ASTM D5114-90(1998)
(Test Method)Standard Test Method for Laboratory Froth Flotation of Coal in a Mechanical Cell
Standard Test Method for Laboratory Froth Flotation of Coal in a Mechanical Cell
SCOPE
1.1 This test method covers a laboratory procedure for conducting a single froth flotation test on fine coal (that is, nominal top size of 600 [mu]m (No. 30 U.S.A. Standard Sieve Series) or finer) using a defined set of starting point conditions for the operating variables.
1.2 This test method does not completely cover specific procedures for the investigation of flotation kinetics. Such a test is specialized and highly dependent upon the objective of the data.
1.3 Since optimum conditions for flotation are usually not found at the specified starting points, suggestions for development of grade/recovery curves are given in Appendix X1. Such a procedure is very case-specific and involves running a series of flotation tests in which some of the operating variables are changed in order to optimize conditions for either yield or grade.
1.4 Laboratory flotation results need not be representative of the flotation response of coal in full-scale situations, but a consistent baseline can be established against which full-scale performance can be compared.
1.5 The values stated in SI units are to be regarded as standard. The values in parentheses are provided for information only. The values stated in each system may not be exact equivalents; therefore, each system must be used independently of the other, without combining values in any way.
1.6 This standard does not purport to address the safety problems 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.
1.6.1 Material Safety Data Sheets (MSDS) for reagents used are to be obtained from suppliers who are to be consulted prior to work with any chemicals used in this test method.
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Designation: D 5114 – 90 (Reapproved 1998)
Standard Test Method for
Laboratory Froth Flotation of Coal in a Mechanical Cell
This standard is issued under the fixed designation D 5114; 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
Froth flotation of coal, the separation of ash-bearing minerals from combustibles via differences in
surface chemistry, has been steadily increasing in use as a means to treat 600-μm (No. 30 U.S.A.
Standard Sieve Series) or finer coal. The process is one in which many variables need to be monitored
and regulated. Because of this complexity, rigorous laboratory testing is difficult to standardize.
This test method outlines the types of equipment and procedures to apply on a laboratory scale to
isolate key process variables and minimize the variations associated with the design and execution of
a froth flotation test. The objective of the test method is to develop a means by which repeatable
grade/recovery results are ascertained from froth flotation testing of coal without imposing
unnecessary limitations on the applicability of the test results in coal preparation practice.
It is recognized that sample preparation, particularly comminution, has a significant impact on froth
flotation response. This test method does not attempt to define sample preparation and size reduction
practices as part of a froth flotation testing program.
This test method also does not completely cover specific procedures for the investigation of flotation
kinetics. Such a test is specialized and is highly dependent upon the end use of the data.
1. Scope tion only. The values stated in each system may not be exact
equivalents; therefore, each system must be used indepen-
1.1 This test method covers a laboratory procedure for
dently of the other, without combining values in any way.
conducting a single froth flotation test on fine coal (that is,
1.6 This standard does not purport to address the safety
nominal top size of 600 μm (No. 30 U.S.A. Standard Sieve
concerns, if any, associated with its use. It is the responsibility
Series) or finer) using a defined set of starting point conditions
of the user of this standard to establish appropriate safety and
for the operating variables.
health practices and determine the applicability of regulatory
1.2 This test method does not completely cover specific
limitations prior to use.
procedures for the investigation of flotation kinetics. Such a
1.7 Material Safety Data Sheets (MSDS) for reagents used
test is specialized and highly dependent upon the objective of
are to be obtained from suppliers who are to be consulted
the data.
before work with any chemicals used in this test method.
1.3 Since optimum conditions for flotation are usually not
found at the specified starting points, suggestions for develop-
2. Referenced Documents
ment of grade/recovery curves are given in Appendix X1. Such
2.1 ASTM Standards:
a procedure is very case-specific and involves running a series
D 121 Terminology of Coal and Coke
of flotation tests in which some of the operating variables are
D 2013 Method of Preparing Coal Samples for Analysis
changed in order to optimize conditions for either yield or
D 2015 Test Method for Gross Calorific Value of Coal and
grade.
Coke by the Adiabatic Bomb Calorimeter
1.4 Laboratory flotation results need not be representative of
D 2234 Practice for Collection of a Gross Sample of Coal
the flotation response of coal in full-scale situations, but a
D 3173 Test Method for Moisture in the Analysis Sample of
consistent baseline can be established against which full-scale
Coal and Coke
performance can be compared.
D 3174 Test Method for Ash in the Analysis Sample of Coal
1.5 The values stated in SI units are to be regarded as
and Coke from Coal
standard. The values in parentheses are provided for informa-
D 3177 Test Methods for Total Sulfur in the Analysis
Sample of Coal and Coke
This test method is under the jurisdiction of ASTM Committee D-5 on Coal and
Coke and is the direct responsibility of Subcommittee D05.07 on Physical
Characteristics of Coal.
