Transcript Selenium Analysis of Coal, Overburden, and Mining

Selenium Analysis of
Overburden, Coal, and
Related Water Samples
Clarence L. Haile, Ph.D.
General Manager,
REI Consultants, Inc.
Analysis Process Components
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Obtaining a representative sample
Sample preparation
Sample digestion
Instrumental analysis
Obtaining a Representative
Sample
• Identifying geologic intervals
• Selecting the length of core segments
• Selecting the core section in each
segment for analysis
REIC Approach and Experience
• All cores are reviewed and sections
selected by an Experienced Soil Scientist
or Geologist
• Selenium levels are frequently higher in
silt, clay, or carbonaceous zones near and
within the coal strata
Sample Preparation
• Grinding and homogenizing the core
sections
• Sub sampling for analysis
• REIC Approach – Utilize EPA-600/2-78054, Field and Laboratory Methods
Applicable to Overburden and Minesoils
Lower Reporting Level Objectives
for Selenium
• Overburden and Coal
– 0.2 mg/kg
• Water Samples
– 0.6 μg/L
Sample Digestion
• Digest by heating with strong acids to
dissolve Se
• Sample concentration
– Solids – 1 g, concentrate to 50-mL final
volume
– Waters – 50-mL or 10-mL aliquot with same
final volume, no dilution
Instrumental Analysis Methods
• Optical ICP – ICP-OES
• ICP-MS
• Hydride Generation AAS
• GFAAS
Optical ICP
• Emission Spectroscopy
– Multi-element capability
– Digestate aliquot excited by plasma torch
– Measures emission of characteristic
wavelengths
• Good precision
• Robust for high dissolved solids digestates
• Typically cannot achieve required reporting
levels
ICP-MS
• Mass Spectrometry
– Multi-element capability
– Digestate aliquot excited by plasma torch
– Measures individual elements with a mass
selective detector
• Very low detection level capability
• Typically cannot tolerate high dissolved
solids
Hydride Generation Atomic
Absorption Spectroscopy
• Absorption Spectroscopy
– Digestate aliquot reduced with a hydride
reagent to form gaseous selenium hydride
– Selenium measured in gaseous hydride by
absorption of light from Se lamp
• Good sensitivity
• Results from manual reaction systems
can be variable
Graphite Furnace Atomic
Absorption Spectroscopy
• Absorption Spectroscopy
– Digestate aliquot heated in graphite tube –
dry, combust, and volatize metals
– Selenium measured in vaporized aliquot by
absorption of light from Se lamp
• Good sensitivity
• Generally tolerant to high dissolved solids
• Acceptable compromise between variability and
sensitivity
REIC Analysis Approach
• Employ GFAAS Analysis using EPA
Methods
• Conduct all analyses under a rigorous
Quality Assurance Program – including
full Quality Control procedures
Analytical Methods
• Solid Samples – Overburden and Coal
– Digestion using SW-846-3050
– Analysis by GFAAS using SW-846-7740
• Water Samples
– Digestion using EPA Method 200.2
– Analysis using GFAAS using EPA Method
200.9 or 270.2
Quality Control Procedures -Digestion
• Maximum of 20 samples per batch
• Method Blank – background check
• Laboratory Control Sample – accuracy
check
• Matrix Spike – accuracy check
• Duplicate Sample – precision check
Quality Control Procedures –
GFAAS Analysis
• Calibration -- Min of 3 standard levels,
plus blank
• Initial Calibration Checks – verify
instrument response and standards
• Continuing Calibration Checks -- verify
continuing calibration
Quality Control Procedures
• Method Lower Reporting Levels -evaluation and verification of MDLs and
PQLs
• Post-Digestion Spikes – check for matrix
interferences
• Sample Dilution – check for matrix
interferences
Additional Practices for Low
Level Se Measurements
• Zeeman background correction –
reduce matrix interferences and false
positives
• Tailored GFAAS temperature program
• Matrix modifiers
• Continuously monitor analysis to
ensure consistent sample introduction
• Maintain low signal baseline
REIC Approach Summary
• Cores reviewed and samples selected by
experienced soil scientist
• Sample preparation by EPA methods
• Sample aliquot digestion and GFAAS
analysis by EPA methods
• All analysis conducted under strong QA
program using appropriate QC procedures
Primary Contributors – REIC Team
• Tim Keeney – Research Soil Scientist
• Ivan Leef – Inorganic Manager
• Dennis Layne – Metals Supervisor