Reaction of CO2 with clean coal technology ash to reduce trace element mobility

The combustion of coal in power plants generates solids (e.g., fly ash, bottom ash) and flue gas (e.g., SO _x , CO₂). New Clean Air Act mandated reduction of SO _x emissions from coal burning power plants. As a result, a variety of Clean Coal Technologies (CCT) are implemented to comply with these amendments. However, most of the CCT processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue gas to CCT ash. The objective of this study was to determine the effect of a pressurized CO₂ treatment on the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized bed combustion, and sodium carbonate injection processes were reacted under different CO₂ pressure treatment conditions. Treated and untreated samples were subjected to various experiments including, X-ray diffraction (XRD) analysis, calcium carbonate solubility studies, and trace element extraction studies. Factors influencing the efficiency of a CO₂ treatment for CCT ash samples include combustion process, moisture, CO₂ concentration, and pressure. The CO₂ pressure treatment resulted in the precipitation of calcite in CCT ash samples, and thus lowered the pH and the concentration of extractable trace elements (e.g., Cd, Pb, Cr, As, Se). Furthermore, we found that CO₂ pressure treatment was more effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium carbonate injection processed samples.     

Boron availability to plants from coal combustion by-products

Agronomic use of coal combustion by-products is often associated with boron (B) excess in amended soils and subsequently in plants. A greenhouse study with corn (Zea mays L.) as test plant was conducted to determine safe application rates of five fly ashes and one flue gas desulfurization gypsum (FDG). All by-products increased soil and corn tissue B concentration, in some cases above toxicity levels which are 5 mg hot water soluble B (hwsB) kg^?1 soil and 100 mg B kg^?1 in corn tissue. Acceptable application rates varied from 4 to 100 Mg ha^? for different by-products. Leaching and weathering of a high B fly ash under ponding conditions decreased its B content and that of corn grown in fly ash amended soil, while leaching of the same fly ash under laboratory conditions increased fly ash B availability to corn in comparison to the fresh fly ash. Hot water soluble B in fly ash or FDG amended soil correlated very well with corn tissue B. Hot water soluble B in fly ash amended soil could be predicted based on soil pH and B solubility in ash at different pH values but not so in the case of FDG. Another greenhouse study was conducted to compare the influence of FDG and Ca(OH)₂ on B concentration in spinach (Spinacia oleracea L.) leaves grown in soil amended with the high B fly ash. The Ca(OH)₂ significantly decreased tissue B content, while FDG did not affect B uptake from fly ash amended soil.     

Specifics and Temporal Changes in Air Pollution in Areas Affected by Emissions from Oil Shale Industry, Estonia

Atmospheric air pollution levels and long-term effects on the environment caused by simultaneous presence of SO₂ and oil shale alkaline fly ash during the last five decades (since 1950) were investigated. The annual critical value of SO₂ for forest (20 µg m^?3) was surpassed in 1% (～35 km²) of the study area where the load was 30–40 µg m^?3. No effect of long-term SO₂ concentrations of up to 10–11 µg m^?3 (0.5-h max up to 270 µg m^?3) and simultaneous fly ash loads of up to 95 µg m^?3 (1000 µg m^?3) on the growth and needle longevity of Pinus sylvestris was established. The yearly deposition (average load up to 20–100 kg S ha^?1) was alkaline rather than acidic due to an elevated base cation deposition in 1960–1989. Since 1990, the proportion of SO₂ in the balance of components increased: about 70–85% of the total area was affected while the ratio of annual average concentrations of SO₂ to fly ash was over 1. The limit values of fly ash for Sphagnum mosses and conifers in the presence of SO₂ are recommended.     

