SOIL ANALYSIS

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SOIL ANALYSIS
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SAMPLE COLLECTION

• SAMPLES COLLECTED WITH CARE TO
• Represent sampling area (sub-samples collected
  and mixed together to reduce influence of soil
  variability on results)
• Avoid contamination and loss (wear rubber gloves,
  careful cleaning of equipment between samples)
• DRIED BELOW 40 ºC UNTIL CONSTANT MASS
• Samples continue to alter after removal from
  ground
• Handling problems are reduced
• SIEVED TO REMOVE GREATER THAN 2 mm MATERIAL
• Larger solid fractions are generally un-reactive

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SOIL CHARACTERIZATION

• Metal content
• pH
• ISO 103901994 Determination of pH
• Cation Exchange Capacity
• ISO 112601994 Determination of effective
  cation exchange capacity
• Particle Size Distribution
• ISO 112771998 Determination of particle size
  distribution in mineral soil material
• Organic Carbon content
• ISO 106941995 Determination of organic and
  total carbon after dry combustion

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EXTRACTION OF METALS FROM SOIL

• PSEUDO-TOTAL METAL CONTENT
• Small portion of soil dissolved in hot acid to
  release nearly all metals from original sample
• FRACTIONATION
• Same portion of soil treated with series of
  reagents to extract metals
• Reagents chosen to
• Dissolve particular geochemical phases and
  release associated elements
• Simulate environmental changes that might affect
  the soil
• Indicate what might be available to plants or
  humans

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APPROACHES TO TRACE METAL ANALYSIS1

• total metal content (HF digestion)
• pseudo-total content (aqua regia leaching) -
  maximum amount of metal species which could
  potentially be mobilised
• sequential extraction - reservoirs of metal
  potentially mobile under different conditions
  (pH, Eh etc)
• single extraction (e.g. EDTA to indicate
  plant-available species,
• physiologically-based extraction to indicate
  human bioaccessibility).

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SUMMARY OF EXTRACTION
1 then 2 then 3 then 4
1 2 3 4
SEQUENTIAL EXTRACTION AND DIGESTION
DRIED, SIEVED SAMPLE
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TOTAL DIGESTION
FOR MORE DETAIL ON METHOD SEE NEXT SLIDE
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METAL EXTRACTION
SEQUENTIAL EXTRACTION TEST PORTION
TOTAL METAL CONTENT TEST PORTION
DRIED, SIEVED SAMPLE
EXTRACTION OF METALS
DIGESTION FILTRATION
CENTRIFUGE DECANT

1 2 3 4 5
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SOLUTION ANALYSIS EMISSION SPECTROMETRY2
WHEN HEATED AND ATOMISED DIFFERENT ELEMENTS EMIT
LIGHT Qualitative analysis different colours
tell us which element is present Quantitative
analysis light intensity tell us how much of the
element is present
CALIBRATION known amount of element (metal
analyte) dissolved. Then heated in plasma to
produce emission, intensity of specific colour
for each analyte recorded.
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SOLUTION ANALYSIS
COLOUR INTENSITY
INTENSITY OF COLOUR FROM SAMPLE ALLOWS
CALCULATION OF ANALYTE CONCENTRATION
METAL CONCENTRATION
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REFERENCES
1. Adapted from Chemical speciation in the
environment, A.M. Ure and C.M.Davidson,
Blackwell, Oxford, 2002. 2. http//www.mrl.ucsb.ed
u/mrl/centralfacilities/chemistry/icp.pdf THIS
IS AN OVERSIMPLIFICATION OF A COMPLEX PROCESS TO
FIND OUT MORE BOOKS, WEB PAGES ETC with more
detailed descriptions of theory etc.!