Table 5-1
Table 5-1: Methods for Geochemical Characterization
Return to: 5.3.2 Description of Phases
Test Type |
Test Methods |
Use in Geochemical Characterization and Water Quality Prediction |
Advantages |
Limitations |
Grain Size |
Sieve |
Predict reactivity on basis of available surface area |
Relatively rapid, less expensive |
Little information on fine fraction |
Hydrometer |
Information on fine fraction |
More time consuming, more expensive |
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BET method |
Sophisticated technique |
Time consuming and expensive |
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Chemical Composition |
Digestion using various acids for analysis by multiple quantitative techniques (ICP-AES, ICP-MS, AAS, NAA) |
Determines total potential load of constituents to environment. |
Comparison against site-specific baseline values and reference geologic materials Surrogate for and confirmation of ABA parameters (e.g., Ca, S)Evaluation of sample set representativeness |
Instrument-specific interferences VolatilizationElevated detection limits due to dilution |
Preparation of bead/powder sample for semi-quantitative analysis by XRF |
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Portable equipment (XRF) |
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Paste pH/Paste Conductivity |
Mixture of solution and solid in desired ratio (typically 1:1 to 5:1) followed by pH/electrical conductivity measurement |
Determines potential short-term effect of surficial/soluble salts on water quality |
Quick, inexpensive, easy to perform in field and laboratory |
Lack of ability to predict long-term conditions |
Acid Base Accounting (ABA) |
Sobek Method AP commonly from total sulphurNP by boiling, HCl to pH 0.8-2.5 |
All Methods: Establish overall acid generating and acid neutralizing capability of a material through independent determinationIdentification of the need for and samples that require kinetic testing |
All Methods: Most techniques well establishedProvide operational screening criteria for mine waste classification and management |
All Methods: Provide no information on relative rates of acid generation and neutralizationAcid addition dependent on a subjective fizz test which can affect accuracy |
Modified Sobek (Lawrence Method) AP from sulphide sulphurNP at ambient temperature for 24 hours near boiling, HCl to pH 2.0-2.5 |
Prevent over-estimation of NP or AP relative to Sobek method |
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Lapakko |
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BC Research Inc. (BCRI) Initial |
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Sobek Siderite Correction |
Accounts for complete oxidation of soluble metals during titration |
ASTM draft method uses sulphuric acid Requires no fizz test Uses pH to determine acid addition requirementsNegative values indicate stored acid |
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Net Carbonate Value (NCV),%CO2 NCV = ANP + AGP, whereANP = 3.67[(total carbon) - (carb on after HCl digestion)] (=see TIC) |
Developed by Newmont Negative ANP and positive AGP must be corrected to zeroConfirm NCV classification using BC Research Confirmation on zone composites |
Standardized as ASTM E-1915 Waste rock composites characterized with metallurgical suite for oresClassification system limits uncertainty |
Requires carbon-sulphur sophisticated combustion-infrared instrumentation similar to Sobek Results require conversion for comparison against data from other ABA tests in order to differentiate methodsDoes not account for silicate buffering or stored acidity |
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Acid Buffering Characteristic Curve(ABCC) |
Provides an indication of the portion of the NP that is readily available for neutralization Used principally in AustraliaSimilar in nature to the BCRI Initial test |
Can be used to identify minerals responsible for neutralization by comparing against ABCCs for reference minerals Well suited for measuring actual NP vs. total NPRepresents a less conservative method of measuring NP |
Only feasible to do on selected samples due to long test time |
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Total Inorganic Carbon (TIC) |
Measures NP associated with carbonates only |
Only provides carbonate fraction of NP Can only be used in concert with total NP resultsNot suitable for materials with low NP |
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Sulphur Analysis (total S, pyritic S, sulphide S, organic S, sulphate S, residual S)Removal of non-sulphide and/or targeted sulphide minerals to determine sulphur species |
Potential of samples to generate acid |
Distinguishes between sulphur forms and allows identification of "reactive" sulphur species |
Does not confirm the identity of the sulphur-bearing mineral(s) |
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Chromium Reducible Sulphur |
Used principally in acid sulphate soils investigations. CRS is also useful for sulphide analysis in coal and coal reject materials |
Considered a very reliable method for measuring low-level sulphur concentrations |
Limited basis for direct comparison against results from more "traditional" ABA tests |
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Total Actual Acidity (TAA) |
Can define actual acidity in low-pH samples that have oxidized |
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Total Potential Acidity (TPA) |
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Net Acid Generating (NAG) |
Single addition NAG |
All Methods: Establishes overall acid generating capability of a material through simultaneous reaction of acid generating and acid neutralizing componentsIdentification of the need for and samples that require kinetic testing Used in conjunction with ABA or stand alone field test when calibrated |
