Test Type |
Test Methods and Description |
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
No information on "reactive" fraction |
Hydrometer |
Information on fine fraction |
More time consuming, more expensive
No information on "reactive" fraction |
BET method |
Sophisticated technique
Information on "reactive" fraction through measurement of total and specific surface area |
Time consuming and expensive
Requires specialized equipment and personnel |
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)
Surrogate for and confirmation of mineralogical composition
Evaluation of sample set representativeness |
Instrument-specific interferences
Volatilization
Elevated detection limits due to dilution |
Preparation of bead/powder sample for semi-quantitative analysis by XRF |
Portable equipment (XRF) |
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
Can be useful monitoring test for operational mine waste management |
Lack of ability to predict long-term conditions
Measures stored acidity |
Acid Base Accounting (ABA) |
Sobek Method
AP commonly from total sulphur
NP by boiling, HCl to pH 0.8-2.5 |
All Methods:
Establish overall acid generating and acid neutralizing capability of a material through independent determination
Identification of the need for and samples that require kinetic testing |
All Methods:
Most techniques well established
Generally relatively fast and inexpensive
Provide operational screening criteria for mine waste classification and management |
All Methods:
Provide no information on relative rates of acid generation and neutralization
Assume NP and AG sulfur or minerals are completely available for reaction
Can over- or under-estimate AG or NP depending on method used
NPR cannot be calculated in the absence of sulphur and sulphide
Acid addition dependent on a subjective fizz test which can affect accuracy |
Modified Sobek (Lawrence Method)
AP from sulphide sulphur
NP at ambient temperature for 24 hours near boiling, HCl to pH 2.0-2.5 |
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Prevent over-estimation of NP or AP relative to Sobek method
Widely used |
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Lapakko
NP at ambient temperature up to 1 week, H2SO4 to pH 6.0 |
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BC Research Inc. (BCRI) Initial
NP at ambient temperature for 16-24 hours, H2SO4 to pH 3.5 |
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Sobek Siderite Correction
as Sobek, but with H2O2 |
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 requirements
Negative values indicate stored acid |
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Net Carbonate Value (NCV),%CO2
NCV = ANP + AGP, where
AGP = -1.37[(total sulphur) - (residual sulphur after pyrolysis)]
ANP = 3.67[(total carbon) - (carb on after HCl digestion)] (=see TIC) |
Developed by Newmont
Negative ANP and positive AGP must be corrected to zero
Negative NCV indicates acid generation potential
Confirm NCV classification using BC Research Confirmation on zone composites |
Standardized as ASTM E-1915
Waste rock composites characterized with metallurgical suite for ores
Several options for sulphide confirmation depending on mineralogy
Classification 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 methods
Metal carbonates overestimate ANP
Does not account for silicate buffering or stored acidity |
Acid Buffering Characteristic Curve (ABCC)
Titration of sample with acid while continuously monitoring pH |
Provides an indication of the portion of the NP that is readily available for neutralization
Used principally in Australia
Similar 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 NP
Represents a less conservative method of measuring NP |
Only feasible to do on selected samples due to long test time
Limited basis for comparison against results from more "traditional" ABA tests due to limited use to date |
Total Inorganic Carbon (TIC)
TIC = (total carbon) - (carbon after HCl digestion) |
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Measures NP associated with carbonates only |
Only provides carbonate fraction of NP
Can only be used in concert with total NP results
Will include carbonates that do not contribute NP (e.g., siderite)
Not suitable for materials with low NP |
Sulphur Analysis
(total S, pyritic S, sulphide S, organic S, sulphate S, residual S)
Analysis requires selective digestion of ground sample and measurement of sulphur by infrared or titration after combustion
Removal of non-sulphide and/or targeted sulphide minerals to determine sulphur species |
