『Abstract
In the present study, different leaching tests were applied on
well-characterised samples in order to obtain information on the
potential mobility of heavy metals and arsenic. The information
deduced from the different methods was compared and evaluated.
Besides the comparison of heavy metal release in cascade-, column-
and pHstat leaching tests, attention was
also paid to the assessment of release kinetics during leaching
tests and to the mathematical modelling of leaching behaviour.
The aim of this study was to understand the origin of possible
discrepancies between the results of different leaching tests.
The compatibility of the results of different leaching tests is,
besides the inherent differences between methods (single batch
tests versus dynamic leaching tests, the duration of the tests,
liquid/solid (L/S) ratio,...) to a major extent determined by
key-factors such as pH and redox potential. Depending on soil
and sediment properties (e.g. acid neutralizing capacity (ANC))
these ‘key-factors’ varied during and at the end of extractions
and leaching tests, even when the initial test conditions (e.g.
the pH of the reagent) were equal for all test cases. During cascade-
and column leaching tests, pH (which is initially 4) will mostly
increase, but the extent of this pH-increase mainly depends on
the acid neutralizing capacity of the sample. Therefore, measuring
the pH of all leachates that are collected during these tests
is mandatory for the interpretation of the results. Moreover,
the monitoring of other variables such as DOC, anions and major
elements can give indications on the reactions that are responsible
for the release of elements (e.g. the dissolution of organic matter)
and greatly improve the interpretation of the results.
Keywords: Acid neutralizing capacity; Contamination; Leaching
tests; pH』
1 Introduction
1.1 Column leaching test and cascade leaching test
1.2 pHstat leaching tests
2 Materials and methods
2.1 Samples
2.2 General sample characterization
2.3 Column test
2.4 Cascade leaching test
2.5 pHstat test
2.6 Analysis of the leachates
3 Results
3.1 Physico-chemical and mineralogical sample characteristics
3.2 Column leaching test
3.3 Cascade leaching test
3.4 pHstat
3.4.1 pH-dependent leaching behaviour
3.4.2 Release rate of heavy metals during pHstat
leaching at pH 4
4 Discussion
4.1 pHstat leaching
4.1.1 Leaching as a function of pH during pHstat
leaching
4.1.2 Assessment of equilibrium conditions
4.2 Influence of ‘Key-factors’ in the column leaching test
4.3 Compatibility of cascade- and column leaching
4.4 Compatibility of cascade- and column leaching with pHstat leaching
5 Conclusion
Acknowledgements
References