ASTM D5744-96(2001)
(Test Method)Standard Test Method for Accelerated Weathering of Solid Materials Using a Modified Humidity Cell
Standard Test Method for Accelerated Weathering of Solid Materials Using a Modified Humidity Cell
SCOPE
1.1 This test method covers a procedure that accelerates the natural weathering rate of a solid material sample so that diagnostic weathering products can be produced, collected, and quantified. Soluble weathering products are mobilized by a fixed-volume aqueous leach that is performed, collected, and analyzed weekly. When conducted in accordance with the following protocol, this laboratory test method has accelerated metal-mine waste-rock weathering rates by at least an order of magnitude greater than observed field rates (1).
1.1.1 This test method is intended for use to meet kinetic testing regulatory requirements for mining waste and ores.
1.2 This test method is a modification of an accelerated weathering test method developed originally for mining wastes (2-4). However, it may have useful application wherever gaseous oxidation coupled with aqueous leaching are important mechanisms for contaminant mobility.
1.3 This test method calls for the weekly leaching of a 1000-g solid material sample, with water of a specified purity, and the collection and chemical characterization of the resulting leachate over a minimum period of 20 weeks.
1.4 As described, this test method may not be suitable for some materials containing plastics, polymers, or refined metals. These materials may be resistant to traditional particle size reduction methods.
1.5 Additionally, this test method has not been tested for applicability to organic substances and volatile matter.
1.6 This test method is not intended to provide leachates that are identical to the actual leachate produced from a solid material in the field or to produce leachates to be used as the sole basis of engineering design.
1.7 This test method is not intended to simulate site-specific leaching conditions. It has not been demonstrated to simulate actual disposal site leaching conditions.
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 and analytical requirements that may be associated with its application.
1.9 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.10 This standard does not purport to address all of the safety concerns, 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.
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Designation: D 5744 – 96 (Reapproved 2001)
Standard Test Method for
Accelerated Weathering of Solid Materials Using a Modified
Humidity Cell
This standard is issued under the fixed designation D5744; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope generate leachates. It does not describe all types of sampling
and analytical requirements that may be associated with its
1.1 This test method covers a procedure that accelerates the
application.
natural weathering rate of a solid material sample so that
1.9 The values stated in SI units are to be regarded as the
diagnosticweatheringproductscanbeproduced,collected,and
standard. The values given in parentheses are for information
quantified. Soluble weathering products are mobilized by a
only.
fixed-volume aqueous leach that is performed, collected, and
1.10 This standard does not purport to address all of the
analyzed weekly. When conducted in accordance with the
safety concerns, if any, associated with its use. It is the
following protocol, this laboratory test method has accelerated
responsibility of the user of this standard to establish appro-
metal-mine waste-rock weathering rates by at least an order of
2 priate safety and health practices and determine the applica-
magnitude greater than observed field rates (1).
bility of regulatory limitations prior to use.
1.1.1 This test method is intended for use to meet kinetic
testing regulatory requirements for mining waste and ores.
2. Referenced Documents
1.2 This test method is a modification of an accelerated
2.1 ASTM Standards:
weatheringtestmethoddevelopedoriginallyforminingwastes
D75 Practices for Sampling Aggregates
(2-4). However, it may have useful application wherever
D276 Test Methods for Identification of Fibers in Textiles
gaseousoxidationcoupledwithaqueousleachingareimportant
D420 Guide to Site Characterization for Engineering, De-
mechanisms for contaminant mobility.
sign and Construction Purposes
1.3 This test method calls for the weekly leaching of a
D653 Terminology Relating to Soil, Rock, and Contained
1000-g solid material sample, with water of a specified purity,
Fluids
and the collection and chemical characterization of the result-
D737 Test Method forAir Permeability of Textile Fabrics
ing leachate over a minimum period of 20 weeks.
D1067 Test Methods for Acidity or Alkalinity of Water
1.4 As described, this test method may not be suitable for
D1125 Test Methods for Electrical Conductivity and Re-
some materials containing plastics, polymers, or refined met-
sistivity of Water
als.These materials may be resistant to traditional particle size
D1193 Specification for Reagent Water
reduction methods.
D1293 Test Methods for pH of Water
1.5 Additionally, this test method has not been tested for
D1498 PracticeforOxidation-ReductionPotentialofWater
applicability to organic substances and volatile matter.