Current edition approved Aug. 31, 1990. Published December 1990. 2
Annual Book of ASTM Standards, Vol 05.05.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5114 – 90 (1998)
D 4239 Test Methods for Sulfur in the Analysis Sample of 3.2.8 frother—a reagent used in froth flotation to control the
Coal and Coke Using High Temperature Tube Furnace size and stability of the air bubbles, principally by reducing the
Combustion Methods surface tension of water.
D 4749 Test Method for Performing Sieve Analysis of Coal 3.2.9 grade/recovery—the relationship between quality and
quantity of the clean coal product. The quality can be defined
and Designating Coal Size
in terms of ash, sulfur, or Btu content. The quantity can be
designated as yield or heating value recovery (Btu or combus-
3. Terminology
tibles).
3.1 Definitions—For definitions of terms used in this test
3.2.10 mechanical cell—a type of flotation cell that em-
method, see Terminology D 121.
ploys mechanical agitation of a pulp by means of an immersed
3.2 Definitions of Terms Specific to This Standard:
impeller (rotor) and stator stirring mechanism. Aeration to the
3.2.1 collector—a reagent used in froth flotation to promote
cell can be from an external pressurized air source or self-
contact and adhesion between particles and air bubbles.
induced air.
3.2.2 combustibles—the value obtained by subtracting the
3.2.11 natural pH—the measured pH of the pulp prior to the
dry weight (in percent) of the ash (as determined in Test
addition of collector, frother, or any conditioning agents.
Method D 3174) from 100 % representing the original weight
3.2.12 pulp—a fluid mixture of solids and water, also
of the analyzed sample.
known as slurry.
3.2.3 concentrate—the froth product recovered in coal froth
3.2.13 recovery—the percent of the valuable component
flotation.
(that is, Btu or combustible) from the feed that reports to the
3.2.4 conditioning agents—all chemicals that enhance the
froth concentrate product.
performance of the collectors or frothers. Conditioning agents
3.2.14 solids concentration—the ratio, expressed as a per-
change the characteristics of the surface of the minerals or the
cent, of the weight (mass) of solids to the sum of the weight of
environment. There are many subgroups according to function:
solids plus water.
activators, depressants, emulsifiers, dispersants, flocculants,
3.2.15 tailings—the underflow product from coal froth flo-
chelating reagents, froth depressants, pH modifiers, and so
tation.
forth.
3.2.16 yield—the weight percent of the feed that reports to
3.2.5 flotation cell—the vessel or compartment in which the
the concentrate.
flotation test is performed.
3.2.6 froth—a collection of bubbles and particles on the
4. Significance and Use
surface of a pulp in a froth flotation cell.
4.1 This test method uses specific starting point conditions
3.2.7 froth flotation—a process for cleaning fine coal in
for the froth flotation response to accomplish the following:
which hydrophobic particles, generally coal, attach to air
4.1.1 Assess responses of one or more coals or blends of
bubbles in a water medium and rise to the surface to form a
coal, and
froth. The hydrophilic particles, generally the ash-forming
4.1.2 Evaluate and determine froth flotation circuit perfor-
matter, remain in the water phase.
mance.
5. Apparatus
5.1 Laboratory Flotation Machine, with a minimum volume
of 2 L and a maximum volume of 6 L. Fig. 1 schematically
depicts a batch mechanical flotation cell which can be used in
conjunction with this test method. The major criterion is that
the unit must be able to provide for constant mechanical
removal of froth from the cell. In addition, the laboratory unit
must have some means of automatic liquid level control.
5.1.1 An example of a mechanical paddle laboratory froth
flotation apparatus is shown in Fig. 1. The froth paddles are
rotated at approximately 30 r/min, thus avoiding variation
caused by manual removal of froth. The froth paddle shall not
rotate below the pulp surface and not more than 6 mm ( ⁄4 in.)
above the pulp level. The distance between the overflow lip and
the edge of the froth paddle shall be at least 3 mm ( ⁄8 in.) but
not more than 6 mm ( ⁄4 in.).
5.1.2 The pulp in the cell is maintained at a constant level by
a small tank with an overflow at precisely the desired level to
be maintained in the flotation cell.
A suitable cell, available from WEMCO, 1796 Tribute Rd., Sacramento, CA
FIG. 1 5.5-L Mechanical Paddle Laboratory Froth Flotation Cell 95815, or equivalent can be used.
D 5114 – 90 (1998)
NOTE 1—Another suitable slurry level control system consists of a
7.6 Wetting of Coal—Before the addition of reagents and
resistance type level probe, a resistance sensor relay, a solenoid valve, and
subsequent flotation, it is important to ensure that the proper air
associated connecting wires. The level probe is mounted inside the cell
bubble attachment can take place at the coal-water interface.
and is connected to the resistance relay which operates the solenoid valve.
