Metals In Ash Research Articles

Effect of reinforcement and applied load on three-body dry sand abrasive wear behavior of A356 bottom ash metal matrix composites

In the present study, effect of reinforcement and applied load on three-body dry sand abrasive wear behavior of A356-bottom ash metal matrix composites was carried out. The composites were fabricated using liquid metrological technique. The obtained as-cast specimens were heat treated at solutionizing temperature of 530 °C for 6 h followed by ice quenching with ageing time of 2 h. The sand abrasive wear tests were conducted at room temperature using silica sand of 200 µm as an abrasive medium as per ASTM standard G 65–81. Speed of 200 rpm, time of 30 min was kept constant for all the tests and wt% of reinforcement (2, 4, 6, 8, 10 wt%) and load of (2, 4, 6, 8, 10 N) was varied for five levels. The obtained results revealed that, the wear rate is affected from heat treatment and varying wt% of reinforcement and applied load. The wear resistance increases with the increase in percentage of reinforcement and decreases with the increase in the applied load for the given speed and time. Further, worn surfaces and wear mechanism was analyzed by using scanning electron microscope.

The Nutritional Effects of Digested and Undigested Organic Wastes Combined with Wood Ash Amendments on Carrot Plants

The impact of digestate and fresh animal manure (with and without ash) on soil fertility, carrot productivity, and metal uptake from soil to carrot was studied. Ash might contain high concentrations of metals. Since the impact of fiber and whole digestate with ash, on plant growth and metal uptake, remains unclear, their suitability as alternatives to inorganic fertilizer was assessed. Soil treatments included animal manure (AM), whole digestate (WD), fiber digestate (FD), animal manure with ash (AM+A), whole digestate with ash (WD+A), fiber digestate with ash (FD+A), inorganic fertilizer (positive control), and unamended (negative control). Impacts on soil properties were assessed initially and after a 6-week incubation, with plant morphometry and elemental composition, including nutrient and potential toxic element (PTE) uptake, determined. Performance of WD on carrot productivity was better than FD and AM. There was an overall positive effect of wood ash on the soil resulting in higher concentrations of all major elements. However, ash treatments had lower uptake and transfer factors of the metals while IF treatment had the highest transfer factors for Cr (16.3) and Ni (12.2). Also, based on carrot productivity, addition of wood ash mainly improved the performance of FD, having a slightly negative effect on AM. Despite the higher concentrations of trace metals in wood ash, it did not significantly increase the uptake of PTEs. The digestates and wood ash mixture had a positive effect on bioavailability of heavy metals in carrot plant and therefore can be a sustainable alternative amendment for root crops.

Mineralogy Characteristic Study and Exploration on the Valuable Metals Enrichment of Coal Fly Ash

The separation and enrichment can be targeted to enrich in fly ash and reduce the cost of leaching and recovering of fly ash. Regarding their different properties, the single-component separation was used to obtain uncompleted burned carbon, glass microbeads, minerals, and other characteristic components from the ash. Also, the mineral composition of each component was analyzed by electron microscopy. The metal minerals were mainly concentrated in the mineral components. Besides, the electron probe microanalysis shows that the Pt content in the minerals of fly ash was significantly correlated with the metal contents of Ni and Cu. After the obtainment of the characteristics of fly ash metal enrichment, the heavy minerals with Cu, Ni, Pt, Pd, and other target metal elements were enriched by gravity separation and flotation. The enrichment coefficients of Cu, Ni, Pt, and Pd were 1.45, 1.33, 1.90, and 1.60, respectively, and the recovery rates were 77%, 81%, 97%, and 88%, respectively. Since the yield of heavy minerals obtained by separation was 62.24%, it indicated the physical separation method could significantly reduce the cost of leaching and recovering of fly ash metal resources.

