ASTM D4371-91(1998)
(Test Method)Standard Test Method for Determining the Washability Characteristics of Coal
Standard Test Method for Determining the Washability Characteristics of Coal
SCOPE
1.1 This test method describes procedures for determining the washability characteristics of coarse-coal fractions and fine-coal fractions. Each sample being tested can have more than one coarse-coal size fraction and more than one fine-coal size fraction (see Annex A1). Each such size fraction has an upper size limit and a lower size limit, neither of which overlaps with the next larger nor smaller size fraction. (See Test Method D4749.)
1.2 While, in general, this test method has useful application in determining the washability characteristics of low-rank coals, in the strictest sense, it is not necessarily the most technically correct test method to determine washability characteristics of low-rank coals because of problems relative to the loss of moisture through drying during sample preparation and analysis. Methods that are directly applicable to low-rank coals are to be developed.
1.3 The values stated in SI units are to be regarded as the standard. The values shown in parentheses are for information only.
1.4 This standard does not purport to address the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see Section 8 and Appendix X1.
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Designation: D 4371 – 91 (Reapproved 1998)
Standard Test Method for
Determining the Washability Characteristics of Coal
This standard is issued under the fixed designation D 4371; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The American Society for Testing and Materials has recognized the need for a standard procedure
to conduct washability analyses that will serve as an aid to technical communication among
individuals and organizations that supply, purchase, and utilize coal. This test method standardizes
procedures utilized for performing washability analyses, the data from which can be used for
interpreting preparation plant efficiency, for determining preparation plant design, and for determining
the potential recovery and quality of coal reserves.
1. Scope 2. Referenced Documents
1.1 This test method describes procedures for determining 2.1 ASTM Standards:
the washability characteristics of coarse-coal fractions and D 2013 Method of Preparing Coal Samples for Analysis
fine-coal fractions. Each sample being tested can have more D 2234 Practice for Collection of a Gross Sample of Coal
than one coarse-coal size fraction and more than one fine-coal D 4749 Test Method for Performing SieveAnalysis of Coal
size fraction (see Annex A1). Each such size fraction has an and Designating Coal Size
upper size limit and a lower size limit, neither of which D 4915 Guide for Manual Sampling of Coal from Tops of
overlaps with the next larger nor smaller size fraction. (See Railroad Cars
Test Method D 4749.) E 11 Specification for Wire-Cloth Sieves for Testing Pur-
1.2 While,ingeneral,thistestmethodhasusefulapplication poses
in determining the washability characteristics of low-rank E 100 Specification for ASTM Hydrometers
coals, in the strictest sense, it is not necessarily the most E 126 Test Method for Inspection and Verification of Hy-
technically correct test method to determine washability char- drometers
acteristicsoflow-rankcoalsbecauseofproblemsrelativetothe E 323 Specification for Perforated-Plate Sieves for Testing
loss of moisture through drying during sample preparation and Purposes
analysis. Methods that are directly applicable to low-rank coals
3. Terminology
are to be developed.
3.1 Definitions:
1.3 The values stated in SI units are to be regarded as the
standard. The values shown in parentheses are for information 3.1.1 coal washability—the determination of the theoretical
limits for the removal of mineral impurities from coal by
only.
1.4 This standard does not purport to address the safety beneficiation processes that rely on specific gravity separa-
tions.
concerns, if any, associated with its use. It is the responsibility
3.2 Definitions of Terms Specific to This Standard:
of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory 3.2.1 washability analysis of coal—the analysis of the
specific gravity distribution of chemical and physical charac-
limitations prior to use. For specific hazard statements, see
Section 8 and Appendix X1. teristics of coal.
3.2.1.1 Discussion—In this test method, the specific gravity
fractions are obtained by subjecting the material being studied
to a series of solutions, each with a discrete specific gravity,
ThistestmethodisunderthejurisdictionofASTMCommitteeD-5onCoaland
Coke and is the direct responsibility of Subcommittee D05.07 on Physical
Characteristics of Coal. Annual Book of ASTM Standards, Vol 05.05.
Current edition approved Feb. 22, 1991. Published May 1991. Originally Annual Book of ASTM Standards, Vol 14.02.
published as D 4371 – 84. Last previous edition D 4371 – 84. Annual Book of ASTM Standards, Vol 14.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4371
thatcovertherangeofspecificgravitiesinquestion.Inthecase particles are allowed to either float or sink. The material that
of the washability analysis of coal, these solutions are obtained floats on the solution is removed first, followed by the portion
bythemixingofvariousorganicliquidsthatarerelativelyinert of sample that sinks.
toward the majority of coal types. The distribution, as deter- 4.2 Procedure B—Describes a washability procedure for
mined by the analysis, is affected by the physical condition of coal fractions composed of particles of coal that are smaller
the sample subjected to the washability analysis, for example, thanthespecified,predeterminedsizechosenin4.1.Thesecoal
the moisture content and the size content of the material. fractions will be referred to as fine-coal fractions.
