Table 5-1

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Table 5-1: Methods for Geochemical Characterization

Return to: 5.3.2 Description of Phases

Test Type

Test Methods and Description

Use in 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

 

Prevent over-estimation of NP or AP relative to Sobek method
Widely used

 

Lapakko
NP at ambient temperature up to 1 week, H2SO4 to pH 6.0

     

BC Research Inc. (BCRI) Initial
NP at ambient temperature for 16-24 hours, H2SO4 to pH 3.5

     

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

 

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)

 

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

 

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

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

 

Semi-quantitative at best

     

High detection limit ~1%

     

Capable of identifying crystalline minerals only

Petrographic analysis
Reflection or transmission petrographic microscope

 

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

 

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

 

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)

 

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


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