D2234 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
D3370 Practices for Sampling Water
material in the field or to produce leachates to be used as the
E276 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 Thistestmethodisnotintendedtosimulatesite-specific
and Related Materials
leaching conditions. It has not been demonstrated to simulate
E877 PracticeforSamplingandSamplePreparationofIron
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
3. Terminology
3.1 Definitions:
This test method is under the jurisdiction ofASTM Committee D34 on Waste
Management and is the direct responsibility of Subcommittee D34.01.04 on Waste For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Leaching Techniques. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved March 10, 1996. Published May 1996. Standards volume information, refer to the standard’s Document Summary page on
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof the ASTM website.
this standard. Withdrawn.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5744 – 96 (2001)
3.1.1 acid producing potential (AP), n—the potential for a 5. Significance and Use
solid material sample to produce acidic effluent, based on the
5.1 The purpose of this accelerated weathering procedure is
percent of sulfide contained in that sample as iron-sulfide
to determine the following: (1) whether a solid material will
mineral (for example, pyrite or pyrrhotite) (3). The AP is
produceanacidic,alkaline,orneutraleffluent,(2)whetherthat
commonly converted to the amount of calcium carbonate
effluentwillcontaindiagnosticcations(includingtracemetals)
required to neutralize the resulting amount of acidic effluent
and anions that represent solubilized weathering products
producedbytheoxidationofcontainedironsulfideminerals;it
formed during a specified period of time, and (3) the rate at
is expressed as the equivalent tons of calcium carbonate per
which these diagnostic cations and anions will be released
1000 tons of solid material (4). TheAP is therefore calculated
(from the solids in the effluent) under the closely controlled
by multiplying the percent of sulfide contained in the material
conditions of the test.
by a stoichiometric factor of 31.25 (5).
3.1.2 interstitial water, n—the residual water remaining in NOTE 1—Examples of products that can be produced from the test
include the following: (1) weekly effluent acidity and alkalinity deter-
the sample pore spaces at the completion of the fixed-volume
mined by titration and (2) weekly aqueous concentrations of cations and
weekly leach.
anionsconvertedtotheirrespectivereleaserates(forexample,theaverage
3.1.3 leach, n—a weekly addition of water to solid material
release of µg sulfate ion/g of solid material sample/week, over a 20-week
that is performed either dropwise or by flooding for a specified
period).Inaciddrainagestudies,forexample,theaverageweeklyratesof
time period.
acid production (measured as µg/g/wk of sulfate released) determined
3.1.4 loading, n—the product of the weekly concentration
from accelerated weathering tests of mine waste samples are compared
foraconstituentofinterestandtheweightofsolutioncollected withtheAPpresentineachsample.Thenumberofyearsofacidiceffluent
expected to be produced under laboratory accelerated weathering condi-
that may be interpreted for water quality impacts.
tionscanthenbeestimatedfromthiscomparison.Theyearsofaccelerated
3.1.5 mill tailings, n—finelygroundminewaste(commonly
weathering required to deplete a mine waste sample’s NP are calculated
passing a 150-µm (100 mesh screen) resulting from the mill
similarly by determining the average weekly calcium and magnesium
processing of ore.
release rates and dividing the sample’s NP by the sum of those rates (7).
3.1.6 neutralizing potential (NP), n—the potential for a
5.2 The principle of the accelerated weathering test method
solid material sample to neutralize acidic effluent produced
is to promote more rapid oxidation of solid material constitu-
from the oxidation of iron-sulfide minerals, based on the
ents than can be accomplished in nature and maximize the
amount of carbonate present in the sample. The NP is also
loadings of weathering reaction products contained in the
presented in terms of tons of calcium carbonate equivalent per
resulting weekly effluent. This is accomplished by controlling
1000 tons of solid material (4). It is calculated by digesting the
the exposure of the solid material sample to such environmen-
solid material with an excess of standardized acid and back-
tal parameters as temperature, volume, and application rate of
titrating with a standardized base to measure and convert the
water and oxygen. Specifically, an excess amount of air
acid consumption to calcium carbonate equivalents (3, 6).
pumped up through the sample during the dry- and wet-air
3.1.6.1 Discussion—The AP and NP are specifically appli-
portions of the weekly cycle ensures that oxidation reactions
cable to the determination of AP from mining wastes com-
are not limited by low oxygen concentrations. Weekly leaches
prisedofiron-sulfideandcarbonateminerals.Thesetermsmay
with low ionic strength water ensure the removal of leachable
be applicable to any solid material containing iron-sulfide and
oxidation products produced from the previous week’s weath-
carbonate minerals.
ering cycle.The purpose of the three-day dry-air portion of the
3.1.7 run-of-mine, adj—usage in this test method refers to
weekly cycle is to evaporate water that remains in the pores of
ore and waste rock produced by excavation (with attendant
the sample after the weekly leach. Evaporation increases pore
variable particle sizes) from open pit or underground mining
water cation/anion concentrations and may also cause in-
operations.
creased acidity (for example, by increasing the concentration
3.1.8 waste rock, n—rock produced by excavation from
of hydrogen ion generated from previously oxidized iron
open pit or underground mining operations whose economic
sulfide). Increased acid generation will accelerate the dissolu-
mineral content is less than a specified economic cutoff value.