3.2.2 coarse coal—that portion of a coal sample being 4.2.1 Each fine-coal size fraction is separated into two
subjected to a washability study that is larger than a specific distinct specific gravity fractions by placing a portion of the
predetermined particle size, generally between 2.36 mm (No. 8 fine-coalsampleintoafloat/sinkflaskofsufficientcapacity,for
USA Standard Sieve Series) and 9.5 mm ( ⁄8 in.) round in example, 2 to 4 L (0.5 to 1 gal), containing a solution of
diameter. organic liquids adjusted to the required specific gravity (Note
3.2.2.1 Discussion—This same particle size breakpoint 1, Note 2, Note 3, and Note 4). Extreme care must be exercised
should then be used in subsequent washability studies of the to avoid overloading the float/sink flask. This suspension is
same material sampled from the same location for the same thenstirredtobecertainthateachindividualparticleisallowed
application.This breakpoint is determined by the analyst or the to float or sink. The material that floats is removed first by
person designing the test procedure as the point that best suits carefully inserting a stopper into the neck of the flask and
the application.This coarse-coal fraction may be further sieved pouring the organic solution and float material from the upper
(generally by dry-sieving) to produce additional size fractions, portion of the float/sink flask through a filtering medium that
each of which is processed through the desired specific gravity traps the float material. The sink material is then removed and
solutions. captured in a similar manner.
3.2.3 fine coal—that portion of a coal sample being sub-
NOTE 1—A limited number of laboratories are currently using separa-
jected to a washability study that is smaller than the predeter-
tory funnels for the separation of fine coal particles having a diameter less
mined particle size generally between 2.36 mm (No. 8 USA
than one third the diameter of the stopcock port.
Standard Sieve Series) and 9.5 mm ( ⁄8 in.) round in diameter,
NOTE 2—Some laboratories use centrifugal methods of separating
which is specified in 3.2.2. fine-coal density fractions. Centrifugal methods are not a part of this test
method.Apossible source of information is the Bureau of Mines’ Report
3.2.3.1 Discussion—This same particle size breakpoint
of Investigations 5741 (1), or the Department of Energy, Pittsburgh
should then be used in subsequent washability studies of the
Energy Technology Center, Coal Preparation Branch, P.O. Box 10940,
same material sampled from the same location for the same
Pittsburgh, PA 15236.
application.This breakpoint is determined by the analyst or the
NOTE 3—Preparation and adjustment of the organic solutions should be
person designing the test procedure as the point which best
done in an unrestricted container to allow proper mixing of the reagents
suits the application. This fine-coal fraction may be further
prior to their introduction into the float/sink flasks.
sieved (generally by wet-sieving) to produce additional size
NOTE 4—It is a general guide that the depth of the particles floating
fractions, each of which is processed through the desired
should not exceed three to five times the mean diameter of the particles in
specific gravity solutions. the sample. It is suggested to use 200 g, or less.
3.2.4 float/sink—a reference to the physical action that
4.3 Preparation of Test Sample, Sieving:
particles undergo when immersed in a liquid of a predeter-
4.3.1 The bulk sample should be spread on an impervious
mined specific gravity.
base, preferably under shelter. The sample should be dried and
3.2.4.1 Discussion—Aseriesoffloat/sinktestsisconsidered
sieved in accordance with Test Method D 4749, using a
as being synonymous with a washability analysis. A float
suitable range of apertures. (Apertures must conform to Speci-
fraction or float material is the material or the specific gravity
fication E 11 or E 323.)
fraction that floats in a certain solution of specific gravity
4.3.2 Where it is possible that some fines agglomerate or
liquids. A sink fraction or sink material is the material or the
adhere to larger particles, it is important that wetsieving be
specific gravity fraction that sinks in a certain solution of
used to ensure that fine material reports to the correct particle
specific gravity liquids.
size fraction. However, under normal circumstances where
air-drying has occurred, it should not be necessary to wet-sieve
4. Summary of Test Method
the material larger than 3.15 mm ( ⁄8 in.).
