Behavior of Pb During Coal Combustion: An Overview

Migration and transformation of trace elements during sewage sludge and coal slime Co-combustion

Co-combustion of sewage sludge (SS) and coal slime (CS) could improve the combustion properties of the two materials, however, high levels of trace elements (TEs) can be released from the two wastes, resulting in secondary pollution. The migration and transformation behavior of As, Cr, Pb, Zn, and Mn during co-combustion is explored in current research. The results showed co-combustion could inhibit the emission of Zn, As, Pb, and Mn, and the effect was more pronounced for Zn, As and Mn. Meanwhile, minerals like kaolinite and gypsum were found to generated in the ash from co-combustion but not solo-combustion. Model experiments demonstrated that kaolinite captured As, Pb and Mn, while gypsum captured Zn, As and Mn but facilitated the emission of Pb and Cr. This well explained the distinct TEs emission characteristics between co-combustion and solo combustion. As the temperature elevated, kaolinite in co-combustion ash decomposed and the generation of gypsum was promoted. In this way, the emission ratios of Zn, As, and Mn initially increased but subsequently decreased between 700 and 1300 °C, whereas Pb and Cr emission ratios increased by twofold within the same temperature range. Leaching characteristics and risk assessment code on co-combustion ashes were also conducted in this study. The results indicated a marginal elevation in the risk associated with trace elements (TEs) following co-combustion, provided that all five TEs remained within the limits of national standards.

Isotopic Signatures and Outputs of Lead from Coal Fly Ash Disposal in China, India, and the United States

Despite extensive research and technology to reduce the atmospheric emission of Pb from burning coal for power generation, minimal attention has been paid to Pb associated with coal ash disposal in the environment. This study investigates the isotopic signatures and output rates of Pb in fly ash disposal in China, India, and the United States. Pairwise comparison between feed coal and fly ash samples collected from coal-fired power plants from each country shows that the Pb isotope composition of fly ash largely resembles that of feed coal, and its isotopic distinction allows for tracing the release of Pb from coal fly ash into the environment. Between 2000 and 2020, approx. 236, 56, and 46 Gg Pb from fly ash have been disposed in China, India, and the U.S., respectively, posing a significant environmental burden. A Bayesian Pb isotope mixing model shows that during the past 40 to 70 years, coal fly ash has contributed significantly higher Pb (∼26%) than leaded gasoline (∼7%) to Pb accumulation in the sediments of five freshwater lakes in North Carolina, U.S.A. This implies that the release of disposed coal fly ash Pb at local and regional scales can outweigh that of other anthropogenic Pb sources.

A multi-criteria approach to investigate spatial distribution, sources, and the potential toxicological effect of polycyclic aromatic hydrocarbons (PAHs) in sediments of urban retention tanks

Bottom sediments deposited in retention tanks (RTs) located on two urban streams (Oliwski and Strzyza) in the central part of Gdansk (Poland) were analysed for polycyclic aromatic hydrocarbons' (PAHs) content. PAHs were extracted from samples with methylene chloride, then the extracts were subjected to clean-up applying the solid phase extraction (SPE) method. Quantitative and qualitative determination of 16 PAHs was performed with the use of gas chromatography/mass spectrometry technique. A multi-dimensional approach was applied to analyse PAHs' spatial distribution, source, and contamination status. Potential sources of PAHs were verified using isomer ratios supported by a statistical approach. The Σ16PAHs (in mg/kg d.w.) ranged from 1.95 ± 0.64 to 20.4 ± 6.8 for RTs located on the Oliwski Stream and from 0.50 ± 0.17 to 8.6 ± 2.9 for RTs located on the Strzyza Stream. PAHs detected in bottom sediments were mainly composed of 4- and 5-ring compounds. PAH isomer ratios such as Phen/Anth, Flth/Pyr, B(a)A/B(a)A + Chry, Inpy/Inpy + B(ghi)P, Flth/Flth + Pyr, Anth/Anth + Phen, and Flth/Flth + Pyr suggested delivery pathways for biomass, coal, and petroleum combustion. Petrogenic PAHs related to fuel leaks from cars were not detected. Statistical analyses confirmed traffic and heating system sources, while factor analysis (FA) pointed out the abrasion of wasting parts of vehicles. Based on threshold levels presented in sediment quality guidelines (SQGs), in most cases, PAHs were at low levels with occasional negative biological effects on organisms. Only sediments deposited in two RTs located on the Oliwski Stream presented harmful features for sediment-dwelling organisms. The risk assessment performed accordingly to the Σ16PAHs presented a moderate and high risk for biota. This study not only reflects the direct threat related to PAH content in bottom sediments, but also highlights the overall pollution of an area, considered to be a recreational part of the city (Oliwski Stream catchment). The findings of this study highlight the need to launch preventative methods to protect the area against pollution from heating system emission and traffic.

