Book ChapterDOI
Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate
O P Mehra,M L Jackson +1 more
- Vol. 7, pp 317-327
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TLDR
In this article, the bicarbonate-buffered Na 2 S 2 O 4 -citrate system was used for removing free iron oxides from latosolic soils, and the least destructive of iron silicate clays.Abstract:
The oxidation potential of dithionite (Na 2 S 2 O 4 ) increases from 0.37 V to 0.73 V with increase in pH from 6 to 9, because hydroxyl is consumed during oxidation of dithionite. At the same time the amount of iron oxide dissolved in 15 minutes falls off (from 100 percent to less than 1 percent extracted) with increase in pH from 6 to 12 owing to solubility product relationships of iron oxides. An optimum pH for maximum reaction kinetics occurs at approximately pH 7.3. A buffer is needed to hold the pH at the optimum level because 4 moles of OH are used up in reaction with each mole of Na 2 S 2 O 4 oxidized. Tests show that NaHCO 3 effectively serves as a buffer in this application. Crystalline hematite dissolved in amounts of several hundred milligrams in 2 min. Crystalline geothite dissolved more slowly, but dissolved during the two or three 15 min treatments normally given for iron oxide removal from soils and clays. A series of methods for the extraction of iron oxides from soils and clays was tested with soils high in free iron oxides and with nontronite and other iron-bearing clays. It was found that the bicarbonate-buffered Na 2 S 2 O 4 -citrate system was the most effective in removal of free iron oxides from latosolic soils, and the least destructive of iron silicate clays as indicated by least loss in cation exchange capacity after the iron oxide removal treatment. With soils the decrease was very little but with the very susceptible Woody district nontronite, the decrease was aboout 17 percent as contrasted to 35-80 percent with other methods.read more
Citations
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Book ChapterDOI
Particle-size analysis.
G. W. Gee,J. W. Bauder +1 more
TL;DR: In this article, the authors describe methods of particle-size analysis for soils, including a variety of classification schemes and standard methods for size distributions using pipet and hydrometer techniques.
Journal ArticleDOI
Kinetic control of dissolved phosphate in natural rivers and estuaries: A primer on the phosphate buffer mechanism1
TL;DR: The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process as discussed by the authors, which is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer.
Journal ArticleDOI
Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates
TL;DR: In this paper, the development of a sequential extraction procedure for iron in modern and ancient sediments is presented, which recognizes seven operationally derived iron pools: (1) carbonate associated Fe (Fe carb ), including siderite and ankerite; (2) easily reducible oxides (Fe ox1 ), including ferrihydrite and lepidocrocite; and (3) reducible Oxides(Fe ox2 ), including goethite, hematite and akaganeite, (4) magnetite (Fe mag ); (5)
Journal ArticleDOI
First-order reversal curve diagrams: A new tool for characterizing the magnetic properties of natural samples
TL;DR: For example, first-order reversal curves (FORC) diagrams as mentioned in this paper can be used to identify and discriminate between the different components in a mixed magnetic mineral assemblage, such as superparamagnetic, single-domain, and multidomain grains.
Journal ArticleDOI
Preservation of organic matter in sediments promoted by iron
TL;DR: It is suggested that reactive iron phases serve as an efficient ‘rusty sink’ for organic carbon, acting as a key factor in the long-term storage of organic carbon and thus contributing to the global cycles of carbon, oxygen and sulphur.
References
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Journal ArticleDOI
Iron Oxide Removal from Soils and Clays1
N. H. Aguilera,M. L. Jackson +1 more
TL;DR: In this article, a procedure is presented which employs sodium dithionite (Na2S2O4, hyposulfite, or "hydrosulfite") as the reductor, and 0.3 molar citrate with or without Fe-3 specific Versene as the chelating reagent.
Journal ArticleDOI
A Rapid Method for the Removal of Free Iron Oxides in Soil Prior to Petrographic Analysis1
TL;DR: Truog et al. as mentioned in this paper used oxalic acid to remove free iron oxides in soils free of organic matter and demonstrated that these compounds not only obscure the optical properties of soil min-> erals, but also serve as cementing agents which tend to produce mineral aggregates that resist mechanical separation.