4.1 Procedure A—Describes a washability procedure for
4.3.3 As a practical guide, the presence of minus 75-µm
coal fractions composed of particles of coal that are larger than
(No. 200 USA Standard) material should be minimized,
a specified, predetermined size, generally between 2.36 mm
because Brownian movement or molecular interference can be
(No. 8 USA Standard Sieve Series) and 9.5 mm ( ⁄8 in.) round
detrimental to proper and efficient separations. Minus 75-µm
in diameter. These coal fractions will be referred to as
(No. 200 USA Standard) material can then be processed using
coarse-coal fractions.
separate test procedures. (See, for example, the reference in
4.1.1 Each coarse-coal size fraction is independently sepa-
Note 2.)
rated into two distinct specific gravity fractions by placing the
sample into a large tank of sufficient capacity, for example, 40
to 80 L (10 to 20 gal), containing a screen basket insert and a
solution of organic liquids adjusted to the required specific
The boldface numbers in parentheses refer to the list of references appended to
gravity. The suspension is stirred gently to assure that all this standard.
D 4371
4.3.4 When required, material which is larger than the principal criteria being that it should be unaffected by the
desired topsize is broken by hand or machine-crushed accord- solutions involved (that is, the organic liquids do not corrode,
ing to the topsize required, or, if applicable, by simulating the etch, or otherwise react with the materials from which the
relevant part of the crushing circuit. apparatus is constructed) and that it should be convenient for
use (see X1.3). Types of apparatus that have been found to be
5. Significance and Use
suitable are discussed in the following subsections and are
illustrated in Fig. 1, Fig. 2, and Fig. 3.
5.1 Although the determination of the washability charac-
6.2 Suitable Float/Sink Container for Coarse-Coal
teristics of coal is not an exact science, this washability test
Fractions—The float/sink apparatus may consist of a wire
method can be used to investigate the cleaning characteristics
mesh insert and a holding tank (Fig. 1 and Fig. 2). The wire
of coarse- and fine-coal fractions. However, especially with the
mesh insert should consist entirely of wire mesh, have solid
fine-coal fractions, this test method may not be applicable for
low-rank coals for reasons explained in 1.2. sides with a wire mesh bottom, or have a solid bottom with
wire mesh sides. The wire mesh used must be smaller than one
5.2 The usefulness of this test procedure and the usefulness
of the results derived from washability testing are directly half the size of the finest coal in the fraction. The insert fits
inside the holding tank. The insert may have handles attached
related to the care exercised in developing and following the
or may utilize an overhead lifting device to facilitate removal
sampling regime while taking into consideration the desired
from the tank. A typical laboratory holding tank has approxi-
degree of precision. For more exacting work, it will be
mately 40 to 80-L(10 to 20-gal) capacity.Tank and insert must
necessarytoknowthegeneralwashabilitycharacteristicsofthe
be designed so as to be compatible.
material in question. This can be done only through pilot
testing as described in 9.6 and Annex A3.
NOTE 5—It is possible that the geometry of the tank may have some
5.3 This test method, in conjunction with the advice of
effect on the ease with which the materials are removed from the tank.
experts and with knowledge of the particle size analysis (see
Square tanks have the following disadvantages: (a) it is difficult to get the
wire mesh strainer into the corners to remove all of the float material, and
Test Method D 4749), is used for the engineering design of
(b) material, especially the sink fraction, may be trapped in the corners
coal preparation facilities.
while the material is being removed from the tank.
5.4 This test method is also used to assist in process control
and to determine the efficiency of operating preparation plants. 6.3 SuitableFloat/SinkFlaskforFine-CoalFractions—The
float/sink flasks, that typically have a capacity of 2 to 4 L (0.5
5.5 This test method is used in core studies to determine the
qualitywashabilitycharacteristicsofcoalreserves;however,in to 1 gal), should be constructed with ground glass connecting
joints (see Fig. 3).
these instances the typical mass of raw coal from Table 1 may
be neither applicable nor practical. For this reason, core 6.4 Additional Apparatus:
diameter should be as large as possible and subdivision of the 6.4.1 Balance,suggested2000-gcapacity,sensitiveto 60.1
core section by any means or for any purpose prior to g, for weighing small samples or fractions.
washability testing should be avoided. Care must be exercised 6.4.2 Balance, suggested 0 to 110-kg (0 to 250-lb) capacity,
in the design of the coring programs, including the consider- sensitive to 645 g (0.10 lb) for weighing large samples or
ation of appropriate geostatistics, in order that the potential fractions.
recovery and quality of the coal reserves, as defined by the 6.4.3 Wire Mesh Strainers, with mesh size one half of the
washability analysis of the cores, have any practical signifi- size of the smallest particle.
cance. 6.4.4 Vacuu
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