ASTM D5744-96

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: D 5744 – 96
Standard Test Method for
Accelerated Weathering of Solid Materials Using a Modified
Humidity Cell
This standard is issued under the fixed designation D 5744; 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.
1. Scope and analytical requirements that may be associated with its
application.
1.1 This test method covers a procedure that accelerates the
1.9 The values stated in SI units are to be regarded as the
natural weathering rate of a solid material sample so that
standard. The values given in parentheses are for information
diagnostic weathering products can be produced, collected, and
only.
quantified. Soluble weathering products are mobilized by a
1.10 This standard does not purport to address all of the
fixed-volume aqueous leach that is performed, collected, and
safety concerns, if any, associated with its use. It is the
analyzed weekly. When conducted in accordance with the
responsibility of the user of this standard to establish appro-
following protocol, this laboratory test method has accelerated
priate safety and health practices and determine the applica-
metal-mine waste-rock weathering rates by at least an order of
2 bility of regulatory limitations prior to use.
magnitude greater than observed field rates (1).
1.1.1 This test method is intended for use to meet kinetic
2. Referenced Documents
testing regulatory requirements for mining waste and ores.
2.1 ASTM Standards:
1.2 This test method is a modification of an accelerated
D 75 Practices for Sampling Aggregates
weathering test method developed originally for mining wastes
D 276 Test Methods for Identification of Fibers in Textiles
(2-4). However, it may have useful application wherever
D 420 Guide to Site Characterization for Engineering, De-
gaseous oxidation coupled with aqueous leaching are important
sign and Construction Purposes
mechanisms for contaminant mobility.
D 653 Terminology Relating to Soil, Rock, and Contained
1.3 This test method calls for the weekly leaching of a
Fluids
1000-g solid material sample, with water of a specified purity,
D 737 Test Method for Air Permeability of Textile Fabrics
and the collection and chemical characterization of the result-
D 1067 Test Methods for Acidity or Alkalinity of Water
ing leachate over a minimum period of 20 weeks.
D 1125 Test Methods for Electrical Conductivity and Re-
1.4 As described, this test method may not be suitable for
sistivity of Water
some materials containing plastics, polymers, or refined met-
D 1193 Specification for Reagent Water
als. These materials may be resistant to traditional particle size
D 1293 Test Methods for pH of Water
reduction methods.
D 1498 Practice for Oxidation-Reduction Potential of Wa-
1.5 Additionally, this test method has not been tested for
ter
applicability to organic substances and volatile matter.
D 2234 Test Methods for Collection of a Gross Sample of
1.6 This test method is not intended to provide leachates
Coal
that are identical to the actual leachate produced from a solid
D 3370 Practices for Sampling Water
material in the field or to produce leachates to be used as the
E 276 Test Method for Particle Size or Screen Analysis at
sole basis of engineering design.
No. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Ores
1.7 This test method is not intended to simulate site-specific
and Related Materials
leaching conditions. It has not been demonstrated to simulate
E 877 Practice for Sampling and Sample Preparation of Iron
actual disposal site leaching conditions.
Ores and Related Materials
1.8 This test method is intended to describe the procedure
for performing the accelerated weathering of solid materials to
generate leachates. It does not describe all types of sampling
Annual Book of ASTM Standards, Vol 04.03.
Annual Book of ASTM Standards, Vol 07.01.
1 5
This test method is under the jurisdiction of ASTM Committee D-34 on Waste Annual Book of ASTM Standards, Vol 04.08.
Management and is the direct responsibility of Subcommittee D34.02 on Physical Discontinued; see 1994 Annual Book of ASTM Standards, Vol 07.01.
and Chemical Characterization. Annual Book of ASTM Standards, Vol 11.01.
Current edition approved March 10, 1996. Published May 1996. Annual Book of ASTM Standards , Vol 05.05.
2 9
The boldface numbers in parentheses refer to the list of references at the end of Annual Book of ASTM Standards, Vol 03.05.
this standard. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 5744
3. Terminology humidity) pumped up through the sample, followed by a leach
with water on Day 7. A test duration of 20 weeks is recom-
3.1 Definitions:
mended (3, 4).
