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Identification of Clay Minerals in Soil: The Effect of Sodium‐Pyrophosphate
Author(s) -
Omueti J. A. I.,
Lavkulich L. M.
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200010051x
Subject(s) - montmorillonite , clay minerals , kaolinite , chemistry , allophane , chlorite , mineralogy , halloysite , soil water , pyrophosphate , silicate , nuclear chemistry , quartz , geology , materials science , metallurgy , biochemistry , enzyme , organic chemistry , geochemistry , soil science
The effect of Na 4 P 2 O 7 on soil clay minerals, layer silicate clays, and chloritized montmorillonite (synthetic) was investigated by x‐ray diffraction. The soil samples were treated with 30% H 2 O 2 , boiled, and water‐washed by centrifugation. The resulting organic‐free solids were dispersed as follows: shaken with 0.1 M Na 4 P 2 O 7 · 10H 2 O for 16 h only; treated with dithionite‐citrate‐bicarbonate (DCB); and treated with DCB followed by 0.1 M Na 4 P 2 O 7 · 10H 2 O. The 0.1 M Na 4 P 2 O 7 · 10H 2 O treatment caused the peak at 1.403 nm in the soil samples to become enlarged, sharp, and move to 1.339 nm. Other sharp peaks were also produced at 0.666, 0.637, 0.590, 0.561, 0.444, and 0.334 nm. These peaks were not observed in the x‐ray diffractograms of kaolinite and halloysite, but those of montmorillonite, chloritized montmorillonite, and chlorite were very similar to those of the soils. Heat treatment at 100°C destroyed the 0.637‐, 0.590‐, and 0.561‐nm peaks in some of the soil clay samples. At 300° the remaining peaks disappeared suggesting that sharp peaks resulting from the 0.1 M Na 4 P 2 O 7 treatment may be the result of mineral hydration. Some of these new peaks from 0.1 M Na 4 P 2 O 7 treatment of soil clays, the 0.334‐nm peak for example, can be mistaken as indicative of quartz in samples that do not contain this mineral. Thus the continued use of this reagent for mineralogical studies is not recommended.