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EGG – Environmental Geochemistry Group
Application of extraction
and leaching methods
and their
interpretations
Vojtěch Ettler Institute of Geochemistry, Mineralogy and Mineral Resources
Charles University in Prague, Czech Republic
Presentation outline
• introduction – what is leaching?
• single extractions
• sequential extraction procedures (SEP)
• leaching tests for wastes
methods and their applicability
problems
certified reference materials
Introduction – why and how?
• leaching/extraction tests
• interaction between solution and solid
• analysis of compounds in solution
• application for contaminants
• determination of their mobility & bioavailability
• environmental sciences (geochemistry,
agrochemistry, waste management)
Leaching process - interactions
Single extractions
Part 1
Methods and their applications
• experimentally simple, easy and quick
• determination of leachability of a given
element from the solid to the
• soils and sediments
• „bioavailability“, mainly for plants
• „(bio)available“ – leachable in the root zone
of plants - rhizosphere
• solid sample
• PE bottle
• leaching solution
• liquid-to-solid ratio (L/S)
L/S = 2 to 10
• time of shaking 1-24 h
• centrifugation – filtration
• solution analysis, recalculation mg/l mg/kg
• expressed as % element leachability
Experimental protocols
Inorganic extracting solutions
• deionized water
• „exchangeable“ fraction
• 0.01-1 M solutions of inorganic salts
• 0.01 M CaCl2
composition and ionic strength as a soil
solution
• 1 M NH4NO3
standard method (Germany), agrochemistry
0.01 M CaCl2 extraction - Cd & Zn
Element measured in soil water from lysimeters versus in 0.01 M CaCl2
Degryse et al. (2003) Eur. J. Soil. Sci. 54, 149
Cd Zn
Organic extractants – why?
• acidification
• complexation
fungi hyphae
plant roots
Organic extractants – why?
hydrated surface
of a silicate mineral
Mg-phtalate
• chelating reactions
• promoting dissolution
of primary minerals
acidic
conditions
phtalate
Organic extractants - methods
• acetic acid (0.11-0.43 M)
• EDTA – ethylendiaminetetraacetic a.(0.05 M)
• DTPA – diethylentriaminepentaacetic a.
(0.005 M + 0.01 M TEA a CaCl2)
• used in standardized protocols
• often buffered solutions or pH adjusted to
the value of 7
• time of extraction 1-2 h
Problem #1 – kinetics of the extraction
Pb
Cd
Cr
Zn
Cu
Ni
Leachability in the mixture of low-molecular-weight organic acids
[10 mM]
Feng et al. (2005) Environ. Pollut. 137, 231.
Problem #2 – buffering capacity
• the buffering capacity of extractant can be
exhausted during the interaction with soil
• DTPA buffered to pH 7.3
• for highly organic acidic soil >>> lowering the
pH of the extract
Eg. Polluted forest soil (37-46% TOC, pH 3.5-3.7). During extraction with
DTPA buffered to pH 7.3 the final pH of the extract is 3.4-3.9.
Resulting mobile concntration of a given element is a combination of
effects related to complexating reactions and pH.
Ettler et al. (2007) Anal. Chim. Acta 602, 131.
Problem #3 - oxyanions
• some contaminant are present as anions
• As: [As(III)] AsO33- & [As(V)] AsO4
3-
• Sb: [Sb(III)] Sb(OH)30 & [Sb(V)] Sb(OH)6
-
• easy binding to + charged surfaces
Fe oxyhydroxides at low pH and humic
substances via aminogroups
HA-NH2 + HX (weak acid) = HA-NH3+X-
HA-NH3+Sb(OH)6- + OH- = HA-NH3
+OH- + Sb(OH)6-
Problem #3 - oxyanions
Ion exchange
Sb(OH)6- ↔ Cl-
Sb(OH)6- ↔ NO3
-
Specific sorption
Sb(OH)6- ↔ PO4
3-
Ettler et al. (2007) Chemosphere 68, 455.
Certified reference materials (CRM)
• European Commission´s Measurement and Testing
Program (IRMM, Belgium)
• EDTA & acetic acid (Cd, Cr, Cu, Ni, Pb a Zn)
BCR-483 (sewage sludge amended soil)
BCR-484 (sewage slunge amended terra rosa soil)
BCR-700 (organic rich soil)
• CaCl2, NaNO3, NH4NO3 (indicative values)
BCR-483
Sequential extraction
procedures (SEP)
Part 2
Basic facts
• „selective“ or „sequential“ extraction
• higher number of extracting solutions
• 1 g of sample (sediment, soil)
• successive leaching using extracting solutions
with increasing extractability
• based on SEP proposed in 1979 by
André Tessier et al.
SEP applications 1970-2006
Bacon a Davidson (2008) Analyst 133, 25.