Catalytic effect of alkali metal in biomass ash on the gasification of coal char in CO2

Biomass ash rich in alkali metals has been proven as a natural and disposable catalyst for the thermal conversion of carbon-containing materials. The application of biomass ash as a catalyst for coal gasification shows an economic and promising scenario. The effects of addition ratio of biomass ash, alkali metal compounds in biomass ash and mineral matter in the coal on anthracite char gasification were studied with a thermogravimetric analyzer under CO2 atmosphere. The chemical fractionation method was used to prepare three kinds of biomass ash with different alkali metals containing chemicals. The morphology and elemental composition of solid samples were analyzed with a scanning electron microscope coupled with an energy-dispersive X-ray spectrometer. The achieved results revealed that the gasification conversion of anthracite char increased with the addition of biomass ash. However, it was also observed that 50% biomass ash addition resulted in the agglomeration of the co-gasification ash. The majority of the catalytic effect of alkalis in biomass ash was attributed to the H2O-soluble forms of alkali metal containing chemicals. Co-gasification of demineralized coal char and biomass ash showed that the catalytic activity of 2.5% biomass ash addition to demineralized coal char is similar to the 30% biomass ash addition to coal char. The mineral matter in the coal was observed to decrease the catalytic activity of the biomass ash. The catalytic mechanism of biomass ash on coal char gasification was elucidated.

Bottom ash utilization: A review on engineering applications and environmental aspects

Bottom ash produced from coal-fired power plants has been utilized in engineering applications for the purpose of recycling and solving disposal issue of bottom ash. This study reviews various applications of bottom ash in engineering fields. The engineering properties exhibited by bottom ash in terms of free draining, granular, lightweight and interlocking nanostructures allow them to be used for different functions. The bottom ash used is not limited to its raw state, but can be mixed and modified for advanced applications without neglecting the impacts on the environmental. The presence of metals in bottom ash are well known and being discussed whether they are harmful to the environment. Many countries have their own threshold limit of maximum contaminants, hence TCLP result will determine the hazardous status of bottom ash. This review helps in promoting the solution and potential usage of bottom ash, since coal is one of the dominant source of energy in power generation sector.

Behaviors, product characteristics and kinetics of catalytic co-pyrolysis spirulina and oil shale

• Oil shale restrained the thermal decomposition of organic matters in spirulina. • HZSM-5 and CaO promoted the deoxygenization and aromatization of co-pyrolysis. • The minimum E value of catalytic pyrolysis was achieved at 1HZSM-5/3CaO. • A significant synergistic effect was achieved at the percentage of 30% oil shale. The catalytic co-pyrolysis behaviors, kinetics and products distribution of spirulina (SP) and oil shale (OS) were studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that OS delayed the thermal decomposition of organic matters in SP; there existed inhibition for aromatics production under 310 °C and synergistic effects at high temperatures, and a maximum synergistic effect was achieved with 30% OS. HZSM-5 and CaO enhanced the deoxygenation and aromatization reaction, resulting in a prominent decrease of acids and phenols. With the increase of CaO ratio, the relative content of aliphatic hydrocarbons increased from 9.57% to 17.48%, while the relative content of aromatics increased first and then decreased, and the maximum yield of aromatics (15.92%) was obtained at 1CaO/3HZSM-5. The appropriate CaO/HZSM-5 mass ratio contributed to the production of desired pyrolysis product. The kinetic parameters were determined by using Friedman and Flynn–Wall–Ozawa (FWO) method. As the oil shale blending ratio increased, the average activation energy (E) of mixtures decreased from 278.84 kJ/mol to 192.53 kJ/mol (from 265.51 kJ/mol to 189.63 kJ/mol), related to the catalytic decomposition of organic matter by alkaline earth metals in OS ash. The minimum E value of catalytic pyrolysis 5SP/5OS was achieved at 1HZSM-5/3CaO (257.29 kJ/mol and 269.62 kJ/mol). This paper could offer significant pyrolysis knowledge for obtaining high-grade oil from SP and OS with HZSM-5 and CaO.

The Chemical Fractions and Leaching of Heavy Metals in Ash from Medical Waste Incineration using Two Different Sequential Extraction Procedures

The paper presents the chemical fractions and leaching of the heavy metals in the bottom and filter ashes from the incineration of medical waste by two comparative methods of sequential extraction and by Toxicity Characteristic Leaching Procedure test (TCLP). The BCR classic method has higher extraction percentages than proposed modified BCR method. In both ashes, the metals are predominantly bounded in F1 (exchangeable) and F2 (iron and manganese oxides) fractions. Due to the high content of metals in filter ash, representing over 17,000 mg/kg dry matter for Zn, 7,000 mg/kg dry matter for Pb, and 1,400 mg/kg dry matter for Cr and Cu in F1 and F2 fractions, a special attention should be given to the management and storage of this waste.