3.1.1 acid producing potential (AP), n—the potential for a
solid material sample to produce acidic effluent, based on the
5. Significance and Use
percent of sulfide contained in that sample as iron-sulfide
5.1 The purpose of this accelerated weathering procedure is
mineral (for example, pyrite or pyrrhotite) (3). The AP is
to determine the following: (1) whether a solid material will
commonly converted to the amount of calcium carbonate
produce an acidic, alkaline, or neutral effluent, (2) whether that
required to neutralize the resulting amount of acidic effluent
effluent will contain diagnostic cations (including trace metals)
produced by the oxidation of contained iron sulfide minerals; it
and anions that represent solubilized weathering products
is expressed as the equivalent tons of calcium carbonate per
formed during a specified period of time, and (3) the rate at
1000 tons of solid material (4). The AP is therefore calculated
which these diagnostic cations and anions will be released
by multiplying the percent of sulfide contained in the material
(from the solids in the effluent) under the closely controlled
by a stoichiometric factor of 31.25 (5).
conditions of the test.
3.1.2 interstitial water, n—the residual water remaining in
NOTE 1—Examples of products that can be produced from the test
the sample pore spaces at the completion of the fixed-volume
include the following: (1) weekly effluent acidity and alkalinity deter-
weekly leach.
mined by titration and (2) weekly aqueous concentrations of cations and
3.1.3 leach, n—a weekly addition of water to solid material
anions converted to their respective release rates (for example, the average
that is performed either dropwise or by flooding for a specified
release of μg sulfate ion/g of solid material sample/week, over a 20-week
time period.
period). In acid drainage studies, for example, the average weekly rates of
3.1.4 loading, n—the product of the weekly concentration
acid production (measured as μg/g/wk of sulfate released) determined
from accelerated weathering tests of mine waste samples are compared
for a constituent of interest and the weight of solution collected
with the AP present in each sample. The number of years of acidic effluent
that may be interpreted for water quality impacts.
expected to be produced under laboratory accelerated weathering condi-
3.1.5 mill tailings, n—finely ground mine waste (commonly
tions can then be estimated from this comparison. The years of accelerated
passing a 150-μm (100 mesh screen) resulting from the mill
weathering required to deplete a mine waste sample’s NP are calculated
processing of ore.
similarly by determining the average weekly calcium and magnesium
3.1.6 neutralizing potential (NP), n—the potential for a
release rates and dividing the sample’s NP by the sum of those rates (7).
solid material sample to neutralize acidic effluent produced
5.2 The principle of the accelerated weathering test method
from the oxidation of iron-sulfide minerals, based on the
is to promote more rapid oxidation of solid material constitu-
amount of carbonate present in the sample. The NP is also
ents than can be accomplished in nature and maximize the
presented in terms of tons of calcium carbonate equivalent per
loadings of weathering reaction products contained in the
1000 tons of solid material (4). It is calculated by digesting the
resulting weekly effluent. This is accomplished by controlling
solid material with an excess of standardized acid and back-
the exposure of the solid material sample to such environmen-
titrating with a standardized base to measure and convert the
tal parameters as temperature, volume, and application rate of
acid consumption to calcium carbonate equivalents (3, 6).
water and oxygen. Specifically, an excess amount of air
3.1.6.1 Discussion—The AP and NP are specifically appli-
pumped up through the sample during the dry- and wet-air
cable to the determination of AP from mining wastes com-
portions of the weekly cycle ensures that oxidation reactions
prised of iron-sulfide and carbonate minerals. These terms may
are not limited by low oxygen concentrations. Weekly leaches
be applicable to any solid material containing iron-sulfide and
with low ionic strength water ensure the removal of leachable
carbonate minerals.
oxidation products produced from the previous week’s weath-
3.1.7 run-of-mine, adj—usage in this test method refers to
ering cycle. The purpose of the three-day dry-air portion of the
ore and waste rock produced by excavation (with attendant
weekly cycle is to evaporate water that remains in the pores of
variable particle sizes) from open pit or underground mining
the sample after the weekly leach. Evaporation increases pore
operations.
water cation/anion concentrations and may also cause in-
3.1.8 waste rock, n—rock produced by excavation from
creased acidity (for example, by increasing the concentration
open pit or underground mining operations whose economic
of hydrogen ion generated from previously oxidized iron
mineral content is less than a specified economic cutoff value.
