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Leaching:
Test methods
pH dependence leaching test
Test conditions:
- Batch test
- 8 final pH values (pH 4 - 12)
- Leachant: predetermined amounts of acid or base
- Liquid to solid ratio (l/s) = 10
- Results in mg/l (geochemical modelling) or mg/kg
(release evaluation)
Advantages:
- Identification of sensitivity of leaching to
small pH changes
- Provides information on pH conditions imposed
by external influences
- Basis for comparison of international leaching
tests
- Basis for geochemical speciation modelling
- Provides acid neutralization capacity information
- Mutual comparison of widely different materials
to assess similarities in leaching behaviour
- Recognition of factors controlling release
- For non-interacting species possible to assess
sub-sampling error
- Applicable to almost any material
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Percolation leaching test
 Liquid
to solid ratio (L/S) related to a time scale by infiltration rate,
density and height of application.
Test conditions:
- Pre-equilibration after
saturation for more than 48 hrs
- Up-flow
- L/S range 0.1 - 10 (100
- 1000 yrs)
- Test data in mg/l or mg/kg cumulative
Advantages:
- Identification of solubility control versus
wash out
- Indication of pore water concentrations relevant
to field leachate from low L/S data
- Local equilibrium established quite rapidly
- Basis for geochemical speciation modelling
- Allows comparison with lysimeter and field data
provided L/S value can be obtained from such measurements
- Projection towards long term behaviour
possible
- Solubility controlled release
- Wash-out of non-interacting species
- Applicable to many materials
Limitations:
- Limited or not applicable to clayey soils
and sediments (low permeability).
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Tank leaching test
Test conditions:
- First step: pre-equilibration for 48 hrs at
liquid to volume ratio: 5
- Second step: leaching at low L/V ratio (1) for
24 hrs
- Then contact times: 2, 4, 8,16, 32 and 64 days
- Leachant: demineralised water (own pH)
- Expression of results in mg/m2
(cumulative) against time
Advantages:
- Relevant for materials with monolithic character
(durable materials) or materials behaving as monolith (low permeability
soil and sediments)
- Identification of solubility control versus
dynamic leaching possible
- Isolation of surface wash-off effects
- Quantification of intrinsic release parameters
- Basis for reactive/transport modelling
- Projection towards long term behaviour possible
- Applicable to a wide range of monolithic construction
products
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