All Methods: Evaluates net acid-base balanceIn combination with ABA improves prediction reliability and range of uncertainty |
All Methods: Does not distinguish between AP and NPQuality of H2O2 may vary: some H2O2 brands required pre-treatment for NAG test use |
Sequential NAG |
Overcomes incomplete oxidation in high-sulphur samples |
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Extended Boil and Calculated NAG As single addition NAG, but accounts for potential effect from organic matterExtended boiling and assay of the NAG solution for S, Ca, Mg, Cl, Na and K |
Accounts for potential effect from organic matter |
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Kinetic NAG |
Provides qualitative estimate of reaction kinetics and lag time (i.e., weeks, months, years) |
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Mineralogical Composition |
Visual/Optical Microscopy |
All Methods: Identify primary and secondary minerals that could affect acid generation potential and contact water qualityWith increasing sophistication of techniques, also information on texture, mineral composition and morphology to evaluate mineral reactivity and availability for weathering reactions that can affect acid generation and leaching potential |
All Methods: Provide information on acid generating potential and NP, availability of minerals for weatheringEssential for understanding of geochemical controls on contact water quality and as inputs to geochemical model simulations |
Qualitative |
X-ray diffraction (XRD) |
Semi-quantitative at best High detection limit ~1% Capable of identifying crystalline minerals only |
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Petrographic analysis |
Requires sophisticated instrumentation and specialized personnel for interpretation |
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SEM/EDS |
Surpasses combustion-infrared methods in quantifying trace sulfide mineral concentrations |
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Electron microprobe |
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Portable equipment (PIMA) |
Portable |
Not capable of identifying all minerals |
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Short-Term Leach Tests |
SPLP (Synthetic Precipitation Leaching Procedure) US EPA Method 1312ASTM D 6234 |
All Methods: |
All Methods: Provides indication of short-term leaching of soluble constituents.Identifies readily dissolvable constituents |
All Methods: Provides no information on transient processes and long-term conditions.Grain size reduction may increase reactivity |
TCLP (Toxicity Characteristic Leaching Procedure) US EPA Method 131118 ± 2 hours |
Used to determine if waste is hazardous under RCRA |
Applicable standards available |
Use of acetic acid/acetate buffers not appropriate for mining applications, Short list of metals evaluated |
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Meteoric Water Mobility Procedure (MWMP) 1:1 solution to solid ratio< 48 hours |
Same as for SPLP |
Quasi-dynamic test More realistic than SPLP due to higher solid to solution ratio, longer duration and coarser materialApplicable standards available |
Weaker lixiviant than acidified SPLP |
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California Waste Extraction Test (WET) 10:1 solution to solid ratio48 hours |
Intended to simulate municipal landfill containing organic wastes |
Lower liquid to solid ratio and longer test duration than SPLP and TCLP |
Use of sodium citrate not appropriate for mining applications |
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Modified Test for Shake Extraction of Solid Waste with Water 4:1 solution to solid ratio18 hours |
Same as for SPLP |
Lower liquid to solid ratio than SPLP |
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British Columbia Special Waste Extraction Procedure (BC SWEP) 20:1 solution to solid ratiodilute hydrochloric acid |
Similar to TCLP for normal procedure |
Modified: lower solution to solid ratio than SPLP and ASTM |
Intended to simulate municipal landfill containing organic wastes |
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NAG Test with Leachate Analysis 100:1 solution to solid ratioUntil boiling or effervescing ceases |
Can be used to determine total potential loading or release of metals after complete oxidation of reactive sulphides |
"Short-cut" to conditions representative of complete sulphide oxidation |
Leachate contains all reaction products from sulphide oxidation High solution to solid ratioSignificant grain size reduction |
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Characterization of Waste - Leaching - Compliance Test for Leaching of Granular Materials and Sludge EN 12457 124 hours |
All European Union (EU) Methods: Basic characterization: obtain information on leaching behavior and characteristicsCompliance: determine whether waste complies with specific reference values |
All European Union (EU) Methods: Test protocol is adjusted based on information needs and site-specific conditionsApplicable standards available (expressed as loadings) |
Same as for SPLP |
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Characterization of Waste - Leaching Behavior Tests - Up-flow Percolation Test CEN/TS 14405duration as needed |
Used to determine leachability of a waste under hydraulically dynamic conditions (EU) |
Test can be used to establish the distinction between various release mechanisms (e.g., first flush vs. steady state leaching) |
Same as for MWMP |
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Characterization of Waste - Leaching Behavior Tests - Influence of pH on Leaching with Initial Acid/Base Addition CEN/TS 1442948 hours |