SEP according to Tessier et al. (1979)
1. Exchangeable fraction
1 mol/l MgCl2 (pH 7)
2. Fraction bound to carbonates
1 mol/l Na-acetate with acetic acid (pH 5)
3. Fraction bound to Fe & Mn oxides
0.04 mol/l hydroxylamine hydrochloride (NH2OH·HCl) in 25%
acetic acid (96°C)
4. Fraction bound to organic matter and sulphides
HNO3/H2O2 (85°C) then ammonium acetate in 20% HNO3
5. Residual fraction
total digestion in mineral acids (HClO4/HF)
Interpretation of the Tessier´s SEP
mobile
fractions
1. Exchangeable fraction
sorption to soil sorption complex
2. Fraction bound to carbonates
dissolution under slightly acidic conditions
3. Fraction bound to Fe and Mn oxides
release during the dissolution of Fe and Mn oxides
4. Fraction bound to organic matter and sulphides
digestion of organic matter and sulphides under highly
oxidizing conditions
5. Residual fraction
bound to „residuum“, in silicates and less soluble oxides
(e.g. spinels)
SEP according to BCR
• simplified methodology
• Exchangeable + acid-extractable fraction
(0.11 mol/l acetic acid)
• Reducible fraction
(0.5 mol/l hydroxylamine hydrochloride at pH 1.5)
• Oxidisable fraction
(H2O2 at 85°C, then 1 mol/l ammonium acetate)
Sum of these fraction substracted from the pseudo-
-total aqua regia digest (HNO3/HCl = 1/3)
~ residual fraction
Problem #1 – selectivity of extractants
Is the element bound to fraction 3 (Fe and Mn oxides)
in the Tessier´s methodology really bound to these
oxides?
COULD NOT BE!
• Extracting solutions should be considered as
„operationally defined“, in terms of chemical reactivity
• It is important to verify the presence/absence of
a given phase using some independent method
(XRD, VMP, EXAFS, SEM)
Problem #1 – selectivity of extractants
Forest soil
(smelter-polluted)
mobile Pb
• Pb bound in mobile (exchangeable fraction), although bound to OM
• OM is also an adsorbing material, to which metals are bound to!!!
Problem #2 – data visualization
• better visualize the data in real concentration than in %
• not misleading!
Problem #3 - oxyanions
• similar problem as for single extractions
• in literature you can find a number of compa-
rative studies and new procedures better
suited for oxyanions (mainly As)
Certified reference materials (CRM)
• CRM for standard SEP according to BCR
BCR-601 (lake sediment, no more available)
BCR-701 (lake sediment)
BCR-483 (sewage sludge amended soil)
values for Cd, Cr, Cu, Ni, Pb, Zn
in the literature also NIST 2711 (Montana soil) etc
• application of BCR SEP is the most practical
Part 3
Bioaccessibility
extractions
Human health implications
• extraction test in vitro
• how contaminants are leached from a given
material (soil, dust) in simulated human body
fluids?
• gastric bioaccessibility (ingestion)
• lung bioaccessibility (inhalation)
• soil ingestion (pica behaviour)
• Simple Bioaccessibility Extraction Test (SBET) – US EPA
• gastric fluid simulation
• 0.4 M glycine, pH 1.5 (HCl), L/S = 100, 2 h extraction at 37°C
Gastric bioaccessibility
Gastro-intestinal
Extraction
Step 1. pH ~ 1
Step 2. pH = 7
Roussel et al. (2010): AECT 58, 945.
Bioaccessibility:
As, Pb (81-100%)
Co, Cu, Zn (58-83 %)
Ettler et al. (2012) J. Geochem. Explor. 113, 68.
Example: mining/smelting soils in Zambia
Lung bioaccessibility
• only solid of grain size < 10 μm should be taken
• fraction accessible for inhalation
• simulated lung fluid:
• L/S = 20, 37°C, 6 days leaching to attain equilibrium
NaCl (110 mM), NaHCO3 (31 mM), Ca acetate (2.5 mM)
CaCl2 (2.5 mM), Mg acetate (1 mM), MgCl2 (1 mM)
KH2PO4 (2 mM), K2SO4 (1 mM), citric acid (1 mM)
albumin (0.2 g/l)
Twining et al. (2005) Environ. Sci. Technol. 39, 7749.
Leaching tests
for mineral wastes
Part 4
E.g.
Germany (norms DIN, www.din.de)
France (norms AFNOR, www.afnor.fr)
Netherlands (norms NEN, www.nen.nl)
Why?