The use of coal fly ash in sodic soil reclamation

An experiment was conducted for two years in northwest India to explore the feasibility of using coal fly ash for reclamation of waterlogged sodic soils and its resultant effects on plant growth in padi–wheat rotation. The initial pH, electrical conductivity, exchangeable sodium percentage and sodium adsorption ratio of the experimental soil were 9.07, 3.87 dS m⁻¹, 26.0 and 4.77 (me l)^−1/2, respectively. The fly ash obtained from electrostatic precipitators of thermal power plant had a pH of 5.89 and electrical conductivity of 0.88 dS m⁻¹. The treatments comprised of fly ash levels of 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 per cent, used alone as well as in combination with 100, 80, 60, 40, 20 and 10 per cent gypsum requirement of the soil, respectively. There was a slight reduction in soil pH while electrical conductivity of the soil decreased significantly with fly ash as measured after padi and wheat crops. The sodium adsorption ratio of the soil decreased with increasing fly ash levels, while gypsum treatments considerably added to its favourable effects. Fly ash application increased the available elemental status of N, K, Ca, Mg, S, Fe, Mn, B, Mo, Al, Pb, Ni, Co, but decreased Na, P and Zn in the soil. An application of fly ash to the soil also increased the concentrations of above elements except Na, P and Zn in the seeds and straw of padi and wheat crops. The available as well as elemental concentrations in the plants was maximum in the 0 per cent fly ash + 100 per cent gypsum requirement treatment except Na and heavy elements like Ni, Co, Cr. The treatment effects were greater in the fly ash + gypsum requirement combinations as compared to fly ash alone. Saturated hydraulic conductivity and soil water retention generally improved with the addition of fly ash while bulk density decreased. Application of fly ash up to 4.5 per cent level increased the straw and grain yield of padi and wheat crops significantly in both years. The results indicated that for reclaiming sodic soils of the southwest Punjab, gypsum could possibly be substituted up to 40 per cent of the gypsum requirement with 3.0 per cent acidic fly ash. Copyright © 2003 John Wiley & Sons, Ltd.     

Alkaline coal fly ash amendments are recommended for improving rice-peanut crops

Abstract

A field experiment investigating amendments of organic material including farmyard manure, paper factory sludge and crop residues combined with fly ash, lime and chemical fertilizer in a rice-peanut cropping system was conducted during 1997–98 and 1998–99 at the Indian Institute of Technology, Kharagpur, India. The soil was an acid lateritic (Halustaf) sandy loam. For rice, an N:P:K level of 90:26.2:33.3 kg ha^?1 was supplied through the organic materials and chemical fertilizer to all the treatments except control and fly ash alone. The required quantities of organic materials were added to supply 30 kg N ha^?1 and the balance amount of N, P and K was supplied through chemical fertilizer. Amendment materials as per fertilization treatments were incorporated to individual plots 15 days before planting of rice during the rainy season. The residual effects were studied on the following peanut crop with application of N:P:K at 30:26.2:33.3 kg ha^?1 through chemical fertilizer alone in all treatments, apart from the control. An application of fly ash at 10 t ha^?1 in combination with chemical fertilizer and organic materials increased the grain yield of rice by 11% compared to chemical fertilizer alone. The residual effect of both lime and fly ash applications combined with direct application of chemical fertilizer increased peanut yields by 30% and 24%, respectively, compared to chemical fertilizer alone. Treatments with fly ash or lime increased P and K uptake in both the crops and oil content in peanut kernel compared to those without the amendments. Alkaline coal fly ash proved to be a better amendment than lime for improving productivity of an acid lateritic soil and enriching the soil with P and K.     

Trace metals concentrations in marine organisms from the coastal areas of Bahrain,Arabian Gulf

A total of 162 fish and shellfish samples representing important species have been collected from different coastal areas of Bahrain in the Arabian Gulf, and analyzed for lead, cadmium, mercury, and arsenic using electrothermal atomic absorption spectrophotometric method. The dverall mean levels for Pb, Cd, Hg and As in fish samples were 0.132, 0.032, 0.084 and 1.7 µg g^?1 wet weight, respectively, whereas for shellfish they were 0.149, 0.045, 0.042 and 3.61 µg g^?1 wet weight. These values indicate higher levels of metals in shellfish when compared with fish, except for mercury, and reveal that generally the levels of metals in these organisms are lower than existing guidelines, except for arsenic. The provisional tolerable weekly intake of Pb, Cd, Hg and As through fish was estimated to be 0.7, 0.17, 0.45 and 9 µg kg^?1 bodyweight per week, respectively. Our results did not reveal a clear pattern regarding variations of metals concentration between areas and species.     

