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Environmental
impact to soil and groundwater
Testing framework
A robust and scientifically sound, while
practical, framework for characterisation of environmental behaviour
of soils, sludges, sediments, wastes and constructions materials
in a range of applications and exposure scenarios has been developed.
The framework is a tiered approach, allowing the user to select
the level of testing and evaluation required based on the degree
of conservatism needed, prior information available, and balancing
costs of testing against benefits from more detailed information.
Test
methods
Worldwide there are many leaching tests.
However, most of them are single step leaching tests, which give
very limited information and do not allow establishing systematic
relationships between materials, nor do they allow interpretation
of the information in relation to possible environmental impact.
For that purpose more extended testing is needed. Below the characterisation
tests suitable for assessing impact from a wide range of materials
in a wide range of scenarios.
Basic characterisation test approach
The combination of pH dependence and percolation
test for granular materials and the combination of pH dependence
and tank test for monolithic materials form the basis for judging
of environmental impact in more than 80 % of the cases and for almost
any material. In some specific cases additional properties (redox
and particle size effects) may need to be taken into account, but
such aspects are best dealt with in the scenario description for
the application considered. This basic approach provides comparability
between productions and across different fields (Figure 1).
Figure 1: Basic test approach
Leaching test data for
cement-based materials
Using LeachXS (database/expert
system Leaching) the experimental data for more than 50 cement mortars
are compared. In Figure 2 an illustration is given for Cr
and Zn leaching from cement mortar. This illustrates for Cr very
significant differences in leaching as a function of pH, where content
does not show such major differences. For Zn the range in leachability
for cements from widely different sources does not scatter so much
in the pH dependence test. In the tank test (service life) the results
scatter much less than in the pH stat, which is caused by the diffusion
dominated release process (Cr about 2 orders of magnitude; Zn about
one order of magnitude).
Figure
2: Cr and Zn leaching from cement mortar
Cr reduction
A new EU regulation on Cr reduction in cements
(EU Directive 2003/53/EC, January 15th, 2005) will come
in force shortly. The objective is to reduce the formation of chromate
upon wetting cement and the occupational exposure of the skin due
to this chemical. The method to be applied involves an extraction
with water and is analysed spectrophotometrically at 540 nm. From
figure B it is clear that there is no direct relationship between
Cr VI in cement and total Cr in cement. The Cr VI measurements may
have been carried out at a time beyond the time scale considered
safe for having an active ingredient. This implies that some data
should have been lower than observed here. This aspect can become
a serious limitation. The relationship between leachable Cr VI (All
Cr leached at pH > 7 is chromate) and total Cr is lacking for blast
furnace slag (BFS) cement, blended cement, fly ash cement, lime
cement and Cr reduced cements. The shelf life of Cr reducing additions
are limited in most cases, which could pose a problem in the market.
For CEM I, there appears to be a rather good correlation between
leachable Cr VI and total Cr (Figure 3). This relationship
shows that a more or less fixed fraction of the total Cr entering
the kiln is converted to Cr VI. Leachable Cr (L/S=10, pH 9 - 10,
24 hrs) mg/kg = 0.11 (± 0.02) * Total Cr (mg/kg) This relationship
is applicable to Portland cement only.
Figure 3: Relationship
between Cr IV and Cr in cement
BFS cement and blended cements containing
slag all show a low Cr VI leachability. Thus blending of cement
with slag reduces Cr VI leachability drastically.
Hierarchy in testing
Once the leaching character of a material
is well established there is no need to test all parameters relevant
for regulations as not all parameters will be critical in a given
matrix. In addition, the level of testing can be reduced to one
or two step procedure, provided the results are presented in conjunction
with the previous characterisation data. Several existing single
step procedures can be placed in perspective to these characterisation
methods. and may be used
Impact evaluation in different
scenarios
A limited set of scenarios is relevant to assess
the impact to soil and groundwater. These comprise:
- a scenario for drinking water pipes of concrete
- a scenario for basins and concrete structures
permanent in contact with water
- a scenario for intermittent exposure to rain
- a scenario for debris (recycling, reuse) with
different particles size distributions
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