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-
tionpermitsthesimultaneoustestingofdifferentsolidmaterial 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 tionofsuchconstituentsasironsulfide.Thewet(saturated)-air
three days of water-saturated air (approximately 95% relative portion of the weekly cycle enhances the bacteria-catalyzed
humidity) pumped up through the sample, followed by a leach oxidation of solid material sample constituents (for example,
with water on Day 7. A test duration of 20 weeks is recom- iron sulfide) by providing a moist micro-environment through-
mended (3, 4). out the available surface area of the 1000-g sample. This
D 5744 – 96 (2001)
micro-environment promotes the diffusion of weathering prod- used to accommodate coarse solid material samples that have
ucts (for example, resolubilized precipitation products) and been either screened or crushed to 100% passing 6.3 mm ( ⁄4
metabolic byproducts (for example, ferric iron) between the in.).
microbes and the substrate without saturating the sample and
6.1.2 Cells with suggested dimensions of 20.3-cm (8.0-in.)
affecting oxygen diffusion adversely.
ID by 10.2-cm (4.0-in.) height can be used to accommodate
solid material samples that pass a 150-µm (100-mesh) screen
NOTE 2—Under idealized conditions (that is, infinite dilution in air and
(examples would be processed mill tailings or fly ash).
water),publishedoxygendiffusionratesinairarefiveordersofmagnitude
2 −1 −5 2 −1
greaterthaninwater(0.178cm ·s versus2.5 310 cm ·s at0and 6.1.3 A perforated disk (comprised of materials suitable to
25°C,respectively)(8).However,inthehumiditycellsetting,correspond-
the nature of analyses to be performed), approximately
ing oxygen diffusion rates in porous media are also functions of solid 1
3.15-mm ( ⁄8-in.) thick, with an outside diameter (OD) suitable
phase porosity and attendant tortuosity. Actual diffusion rates will there-
to the suggested vessel ID (6.1.1 and 6.1.2) is elevated
fore be somewhat slower than five orders of magnitude.
approximately 12.5 mm ( ⁄2 in.) above the cell bottom to
5.3 This test method has been tested on both coal and metal support the solid material sample (see Fig. 1).
mine wastes to classify their respective tendencies to produce
NOTE 4—The cell and particle size dimensions described above are
acidic, alkaline, or neutral effluent, and to subsequently mea-
those used commonly for assessing the potential of waste-rock and
sure the concentrations of selected inorganic components
mill-tailings samples associated with coal and metal mining operations to
leachedfromthewaste(2-4,7).Thefollowingareexamplesof
produce acidic effluent. A “shoe box”-shaped cell design with similar
parameters for which the weekly effluent may be analyzed:
dimensions is preferred by some researchers (6).
5.3.1 pH,Eh(oxidation/reductionpotential),andconductiv-
6.2 Cylindrical Humidifier, with suggested dimensions of
ity (see Test Methods D1293, Practice D1498, and Test
12.1-cm (4.75-in.) ID by 134.6-cm (53.0-in.) length. The
Methods D1125, respectively, for guidance);
following associated equipment are needed to provide satu-
5.3.2 Dissolved gaseous oxygen and carbon dioxide;
rated air for the three-day wet-air portion of the weekly cycle:
5.3.3 Alkalinity/acidity values (see Test Methods D1067
6.2.1 Athermostaticallycontrolledheatingelementtomain-
for guidance);
tain the water temperature at 30°C during the wet-air cycle.
5.3.4 Cation and anion concentrations; and
6.2.2 Anaerationstone(similartoaquarium-aerationequip-
5.3.5 Metals and trace metals concentrations.
ment) or commercially available gas dispersion fritted cylin-
NOTE 3—Sulfate and iron concentrations in the weekly leachates from
ders or disks to bubble air into the humidifier water.
solid material containing iron-sulfide minerals should be monitored
6.3 Flowmeter, capable of delivering air to each humidity
because their release rates are critica
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