Potential of samples to generate acid
Used as part of ABA testing |
Distinguishes between sulphur forms and allows identification of "reactive" sulphur species |
Does not confirm the identity of the sulphur-bearing mineral(s)
Can overestimate or underestimate reactive sulphur content |
Chromium Reducible Sulphur
Targets acid-volatile sulphur, elemental sulphur and pyrite sulphur through HCl digestion |
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
Only measures sulphide minerals |
Limited basis for direct comparison against results from more "traditional" ABA tests |
Total Actual Acidity (TAA)
Titration of KCl extract to pH 5.5 with NaOH |
Can define actual acidity in low-pH samples that have oxidized |
Total Potential Acidity (TPA)
Heating of KCl extract with H2O2 and titration to pH 5.5 with NaOH |
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Net Acid Generating (NAG) |
Single addition NAG
Reaction with H2O2, measurement of the NAG pH and titration to pH 4.5 and pH 7.0 with NaOH |
All Methods:
Establishes overall acid generating capability of a material through simultaneous reaction of acid generating and acid neutralizing components
Identification of the need for and samples that require kinetic testing Used in conjunction with ABA or stand alone field test when calibrated
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All Methods:
Evaluates net acid-base balance
Generally relatively fast and inexpensive
Provides operational screening criteria for mine waste classification and management
Greatly reduces false positive and false negative ABA results
Confirmation results for unreactive materials
In combination with ABA improves prediction reliability and range of uncertainty |
All Methods:
Does not distinguish between AP and NP
Potential interferences in presence of organic carbon and copper
May underestimate ARD potential in high-sulphide material due to incomplete oxidation (Sequential NAG addresses this limitation)
Quality of H2O2 may vary: some H2O2 brands required pre-treatment for NAG test use |
Sequential NAG
Multi-stage repeat of single-addition NAG tests until NAG pH is greater than 4.5 |
Overcomes incomplete oxidation in high-sulphur samples
Can provide qualitative estimate of approximate lag time to acid generation |
Extended Boil and Calculated NAG
As single addition NAG, but accounts for potential effect from organic matter
Extended boiling and assay of the NAG solution for S, Ca, Mg, Cl, Na and K |
Accounts for potential effect from organic matter |
Kinetic NAG
As single addition NAG but with monitoring of temperature and pH during reaction with H2O2 |
Provides qualitative estimate of reaction kinetics and lag time (i.e., weeks, months, years) |
Mineralogical Composition |
Visual/Optical Microscopy
Hand lens, binocular microscope |
All Methods:
Identify primary and secondary minerals that could affect acid generation potential and contact water quality
With 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 weathering
Corroborate lithologic information
Essential for understanding of geochemical controls on contact water quality and as inputs to geochemical model simulations |
Qualitative |
X-ray diffraction (XRD)
Qualitative or semi-quantitative (Rietveld) analysis |
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Semi-quantitative at best
High detection limit ~1%
Capable of identifying crystalline minerals only |
Petrographic analysis
Reflection or transmission petrographic microscope |
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Requires sophisticated instrumentation and specialized personnel for interpretation |
SEM/EDS
Electron beam scan for mineral identification |
Surpasses combustion-infrared methods in quantifying trace sulfide mineral concentrations |
Electron microprobe
Like SEM but optimized for chemical analysis |
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Portable equipment (PIMA)
Infrared analyzer |
Portable
Particularly suited for hydrated minerals |
Not capable of identifying all minerals |
Short-Term Leach Tests |
SPLP (Synthetic Precipitation Leaching Procedure)
US EPA Method 1312
20:1 solution to solid
Deionized water or dilute sulphuric/nitric acid to pH 4.2 or 5.0
< 9.5 mm
18 ± 2 hours
Variant: Standard Test Method for Shake Extraction of Mining Waste by the Synthetic Precipitation Leaching Procedure
ASTM D 6234 |
All Methods:
Measures readily soluble constituents of mine and process wastes |
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.
