|
|
CCB CHARACTERIZATION (PHYSICAL/CHEMICAL)
(Updated 10/15/98)
OUTLINE
BULK CHEMICAL AND PHYSICAL CHARACTERISTICS
Fly Ash - Fly ash is comprised of very fine particles. The
majority are glassy spheres, scoria, iron rich fractions, crystalline matter,
and carbon. Due to its size and shape, the characteristics of fly ash are that
of a high surface area to volume ratio solid that has agglomerated materials on
its surface. In general, the composition of the spherical portion of the fly ash
is somewhat immune to dissolution due to its glassy structure. The nature of
this spherical portion is quite similar to glass, both in elemental composition
and leaching properties, and as such is relatively inert. However, on the
surface of the spheres exists either easily exchangeable or adsorbed molecules
which, when in the presence of a liquid, become dissolved. It is this mechanism,
some researchers believe, which ultimately produces leachate. Some of the very
minute spheres may also dissolve into solution and contribute to the leachate.
The elemental composition of the structure and surface material is a function of
not only the feed coal, but also the combustion sequence and method of
collection.
The predominant constituents in fly ash are inert mineral oxides. Approximately
95 percent of the ash is made up of silicon, aluminum, iron, and calcium in
their oxide forms. Oxides of magnesium, potassium, sodium, titanium, and sulfur
are also present in lesser amounts. The type and proportion of trace elements in
fly ash are highly variable. A typical fly ash contains about 0.1 percent by
weight of trace elements. Trace elements that have been found in fly ash include
Arsenic, Boron, Barium, Beryllium, Cadmium, Cobalt, Chromium, Copper, Gallium,
Germanium, Lanthanum, Manganese, Mercury, Nickel, Lead, Scandium, Silver, Tin,
Strontium, Vanadium, Yttrium, Ytterbium, Zinc, and Zirconium.
Physical and Hydraulic Properties of Fly Ash and Other
By-Products From Coal Combustion -- Young, S. C., et al. 1993.
ENGINEERING CHARACTERISTICS
LEACHING TESTS
Inorganic and Organic Constituents in Fossil Fuel Combustion
Residues (Vol. 1: A Critical Review)--EPRI. 1987.
Inorganic and Organic Constituents in Fossil fuel Combustion
Residues:
Volume 2, An Annotated Bibliography. - -Rai, Dhanpat. 1987.
Speciation of Selenium and Arsenic in Natural Waters and
Sediments: Volume 1, Selenium Speciation. - -Old Dominion University Foundation.
1986.
Speciation of Selenium and Arsenic in Natural Waters and
Sediments: Volume 2, Arsenic Speciation. -- Battelle Pacific Northwest
Laboratories. 1986
Spectrochemical Analyses of Coal Ash for Trace Elements.
-- Abernethy, R. F., et al. 1969.
ABSTRACTS and LOCATION
Abernethy, R. F., et al. 1969. Spectrochemical Analyses of
Coal Ash for Trace Elements. U.S. Bureau of Mines, Washington, D.C. 30 pp.
The Bureau of Mines made spectrochemical analyses of ash from 827 U.S.
commercial coals for barium, beryllium, boron, chromium, cobalt, copper,
gallium, germanium, lanthanum, lead , lithium, manganese, molybdenum, nickel,
scandium, strontium, tin, vanadium, ytterbium, yttrium, zinc, and zirconium.
These 22 elements were detected in almost all of the ash
samples examined. In addition, arsenic, bismuth, cerium, neodymium, niobium
(columbium), rubidium, and thallium were detected in many samples.
Ordering Info:
Interlibrary Loan Request: Debbie McGinnis, Office of Surface Mining,
1999 Broadway, Suite 3320, Denver, CO 80202-5733. (303) 844-1436; fax (303)
844-1545; email: dmcginni@osmre.gov.