Response of PM2.5-bound elemental species to emission variations and associated health risk assessment during the COVID-19 pandemic in a coastal megacity

The coronavirus (COVID-19) pandemic is disrupting the world from many aspects. In this study, the impact of emission variations on PM_2.5-bound elemental species and health risks associated to inhalation exposure has been analyzed based on real-time measurements at a remote coastal site in Shanghai during the pandemic. Most trace elemental species decreased significantly and displayed almost no diel peaks during the lockdown. After the lockdown, they rebounded rapidly, of which V and Ni even exceeded the levels before the lockdown, suggesting the recovery of both inland and shipping activities. Five sources were identified based on receptor modeling. Coal combustion accounted for more than 70% of the measured elemental concentrations before and during the lockdown. Shipping emissions, fugitive/mineral dust, and waste incineration all showed elevated contributions after the lockdown. The total non-carcinogenic risk (HQ) for the target elements exceeded the risk threshold for both children and adults with chloride as the predominant species contributing to HQ. Whereas, the total carcinogenic risk (TR) for adults was above the acceptable level and much higher than that for children. Waste incineration was the largest contributor to HQ, while manufacture processing and coal combustion were the main sources of TR. Lockdown control measures were beneficial for lowering the carcinogenic risk while unexpectedly increased the non-carcinogenic risk. From the perspective of health effects, priorities of control measures should be given to waste incineration, manufacture processing, and coal combustion. A balanced way should be reached between both lowering the levels of air pollutants and their health risks.

Lead removal in flue gas from sludge incineration by denitrification: Insights from metagenomics and metaproteomics

Flue gas lead emission during sludge incineration damages to human health and ecological environment seriously. Therefore, a denitrifying bio-trickling filter (DNBTF) for lead removal in flue gas from sludge incineration was investigated. Lead removal efficiency was up to 90.7% in 60 days' operation. Lead speciation in biofilms of DNBTF consists of 84.27% residue lead, 15.18% organic bound lead, and less than 1% exchangeable and reducible lead. Lead resistant bacteria and lead resistant-denitrifying bacteria accounted for 85.04% and 58.25%, respectively. Lead resistant microorganisms(Pseudomonas, Azoarcus, Stappia, Pararhodobacter, Paracoccus, Azospirillum, Hyphomonas, Rhodobacter, Polymorphum, Brevunimonas, Stenotrophomonas) could resist the toxicity of Pb²⁺ in flue gas by transport protein and binding protein, and detoxify Pb²⁺ in flue gas by extracellular polymeric substances (EPS) adsorption, protein binding and precipitation under the action of resistance genes, such as pbrAB, golT, troABCD, znuABC, czcABCD, pcoB, copA, as shown by integrated metagenomic and metaproteomic analyses. The biofilm was characterized by FTIR, XRD, 3D-EEM, and SEM-EDS. XRD and SEM-EDS spectra indicated the formation of pyromorphite from bioconversion of lead in flue gas. Lead-containing flue gas was bio-stabilized in the form of pyromorphite and HA-Pb via complexation of humic acids in extracellular polymeric substances (EPS), biosorption and biodeposition. This provides a new way of sludge incineration flue gas lead removal using a denitrifying biotricking filter.