Effects of the <i>Camellia oleifera </i>Shell Substrate on the Yield and Nutritional Composition of <i>Pleurotus geesteranus</i>

Pleurotus geesteranus was cultivated on the substrates blended with different ratios of treated and untreated Camellia oleifera shells using cottonseed hull as the control substrate. The mycelial growth rate, yield, nutritional composition, ash and heavy metals of the Pleurotus geesteranus cultivated on these substrates were compared. The results suggest that the Camellia oleifera shell in substrate can accelerate the mycelial growth and increase the yield, nutrients and the contents of protein, ash, crude fiber and amino acid of Pleurotus geesteranus. It was found that the contents of tannin and saponin in Camellia oleifera shell affected the mycelial growth rate. The optimal C/N of the substrate for the growth of Pleurotus geesteranus was determined to be 27 ± 0.7. The C/N ratios higher than 30 reduced the protein, fat and soluble sugar contents of the cultivated Pleurotus geesteranus. The contents of heavy metals including Hg, As, Cd and Pb were found in Pleurotus geesteranus cultivated on the substrates containing Camellia oleifera shell complex.

Evaluation of the phytotoxicity of coal ash on lettuce (Lactuca sativa L.) germination, growth and metal uptake

Land application of coal ash is considered an environmentally friendly option to improve soil quality, but limited information exists on metal bioavailability and phytotoxicity of coal ash to sensitive plant species such as lettuce (Lactuca sativa L.). Germination and pot bioassay experiments were conducted at six coal application rates (0% (control), 5%, 15%, 25%, 50% and 75% v/v) to investigate the hypothesis that, coal ash will have a hormetic effect on germination, growth, metal uptake and biomass yield of lettuce, characterized by stimulatory and phytotoxicity effects at low and high application rates, respectively. Total concentrations (mg/kg) of metals in coal ash spanned several orders of magnitude, and decreased in the order: Fe (5150.5), Mn (326.0), Zn (102.6), Cu (94.7), Ni (74.7) and Pb (11.6). Bioavailable concentrations of metals were very low (0.0–14.1 mg/kg), accounting for less than 2% of the total concentrations. Coal ash had no significant effect on germination indices, but had hormetic effects on radicle elongation, evidenced by stimulatory and phytotoxicity effects at low (5–25%) and high (50–75%) application rates, respectively. Coal ash application at 50% and 75% significantly (p < 0.05) reduced lettuce growth and edible biomass yield, but lower application rates (5–25%) were similar to the unamended soil (control). Fe, Mn, Zn, Cu and Ni bioavailability and plant uptake generally decreased with increasing coal ash application rates particularly at 50% and 75%. Soil pH significantly increased (p < 0.05) from 6.5 for the control to about 8 for 75% coal ash, while electrical conductivity (EC) increased by 2–7 times to about 0.9 and 1.5 dS/m at 50% and 75% coal ash, respectively. Significant inverse linear relationship (p < 0.05; r2 = 0.80) were observed between edible and total biomass yields and EC, suggesting that increased salinity at high coal ash application rates could account for reduced growth and biomass. Partial elemental balances showed that plant uptake of metals was very low, accounting for just less than 2% of the bioavailable concentrations, while the bulk of the metals (98–99%) remained in the soil. In conclusion, the current findings show that coal ash may have hormetic and phytotoxic effects on sensitive plant species, an observation contrary to the bulk of earlier literature documenting beneficial effects of coal ash application to soils. Long-term field studies are required to confirm the current findings based on laboratory and pot bioassay experiments.