Characteristics of synthetic soil aggregates produced by mixing acidic “Kunigami Mahji” soil with coal fly ash and their utilization as a medium for crop growth

Abstract

This study was carried out to examine the characteristics and potential utilization of synthetic soil aggregates (SSA) produced by mixing acidic “Kunigami Mahji” soil in Okinawa, Japan, with waste materials, such as coal fly ash, used paper and starch, as media for crop growth. A series of different SSA were produced by incorporating various percentages (i.e. 0, 20, 40, 60, 80 and 100%) of coal fly ash into the “Kunigami Mahji” soil with used paper and starch. The particle density and bulk density of the original “Kunigami Mahji” soil were 2.67 and 1.23 g cm^?3, respectively. The increased percentages of added coal fly ash, used paper and starch significantly decreased the particle and bulk densities of SSA compared with the original “Kunigami Mahji” soil because of the low particle and bulk densities of the coal fly ash (2.10 and 0.96 g cm^?3, respectively). The SSA particle density varied between 2.39 and 2.14 g cm^?3, and bulk density varied between 0.72 and 0.81 g cm^?3, depending on the additional percentages of coal ash from 20–100%. Maximum water-holding capacity and saturated hydraulic conductivity were increased with the formation of SSA with coal fly ash, used paper and starch binder compared with the original “Kunigami Mahji” soil. The saturated hydraulic conductivity values of the SSA increased because of their low bulk density compared with the original soil. The addition of coal fly ash, used paper and starch to the acidic (pH = 4.62) “Kunigami Mahji” soil to form SSA increased the pH (6.70–9.96), electrical conductivity, exchangeable cation concentration and cation exchange capacity. The addition of coal fly ash up to 60% increased the aggregate strength. The growth and yield of komatsuna and soybean crops with SSA as a crop growth medium was assessed. Both crops showed the highest growth and yield when grown with SSA containing 20% of coal fly ash. Synthetic soil aggregates containing more than 20% of coal fly ash reduced plant growth and yield. Therefore, SSA produced from “Kunigami Mahji” soil with 20% of coal fly ash, used paper and starch can be successfully used as a medium for crop growth.     

Nutrient dynamics,dehydrogenase activity,and response of the rice plant to fertilization sources in an acid lateritic soil

Abstract

Rice variety IR 36, grown under flooding, was studied in 1998 to determine the effects of fly ash, organic, and inorganic fertilizers on changes in pH and organic carbon, release of nutrients (NH₄ ⁺-N, Bray's P, and NH₄OAc K), and dehydrogenase activity in an acid lateritic soil at 15-day intervals. Application of fly ash at 10?t?ha^?1 alone did not improve the availability of NH₄ ⁺-N, or P, as well as the rice grain yield. Availability of NH₄ ⁺-N (35.3–36.9?mg?kg^?1), and P (12.3–14.6?mg?kg^?1) at 15 days after transplanting, and rice grain yields (48.0–51.7?g per pot) were similar under the various fertilization sources such as inorganic fertilizer alone, inorganic fertilizer?+?fly ash or inorganic fertilizer?+?green manure?+?fly ash. Mean dehydrogenase activity was the highest (8.47?µg triphenyl formazon g^?1 24?h^?1) under the mixed fertilization treatments with green manure. At the end of the cropping season (75 days after transplanting), pH, organic carbon, and dehydrogenase activity were higher under the mixed fertilization treatments involving green manure by 3, 15 and 154%, respectively, compared with the inorganic fertilizer alone.     

Pb/Ca in Thailand Coral Determined by LA-ICP-MS: Anthropogenic Pb Input of River Run-off into a Coral Reef from Urbanised Areas

In order to monitor lead pollution from urban areas to coral reefs in the Gulf of Thailand, linear and two-dimensional distributions of Pb in corals from Khang Khao Island, Thailand and Rukan-sho, Okinawa, were analysed with high resolution. Laser ablation inductively coupled plasma mass spectrometry was applied to measure Pb content in coral skeletons using synthetic Pb standards in a CaCO₃ matrix as calibration materials. Linear and two-dimensional ablation schemes were applied to determine the Pb content in corals collected from Khang Khao Island, Thailand and Rukan-sho, Okinawa. The coral skeleton was ablated by Nd:YAG laser (wavelength of 266 nm, beam diameter of 155 µm, scanning speed of 10 µm s^?1 and frequency of 10 Hz) along the growth axis, and ion counts for ²⁰⁸Pb were normalised to ⁴²Ca. Lead content in the corals was determined using a calibration curve obtained from the synthetic Pb standards (0–141 µg g^?1). The linear ablation track of the sample from Khang Khao showed over 30 peaks of Pb with an average value of 3.55 µg g^?1, while Pb content in the coral from Rukan-sho showed relatively small variation with an average value of 0.132 µg g^?1. Two-dimensional imaging of Pb in the coral skeletons was also carried out for an area of 7?×?20 mm on the sample from Khang Khao. The distribution patterns of Pb and Ba in the Thailand coral co-varied. These observations from the linear and imaging analyses suggest discontinuous inputs of anthropogenic Pb from rivers to the Gulf of Thailand.     