• determination of hazardous properties
(contaminant release/leaching)
• standardized leaching tests
• defined by legislation at national and
at international level
Network on Harmonization of Leaching/Extraction Tests
• definition of EU testing methods under CEN
(Comité Européen de Normalisation)
• norms CEN TC 292 WG6 - Characterization of
waste (partly validated, some tests under construction)
• based on national tests applied for waste testing and
international ISO norms
EU framework – www.leaching.net
• first part ” Characterization of waste” validated
in EU states as EN 12457 (parts 1-4)
EN 12457
Characterisation of waste - Leaching
-Compliance test for leaching of
granular waste materials and sludges
batch reactor (PE, HDPE)
crushed waste (< 4mm)
leaching solution (DI water)
L/S = 2 – 10
• shaked on a table shaker for 24 h
• filtration (0.45 μm) and analysis of leachate
• limit criteria (inert, non-hazardous, hazardous)
Batch leaching test EN 12457
NH/N H non-hazardous hazardous
As
Cd
Cr
Cu
Hg
Pb
Sb
Zn
mg/kg
2
1
10
50
0,2
10
0,7
50
25
5
70
100
2
50
5
200 If the limit for hazardous waste is exceeded, the material must be
stabilized/solidified and test repeated before being landfilled.
Limit criteria (test EN 12437-2, L/S = 10)
Advantages of the batch test: • simple experimental protocol
• quick and cheap
Drawbacks of the batch test: • only short-term interaction (24 h)
• solid sample and liquid may not be in equilibrium
• no long-term predictions can be done using this
batch test
Problem #1
• paralel extractions at L/S = 10 (for 48 h) at a range
of pH (at least 8 values of pH)
• pH controlled by addition of HNO3 or NaOH
pH-static leaching test
• CEN/TS 14429 – pH dependence leaching test
(initial acid/base addition) – published 2005
• CEN/TS 14997 – pH dependence leaching test
(continuous pH control) – published 2006
Experimental setup of pH-stat test
(1)
(2)
(3)
(4)
(1) ingestion
(2) acidic soils
(3) neutral soils
(4) stabilized soils
(cementation)
Output of the pH-stat test
Advantages of the pH-stat test: • information useful for geochemical modelling
• pH is a key parameter influencing the leachability
• material behaviour in extreme conditions
(worse-case scenario)
Drawbacks of the pH-stat test: • interaction process may not be in equilibrium
even after 48 hours of leaching
• installation of natural steady-state pH not possible
Problem #2
• based on Dutch test NEN 7343
crushed sample, 95% of grains
• must be < 4 mm
• 0,8 l of sample is leached (ca. 3 kg)
• procedure of sample insertion
in the column is strictly defined
in the norm
Column leaching test (percolation)
Percolation test (CEN/TS 14405
- column test) with up-flow setup
- published 2004
peristaltic pump
waste column
autosampler
leaching solution
filter
pressure control (CO2)
Experimental setup
• flow in the column is ca. 15 cm/day
(12 ml/h for column 5 cm, 48 ml/h for 10 cm) • sampling of leachate fractions
cumulative ratio L/S (liquid-to-solid in l/kg)
- volume of solution interacting with waste
solid
- total of 7 fractions
L/S = 0,1; 0,2; 0,5; 1,0; 2,0; 5,0; 10,0
• filtration and subsequent analysis of the leachate
• experiment duration ca. 30 days
Experimental setup
Experimental setup of column test
Replication of experimental columns
L/S = 10
defined in the norm
Output of the column leaching test
Liquid to solid ratio defines the volume of water that has been
in contact with one kilogram of solid material
Net infiltration rate, I
Bulk density, D
Height, H
Time until the first
leachate appears
Example:
L/S = 2 L/kg
D = 1 kg/dm3
H = 10 m
I = 200 mm/yr
t = (2 * 1 * 10)/0.2 = 100 years
L/S = (I * t) / (D * H)
t = (L/S * D * H) / I
L/S concept – what the L/S ratio says?
Advantages of the column test: • better simulates real-life conditions (scenarios)
such as dumping in a disposal site
• longer-term test
Drawbacks of the column test: • sometimes difficult interpretation
• preferential path of water percolation through
the column
Problem #3
Leaching results - interpretations
• availability (combination with in situ experiments)
• geochemical behaviour
(combination with geochemical models:
PHREEQC-2, ORCHESTRA - speciation, sorption,
ionic exchange, precipitation of solids) • mobility in a disposal site
(combination with speciation/transport modelling
PHAST) • mineralogical studies (speciation in solid phase)
Concluding remarks
• extraction/leaching methods
• routinely used in environmental sciences s.l.
• relatively cheap tools in comparison with
e.g. biological techniques
• studies on contaminant mobility and various
geochemical interactions between solid and
solutions
• CRM available for some extraction
(QC/QA feasible)
Literature – see for example:
Journals:
Analytica Chimica Acta
TrAC-Trends in Analytical Chemistry
Analyst
Environmental Science & Technology
Internet:
www.leaching.net
