solid phase and gaseous) is usually assumed as rather minor (10–30% from initial As in coal). However, fly ash disposal creates some difficult environmental problems because it is potentially toxic in natural waters and soils. The As leaching rate from ash disposal is greatly controlled by the ash chemistry. In natural environment, As can be readily leached from acid (SiO2-rich) bituminous coal ashes but can be very difficult from alkali (CaO-rich) lignite ashes.If the Aspyr form dominates, conventional coal cleaning may be an efficient tool for the removing As from coal. However, organic-bound or micromineral arsenic (“shielded” grains of As-bearing sulphides) are not removed by this procedure.Some considerations show that “toxicity threshold” of As content in coal (permissible concentration for industrial utility) may be in the range 100–300 ppm As. However, for different coals (with different proportions of As-forms), and for different combustion procedures, this “threshold” varies.
With the aim of better understanding the distribution of arsenic, 144 coal samples were collected from southwestern Guizhou, and the concentrations of arsenic were determined by atomic fluorescence spectrometry (AFS) and inductively coupled plasma mass spectrometry (ICP-MS). The content of arsenic varies from 0.3 ppm to 3.2 wt.%. In most coal samples, the arsenic content was lower than 30 ppm, which was close to a representative value of arsenic concentration of coal in China. Arsenic contents in 37 samples, which were from several small coal mines, were more than 30 ppm, among which only 16 samples were more than 100 ppm, and only a few samples contained more than 1000 ppm, which were very restricted and the coal seams were generally unworkable. Combustion of two kinds of high arsenic coal with and without CaO additive was studied in a bench scale drop tube furnace (DTF) to understand the partition and emission of arsenic in the process. The PM was size segregated by low pressure impactor (LPI) into 13 size stages ranging from 9.8 to 0.0281 μm. X-ray fluorescence spectrometry (XRF) was used to determine the chemical composition of the PM, and inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the arsenic content. A bimodal mode distribution of the PM was formed during coal combustion; the large mode (coarse particle) was formed at 4.0 μm, and the other mode (fine particles) was at about 0.1 μm. A middle mode was gradually obvious in high temperature for both of the two coal combustions, which may have been derived from coagulation and agglomeration of metal elements vapors. More gaseous arsenic was formed in 50% oxygen content than 20% oxygen content. Arsenic in sulfide is easier to vaporize than as arsenate. Along with the increasing temperature from 1100 °C to 1400 °C, the arsenic concentration in PM1 increased from 0.07 mg/N m3 to 0.25 mg/N m3. With the addition of the calcium based sorbent, the arsenic concentration in PM1 decreases sharply from 0.25 mg/N m3 to 0.11 mg/N m3. Thus, the calcium based sorbent is an effective additive to control the emission of arsenic during coal combustion.
Arsenic emissions are currently considered to be one of foremost importance. Arsenic volatility is higher than most of trace elements, but its vaporization behaviour is strongly dependent on the atmosphere composition. In this sense, thermodynamic equilibrium calculations, using HSC-Chemistry 5.0 software, were performed to evaluate the influence of different compounds in the distribution and mode of occurrence of arsenic in co-combustion processes. The influence of different parameters influencing arsenic behaviour, such as temperature, pressure, trace element concentration and flue gas composition on equilibrium composition were also evaluated. Predicting arsenic species, based on combustion conditions and fuel composition, will be useful to choose the best available control technology to reduce arsenic emissions. Finally, the possible interactions between arsenic and different trace elements (TE), mercury, cadmium and antimony, relevant from an environmental point of view, have also been studied; these interactions are not usually considered in thermodynamic studies; however, TE’s interactions affects the behaviour of a single TE, not only as a result of the formation of new species, but also, because of the different reactivity of TEs towards different elements which may affect TE’s volatilization behaviours. From results obtained in this study it may be concluded that in most cases, arsenic is mainly captured in ashes as a result of the formation of thermally stable species both from interactions with bulk ash and TE’s interactions. Nevertheless, the presence of some compounds (silicon, chlorine and sulphur) may enhance arsenic volatilization.
Arsenic, one of the most hazardous elements occurring in coals, can be released to the environment during coal processing and combustion. Based on the available literature and published results obtained in our laboratory, the content, distribution and the modes of occurrence of As in Chinese coals, and its environmental and impacts are reviewed in this article. With the 4763 sets of data (from the literature) rearranged, the arithmetic mean As concentration of each province and weighted mean As concentration of the entire country (using the expected coal reserves as the weighting factor) were calculated. The weighted mean As concentration in Chinese coals is 3.18 mg/kg, with As concentration increasing from northern China to southern China. The As concentration in coal varies with coal-forming ages and coal ranks. Arsenic has several modes of occurrence in coals. According to results obtained by other studies and our own experiments, As is mainly associated with mineral matter (such as pyrite and other sulfide minerals) in coals, although a significant amount of arsenic is associated with organic matter. The accumulation of As in coal is controlled by many geological factors during coal-forming processes, including plant decomposition, sedimentary environments, and epigenetic hydrothermal activity. During the combustion of coal, As is released to the air, water, and soil, causing serious environmental pollution. More than 45% of the coal consumed in China is utilized by power plants, and it is estimated that nearly 522 tonnes, 21 tonnes and 252 tonnes of As are emitted into the atmosphere by industries, residential buildings and coal-fired power plants, respectively, every year.
The arsenic concentrations in 297 coal samples were collected from the main coal-mines of 26 provinces in China were determined by molybdenum blue coloration method. These samples were collected from coals that vary widely in coal rank and coal-forming periods from the five main coal-bearing regions in China. Arsenic content in Chinese coals range between 0.24 to 71 mg/kg. The mean of the concentration of Arsenic is 6.4+/-0.5 mg/kg and the geometric mean is 4.0+/-8.5 mg/kg. The level of arsenic in China is higher in northeastern and southern provinces, but lower in northwestern provinces. The relationship between arsenic content and coal-forming period, coal rank is studied. It was observed that the arsenic contents decreases with coal rank in the order: Tertiary>Early Jurassic>Late Triassic>Late Jurassic>Middle Jurassic>Late Permian>Early Carboniferous>Middle Carboniferous>Late Carboniferous>Early Permian; It was also noted that the arsenic contents decrease in the order: Subbituminous>Anthracite>Bituminous. However, compared with the geological characteristics of coal forming region, coal rank and coal-forming period have little effect on the concentration of arsenic in Chinese coal. The average arsenic concentration of Chinese coal is lower than that of the whole world. The health problems in China derived from in coal (arsenism) are due largely to poor local life-style practices in cooking and home heating with coal rather than to high arsenic contents in the coal.
Study on the influence factors of calcium-based arsenic capture sorbent in coal combustion
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Study of simultaneous dearsenic and desulfurization by calcium -based materials during coal combustion
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On oxidation and leaching pollution of high-As coal gangue under high-temperature condition in Guizhou
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Study of arsenic in coal and technology of arsenic retention. Sichuan Environ
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Study on the arsenic capture sorbent of richer arsenic coal
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