Source of Metals in Incineration Ash

Source of Metals in Incineration Ash

Evaluation of the Physical, Chemical and Thermal Properties of Portuguese Maritime Pine Biomass

A characterisation of Pinus pinaster Aiton. (Maritime Pine) woody biomass and ashes is presented in this study. Physical, thermal and chemical analysis, including density, moisture content, calorific value, proximate and ultimate analysis, were carried out. The fuel Energy Density (Ed) and the Fuelwood Value Index (FVI) were assessed by ranking the fuelwood quality. Furthermore, the determination of the ash metal elementals was performed. The results from this study indicated, for Pinus pinaster biomass tree components, carbon content ranging from 46.5 to 49.3%, nitrogen content from 0.13 to 1.18%, sulphur content from 0.056 to 0.148% and hydrogen content around 6–7%. The ash content in the tree components ranged from 0.22 to 1.92%. The average higher heating value (HHV) was higher for pine needles (21.61 MJ·kg−1). The Ed of 8.9 GJ·m−3 confirm the good potential of Pinus pinaster biomass tree components as fuel. The FVI ranked the wood stem (4658) and top (2861.8) as a better fuelwood and pine needles (394.2) as inferior quality. The chemical composition of the ashes revealed that the elemental contents are below the national and most European countries legislation guidelines for the employment of ash as a fertiliser.

Effect of Source-Classified Collection of Municipal Solid Waste on Heavy Metals and Pozzolanic Properties of Incineration Residues

The adoption of source-classified collection of municipal solid waste (MSW) systems has improved waste management and resource conservation in developing countries, including China. Here, we evaluated the effects of a new MSW source-classified collection system on the distribution and leaching of heavy metals in incineration residues as well as on the pozzolanic properties of residues used as additives in cement production. Cu, Cr, and Mn were found primarily in bottom ash, while the volatile metals Zn, Pb, and Cd became enriched primarily in fly ash during combustion. However, effective presorting of MSW prior to incineration reduced the heavy metal content of the MSW source material and increased the combustion efficiency and heat values of MSW. The system of source-classified collection of MSW resulted in decreased concentrations of heavy metals in bottom ash, as well as decreased leachate toxicity, which improved the viability of bottom ash for use as a non-hazardous raw material in cement production. The consistently high temperatures sustained during incineration of source-classified MSW increased the concentrations and leachate toxicity of Cd, Pb, Cu, Zn, and Cr in fly ash. Pozzolanic activity testing revealed that bottom ash may be used as a pozzolanic material in cement production, but that fly ash is not suitable. In contrast to bottom ash from the incineration of mixed MSW, bottom ash from the incineration of source-classified MSW fully satisfies China’s “Pozzolanic materials used for cement production” standards due to its low loss on ignition, high grindability, and the desired rupture strength, compressive strength, and stability that it adds to mortar mixtures.

Metal concentrations in recent ash fall of Popocatepetl volcano 2016, Central Mexico: Is human health at risk?

The present study addresses the metal concentration pattern and associated human health risks in ash samples of Popocatepetl volcano. In this regard, 12 ash samples from different regions of Puebla City were collected and analyzed for 28 major and trace metals, out of which exclusively 8 metals of potential risk (Cd, Co, Cr, Cu, Mn, Ni, Pb & Zn) were selected for human health risk validation. The metal concentration pattern showed an enriching trend for ferromagnesium and carbonate elements compared to previous ash eruptions. Enrichment factor and geoaccumulation indices displayed a least significant enhancement of metals from baseline concentrations. More likely, the potential ecological risk index suggested no harmful biological effects due to the presence of these metals in ash. Concurrently, in the human health risk assessment model, the hazard quotient and hazard index values < 1 indicated safe levels and no carcinogenic effects. All-inclusive, this study highlights the context of metals in ash fall of Popocatepetl which presents no adverse effects over the human population.

Investigation of the pollution risk of residues from a laboratory-scale underground coal gasification of Malkara (Turkey) lignite

The aim of this study was to examine the risk of heavy metal, ammonia and sulfate transition from underground coal gasification (UCG) chars and process water of Malkara lignite to the groundwater around the UCG cavity. The residues were collected during laboratory-scale underground coal gasification studies of Malkara lignite in ex situ gasification simulator. In order to compare gasification with combustion in terms of water pollution, ash samples were obtained by combustion of Malkara lignite. To determine the leaching behavior of the char and ash samples, two leaching tests (EPA TCLP and EN 12457-2 methods) were applied. The concentration of heavy metals in char, ash and process water samples was determined by ICP-OES. Additionally, ammonia and sulfate analyses were conducted for process water. Based on the results of this study, it has been found that the concentration of some elements, such as B, Sb and Al in char and ash eluates exceeded the maximum level of drinking water standards. However, there is no landfill concern about char samples according to EU Landfill Directive. A significant increase in B concentration was observed in ash samples. Considering B and some other elements combustion residues were identified with much higher water contamination ability, compared to gasification residues. Ammonia concentration was observed extremely high in process water of the gasification tests. UCG technique may be more environmentally applicable technology compared to combustion for Malkara lignite reserves. However, further detailed studies are necessary in the early stage of the UCG field test design and application.