Battelle Pacific Northwest Laboratories. 1986. Speciation of
Selenium and Arsenic in Natural Waters and Sediments: Volume 2, Arsenic
Speciation. Electric Power Research Institute, Palo Alto, CA. 88 pp.
The disposal of coal combustion wastes is an environmental concern to the
electrical power utilities because high concentrations of potentially toxic
water-soluble trace elements, such as arsenic (As), may be released. During the
last two years research was conducted to (1) develop a methodology for As
speciation in waters and sediments, (2) predict the equilibrium speciation of As
in natural waters using geochemical modeling techniques, and (3) determine the
chemical speciation of As in fresh water and sediment of a reservoir which
receives coal fly ash.
The analytical methodologies have been developed for collection, storage and
analysis of fresh water and sediment without significantly altering the
speciation of As. Arsenic speciation of water and sediment is simply and
reproducibly achieved using hydride generation in conjunction with atomic
absorption detection. Very rapid freezing by immersion in liquid nitrogen
followed by storage at -80oC is necessary to prevent oxidation of As
(III) to As (V) during storage of water samples. Arsenic species are selectively
extracted from sediment. At pH 2.3, As (III) is extracted and at pH 11.9 As (V)
MMA and DMA are extracted.
The geochemical modeling results indicated the principal controls on
distribution of the aqueous species of As are EH and pH. Under most
environmental conditions As is present in the (V) valence state as the H2AsO4-
species, while As (III) as the H3AsO3o species,
is only dominant in low pH and low EH environments. Sorption of
arsenic as As (V) on iron and aluminum oxides could control arsenic
concentrations in natural waters.
Field samples were collected from Hyco reservoir in February and July 1984. The
reservoir is apparently contaminated by As discharged from a coal fly ash pond.
The majority of As is in the (V) valence stage in the water column and ash pond.
However, in the interstitial water squeezed from the reservoir sediments, As is
equally divided between (V) and (III).
Ordering Info:
Interlibrary Loan Request: Debbie McGinnis, Office of Surface Mining,
1999 Broadway, Suite 3320, Denver, CO 80202-5733. (303) 844-1436; fax (303)
844-1545; email: dmcginni@osmre.gov.
EPRI. 1987. Inorganic and Organic Constituents in
Fossil Fuel Combustion Residues, (Vol. 1: A Critical Review). EPRI EA-5176. EPRI,
Palo Alto, CA.
The literature on selected inorganic and organic constituents of fly ash, bottom
ash, flue gas desulfurization (FGD) sludge, and oil ash as reviewed to summarize
the available data on the concentrations an leachability of 28 selected elements
in the wastes and to determine the availability of mechanistic data for
describing the leachability of the elements. The data summarized and critiqued
for each of the 28 elements included: (1) the content of the element in the
wastes; (2) the relative distribution of the element in different particle size
fractions and at the surface or interior of the particles; (3) the predicted and
observed solid phases of the element; (4) the leachability of the element in
different solutions; (5) fundamental reactions of the element in fossil fuel
wastes; and (6) thermochemical and geochemical data for the element that are
applicable to fossil fuel wastes.
General and specific conclusions that can be drawn are as follows: (1) the
content of the elements in different wastes types varies considerably; (2) oil
ash is enriched in a number of elements including Sb, Cu, Pb, Mo, Ni, Se, V, and
Zn; (3) fly ash and bottom ash show a marked similarity in the content of
nonvolatile elements (e.g., Al, Ca, Fe, and Si); (4) volatile elements (e.g. B,
F, and Se) are generally concentrated in fly ash and FGD sludge; (5) the
composition of water extracts from the wastes is extremely variable and appears
to be related to pH, the degree of aqueous complexation of elements, and the
types of solubility-controlling solids formed; (6) aqueous concentrations of
several elements in fly ash (e.g., Al, Ba, Ca, Fe, Si, and S) appear to be
controlled by precipitation/dissolution reactions; (7) several trace elements
(e.g., As, Cu, Ni, and Zn) show pH-dependent solubilities and at pH values above
5 are present at or near the detection limits in most aqueous extracts from fly
ash; and (8) very few data on the organic constituents of wastes are available.
