1、Designation: D 5744 96 (Reapproved 2001)Standard Test Method forAccelerated Weathering of Solid Materials Using a ModifiedHumidity Cell1This standard is issued under the fixed designation D 5744; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure that accelerates thenatural weathering rate of a solid m
3、aterial sample so thatdiagnostic weathering products can be produced, collected, andquantified. Soluble weathering products are mobilized by afixed-volume aqueous leach that is performed, collected, andanalyzed weekly. When conducted in accordance with thefollowing protocol, this laboratory test met
4、hod has acceleratedmetal-mine waste-rock weathering rates by at least an order ofmagnitude greater than observed field rates (1).21.1.1 This test method is intended for use to meet kinetictesting regulatory requirements for mining waste and ores.1.2 This test method is a modification of an accelerat
5、edweathering test method developed originally for mining wastes(2-4). However, it may have useful application wherevergaseous oxidation coupled with aqueous leaching are importantmechanisms for contaminant mobility.1.3 This test method calls for the weekly leaching of a1000-g solid material sample,
6、with water of a specified purity,and the collection and chemical characterization of the result-ing leachate over a minimum period of 20 weeks.1.4 As described, this test method may not be suitable forsome materials containing plastics, polymers, or refined met-als. These materials may be resistant
7、to traditional particle sizereduction methods.1.5 Additionally, this test method has not been tested forapplicability to organic substances and volatile matter.1.6 This test method is not intended to provide leachatesthat are identical to the actual leachate produced from a solidmaterial in the fiel
8、d or to produce leachates to be used as thesole basis of engineering design.1.7 This test method is not intended to simulate site-specificleaching conditions. It has not been demonstrated to simulateactual disposal site leaching conditions.1.8 This test method is intended to describe the procedurefo
9、r performing the accelerated weathering of solid materials togenerate leachates. It does not describe all types of samplingand analytical requirements that may be associated with itsapplication.1.9 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are f
10、or informationonly.1.10 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to
11、 use.2. Referenced Documents2.1 ASTM Standards:3D75 Practices for Sampling AggregatesD 276 Test Methods for Identification of Fibers in TextilesD 420 Guide to Site Characterization for Engineering, De-sign and Construction PurposesD 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 737 Te
12、st Method for Air Permeability of Textile Fabrics4D 1067 Test Methods for Acidity or Alkalinity of Water4D 1125 Test Methods for Electrical Conductivity and Re-sistivity of WaterD 1193 Specification for Reagent WaterD 1293 Test Methods for pH of WaterD 1498 Practice for Oxidation-Reduction Potential
13、 of WaterD 2234 Test Methods for Collection of a Gross Sample ofCoalD 3370 Practices for Sampling WaterE 276 Test Method for Particle Size or Screen Analysis atNo. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Oresand Related MaterialsE 877 Practice for Sampling and Sample Preparation of IronOres an
14、d Related Materials3. Terminology3.1 Definitions:1This test method is under the jurisdiction of ASTM Committee D34 on WasteManagement and is the direct responsibility of Subcommittee D34.01.04 on WasteLeaching Techniques.Current edition approved March 10, 1996. Published May 1996.2The boldface numbe
15、rs in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page ont
16、he ASTM website.4Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.1 acid producing potential (AP), nthe potential for asolid material sample to produce acidic effluent, based on thepercent of sulfide contained in that sa
17、mple as iron-sulfidemineral (for example, pyrite or pyrrhotite) (3). The AP iscommonly converted to the amount of calcium carbonaterequired to neutralize the resulting amount of acidic effluentproduced by the oxidation of contained iron sulfide minerals; itis expressed as the equivalent tons of calc
18、ium carbonate per1000 tons of solid material (4). The AP is therefore calculatedby multiplying the percent of sulfide contained in the materialby a stoichiometric factor of 31.25 (5).3.1.2 interstitial water, nthe residual water remaining inthe sample pore spaces at the completion of the fixed-volum
19、eweekly leach.3.1.3 leach, na weekly addition of water to solid materialthat is performed either dropwise or by flooding for a specifiedtime period.3.1.4 loading, nthe product of the weekly concentrationfor a constituent of interest and the weight of solution collectedthat may be interpreted for wat