Evaluation of strategies for mitigating risks associated with metals in pyrite ash

The main objective was to evaluate and optimise strategies for the immobilisation or mobilisation of Cd, Cu, Cr, Ni, Pb, and Zn from pyrite ash. Alkaline amendments were used for the immobilisation test: cement, sandstone, marl, marble waste and calcareous crust. The amendments were mixed with pyrite ash at a 1:2 rate, incubated for 28 days, and leachates analysed at the beginning of the experiment (day 0) and after 2, 7, 14 and 28 days. The mobilisation experiment tested metal release from pyrite ash by four concentrations of H2SO4 (0.25 M, 0.5 M, 1 M and 2 M) and contact times (60, 120, 180 and 240 min). Results for the immobilisation/mobilisation tests for Cr and Ni are not presented due to the low concentration in pyrite ash. In the immobilisation test, optimum results across metals and amendments were obtained after two days with percentages of retention being about 90% compared to leachates from pyrite ash only. The release success (in % of total content) using sulphuric acid followed the order: Cd (75%) > Zn (62%) > Cu (37%) > Pb (7%). The concentration of acid was more important than contact time (release enhanced at higher concentrations) except for Zn. The two strategies tested were successful to reduce the risk posed by metals. In terms of optimization, all alkaline materials showed high efficiency for metal retention after a short contact time; for mobilisation, treatment with sulphuric acid at high concentration (up to 2 M tested) resulted to be the optimum with contact time having limited influence.

Characterization of Al-Cu alloy reinforced fly ash metal matrix composites by squeeze casting method

Metal matrix composites (MMCs) are of great interest in industrial applications for lighter materials with high specific strength, stiffness and heat resistance. The processing of MMCs by casting process is a very promising way of manufacturing near net shape composites at relatively low cost. The liquid metallurgy squeeze casting technique has characteristics such as fine microstructure as a result of rapid cooling, low porosity and good bonding between the particles and base alloy. In this study, the effect of hardness, tensile, compression and impact properties as well as density have been investigated. The Al-4.5wt%Cu alloy was chosen as base matrix casted by both stir and squeeze casting. Fly ash is one of the most inexpensive and low density reinforcement available in large quantities as solid waste is used as reinforcement. The Al-4.5wt%Cu reinforced 3, 6, 9 and 12wt%fly ash composite was squeeze casted with an applied pressure of 120MPa. The results showed that hardness tensile compression and impact values were increased by increasing weight percentage of fly ash reinforcements during squeeze casting. Porosity and other casting defects such as shrinkage cavities were minimised due to pressure applied during solidification. Increase in weight percentage of fly ash composites caused to increase porosity even in squeeze casting but lesser than gravity cast matrix alloy. Microstructure shows the absence of micro porosity, and grain refinement interfacial bond between matrix and reinforcement.Keywords: Metal matrix composite, squeeze casting and fly ash

Optimization of the co-combustion of coal and composite biomass pellets

Abstract Composite biomass pellets (CBPs) are made from catkins, wood waste, and rice straw in China. This paper presents studies on the co-combustion of CBPs and coal by thermogravimetric analyzer and fluidized bed. The combustion parameters indicate that the co-combustion performance is improved gradually with the increase in CBP proportion. The interaction between coal and CBPs at high temperature is significant. The thermogravimetry and differential thermogravimetry (TG-DTG) curves shift toward a high temperature, and the decomposition process is delayed at high heating rates. The CBP blending ratio of 30% is considered the optimum ratio for coal and CBPs, in accordance with the minimum activation energy and slagging problem. The addition of CBPs can reduce the emission of polycyclic aromatic hydrocarbons (PAHs) and trace metals. The capture of trace metals is related to the alkali metals in ash, and the variation of PAHs is mainly attributed to combustion temperature and fuel properties.