Wetting is accomplished in the cell by running the impeller at
When the slurry level drops below the tip of the probe, the relay energizes
the r/min specified for the flotation step with the air off.
the solenoid valve. Then, makeup water flows into the cell. When the level
Perform this step for 5 to 10 min before reagent addition. If the
rises up to the probe, the solenoid valve is de-energized, which stops the
makeup water flow. sample is in slurry form this wetting step is not necessary.
7.7 Reagent Addition—Collector, frother, conditioning
5.2 pH Meter, sensitive to 0.1 units.
agent, or any combination thereof shall be governed by the
5.3 Timing Device that displays cumulative minutes and
requirements of the test. Add reagents to the coal slurry and
seconds.
condition to ensure proper distribution of reagents. Conduct the
5.4 Air Flow Meter.
conditioning step at the same impeller speed as the flotation
5.5 Microsyringes or Pipets.
step with the air flow off.
5.6 Balances, with a readability of at least 0.5 % of the total
7.7.1 Add the reagents using either a calibrated microsy-
weight.
ringe or a pipet.
5.7 Vacuum or Pressure Filter, or a filter funnel for gravity
7.8 Air Flow—Rate shall be measured and recorded.
filtration.
7.9 Impeller Speed—The starting speed shall be 1200 r/min.
5.8 Drying Oven with forced air, capable of maintaining a
maximum temperature of 40°C (104°F) and meeting the
NOTE 2— Impeller speed is an important variable and should be
requirements of Method D 2013. investigated during optimization, depending on the object of the test.
5.9 Rinse Bottle.
TABLE 1 Starting Point Conditions for Laboratory Froth
6. Sample Preparation
Flotation of Coal
6.1 The sample history, moisture content, alteration of the
NOTE 1— Additional time can be required for a slowly responsive coal;
inherent moisture, or alteration of the surface properties have
record any extra time.
considerable effect on the flotation characteristics of the coal. It
Solids concentration 8 % solids
is important that all samples used in flotation testing are stored Total volume 2 to 6 L
Wetting time 5 min
and handled so as to minimize alteration of the surface
pH natural
properties. The origin and history of the sample should be
Impeller speed 1200 r/min
recorded. It is imperative that all samples be prepared in a Reagent additions and conditioning times:
1. Add collector
similar manner. Since the generation of grade/recovery curves
2. Condition for 90 s
will involve several individual tests, sample subdivision and
3. Add frother
preparation must be carefully performed to ensure that each 4. Condition for 30 s
Air flow rate 3 L/min per litre of pulp
subsample is representative of the original whole sample.
Skimmer rotation 30 r/min
Collection increments 15, 30, 60, 90, 120, 240 (cumulative time
7. Flotation Conditions
in seconds)
7.1 The conditions under which a test program is conducted
will be systematically varied to generate grade/recovery curves
8. Procedure
(Appendix X1). Table 1 outlines recommended starting point
conditions for a single laboratory-scale test. These conditions
8.1 Calculate the total mass of coal required for the number
are for laboratory testing parameters and are not designed to
of flotation tests based on the measured cell volume and the test
simulate in-plant operating conditions that can be highly
solids content.
variable, such as water temperature and chemistry.
8.2 Divide the total mass into representative portions by
7.2 Slurry Temperature—The operating temperature shall
riffling, in accordance with Method D 2013. A few small
be 22 6 5°C (72 6 9°F).
increments, totalling no more than 15 % of the total mass, may
7.3 Water—Plant, tap, or distilled water may be used,
be either taken from the subsample or added to the subsample
whichever is consistent with the object of the test. The source
in order to obtain the exact weight.
of water must be recorded.
8.3 Determine the particle size distribution of one of the
7.4 Solids Content—The solids content corresponds with
portions from 8.2 in accordance with Test Method D 4749.
that of the industrial preparation plant slurry, if the object of the
8.4 Rinse the cell thoroughly with water. Add from one half
test is to simulate plant conditions. Otherwise, an 8 % solids
to two thirds of the total required water to the cell. Confirm that
concentration shall be used.
the air is turned off. Turn the impeller on and adjust to the
7.5 Pulp Level—Maintain between 12.7 and 15.9 mm (0.50
desired speed. Transfer a sample into the cell. Be careful to
and 0.62 in.) below the lip of the cell as measured with the air
remove all of the coal from the sides of the transfer container.
on and stirrer operating.
Continue this wetting step for approximately 5 min. Add most
of the additional water but reserve a sufficient quantity for
rinsing (see 8.8).
8.5 Determine the pH and temperature of the slurry with the
A suitable slurry level control system, available from C&R Technology, Inc.,
P.O. Box 114, Fall Branch, TN 37656, or equivalent can be used. air turned off.
D 5114 – 90 (1998)
8.6 Start the timing device. Add the collector to the slurry 8.10 Turn on the froth paddles and start the a
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