Western Australian fly ash on sandy soils for clover production

Abstract

An experiment was conducted to determine the value of fly ash collected from flue gases of the Kwinana coal fired power station in Western Australia, as an amendment for sandy soils and as a replacement for phosphorus or potassium fertilizers. The results showed large increases in clover dry matter production (49% to 278%), attributed to improvements in nutrient and water retention from the fly ash. The fly ash provided a substantial amount of the phosphorus needed by the clover, although application of phosphorus fertilizer further increased dry matter production in the presence of fly ash. No evidence was obtained from plant growth or tissue analysis that the fly ash provided potassium to the pasture. The maximum yield was achieved when 501 ha^‐1 of fly ash was applied to the soil. However, only 10 to 401 ha^‐1 was required to achieve 75 to 90% of the maximum production. Although a statistically significant increase in cadmium and mercury concentration could be attributed to fly ash, the increase was small and within the range of natural variation of levels found at the sites.     

Anomalous contents of heavy metals in soils and vegetation of a mine area in S.W. Sardinia,Italy

Samples of soils and vegetation from the mining area of South-West Sardinia (Italy) were analyzed for Pb, Zn, Cd, and Cu content. The area (more than 100 km²) is inhabited by many thousands of people; land utilization includes mainly grapes on some small plains and permanent sheep pasture on the hills. The levels of Pb, Zn, and Cd were found to be exceptionally high in most samples. Lead concentration was up to 71000 μg g^?1 in the soils and 4000 jig g^?1 in vegetation; Cd concentration was found up to 665 μg g^?1 in soils and 26.5 μg g^?1 in vegetation. The heavy metal content of some soil samples was highly variable. Data show that Pb is easily absorbed by plant roots and translocated to foliage. In spite of the high heavy metal level, no signs of toxicity were apparent in vegetation.     

An input/output flux for lead in a coastal bay off Alexandria region

During 1987, seawater, rain, dust and drainage water samples were collected from Abu-kir bay (360 km²) east of Alexandria city to set up and evaluate the relative importance of different sources to the biogeochemical cycle of Pb in the bay. The mean total concentration of Pb in the bay water was 455 ± 180 and 785 ± 287 ng kg^?1 during low and high flow periods, respectively. About 75 ±12% are in the particulate form. The bay receives annually about 8.12 ± 2.18 and 6.13 ± 1.06 ± of Pb through agricultural and industrial discharge. In addition, 0.48 ± 0.11 ± yr^?1 and 0.23 ± 0.04 t yr^?1 of Pb reaches the bay through wet and dry depositions, respectively. The outflowing surface water from the bay carries 15.4 ± 3.6 t Pb yr^?1 to the southeastern Mediterranean waters. Data from sedimentation traps indicated that the bulk sedimentation rate in the bay was 95 ± 18 kg yr^?1 elevating the concentrations of Pb in sediments to more than 64 μg g^?1. The imbalance in the Pb flux (excess + 0.6 ± 0.08 t) indicates Pb accumulation in the water column. The apparent residence time of Pb in the bay is 62 ± 15 d. The assimilative capacity of Pb in the bay expressed in terms of Pb loading / in bay concentration amounted to 25 ± yr^?1/ μg L^?1. A 10% reduction in the present day load to the bay will yield a Pb concentration of less than 0.1 μg kg^?1 after 11 to 12 yr.     

Effects of Silver Nanoparticles on Soil Ammonia-Oxidizing Microorganisms Under Temperatures of 25 and 5℃