20、er quality impacts.3.1.5 mill tailings, nfinely ground mine waste (commonlypassing a 150-m (100 mesh screen) resulting from the millprocessing of ore.3.1.6 neutralizing potential (NP), nthe potential for asolid material sample to neutralize acidic effluent producedfrom the oxidation of iron-sulfide
21、minerals, based on theamount of carbonate present in the sample. The NP is alsopresented in terms of tons of calcium carbonate equivalent per1000 tons of solid material (4). It is calculated by digesting thesolid material with an excess of standardized acid and back-titrating with a standardized bas
22、e to measure and convert theacid consumption to calcium carbonate equivalents (3, 6).3.1.6.1 DiscussionThe AP and NP are specifically appli-cable to the determination of AP from mining wastes com-prised of iron-sulfide and carbonate minerals. These terms maybe applicable to any solid material contai
23、ning iron-sulfide andcarbonate minerals.3.1.7 run-of-mine, adjusage in this test method refers toore and waste rock produced by excavation (with attendantvariable particle sizes) from open pit or underground miningoperations.3.1.8 waste rock, nrock produced by excavation fromopen pit or underground
24、mining operations whose economicmineral content is less than a specified economic cutoff value.4. Summary of Test Method4.1 This accelerated weathering test method is designed toincrease the geological-chemical-weathering rate for selected1000-g solid material samples and produce a weekly effluentth
25、at can be characterized for solubilized weathering products.This test method is performed on each sample in a cylindricalcell. Multiple cells can be arranged in parallel; this configura-tion permits the simultaneous testing of different solid materialsamples. The test procedure calls for weekly cycl
26、es comprisedof three days of dry air (less than 10 % relative humidity) andthree days of water-saturated air (approximately 95 % relativehumidity) pumped up through the sample, followed by a leachwith water on Day 7. A test duration of 20 weeks is recom-mended (3, 4).5. Significance and Use5.1 The p
27、urpose of this accelerated weathering procedure isto determine the following: (1) whether a solid material willproduce an acidic, alkaline, or neutral effluent, (2) whether thateffluent will contain diagnostic cations (including trace metals)and anions that represent solubilized weathering productsf
28、ormed during a specified period of time, and (3) the rate atwhich these diagnostic cations and anions will be released(from the solids in the effluent) under the closely controlledconditions of the test.NOTE 1Examples of products that can be produced from the testinclude the following: (1) weekly ef
29、fluent acidity and alkalinity deter-mined by titration and (2) weekly aqueous concentrations of cations andanions converted to their respective release rates (for example, the averagerelease of g sulfate ion/g of solid material sample/week, over a 20-weekperiod). In acid drainage studies, for exampl
30、e, the average weekly rates ofacid production (measured as g/g/wk of sulfate released) determinedfrom accelerated weathering tests of mine waste samples are comparedwith theAPpresent in each sample. The number of years of acidic effluentexpected to be produced under laboratory accelerated weathering
31、 condi-tions can then be estimated from this comparison. The years of acceleratedweathering required to deplete a mine waste samples NP are calculatedsimilarly by determining the average weekly calcium and magnesiumrelease rates and dividing the samples NP by the sum of those rates (7).5.2 The princ
32、iple of the accelerated weathering test methodis to promote more rapid oxidation of solid material constitu-ents than can be accomplished in nature and maximize theloadings of weathering reaction products contained in theresulting weekly effluent. This is accomplished by controllingthe exposure of t
33、he solid material sample to such environmen-tal parameters as temperature, volume, and application rate ofwater and oxygen. Specifically, an excess amount of airpumped up through the sample during the dry- and wet-airportions of the weekly cycle ensures that oxidation reactionsare not limited by low
34、 oxygen concentrations. Weekly leacheswith low ionic strength water ensure the removal of leachableoxidation products produced from the previous weeks weath-ering cycle. The purpose of the three-day dry-air portion of theweekly cycle is to evaporate water that remains in the pores ofthe sample after