Source Identification and Apportionment of Potential Toxic Elements in Soils in an Eastern Industrial City, China

The extensive pattern of economic growth has an inestimable negative impact on the ecological environment, which causes the soil pollution problem to become increasingly prominent. In order to improve the effectiveness and rationality of prevention and control of heavy metal pollution in regional soil, it is necessary to understand the current situation of pollution, identify pollution sources and clarify future pollution risks. In this paper, an industrially developed city in eastern China was taken as the study region. The positive matrix factorization model (PMF) model and Unmix model was applied to identify and apportion the pollution sources of soil potential toxic elements after evaluating the ecological risk of soil potential toxic elements. The PMF model identified six factors, including single source and composite source. The Unmix model also identified six sources, including sources of nature, industrial discharge and traffic emissions. The comparison between the two models showed that Hg and Ni pollution, as well as Cr enrichment in the study region, were related to the industrial discharge from enterprises and factories. Cd pollution was related to traffic emission sources. Cu and Zn pollution were related to the multiple sources mixed with soil parent material, traffic emissions and industrial discharge from electronic enterprises. Pb pollution was related to natural sources (e.g., soil pH) but also to industrial sources (e.g., industrial wastes discharge). Enrichment was related to soil parent material and agricultural inputs. Our study also implies that soil heavy metal pollution or enrichment in the study region was mainly from anthropogenic sources and supplemented by natural sources.

Coupling Plant Biomass Derived from Phytoremediation of Potential Toxic-Metal-Polluted Soils to Bioenergy Production and High-Value by-Products—A Review

Phytoremediation is an attractive strategy for cleaning soils polluted with a wide spectrum of organic and inorganic toxic compounds. Among these pollutants, heavy metals have attracted global attention due to their negative effects on human health and terrestrial ecosystems. As a result of this, numerous studies have been carried out to elucidate the mechanisms involved in removal processes. These studies have employed many plant species that might be used for phytoremediation and the obtention of end bioproducts such as biofuels and biogas useful in combustion and heating. Phytotechnologies represent an attractive segment that is increasingly gaining attention worldwide due to their versatility, economic profitability, and environmental co-benefits such as erosion control and soil quality and functionality improvement. In this review, the process of valorizing biomass from phytoremediation is described; in addition, relevant experiments where polluted biomass is used as feedstock or bioenergy is produced via thermo- and biochemical conversion are analyzed. Besides, pretreatments of biomass to increase yields and treatments to control the transfer of metals to the environment are also mentioned. Finally, aspects related to the feasibility, benefits, risks, and gaps of converting toxic-metal-polluted biomass are discussed.

Theoretical study on the adsorption mechanism of PbCl2/CdCl2 by kaolinite during municipal solid waste pyrolysis

In the process of municipal solid waste (MSW) pyrolysis, kaolinite possesses an outstanding trapping effect on semi-volatile metal vapors (Pb, Cd) through physical and chemical adsorption. In this paper, the microscopic mechanism of PbCl₂ and CdCl₂ adsorption on the surface of Al rings and Si rings of kaolinite was investigated by combining Monte Carlo method with density functional theory (DFT). The calculations indicate that the continuously enriched pore structure in the process of dehydroxylation indirectly influences the adsorption of PbCl₂/CdCl₂ by kaolinite. Under the non-bond interaction and electron transfer induction, PbCl₂ molecules are more conveniently adsorbed on the Al-(001) surface than CdCl₂, while the adsorption sites of CdCl₂ molecules are more widely distributed on the Si-(001) surface. Moreover, the transform in the Al-coordination and the exposed active oxygen atoms significantly affect the adsorption activity of kaolinite (the capability to gain and lose electrons). Considering the energy barrier and electrophilic nucleophilic sensitivity, it is more feasible for PbCl₂/CdCl₂ to be adsorbed near IV/V-coordinated Al and active O under Van der Waals action. Subsequently, IV/V-coordinated Al will act as an electron acceptor, and the active oxygen atoms after dehydrogenation will serve as an electron donor. Under the induction of the energy difference of frontier orbitals, the electrons transfer will encourage the formation of more stable adsorption states. The results shed new light on strengthening the adsorption activity of kaolinite to PbCl₂/CdCl₂ in the process of MSW pyrolysis.