The excellent bactericidal performance of silver nanoparticles (Ag NPs) has led to their wide applications, resulting in increasing concerns about their potential environmental impacts. This study evaluated the influences of different concentrations of Ag NPs (0, 1, 10, and 100 μg g^-1 dry soil) on the ammonia-oxidizing microorganisms in soil at cultivation temperatures of 25 and 5℃ for 37 d. The results showed that 1 μg g^-1 dry soil of Ag NPs had no acute effects on the ammonia-oxidizing microorganisms. However, 10 and 100 μg g^-1 dry soil of Ag NPs levels were found to significantly inhibit the activities of soil nitrification, with a decrease of 69.89% and 94.55%, respectively, at 25℃ and 61.65% and 83.79%, respectively, at 5℃ compared to the control (0 μg g^-1 dry soil of Ag NPs). These levels of Ag NPs also obviously decreased soil urease activity from about 380.47 ±0.07 (at 5℃) and 529.76 ±13.44 (at 25℃) mg N g^-1 dry soil d^-1 to 61.70 ±2.97 and 68.29 ±8.22 mg N g^-1 dry soil d^-1, respectively, after 37 d of cultivation. Quantitative polymerase chain reaction showed the abundance of ammonia-oxidizing archaea and bacteria. For the same exposure time, the effects of Ag NPs on the activities of ammonia-oxidizing microorganisms and urease decreased with decreasing temperature. The threshold concentration of Ag NPs that induced negative effects on ammonia-oxidizing microorganisms was higher at 5℃ than at 25℃. Therefore, the temperature has a major impact on the toxicity of Ag NPs to ammonia-oxidizing microorganisms and on the urease activity, with toxicity being reduced with decreasing temperature.     

Toxicity of heavy metals (Zn,Cu, Cd,Pb) to vascular plants

The literature on heavy metal toxicity to vascular plants is reviewed. Special attention is given to forest plant species, especially trees, and effects at low metal concentrations, including growth, physiological, biochemical and cytological responses. Interactions between the metals in toxicity are considered and the role of mycorrhizal infection as well. Of the metals reviewed, Zn is the least toxic. Generally plant growth is affected at 1000 μg Zn L^?1 or more in a nutrient solution, though 100 to 200 µg L^?1 may give cytological disorders. At concentrations of 100 to 200 μg L^?1, Cu and Cd disturb metabolic processes and growth, whereas the phytotoxicity of Pb generally is lower. Although a great variation between plant species, critical leaf tissue concentrations affecting growth in most species being 200 to 300 μg Zn g^?1 dry weight, 15 to 20 μg Cu g^?1 and 8–12 μg Cd g^?1. With our present knowledge it is difficult to propose a limit for toxic concentrations of Zn, Cu, Cd and Pb in soils. Besides time of exposure, the degree of toxicity is influenced by biological availability of the metals and interactions with other metals in the soil, nutritional status, age and mycorrhizal infection of the plant.     

Elemental composition and release characteristics of some South African fly ashes and their potential for land application

Eight fly ash samples collected from South African power stations were evaluated for various chemical properties, liming potential and metal species release under incubation. All fly ashes had alkaline pH ranging from 10.97 to 12.75 with much wider variations of electrical conductivity (range 0.46–8.27 dS m^?1). Their total P content ranged from 553.3 to 1514 mg P kg^?1 and Olsen extractable P from 130 to 345.5 mg P kg^?1. Application of two of the fly ashes to three different soils showed a high ability to neutralize acidity, resulting in an average of 41% change in pH after 8 weeks of incubation. Across all three soils, the fly ash incorporation increased extractable P content from a P-deficient level to levels above 25 mg P kg^?1 in two of the three soils. Except for Cu, all metal species (Cr, Pb, Ni and Fe) showed significantly (P ≤ 0.05) low extractability under fly ash treated soils compared to the soil alone control. These results suggest that the South African fly ashes studied are effective liming materials and can provide essential elements such as P with minimum risk of soil contamination from metal species release.     

Mineralization and volatile loss of nitrogen from soils treated with coal combustion byproducts

There is an increasing need to find a suitable means for disposal of coal combustion byproducts because of the increasing world-wide production of these byproducts. This need has prompted interest in the use of land disposal, but there are concerns that this use may degrade the quality of soil. To determine the influence of coal combustion byproducts on the transformation and fate of soil N and assess the potential impact of land disposal on soil quality, we studied the effects of two combustion byproducts (fly ash and bed ash) applied at rates of 22.5, 45, 90, and 180 Mg ha^-1 on mineralization and volatile loss of N from soil. Studies comparing the influence of the byproducts on these processes showed that whereas fly ash had little influence on the fate of soil N, bed ash caused substantial mineralization of organic soil N and volatile loss of this N as NH₃. Studies monitoring the pH of soils treated with bed ash showed that soil pH increased immediately after this treatment, with values reaching as high as 12.8. These studies indicated that such extreme alkaline conditions caused chemical degradation and volatile loss of as much as 10% of the organic N in soil, and they provide strong evidence that the improper disposal of bed ash on land can have a substantial negative impact on soil quality.     