Only simulates short-term interaction
High liquid to solid ratio may underestimate leachability
Grain size reduction may increase reactivity |
TCLP (Toxicity Characteristic Leaching Procedure)
US EPA Method 1311
20:1 solution to solid ratio
acetic acid/acetate buffer
< 9.5 mm
18 ± 2 hours |
Used to determine if waste is hazardous under RCRA
Intended to simulate municipal landfill containing organic wastes |
Applicable standards available |
Use of acetic acid/acetate buffers not appropriate for mining applications, Short list of metals evaluated |
Meteoric Water Mobility Procedure (MWMP)
1:1 solution to solid ratio
reagent-grade water
< 2 inch
< 48 hours |
Same as for SPLP
Primarily used in Nevada |
Quasi-dynamic test
More realistic than SPLP due to higher solid to solution ratio, longer duration and coarser material
Applicable standards available |
Weaker lixiviant than acidified SPLP |
California Waste Extraction Test (WET)
10:1 solution to solid ratio
dilute sodium citrate solution
< 2 mm
48 hours |
Intended to simulate municipal landfill containing organic wastes
Primarily used in California |
Lower liquid to solid ratio and longer test duration than SPLP and TCLP
Applicable standards available |
Use of sodium citrate not appropriate for mining applications |
Modified Test for Shake Extraction of Solid Waste with Water
4:1 solution to solid ratio
reagent-grade water adjusted to pH 5.5 with carbonic acid
18 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 ratio
acetic acid
< 9.5 mm
24 hours
Modification for mining wastes
3:1 solution to solid ratio
dilute hydrochloric acid |
Similar to TCLP for normal procedure
Similar to SPLP and ASTM for modified procedure |
Modified: lower solution to solid ratio than SPLP and ASTM |
Intended to simulate municipal landfill containing organic wastes
Same as for SPLP |
NAG Test with Leachate Analysis
100:1 solution to solid ratio
15% H2O2 solution
< 75 um
Until 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 ratio
Significant grain size reduction |
Characterization of Waste - Leaching - Compliance Test for Leaching of Granular Materials and Sludge
EN 12457 1
One stage test
2:1 solution to solid ratio
< 4 mm
EN 12457-2
One stage test
10:1 solution to solid ratio
< 4 mm
EN 12457-3
Two stage test
2:1 and 8:1 solution to solid ratios
< 4 mm
EN 12457-4
One stage test
10:1 solution to solid ratio
< 10 mm
All Methods:
distilled/demineralized/deionized water
24 hours |
All European Union (EU) Methods:
Basic characterization: obtain information on leaching behavior and characteristics
Compliance: determine whether waste complies with specific reference values |
All European Union (EU) Methods:
Test protocol is adjusted based on information needs and site-specific conditions
Applicable standards available (expressed as loadings) |
Same as for SPLP |
Characterization of Waste - Leaching Behavior Tests - Up-flow Percolation Test
CEN/TS 14405
10:1 solution to solid ratio
< 10 mm
demineralized water
duration 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
Test developed for landfills |
Characterization of Waste - Leaching Behavior Tests - Influence of pH on Leaching with Initial Acid/Base Addition
CEN/TS 14429
10:1 solution to solid ratio
at least 8 individual solutions of different pH using nitric acid or sodium hydroxide covering the range pH 4-12
95% < 1 mm
48 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 base
Allows evaluation of buffering capacity |
Same as for SPLP
Test developed for landfills |
Characterization of Waste - Leaching Behavior Tests - Influence of pH on Leaching with Continuous pH-Control
EN 14997
10:1 solution to solid ratio
at least 8 individual solutions of different pH using nitric acid or sodium hydroxide covering the range pH 4-12
95% < 1 mm
48 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 base
Allows evaluation of leachability under constant pH |
Same as for SPLP
Test developed for landfills |
Characterization of Waste - Leaching Behavior Tests - Acid and Base Neutralization Capacity Test
CEN/TS 15364
10:1 solution to solid ratio
at least 8 individual solutions of different pH using nitric acid or sodium hydroxide covering the range pH 4-12
95% < 1 mm
48 hours |
Used to determine final pH of a waste as well as assess consequences of external influences (carbonation, oxidation) on the final pH (EU) |
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Same as for SPLP
Test developed for landfills
Leachate only analyzed for pH |
Lixiviação de Resíduos
NBR 10005
16:1 solution to solid ratio