Distribution and Mode of Occurrence of Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Pb in the Feed Coal, Fly Ash, Slag, in the Topsoil and in the Roots of Trees and Undergrowth Downwind of Three Power Stations in Poland

It is supposed that the determination of the content and the mode of occurrence of ecotoxic elements (EE) in feed coal play the most significant role in forecasting distribution of EE in the soil and plants in the vicinity of power stations. Hence, the aim of the work was to analyze the properties of the feed coal, the combustion residues, and the topsoil which are reached by EE together with dust from power stations. The mineral and organic phases, which are the main hosts of EE, were identified by microscopy, X-ray powder diffraction, inductively coupled plasma atomic emission spectrometry, and scanning electron microscope with an energy dispersive X-ray methods. The highest content of elements was observed in the Oi and Oe subhorizons of the topsoil. Their hosts are various types of microspheres and char, emitted by power stations. In the areas of long-term industrial activity, there are also sharp-edged grains of magnetite emitted in the past by zinc, lead, and ironworks. The enrichment of the topsoil with these elements resulted in the increase in the content of EE, by between 0.2 times for Co; and 41.0 times for Cd in the roots of Scots pine, common oak and undergrowth, especially in the rhizodermis and the primary cortex and, more seldom, in the axle roller and cortex cells.

Behavior of Cd during Coal Combustion: An Overview

Due to the unfavorable combination of its toxicity and high volatility, Cd is contained in most lists of potentially hazardous air pollutants with the greatest environmental and human-health concerns. The review paper evaluates the behavior of Cd during combustion (incineration) processes and its redistribution among condensed fractions (bottom ash/slag, fly ash) and volatilized fractions (that passes through most particulate control devices). The paper addresses all important effects of Cd interactions, such as presence of organic or inorganic chlorides, moisture levels, S, P and Na concentrations, flue gas composition etc. Possibilities of using various adsorbents (either within in-furnace regime or applied in post-combustion zone) are evaluated as well. Special attention is paid to mitigating its emissions factors; decreasing Cd volatility and facilitating Cd retention are discussed with the view of various combustion (incineration) conditions and the feed fuel composition.

Spatial Macroscale Variability of the Role of Mineral Matter in Concentrating Some Trace Elements in Bituminous Coal in a Coal Basin—A Case Study from the Upper Silesian Coal Basin in Poland

As there are numerous claims that the mode of occurrence of trace elements in coal influences the quality of the substrates as well as the course and results of the coal preparation processes, it is necessary to analyse the differences in the mode of occurrence of the elements in coal within a coal basin or a coal deposit. With the use of concentration distribution functions and the Pearson correlation coefficient, it was concluded that (1) mineral matter plays a significant and nearly constant or constant role in concentrating V, Cr, Co, As, Rb, Sr, Ba, and Pb in coal; (2) organic matter plays a stable role in concentrating Sn; and (3) there are significant differences in the role of organic and mineral matter in concentrating Mn, Ni, Cu, Zn, Mo, Cd, and Sb in coal throughout the USCB (Upper Silesian Coal Basin). Moreover, there was observed a difference in the mode of occurrence of Cr, Mn, Co, Ni, Cu, Zn, Mo, Cd, Sn, and Sb in coal in the vertical profile of the USCB. At the same time, there were observed no differences and a stable significant role of mineral matter in concentrating V, As, Rb, Sr, Ba, and Pb in coal, while the role of the petrographic groups of the coal components in concentrating the elements in raw coal was differentiated. It is believed that the difference in the mode of occurrence of the trace elements in coal within coal seams and coal deposits is a geochemical regularity.

Distribution of Some Ecotoxic Elements in Fuel and Solid Combustion Residues in Poland

The purpose of this paper is to assess the content and distribution of some elements in coal from two bituminous coal basins and in fly ash and slag derived from combustion of the coals in six power plants in Poland. The petrographic composition and distribution of elements were characterized in the tested samples, using reflected light microscope, X-ray powder diffractometer, inductively coupled plasma atomic emission spectroscopy, and scanning electron microscope with energy dispersive X-ray. The highest content of elements in coal occurs in siderite. In Al-Si particles, as well as in magnetite with skeletal and dendritic structure crystallized on the surface of Al-Si microspheres or cenospheres included in fly ash size < 0.05 mm and in the magnetic fraction of slag, the highest content of elements was noted. Due to the content of elements, fly ash and slag were considered to be neutral for the soil environment. Correlations, which have not been described before, have been observed between the likely mode of binding of some elements in coal and their distribution in fly ash and slag. These correlations could be of particular value when predicting the content and distribution of elements in combustion residues and in the assessment of their environmental toxicity.