Some effects of fly ash (from coal burning) on bush bean plants grown in solution culture

Abstract

Bush bean plants (Phaseolus vulgaris L. C. V. Improved Tendergreen) were grown for 14 days in 3700‐ml solution cultures with varying application rates of fly ash from a coal burning plant in California. Plants were also grown in a solution culture experiment in the presence of tiie chelating agent DTPA (diethylene triamine pentaacetic acid) and also in solutions acidified with HCl. The latter treatments were to determine if metals in the fly ash could be made more available to plants. The higher levels of fly ash (5 to 10 g/3700 ml) resulted in increased Ca, B, Si, Sr, and Ba in leaves, stems, and roots. No plants, however, appeared to have an excess of trace metals. In another experiment DTPA and HCl amendments failed to increase greatly the availability of trace metals from the fly ash in solution culture except for Zn. In this experiment the fly ash was the sole source of Ca and plants were deficient in Ca because insufficient fly ash was added. The fly ash resulted in increased Zn, Ca, Fe, Mn, B, Al, Si, Ti, Mo, Li, Sr, Ba in leaves, stems, and roots and increased V, Co, and Ni in roots. There was 3 to 4 μg/g Sn and 0.6 μg/g Be in the roots of plants grown with fly ash. In another experiment, fly ash supplied all the Ca necessary for plant growth without decreased yields resulting from any trace metal.     

Improvement of wheat (Triticum aestivum) drought tolerance by seed priming with silicon

Silicon has the potential to improve drought tolerance in crops. Seeds primed with silicon were used in the present study to explore its potential benefit to withstand water stress. Seeds of two wheat varieties, NARC-2009 and Chakwal-50, were sown in pots after priming with distilled water and different concentrations (0.5%, 1.0% and 1.5%) of silicon sources (silicic acid, sodium silicate and silica gel) at PMAS, Arid Agriculture University, Rawalpindi. Maximum silicon uptake at three-leaf stage (0.028 µg g^?1 dry weight (DW)), anthesis (0.072 µg g^?1 DW) and maturity (0.103 µg g^?1 DW) was recorded for silica gel. Silicon uptake increased significantly in response to increase in Si concentration from 0.5% to 1.5%. Leaf membrane stability index, epicuticular wax, relative water content and proline remained maximum – 78.90%, 2.6 mg g^?1 DW, 83.88% and 54.90 µg g^?1 – for silica gel treatments compared with others. Silica gel with 1.5% silicon concentration resulted in maximum spike length (14.3 cm), biological yield (7.63 g pot^?1), hundred-grain weight (3.97 g pot^?1) and grain yield (2.46 g pot^?1). Based on the study outcomes, it is concluded that silica gel might be a good priming option with 1.5% silicon concentration to establish plant under drought stress.     

Effects of fly ash on microbial C02 evolution from an agricultural soil

Unweathered, acidic fly ash from a coal-fired power plant was applied to alfalfa meal-amended agricultural soil at levels equivalent to 0, 100, 400, and 700 tonne ha^?1. Amended soils were placed in respirometer jars and monitored for C0₂-C evolution over a 37-day period. Fly ash applications of 400 and 700 tonne ha^?1 reduced C0₂-C production significantly compared to 0 and 100 tonne ha^?1 treatments. Carbon dioxide-carbon from all treatments was considerably greater than that from soil treated with 1000 ppm CdCl₂. The results suggest that soil heterotrophic microbial activity may be impacted minimally by relatively low levels of fly ash application, but may be inhibited by higher levels of fly ash. Several metals were present at potentially toxic levels in the fly ash employed and may have accounted for the inhibition of CO₂ C evolution. The availability of some of these metals was indicated in companion plant uptake experiments.     

Trace element discharges from coal combustion for power production

Partition factors have been calculated to describe the distribution of 38 elements between slag, total fly ash, atmospherically emitted fly ash, and vapors for a coal fired steamplant. These factors have been generalized to other types of boilers, to calculate the annual U.S. discharge of trace elements due to coal combustion for power production. The magnitude of trace element mobilization by coal combustion is compared with industrial consumption of trace elements, and with estimates of their natural mobilization by weathering. Elemental flows due to coal consumption are never less than 1.5% of their weathering mobilization, and coal combustion introduces As, Co, Cu, Fe, Hg, Mo, Ni, Pb, Sc, Se, U, V, and Zn into the environment at rates comparable to their rates of introduction by weathering.