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Sequential Extractions: - PowerPoint PPT Presentation


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Sequential Extractions: Wet chemical procedures utilizing progressively stronger reagents/“solvents” to preferentially remove mineral species, or compounds, to separate them from a complex matrix. Individual procedures are dictated by sample chemistries.

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slide1

Sequential Extractions:

  • Wet chemical procedures utilizing progressively stronger reagents/“solvents” to preferentially remove mineral species, or compounds, to separate them from a complex matrix.
  • Individual procedures are dictated by sample chemistries.
slide2

Weathering crusts forming on the Henryville bed (HEN-2). (photo: Nelson Shafer, IGS)

Example 1:

Copiapites: a hydrated iron sulfate mineral with a formula: Fe2+Fe3+4(SO4)6(OH)2·20(H2O)

X-ray Diffraction (XRD)

10 cm

Zc

Ac

Zc

Ac

G

Zc

G

Ac

A

A

G

G

A

Q

slide3

in 250 ml glass beaker

1-9 g, dry sulfate crust,

homogenized

stirred for 24 hours, at 70oC, filtered with 0.8µm cellulose nitrate filter,

supernatant reserved, residue subtracted from initial mass

100 ml

1.0N HCl

supernatant transferred to a 100 ml volumetric flask and filled to volume

de-ionized H2O

10 ml supernatant transferred back to 250 ml

beaker and NaOH

pellets added to

remove Fe-hydroxides. Sample filtered, Fe-hydroxides discarded. BaCl2added to supernatant to precipitate BaSO4

90 ml supernatant reserved for AAS metals analysis

10 ml

0.5M BaCl2

0.02% HNO3

slide4

Example 2:

Bloomington Soil Pb

34000

32000

house paint

road

slide5

in 50 ml centrifuge tube

2 g, dry soil,

homogenized

25 ml

0.5M KNO3

stirred for 16 hours, centrifuged, filtered with

Whatman#42 filter, supernatant reserved

for analysis

Exchangeable Fraction

stirred for 2 hours, centrifuged, filtered,

supernatant reserved for analysis

25 ml

distilled H2O

Absorbed Fraction

Organically-Bound

Fraction

25 ml

0.5M NaOH

stirred for 16-21 hours, centrifuged, filtered,

supernatant reserved for analysis

stirred for 6 hours, centrifuged, filtered,

supernatant reserved for analysis

Carbonate-Bound

Fraction

25 ml

0.05M Na-EDTA

heated (70-80oC) for 16-21 hours in an oven,

centrifuged, filtered, supernatant reserved

for analysis

25 ml

4.0M HNO3

Residual Fraction

Sposito, G., Lund, L.J., and Chang, A.C., 1982, Trace Metal chemistry in arid-zone field soils amended with sewage sludge: I. Fractionation of Ni, Cu, Zn, Cd, and Pb in solid phases: SSSA Journal, 46:260-264.

slide6

Alva, A.K., Huang, B., Paramasivam, S., 2000, Soil pH affects copper fractionation and Phytotoxicity: Soil Science Society of America Proceedings, 29:955-962.

slide7

Bruchert, V., 1998, Early diagenesis of sulfur in estuarine sediments: the role of sedimentary humic and fulvic acids: Geochimica et CosmochemicaActa, 62:1567-1586.

slide8

Chao, T.T., and Theobald, Jr., P.K., 1976, The significance of Secondary Iron and Manganese Oxides in Geochemical Exploration: Economic Geology, 71:1560-1569.

slide9

Li, X., Coles, B.J., Ramsey, M.H., Thornton, I., 1995, Sequential extraction of soils for multielement analysis by ICP-AES: Chemical Geology, 124:109-123.

(N. Atlantic seafloor manganese nodules )