35、 the weekly leach. Evaporation increases porewater cation/anion concentrations and may also cause in-creased acidity (for example, by increasing the concentrationof hydrogen ion generated from previously oxidized ironsulfide). Increased acid generation will accelerate the dissolu-tion of additional
36、sample constituents. Precipitation occurs asevaporation continues, and the remaining water becomesover-saturated. Some of these precipitated salts are potentialsources of acidity when re-solubilized (for example, melanter-ite, FeSO47H2O; and jarosite, K2Fe6(OH)12(SO4)4). Duringthe dry-air portion of
37、 the cycle, the oxygen diffusion ratethrough the sample may increase several orders of magnitudeas compared to its diffusion rate under more saturated condi-tions of the leach. This increase in the diffusion rate undernear-dryness conditions helps to accelerate the abiotic oxida-tion of such constit
38、uents as iron sulfide. The wet (saturated)-airportion of the weekly cycle enhances the bacteria-catalyzedoxidation of solid material sample constituents (for example,iron sulfide) by providing a moist micro-environment through-out the available surface area of the 1000-g sample. ThisD 5744 96 (2001)
39、2micro-environment promotes the diffusion of weathering prod-ucts (for example, resolubilized precipitation products) andmetabolic byproducts (for example, ferric iron) between themicrobes and the substrate without saturating the sample andaffecting oxygen diffusion adversely.NOTE 2Under idealized c
40、onditions (that is, infinite dilution in air andwater), published oxygen diffusion rates in air are five orders of magnitudegreater than in water (0.178 cm2s1versus 2.5 3 105cm2s1at 0 and25C, respectively) (8). However, in the humidity cell setting, correspond-ing oxygen diffusion rates in porous me
41、dia are also functions of solidphase porosity and attendant tortuosity. Actual diffusion rates will there-fore be somewhat slower than five orders of magnitude.5.3 This test method has been tested on both coal and metalmine wastes to classify their respective tendencies to produceacidic, alkaline, o
42、r neutral effluent, and to subsequently mea-sure the concentrations of selected inorganic componentsleached from the waste (2-4, 7). The following are examples ofparameters for which the weekly effluent may be analyzed:5.3.1 pH, Eh (oxidation/reduction potential), and conductiv-ity (see Test Methods
43、 D 1293, Practice D 1498, and TestMethods D 1125, respectively, for guidance);5.3.2 Dissolved gaseous oxygen and carbon dioxide;5.3.3 Alkalinity/acidity values (see Test Methods D 1067for guidance);5.3.4 Cation and anion concentrations; and5.3.5 Metals and trace metals concentrations.NOTE 3Sulfate a
44、nd iron concentrations in the weekly leachates fromsolid material containing iron-sulfide minerals should be monitoredbecause their release rates are critical measurements of iron-sulfidemineral oxidation rates. Acidic effluent or acid drainage is a consequenceof iron-sulfide mineral oxidation and t
45、he subsequent aqueous transport ofresulting hydrogen ion and oxidation/dissolution products to the receivingenvironment (for example, surface and ground waters).5.4 An assumption used in this test method is that the pH ofeach of the leachates reflects the progressive interaction of theinterstitial w
46、ater with the buffering capacity of the solidmaterial under specified laboratory conditions.5.5 This test method produces leachates that are amenableto the determination of both major and minor constituents. It isimportant that precautions be taken in sample preservation,storage, and handling to pre
47、vent possible contamination of thesamples or alteration of the concentrations of constituentsthrough sorption or precipitation.5.6 The leaching technique, rate, liquid-to-solid ratio, andapparatus size may not be suitable for all types of solidmaterial.6. Apparatus6.1 Humidity CellA modified column
48、constructed of ma-terials suitable to the nature of the analyses to be performed(see Practices D 3370 for guidance). Multiple humidity cellscan be arranged in an array to accommodate the simultaneousaccelerated weathering of different solid material types (Fig.1). Two different sets of humidity cell
49、 dimensions are used toaccommodate particle size differences present in the solidmaterial:6.1.1 Cells having suggested dimensions of 10.2-cm (4.0-in.) inside diameter (ID) by 20.3-cm (8.0-in.) height can beused to accommodate coarse solid material samples that havebeen either screened or crushed to 100 % passing 6.3 mm (14in.).6.1.2 Cells with suggested dimensions of 20.3-cm (8.0-in.)ID by 10.2-cm (4.0-in.) height can be used to accommodatesolid material samples that pass a 150-m (100-mesh) screen(examples would be processed mill tailings or fly ash).6.1.3 A