acetic acid
< 9.5 mm
24 hours |
Used to determine if mine waste is hazardous under solid waste regulations (Brazil)
Intended to simulate municipal landfill containing organic wastes |
Applicable standards available |
Use of acetic acid not appropriate for mining applications |
Solubilização de Resíduos
NBR 10006
4:1 solution to solid ratio
deionized water
grain size not specified
7 days |
Used to evaluate potential for impacts to groundwater by comparison against groundwater quality standards (Brazil) |
Applicable standards available
Lower solution to solid ratio and longer duration than SPLP |
Same as for SPLP |
Test Method Standard for Leaching Toxicity of Solid Wastes - Roll Over Leaching Procedure
GB5086.1-1997
10:1 solution to solid ratio
deionized/distilled water
< 5 mm
18 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 |
Test Method Standard for Leaching Toxicity of Solid Wastes - Horizontal Vibration Extraction Procedure
GB5086.2-1997
10:1 solution to solid ratio
deionized/distilled water
< 3 mm
24 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 |
Sequential Extraction
Variety of methods using different extractants to evaluate leachability from targeted fractions of mine waste
Methods 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
Allows for determination of the labile portion of the solid phase |
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 reagents
Most reagents not uniquely selective to targeted fraction
Use of some reagents precludes analysis of certain constituents
No applicable standards |
Long-Term Leach Tests |
Humidity Cell Test (HCT)
ASTM D5744-96
0.5:1 or 1:1 solution to solid ratio
deionized water
different dimensions for < 6.3 mm and <150 μm
weekly cycle of 3-day alternating dry air and wet air followed by leach
generally 20-week minimum but can run longer
weekly analysis of diagnostic ARD parameters (e.g., pH, SC, Fe, SO4, Eh, Ca, Mg, alkalinity)
generally 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 generation
To provide reaction rates for geochemical modeling |
Standardized test
Provides kinetic and steady-state leaching information and is recommended test for determination of weathering rates of primary minerals |
Not suitable for evaluation of saturated materials
Grain size reduction may increase reactivity
Potential for channel flow
High leaching rate can affect reaction kinetics due to higher pH and undersaturation with secondary minerals |
Column Test
variable solution to solid ratio
generally deionized water, groundwater or natural precipitation
generally < 25 mm
variable dimension, but generally larger than HCT
leaching 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
To simulate environmental performance of amended mine wastes and/or cover designs |
Frequently closer to field conditions than HCT
Can simulate different degrees of saturation
Can simulate remedial alternatives
Simulates combined weathering of primary and secondary minerals |
Not standardized
Potential for channeling through preferential flowpaths
Grain size reduction may increase reactivity
Without entire load of weathering products from primary minerals, reaction rates for primary minerals and extent of secondary precipitation cannot be measured |
Field Tests |
Wall Washing
1L rinse of 1 × 1 m surface area
distilled water |
All Methods:
To estimate short and long-term potential of mine materials to generate acid and leach metals using on-site materials |
Rapid
Measures leachate quality from in situ material
Can 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
deionized water
< 2 mm
5 minutes
http://pubs.usgs.gov/tm/2007/05D03/ |
Can be performed in the field
Rapid and inexpensive method to characterize chemical reactivity and water-soluble fraction
Field screening method that can be used as surrogate for SPLP due to similarity in approach and results |
Same as for SPLP |
Field Cells/Test Pads/Mine Facilities
Monitoring of increasingly larger volumes of mine wastes
Ambient precipitation or irrigation
Degree of grain size reduction required decreases with increasing size of test
Test duration months to years |
Test are conducted under actual field conditions
Can collect samples after transient events
Larger sample size results in enhanced test charge representativeness
With increasing test size, effects from grain size reduction, sample heterogeneity and preferential pathways reduced
With 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 feasible
Complexity of tested system may limit interpretive and predictive value of observations |