Research on Power Plant Ash Impact on the Quality of Soil in Kostolac and Gacko Coal Basins

Increased concentrations of heavy metals in ash can adversely affect the microbiological and pedogenetic processes in soil. The aim of this paper is to determine the impact of ash from unburned coal generated in the Kostolac and Gacko coal basins on the quality of soil in the surrounding environment. The investigation included the surface soil layer that was sampled and tested during 2016 and 2017. A total of 30 samples of Kostolac soil and 9 samples of Gacko soil were analyzed for the content of 8 heavy metals: Cu, Pb, Cd, Zn, Hg, As, Cr and Ni. The analyses were carried out by inductively coupled plasma mass spectrometry (ICPMS) technique according to the EPA 6020A method and the following conclusions were made: Kostolac coal ash affects the quality of the surrounding soil in terms of Ni, Cu and Cr as evidenced by the moderately strong correlation of the Ni-Cu pair (k = 0.71), as well as the Cu-Cr pair (k = 0.73) and strong correlation of the Ni-Cr pair (k = 0.82), while the high recorded concentration of Pb, Hg, As and Zn is attributed to other sources of pollution, such as the traffic network and intensive farming activities, and in some cases, its impact is only local. All recorded concentrations of heavy metals are within the remediation values. The effect of ash on soil contamination in the surroundings of the Gacko coal basin is limited to Ni and Cd, with a strong correlation coefficient of this pair (k = 0.82). The recorded overrun of maximum allowed concentration of Cr is evidenced in only 2 samples, and in terms of this element the contamination of the Gacko soil can be considered to be local. It is concluded that prevailing winds play a part in soil pollution. Cluster analysis showed that Ni, Cr and Zn have very similar values in analyzed soil samples from both basins, while a cluster composed of only Hg, in the case of Gacko, indicates lower contamination with Hg compared to the other heavy metals.

Determination of forms of heavy metals in bottom ash from households using sequential extraction

The paper presents the results of heavy metals mobility obtained by sequential extraction method and leaching test. Heavy metals in solid waste material occur in different forms and phases that differ in terms of the toxicity, mobility and bioavailability. The sequential extraction analysis is widely used in order to predict the behaviour of heavy metals in a solid material. The sequential extraction methods involve a gradual separation of metals in various forms by means of specific extractants. The material used in the research applied bottom ash derived from households. The results of heavy metals concentrations (Cd, Pb, Ni, Cr, Cu, Zn) in extractable forms and total content in waste were presented. The five forms of heavy metals were determined. The concentrations of heavy metals were analyzed by FAAS. The lowest concentrations of analyzed heavy metals were determined in the exchangeable form. The author observed that the particular elements occurred mainly in forms: zinc and cadmium associated with carbonates, lead and copper in the organic and residual form, chromium and nickel in the residual form. Heavy metals in the residual fraction do not pose a possible environment hazard. The application of speciation analysis of heavy metals in bottom ash provide the means to assess the content of dissoluble forms of metals in water relative to their total content. This information is useful in assessing the migration capabilities of heavy metal ions from waste to the ground-water environment. The potential for the reuse of bottom ash was also discussed in the paper.

Properties of ashes formed after the combustion of sewage sludge

The objective of the research presented in the paper was to analyze the ash formed in the process of incineration in the thermal sewage sludge treatment facility being a part of Sitkówka-Nowiny wastewater treatment plant, located in the vicinity of Kielce. The research involved the investigation of heavy metal and total phosphorus content, leachability of certain ions and X-ray phase analysis. The comparison of the obtained results with those available in literature revealed similarities in the crystallographic structure of ashes from different treatment plants. Then, the differences observed in the content of heavy metals in particular ashes are related to the composition of sewage flowing into treatment plants. Attention was also paid to a significant sulphate content revealed in the leachability analysis, found both in the ash from Sitkówka-Nowiny treatment plant and in the ash analyses results available in the literature sources. High sulphate concentration can limit the use of ash for construction purposes.