Used to determine influence of pH on waste leachability and buffering capacity (EU) |
Leachate analyzed for inorganic constituents (as opposed to prCEN/TS 15364) pH is allowed to fluctuate after initial addition of acid or baseAllows evaluation of buffering capacity |
Same as for SPLP |
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Characterization of Waste - Leaching Behavior Tests - Influence of pH on Leaching with Continuous pH-Control EN 1499748 hours |
Used to determine influence of pH on waste leachability (EU) |
Leachate analyzed for inorganic constituents (as opposed to prCEN/TS 15364) pH is maintained at constant value after initial addition of acid or baseAllows evaluation of leachability under constant pH |
Same as for SPLP |
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Characterization of Waste - Leaching Behavior Tests - Acid and Base Neutralization Capacity Test CEN/TS 1536448 hours |
Used to determine final pH of a waste as well as assess consequences of external influences (carbonation, oxidation) on the final pH (EU) |
Same as for SPLP Test developed for landfillsLeachate only analyzed for pH |
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Lixiviação de Resíduos NBR 1000524 hours |
Used to determine if mine waste is hazardous under solid waste regulations (Brazil) |
Applicable standards available |
Use of acetic acid not appropriate for mining applications |
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Solubilização de Resíduos NBR 100067 days |
Used to evaluate potential for impacts to groundwater by comparison against groundwater quality standards (Brazil) |
Applicable standards available |
Same as for SPLP |
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Test Method Standard for Leaching Toxicity of Solid Wastes - Roll Over Leaching Procedure GB5086.1-199718 hours |
Used to determine if mine waste is hazardous under solid waste regulations by comparison against Integrated Wastewater Discharge Standards (China) |
Applicable standards available |
Same as for SPLP |
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Test Method Standard for Leaching Toxicity of Solid Wastes - Horizontal Vibration Extraction Procedure GB5086.2-199724 hours |
Used to determine if mine waste is hazardous under solid waste regulations by comparison against Integrated Wastewater Discharge Standards (China) |
Applicable standards available |
Same as for SPLP |
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Sequential Extraction Variety of methods using different extractants to evaluate leachability from targeted fractions of mine wasteMethods may vary depending on analyte of interest and target fraction of interest |
To evaluate associations between constituents of interests and different fractions of the solid |
Understanding associations of constituents with different fractions of the solid assists in understanding geochemical conditions under which they may be released to the environment |
Involved procedure Many reagentsNo applicable standards |
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Long-Term Leach Tests |
Humidity Cell Test (HCT) ASTM D5744-96generally less-frequent analysis for comprehensive metals and major ions |
To determine long-term weathering rates (sulphide oxidation, dissolution of neutralizing minerals, trace metal release) under oxygenated conditions To evaluate lag time to acid generationTo provide reaction rates for geochemical modeling |
Standardized test |
Not suitable for evaluation of saturated materials Grain size reduction may increase reactivityHigh leaching rate can affect reaction kinetics due to higher pH and undersaturation with secondary minerals |
Column Test variable solution to solid ratioleaching cycles can vary and include maintaining water over sample, alternate flooding and draining, and recirculating leachate |
As above, but can simulate leaching in variably saturated or oxygen-deficient conditions |
Frequently closer to field conditions than HCT Can simulate different degrees of saturationSimulates combined weathering of primary and secondary minerals |
Not standardized Potential for channeling through preferential flowpathsWithout entire load of weathering products from primary minerals, reaction rates for primary minerals and extent of secondary precipitation cannot be measured |
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Field Tests |
Wall Washing 1L rinse of 1 × 1 m surface areadistilled water |
All Methods: |
Rapid Measures leachate quality from in situ materialCan be repeated to obtain temporal component |
May be difficult to establish accurate mass balance due to loss of solution |
US Geological Survey Field Leach Test (FLT) 20:1 solution to solid ratio<a href="http://pubs.usgs.gov/tm/2007/05D03/" title="http://pubs.usgs.gov/tm/2007/05D03/">http://pubs.usgs.gov/tm/2007/05D03/</a> |
Can be performed in the field Rapid and inexpensive method to characterize chemical reactivity and water-soluble fractionField screening method that can be used as surrogate for SPLP due to similarity in approach and results |
Same as for SPLP |
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Field Cells/Test Pads/Mine Facilities Monitoring of increasingly larger volumes of mine wastesTest duration months to years |
Test are conducted under actual field conditions Can collect samples after transient eventsWith increasing test size, empirical results increasingly directly applicable to mine facility |
Comprehensive characterization of test sample may not be feasible Complete understanding of water balance may not be feasibleComplexity of tested system may limit interpretive and predictive value of observations |
Return to: 5.3.2 Prediction during Different Phases of the Mine Life