Although there is a general lack of reliable fundamental data and although the
data that are available are not comprehensive enough to permit accurate
predictions of leachate composition, the data summarized here can be used to
grossly estimate leachate composition and to identify the approach and the
additional data needed to make accurate predictions.
Ordering Info: EPRI Research Reports Center, Box 50490, Palo Alto, CA
94303, (415) 965-4081.
Interlibrary Loan Request: Debra McGinnis, Office of Surface Mining,
1999 Broadway, Denver, CO 80202-5733, (303) 844-1436, FAX (303) 844-1545, email:
dmcginni@osmre.gov.
Old Dominion University Foundation. 1986. Speciation of
Selenium and Arsenic in Natural Waters and Sediments: Volume 1, Selenium
Speciation. Electric Power Research Institute, Palo Alto, CA. 78 pp.
Fossil fuel combustion can lead to an increased mobilization of selenium to the
aquatic environment. In order to examine this process, the different chemical
forms of selenium must be determined in water and sediments with high degrees of
accuracy and precision.
A selective hydride generation procedure was developed to measure the
concentrations of dissolved selenite, selenate, total selenium, and organic
selenides in natural waters. Two detector systems were evaluated, atomic
absorption with quartz tube - air/hydrogen flame atomization, and gas
chromatography with photo ionization detection. Results show that the photo
ionization system has a high detection limit (10 ng Se), and a non-linear
response. In contrast, the atomic absorption technique is able to detect 0.2 ng
Se, and the instrumental response is linear to 96 ng Se. For the determination
of selenium speciation, the precision (as relative standard deviation) is no
greater than 5.4%; accuracy is assured using the standard additions method of
calibration. In sediments, total selenium is solubilized using an oxidative
digest, and a sodium hydroxide leach releases sedimentary selenite and selenate.
Solutions from these pretreatments are analyzed using the dissolved selenium
methods.
Field tests in three power plant cooling reservoirs, representing different
aquatic, sedimentary, and selenium concentration regimes, show the methods to be
versatile, precise, and accurate.
Ordering Info:
Interlibrary Loan Request: Debbie McGinnis, Office of Surface Mining,
1999 Broadway, Suite 3320, Denver, CO 80202-5733. (303) 844-1436; fax (303)
844-1545; email: dmcginni@osmre.gov.
Rai, Dhanpat. 1987. Inorganic and Organic Constituents in
Fossil fuel Combustion Residues:
Volume 2, An Annotated Bibliography. Electric Power Research Institute, Palo
Alto, CA. 87 pp.
An annotated bibliography of the literature pertaining to the chemical behavior
of inorganic and organic constituents present in fossil fuel wastes [fly ash,
bottom ash, flue gas desulfurization (FGD) sludge, and oil ash] is presented in
this report. The steps taken to produce the bibliography included 1) collecting
a complete set of articles through computer searches of major databases,
physical searches of articles published during the last five years in about 50
journals, and searches of references quoted in symposium proceedings and review
articles; and 2) classifying the articles by subject categories. The categories
were selected as being conducive to determining the availability of mechanistic
data needed to predict the geochemical behavior of waste constituents.
References relating to inorganic constituents are listed alphabetically, with
each reference followed by the assigned subject categories. References relating
to organic constituents follow in a separate section. For easy access, all
references for a given subject category are cross-indexed, and the indexes for
the inorganics and organics sections are given at the end of the volume. The
annotated bibliography was important in organizing the literature for a critical
review, which is the subject matter of Volume 1 of this report. The annotated
bibliography also provides 1) a reference volume on the available literature for
the chemical behavior of constituents present in fossil fuel wastes, and 2)
ready access to the literature on subject areas and constituents not considered
in the critical review.