sulfide). Increased acid generation will accelerate the dissolu-
tion of additional sample constituents. Precipitation occurs as
4. Summary of Test Method
evaporation continues, and the remaining water becomes
4.1 This accelerated weathering test method is designed to over-saturated. Some of these precipitated salts are potential
increase the geological-chemical-weathering rate for selected
sources of acidity when re-solubilized (for example, melanter-
1000-g solid material samples and produce a weekly effluent ite, FeSO ·7H O; and jarosite, K Fe (OH) (SO ) ). During
4 2 2 6 12 4 4
that can be characterized for solubilized weathering products. the dry-air portion of the cycle, the oxygen diffusion rate
This test method is performed on each sample in a cylindrical through the sample may increase several orders of magnitude
cell. Multiple cells can be arranged in parallel; this configura- as compared to its diffusion rate under more saturated condi-
tion permits the simultaneous testing of different solid material tions of the leach. This increase in the diffusion rate under
samples. The test procedure calls for weekly cycles comprised near-dryness conditions helps to accelerate the abiotic oxida-
of three days of dry air (less than 10 % relative humidity) and tion of such constituents as iron sulfide. The wet (saturated)-air
three days of water-saturated air (approximately 95 % relative portion of the weekly cycle enhances the bacteria-catalyzed
D 5744
oxidation of solid material sample constituents (for example, 6.1.1 Cells having suggested dimensions of 10.2-cm (4.0-
iron sulfide) by providing a moist micro-environment through- in.) inside diameter (ID) by 20.3-cm (8.0-in.) height can be
out the available surface area of the 1000-g sample. This used to accommodate coarse solid material samples that have
micro-environment promotes the diffusion of weathering prod- been either screened or crushed to 100 % passing 6.3 mm ( ⁄4
ucts (for example, resolubilized precipitation products) and in.).
metabolic byproducts (for example, ferric iron) between the 6.1.2 Cells with suggested dimensions of 20.3-cm (8.0-in.)
microbes and the substrate without saturating the sample and
ID by 10.2-cm (4.0-in.) height can be used to accommodate
affecting oxygen diffusion adversely. solid material samples that pass a 150-μm (100-mesh) screen
(examples would be processed mill tailings or fly ash).
NOTE 2—Under idealized conditions (that is, infinite dilution in air and
6.1.3 A perforated disk (comprised of materials suitable to
water), published oxygen diffusion rates in air are five orders of magnitude
2 −1 −5 2 −1
the nature of analyses to be performed), approximately
greater than in water (0.178 cm ·s versus 2.5 3 10 cm ·s at 0 and
25°C, respectively) (8). However, in the humidity cell setting, correspond- 3.15-mm ( ⁄8-in.) thick, with an outside diameter (OD) suitable
ing oxygen diffusion rates in porous media are also functions of solid
to the suggested vessel ID (6.1.1 and 6.1.2) is elevated
phase porosity and attendant tortuosity. Actual diffusion rates will there-
approximately 12.5 mm ( ⁄2 in.) above the cell bottom to
fore be somewhat slower than five orders of magnitude.
support the solid material sample (see Fig. 1).
5.3 This test method has been tested on both coal and metal
NOTE 4—The cell and particle size dimensions described above are
mine wastes to classify their respective tendencies to produce
those used commonly for assessing the potential of waste-rock and
acidic, alkaline, or neutral effluent, and to subsequently mea-
mill-tailings samples associated with coal and metal mining operations to
sure the concentrations of selected inorganic components
produce acidic effluent. A “shoe box”-shaped cell design with similar
leached from the waste (2-4, 7). The following are examples of
dimensions is preferred by some researchers (6).
parameters for which the weekly effluent may be analyzed:
6.2 Cylindrical Humidifier, with suggested dimensions of
5.3.1 pH, Eh (oxidation/reduction potential), and conductiv-
12.1-cm (4.75-in.) ID by 134.6-cm (53.0-in.) length. The
ity (see Test Methods D 1293, Practice D 1498, and Test
following associated equipment are needed to provide satu-
Methods D 1125, respectively, for guidance);
rated air for the three-day wet-air portion of the weekly cycle:
5.3.2 Dissolved gaseous oxygen and carbon dioxide;
6.2.1 A thermostatically controlled heating element to main-
5.3.3 Alkalinity/acidity values (see Test Methods D 1067
tain the water temperature at 30°C during the wet-air cycle.
for guidance);
6.2.2 An aeration stone (similar to aquar
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