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ASTM D5744-18
Standard Test Method for Laboratory Weathering of Solid Materials Using a Humidity Cell
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NORM herausgegeben am 1.9.2018
Informationen über die Norm:
Bezeichnung normen: ASTM D5744-18
Anmerkung: UNGÜLTIG
Ausgabedatum normen: 1.9.2018
SKU: NS-900163
Zahl der Seiten: 24
Gewicht ca.: 72 g (0.16 Pfund)
Land: Amerikanische technische Norm
Kategorie: Technische Normen ASTM
Kategorie - ähnliche Normen:
Die Annotation des Normtextes ASTM D5744-18 :
Keywords:
chemical weathering, humidity cell, laboratory weathering, mill tailings, ore, oxidation, solid material, waste rock,, ICS Number Code 13.030.10 (Solid wastes),19.040 (Environmental testing)
Ergänzende Informationen
| Significance and Use | ||||||||||||||||||||||||||||||||||||
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5.1 The laboratory weathering procedure will generate data that can be used to: (1) determine whether a solid material will produce an acidic, alkaline, or neutral effluent, (5.2 Data generated by the laboratory weathering procedure can be used to address the following objectives: (5.3 The laboratory weathering procedure provides conditions conducive to oxidation of solid material constituents and enhances the transport of weathering reaction products contained in the resulting weekly effluent. This is accomplished by controlling the exposure of the solid material sample to such environmental parameters as reaction environment temperature and application rate of water and oxygen. 5.4 Because efficient removal of reaction products is vital to track mineral dissolution rates during the procedure, laboratory leach volumes are large per unit mass of rock to promote the rinsing of weathering reaction products from the mine-rock sample. A comparison of laboratory kinetic tests with field tests has shown that more reaction products from mineral dissolution are consistently released per unit weight and unit time in laboratory weathering tests 5.5 Fundamental assumptions governing Options A and B of the procedure: 5.5.1 Option A—An excess amount of air pumped up through the sample during the dry- and wet-air portions of the weekly cycle reduces the potential for oxidation reaction rates being limited by low-oxygen concentrations. Weekly leaches with low-ionic-strength water promote the removal of leachable mineral dissolution products produced from the previous week's weathering cycle. The purpose of the three-day dry-air portion of the weekly cycle is to evaporate some of the water that remains in the pores of the sample after the weekly leach without totally drying out the sample. Consequently, sample saturation is reduced and air flow is enhanced. During the dry-air portion of the cycle, the oxygen diffusion rate through the sample may increase several orders of magnitude as compared to its diffusion rate under more saturated conditions of the leach. This increase in the diffusion rate under near-dryness conditions helps promote the oxidation of such constituents as iron sulfide. Additionally, evaporation from the three days of dry air increases pore water cation/anion concentrations and may also cause increased acidity (for example, by increasing the concentration of hydrogen ion generated from previously oxidized iron sulfide). Increased acid generation will enhance the dissolution of additional sample constituents. As evaporation continues, the remaining water may become oversaturated with respect to some mineral phases, consequently causing them to precipitate. Some precipitated minerals are potential sources of acidity when re-dissolved (for example, melanterite, FeSO4·7H2O; and jarosite, K2Fe6(OH)12(SO4)4). Compared to the three days of dry air where the pore-water mass decreases over time, the wet (saturated)-air portion of the weekly cycle helps maintain a relatively constant mass of pore water in the sample (12). This may help promote some diffusion of weathering products (for example, re-dissolved precipitation products) in the remaining pore water without totally saturating the sample and adversely affecting oxygen diffusion. Note 1: Under idealized conditions (that is, infinite dilution
in air and water), published oxygen diffusion rates in air are five
orders of magnitude greater than in water (0.178 cm2
s–1 versus 2.5 × 10–5
cm2·s–1 at 0 and 25 °C, respectively)
5.5.2 Option B—In contrast to Option A, Option
B protocol does not include dry air or wet air introduction to the
humidity cells during the weekly cycle. Instead, Option B requires
that temperature and relative humidity be maintained within a
constant range by storing the cells in an environmentally
controlled enclosure during the six days following the weekly 500-
or 1000-mL leach. Consequently, oxygen is delivered to the cells by
diffusion (and possibly advection) of ambient air, rather than by
pumping. Because it lacks a dry-air cycle, more interstitial water
is retained in the Option B sample than in the Option A sample
during the weekly cycle. Furthermore, the interstitial water
content for Option B is more constant than that in Option A during
the weekly dry-air cycle. In addition, the interstitial water
content for Option B is less variable over the course of testing
than that in Option A 5.6 This test method has been conducted
on metal-mine wastes to classify their tendencies to produce
acidic, alkaline, or neutral effluent, and to measure the
concentrations of selected inorganic components leached from the
waste Note 2: Interlaboratory testing of this method to date has
been confined to mine waste rock. The method has not been tested
for applicability to metallurgical processing waste. Although the
method has been applied by some practitioners to finely ground
metallurgical processing wastes such as mill tailings, those
materials were not included in the interlaboratory testing of the
method. Consequently, modifications of this method might be
necessary to deal with problems associated with finely ground
materials, which would make this method as written inappropriate
for kinetic testing of finely ground materials. For kinetic testing
of finely ground materials, please refer to the biological acid
production potential method in the appendix of Test Methods
E1915 or other kinetic
methods accepted by the regulatory jurisdiction.