Ordering Info:
Interlibrary Loan Request: Debbie McGinnis, Office of Surface Mining,
1999 Broadway, Suite 3320, Denver, CO 80202-5733. (303) 844-1436; fax (303)
844-1545; email: dmcginni@osmre.gov.
Young, S. C., et al. 1993. Physical and Hydraulic Properties
of Fly Ash and Other By-Products From Coal Combustion. Electric Power Research
Institute, Palo Alto, CalIAOrnia. 83 pp.
This report summarizes physical (e.g., specific gravity, bulk density) and
hydraulic properties (e.g., moisture retention curves, saturated hydraulic
conductivity) of six fly ashes, and wastes from Flue-Gas Desulfurization (FGD)
and Atmospheric Fluidized Bed Combustion (AFBC) pilot plants. A review of the
methods used to measure these properties is provided. The information can be
used to estimate the properties of fly ash, AFBC by-products, or FGD
by-products.
The physical and hydraulic properties are discussed in relation to natural soil
properties and to several semi-empirical formulas to predict hydraulic
properties. With regard to the soil textural triangle, all of the fly ash plot
is silty loam. Because fly ash tends to be both well-sorted and have small-sized
particles, they tend to have relatively high air entry values (e.g., a range
between 100 to 400 cm potential) and relatively sharp breaks in the moisture
retention characteristic curves. For similar reasons some of the AFBC and FGD
by-products also have high air entry values >100 cm.
The Mualem coefficients alpha and N derived by fitting an analytical
equation to moisture retention curves are useful for comparing fly ash
properties to those of natural soils. The values alpha and N can be
considered measures of the air entry value and of sorting, respectively.
Tabulated values for alpha show that they vary from 0.0042 for silt
loam to 0.12 for sand. The alpha for fly ash ranges from approximately
0.001 to 0.004. Compared to the alpha values for silty loam, the fly
ash values are approximately an order of magnitude lower and therefore more
typical of a finer textured soil. The tabulated N values for the six fly ash
samples range from 1.18 for a silt loam to 5.8 for sand. The calculated N values
range from 1.5 to 3.1 and thus fall within the broad range of N values
calculated for natural soils.
Laboratory values of hydraulic diffusivity were compared to theoretical values
calculated from values of alpha and N. A favorable comparison exists
for two fly ash typesthe remaining four have order-of-magnitude differences
between the two curves. The greatest differences were observed for the AFBC and
FGD wastes. In the FGD and AFBC wastes, chemical reactions are likely to occur
and affect the retention of water. Reactions such as hydration of water could
render useless equations for predicting hydraulic diffusivity curves that assume
capillarity is the primary mechanism affecting water retention. In situations
where chemical reactions occur that significantly affect the movement of water
(such as the AFBC by-products), the hydraulic diffusivity curve should not be
calculated by conventional theories based on capillarity.
A concern with laboratory methods for characterizing hydraulic properties of
porous media is whether the laboratory-determined properties are representative
of field conditions. TVA has conducted field and laboratory studies to check the
representativeness of the laboratory measured parameters. In one study, three
different methods were used to estimate the saturated hydraulic conductivity in
dry stacked fly ash. The methods were (1) laboratory permeameter measurements on
undisturbed cores from the dry stack, (2) in situ measurements in the dry stack
with a Guelph permeameter, and (3) laboratory permeameter measurements on packed
fly ash obtained directly from the plant's precipitators. The variation in the
averaged value of saturated hydraulic conductivity for these methods was about a
factor of two. Two factors that could have caused such a range are spatial
variability and different degrees of saturation within the different fly ash
samples being tested.
Ordering Info:
Interlibrary Loan Request: Debbie McGinnis, Office of Surface Mining,
1999 Broadway, Suite 3320, Denver, CO 80202-5733. (303) 844-1436; fax (303)
844-1545; email: dmcginni@osmre.gov.
|
U.S.
Office of Surface Mining, Mid-Continent Region
Accessibility