Application of extraction and leaching methods and their interpretations

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Mineralogy and Mineral Resources Charles

1 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

2 Presentation outline introduction what is leaching? single extractions sequential extraction procedures (SEP) leaching tests for wastes methods and their applicability problems certified reference materials

3 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)

4 Leaching process - interactions

5 Part 1 Single extractions

6 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

7 Experimental protocols 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

8 Inorganic extracting solutions deionized water exchangeable fraction M solutions of inorganic salts 0.01 M CaCl 2 composition and ionic strength as a soil solution 1 M NH 4 NO 3 standard method (Germany), agrochemistry

9 0.01 M CaCl 2 extraction - Cd & Zn Element measured in soil water from lysimeters versus in 0.01 M CaCl 2 Cd Zn Degryse et al. (2003) Eur. J. Soil. Sci. 54, 149

10 Organic extractants why? acidification complexation fungi hyphae plant roots

11 Organic extractants why? phtalate acidic conditions Mg-phtalate hydrated surface of a silicate mineral chelating reactions promoting dissolution of primary minerals

12 Organic extractants - methods acetic acid ( M) EDTA ethylendiaminetetraacetic a.(0.05 M) DTPA diethylentriaminepentaacetic a. (0.005 M M TEA a CaCl 2 ) used in standardized protocols often buffered solutions or ph adjusted to the value of 7 time of extraction 1-2 h

13 Problem #1 kinetics of the extraction Leachability in the mixture of low-molecular-weight organic acids [10 mm] Ni Cu Zn Cr Cd Pb Feng et al. (2005) Environ. Pollut. 137, 231.

14 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 ). During extraction with DTPA buffered to ph 7.3 the final ph of the extract is 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.

15 Problem #3 - oxyanions some contaminant are present as anions As: [As(III)] AsO 3 3- & [As(V)] AsO 4 3- Sb: [Sb(III)] Sb(OH) 3 0 & [Sb(V)] Sb(OH) 6 - easy binding to + charged surfaces Fe oxyhydroxides at low ph and humic substances via aminogroups HA-NH 2 + HX (weak acid) = HA-NH 3+ X - HA-NH 3 +Sb(OH) OH - = HA-NH 3+ OH - + Sb(OH) 6 -

16 Problem #3 - oxyanions Ion exchange Sb(OH) 6 - Cl - Sb(OH) 6 - NO 3 - Specific sorption Sb(OH) 6 - PO 4 3- Ettler et al. (2007) Chemosphere 68, 455.

17 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) CaCl 2, NaNO 3, NH 4 NO 3 (indicative values) BCR-483

18 Part 2 Sequential extraction procedures (SEP)

19 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.

20 SEP applications Bacon a Davidson (2008) Analyst 133, 25.

21 SEP according to Tessier et al. (1979) 1. Exchangeable fraction 1 mol/l MgCl 2 (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 (NH 2 OH HCl) in 25% acetic acid (96 C) 4. Fraction bound to organic matter and sulphides HNO 3 /H 2 O 2 (85 C) then ammonium acetate in 20% HNO 3 5. Residual fraction total digestion in mineral acids (HClO 4 /HF)

22 Interpretation of the Tessier s SEP 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 mobile fractions 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)

23 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 (H 2 O 2 at 85 C, then 1 mol/l ammonium acetate) Sum of these fraction substracted from the pseudo- -total aqua regia digest (HNO 3 /HCl = 1/3) ~ residual fraction

24 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)

$(exchangeable fraction), although bound to OM OM is$

25 Problem #1 selectivity of extractants mobile Pb Forest soil (smelter-polluted) Pb bound in mobile (exchangeable fraction), although bound to OM OM is also an adsorbing material, to which metals are bound to!!!

26 Problem #2 data visualization better visualize the data in real concentration than in % not misleading!

27 Problem #3 - oxyanions similar problem as for single extractions in literature you can find a number of comparative studies and new procedures better suited for oxyanions (mainly As)

28 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

29 Part 3 Bioaccessibility extractions

30 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)

31 Gastric bioaccessibility 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 Gastro-intestinal Extraction Step 1. ph ~ 1 Step 2. ph = 7 Roussel et al. (2010): AECT 58, 945.

32 Example: mining/smelting soils in Zambia Bioaccessibility: As, Pb (81-100%) Co, Cu, Zn (58-83 %) Ettler et al. (2012) J. Geochem. Explor. 113, 68.

33 Lung bioaccessibility only solid of grain size < 10 μm should be taken fraction accessible for inhalation simulated lung fluid: NaCl (110 mm), NaHCO 3 (31 mm), Ca acetate (2.5 mm) CaCl 2 (2.5 mm), Mg acetate (1 mm), MgCl 2 (1 mm) KH 2 PO4 (2 mm), K 2 SO 4 (1 mm), citric acid (1 mm) albumin (0.2 g/l) L/S = 20, 37 C, 6 days leaching to attain equilibrium Twining et al. (2005) Environ. Sci. Technol. 39, 7749.

34 Part 4 Leaching tests for mineral wastes

35 Why? determination of hazardous properties (contaminant release/leaching) standardized leaching tests defined by legislation at national and at international level E.g. Germany (norms DIN, France (norms AFNOR, Netherlands (norms NEN,

36 EU framework 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

37 EN first part Characterization of waste validated in EU states as EN (parts 1-4) Characterisation of waste - Leaching -Compliance test for leaching of granular waste materials and sludges

38 Batch leaching test EN 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)

39 Limit criteria (test EN , L/S = 10) mg/kg NH/N non-hazardous H hazardous As Cd Cr Cu Hg Pb Sb Zn ,2 10 0, If the limit for hazardous waste is exceeded, the material must be stabilized/solidified and test repeated before being landfilled.

40 Problem #1 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

41 ph-static leaching test 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 HNO 3 or NaOH CEN/TS ph dependence leaching test (initial acid/base addition) published 2005 CEN/TS ph dependence leaching test (continuous ph control) published 2006

42 Experimental setup of ph-stat test

43 Output of the ph-stat test (1) (2) (3) (1) ingestion (2) acidic soils (4) (3) neutral soils (4) stabilized soils (cementation)

44 Problem #2 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

Column leaching test (percolation) Percolation test (CEN/TS 14405 - column test) with up-flow setup - published 2004 based on Dutch test NEN 7343

45 Column leaching test (percolation) Percolation test (CEN/TS column test) with up-flow setup - published 2004 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

46 Experimental setup filter pressure control (CO 2 ) autosampler leaching solution peristaltic pump waste column

47 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

48 Experimental setup of column test

49 Replication of experimental columns

50 Output of the column leaching test L/S = 10 defined in the norm

51 L/S concept what the L/S ratio says? 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 L/S = (I * t) / (D * H) t = (L/S * D * H) / I Example: L/S = 2 L/kg D = 1 kg/dm 3 H = 10 m I = 200 mm/yr Time until the first leachate appears t = (2 * 1 * 10)/0.2 = 100 years

52 Problem #3 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

53 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)

54 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)

55 Literature see for example: Journals: Analytica Chimica Acta TrAC-Trends in Analytical Chemistry Analyst Environmental Science & Technology Internet:

56 Thanks for your attention! Questions?

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