Thermal effects on arsenic emissions during coal combustion process

Combating coal-burning-borne endemic arsenism in Shaanxi Province, Northwest China: The impact of high-arsenic coal ban, improved cook-stoves, and health education

To eliminate the epidemic of coal-burning-borne endemic arsenism (CBBA), our study organized and implemented comprehensive measures including high-arsenic coal ban, improved cook-stoves, and health education. We also aimed to promote the application value of these measures in preventing and controlling CBBA to the world. From 2004 to 2005, through a stratified random sampling method, we selected 58,256 individuals to investigate the prevalence of CBBA and the arsenic levels in 1287 environmental and biological specimens. The prevalence of CBBA was 19.26 % and significantly associated with the arsenic levels in coal, pepper, corn and hair, which were at or exceeded national upper limits. To timely prevent and control the disease, the comprehensive measures have been implemented since 2005 to present. Comparison and correlation analyses were utilized to evaluate the effectiveness of these measures in reducing the prevalence of CBBA. According to statistics, 73 high-arsenic coal mines were banned and over 99 % households in endemic areas accepted stove improvements and diversified health education. Monitoring studies during 2010-2019 has confirmed that these measures led to a decrease in urine arsenic levels among endemic residents, and they developed novel dietary practices, such as properly drying, storage, and washing of food. Additionally, the awareness rate of CBBA increased from less than 70 % to over 95 %. Finally, the prevalence of CBBA has decreased to 0.153 % investigated by a census involving 2.076 million endemic residents in 2019. In summary, CBBA in northwest China has been successfully controlled through banning on high-arsenic coal, introducing improved cook-stoves, and providing health education.

Sources apportionments of heavy metal(loid)s in the farmland soils close to industrial parks: Integrated application of positive matrix factorization (PMF) and cadmium isotopic fractionation

Understanding the source identification and distribution of heavy metal(loid)s in soil is essential for risk management. The sources of heavy metal(loid)s in farmland soil, especially in areas with rapid economic development, were complicated and need to be explored urgently. This study combined geographic information system (GIS) mapping, positive matrix factorization (PMF) model and cadmium (Cd) isotope fingerprinting methods to identify heavy metal(loid) sources in a typical town in the economically developed Yangtze River Delta region of China. Cd, As, Cu, Zn, Pb, Ni and Co in different samples were detected. The results showed that Cd was the most severely contaminated element, with an exceedance rate of 78.0 %. GIS mapping results indicated that the hotspot area was located in the northeastern area with prolonged operational histories of electroplating and non-ferrous metal smelting industries. The PMF model analysis also identified emissions from smelting and electroplating enterprises as the main sources of Cd in the soil, counted for 49.28 %, followed by traffic (25.66 %) and agricultural (25.06 %) sources. Through further isotopic analysis, it was found that in soil samples near the industrial park, the contribution of electroplating and non-ferrous metal smelting enterprises to cadmium pollution was significantly higher than other regions. The integrated use of various methodologies allows for precise analysis of sources and input pathways, offering valuable insights for future pollution control and soil remediation endeavors.

In-situ production of iron flocculation and reactive oxygen species by electrochemically decomposing siderite: An innovative Fe-EC route to remove trivalent arsenic

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.

Atmospheric particulate-bound mercury (PBM10) in a Southeast Asia megacity: Sources and health risk assessment

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 PBM₁₀ (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 (R² = 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.

Distribution of As within Magnetic and Non-Magnetic Fractions of Fluidized-Bed Coal Combustion Ash

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).

Assessing the risk of coal-burning arsenic-induced liver damage: a population-based study on hair arsenic and cumulative arsenic

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.

Co-treatment of copper smelting flue dust and arsenic sulfide residue by a pyrometallurgical approach for simultaneous removal and recovery of arsenic

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.

A Model for Predicting Arsenic Volatilization during Coal Combustion Based on the Ash Fusion Temperature and Coal Characteristic

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.

Distribution, source identification, and ecological-health risks of potentially toxic elements (PTEs) in soil of thallium mine area (southwestern Guizhou, China)

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 (I_geo), 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.

Effects of oxygen functional complexes on arsenic adsorption over carbonaceous surface

The adsorption mechanism of As₂O₃ on carbonaceous surface modified with oxygen functional complexes was studied using density functional theory to understand the effect of oxygen functional complexes on arsenic adsorption. Full-parameter geometrical optimization and single point energy were calculated on B3LYP/def2-SVP and B3LYP/def2-TZVP level. Results showed that As₂O₃ adsorption on bare carbonaceous surface took place in physical as well as chemical way. The adsorption energies were between -2.07 kJ/mol to -480.20 kJ/mol. Compared to armchair model, zigzag model was more suitable as a carbonaceous sorbent. The participation of oxygen functional complexes greatly promoted the surface activity of carbonaceous surface and its adsorption capacity on arsenic. The adsorption energies of arsenic on carbonaceous surface with oxygen functional complexes were between -111.56 kJ/mol to -669.46 kJ/mol. The promotion order of oxygen functional complexes on surface activity was: phenol > lactone > carbonyl > semiquinone > carboxyl. Oxygen functional complexes promoted adsorption capacity of carbonaceous surface through enhancing the activities of neighboring carbon atoms rather than directly providing active sites. Mayer bond order was a reliable way to understand the adsorption process of arsenic on carbonaceous surface. This study provides a new idea for using modified carbonaceous sorbent to remove arsenic pollution from power stations.