Selective extraction can be considered as an “operational speciation” as it corresponds to the quantification of elements bound to specific phases of the soil, rather
LEACHING TESTS FOR GRANULAR MATERIALS
|
pH Domain 4-5 |
pH 5-6 |
Material Dictated |
Complexation |
Low L/S |
|
TCLP |
Swiss TVA |
DIN 38414 S4 |
MBLP (Synth) |
MBLP |
|
EPtox |
NFX-31-210 |
(California WET |
EN 12457-3 (at |
|
|
test) |
L/S =2 & 10) |
|||
|
Availability test |
O-norm S2072 |
Wisconsin SLT |
||
|
(NEN 7341) California WET |
EN 12457 |
|||
|
Ontario LEP |
Canada EE MCC-3C |
|||
|
Quebec QRsQ |
ASTM D 3987 |
|||
|
Soil HAc |
Soil — NaNO3 Soil — CaCl2 |
|
Table 7.1 Examples of leaching (and speciation) tests from around the world (adapted from van der Sloot et al. (1997) and from Hill (2004)) |
|
Single Batch Leaching Tests (equilibrium based) |
|
Multiple Batch and Percolation Tests (mostly based on local equilibrium) |
Serial Batch (low L/S) Serial Batch L/S>10 UHHamburg NF-X 31-210
WRU WRU
EN 12457-1 ASTM D4793-88
(at L/S = 2) NEN 7349 (NVN 2508)
MEP method 1320 Sweden ENA
MWEP
EN 12457-2 & -4 (at L/S = 10)
Static Methods Speciation Methods
Pacific Northwest Lab. MCC-1 Pacific Northwest Lab. MCC-2 Compacted granular tank leaching test (Rutgers/ECN)
LEACHING TESTS FOR MONOLITHIC MATERIALS
ANSI/ANS 16.1
Tank leaching test NEN 7345 (a static test, non-agitated)
Spray test (impregnated wood)
Swedish MULP
EN 1744-3 (static test, agitated)
The codes in this table refer to various standards or standards originating organisations. Readers who are uncertain of their meaning are referred to the original sources. L/S = Liquid:solid ratio.
than to an exhaustive analysis of the chemical species in the material. (Tessier et al., 1979; Quevauviller et al., 1993). Selective extraction procedures of pollutants from soils can be simple or can be organised according to a sequential or parallel extraction pattern.
Simple extraction procedures are not much used to determine the operational speciation of metals in materials but are used in soil sciences in order to quantify their potential availability for plants.
Sequential and parallel extractions follow the same principle: to submit the material to a series of reactants in order to identify associations between the different components of the material and the pollutant. Such procedures are more informative than simple extractions as they allow study of the geo-chemical partitioning of pollutants.
Parallel extractions involve different test portions of the same sample subjected to different reactants, while sequential extractions aim to submit the same sample to a well-ordered series of reactants with increasing aggressiveness. Different parallel extraction procedures have been proposed by Seme (1975), Forstner & Patchineelam (1976) and Cazenave (1994) (as cited in Lara-Cazenave, 1994) and also different sequential extraction procedures e. g. Gupta & Chen (1972), Engler et al. (1974), Tessier et al. (1979), Salomons & Fortsner (1980), Meguellati (1982), Welte et al. (1983) and Morrison & Revitt (1987) (as cited in Flores-Rodrigues, 1992).
Associations that are usually studied in most selective extraction protocols are (Colandini, 1997):
• the exchangeable fraction: pollutants are removed from clayey minerals and amorphous materials by simple ion exchange (neutral salts such as MgCl2, BaCl2 or CH3CO2NH4 are used);
• the fraction associated to carbonates: metals (co-)precipitated with natural carbonates are easily dissolved by a pH decrease (a weak acid as CH3COOH is enough to dissolve calcite and dolomite);
• the fraction associated to metal oxides: metals associated to oxides of Fe, Al and Mn are extracted by means of a reducing agent (as hydroxylamine hydrochloride — NH2OH. HCl);
• the organic fraction: under oxidizing conditions (H2O2 is used under acidic conditions) organic compounds are mineralized and metals are released; and
• the residual fraction: includes elements that are naturally present into the matrix of minerals.
In principle the different mineral phases can be quite precisely isolated thanks to the use of a series of extractions. However, the chemical attack on a phase does not always lead to a complete dissolution of pollutants contained in that phase, and for sequential extractions this can result in the dissolution of metals contained in other phases of the sample. Moreover, pollutants released by mineralization of a phase can be reincorporated by remaining phases. Thus, during sequential extraction measuring errors can accrue through the different steps. Despite these drawbacks, there remains a key benefit: that this method requires less material than parallel extraction.
As a conclusion of a European research programme (Ure et al., 1993) a 4-step harmonized sequential extraction method of heavy metals from soils and sediments was proposed by the Bureau Communautaire de Reference: [19]
• extract metals of the oxidizable fraction (using H2O2 8.8 M; CH3COONH4 1M; pH 2); and
• extract the residual fraction (using HF + HCl 15.5 M).