5.7 The following are examples of parameters for which the scheduled weekly, semi-monthly, or monthly collected effluent may be analyzed (see 11.5.2 for suggested effluent collection frequency): 5.7.1 pH, Eh (oxidation/reduction potential), and conductivity (see Test Methods D1293, D1498, and D1125, respectively, for guidance); 5.7.2 Alkalinity/acidity values (see Test Methods D1067 for guidance); 5.7.3 Cation and anion concentrations; 5.7.4 Metals and trace metals concentrations. 5.8 An assumption used in this test method is that the pH of each of the leachates reflects the progressive interaction of the interstitial water with the acid-generating or acid-neutralizing capacity, or both, of the solid material under specified laboratory conditions. 5.9 This test method produces leachates that are amenable to the determination of both major and minor constituents. It is important that precautions be taken in sample collection, filtration, preservation, storage, and handling to prevent possible contamination of the samples or alteration of the concentrations of constituents through sorption or precipitation. 5.10 The leaching technique, rate of leach water addition, liquid-to-solid ratio, and apparatus size may not be suitable for all types of solid material. 5.11 Notable differences have been observed between Option A and Option B protocols: 5.11.1 Water retention in the solid material sample between weekly leaches is more variable for Option A than in Option B; for Option A, standard deviations from the mean water retention can range from 20 to 60 % of the mean value; comparable values for Option B have been reported at less than 9 % (5.11.2 Greater water retention in Option B cells may favor dissolution of, and consequent acid neutralization by, magnesium-bearing minerals; increased retention may facilitate transport of acidic reaction products from iron-sulfide minerals to magnesium-bearing minerals (14). 5.11.3 Comparisons of sulfate mass release from the same sample subjected to Option A and Option B protocols indicate no significant difference in sulfate concentration as a result of water-retention variation between protocols Note 3: Examples of products from the test include the following: (1.1 This kinetic test method covers a laboratory weathering procedure that (1) enhances reaction-product transport in the aqueous leach of a solid material sample of specified mass, and (1.1.1 This test method is intended for use to meet kinetic testing regulatory requirements for mining waste rock and ores sized to pass a 6.3-mm (0.25-in.) Tyler screen. 1.1.2 Interlaboratory testing of this method has been confined to mine waste rock. Application of this test method to metallurgical processing waste (for example, mill tailings) is outside the scope of the test method. 1.2 This test method is a modification of a laboratory weathering procedure developed originally for mining wastes 1.3 This test method calls for the weekly leaching of a well-characterized solid material sample (weighing at least 1000 g) with water of specified purity, and the collection and chemical characterization of the resulting leachate. Test duration is determined by the user’s objectives of the test. See Guide D8187.3 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. Furthermore, the test is not designed to produce effluents that are in chemical equilibrium with the solid phase sample. 1.8 This test method is intended to describe the procedure for performing the laboratory weathering of solid materials. 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 standard. No other units of measurement are included in this standard. 1.9.1 Exception—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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. |
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