Iron Oxide Removal from Soils and Clays by a Dithionite-Citrate System Buffered with Sodium Bicarbonate

Cambridge University Press (CUP) - Tập 7 - Trang 317-327 - 1958
O. P. Mehra1
1Department of Soils, University of Wisconsin, Madison, Wisconsin, USA

Tóm tắt

AbstractThe oxidation potential of dithionite (Na2S2O4) 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 Na2S2O4 oxidized. Tests show that NaHCO3 effectively serves as a buffer in this application. Crystalline hematite dissolved in amounts of several hundred milligrams in 2 min. Crystalline goethite 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 Na2S2O4-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 about 17 percent as contrasted to 35–80 percent with other methods.

Từ khóa


Tài liệu tham khảo

10.2134/agronj1935.00021962002700040011x

10.2136/sssaj1953.03615995001700040015x

Allison, 1942, A biological reduction method for removing free iron oxides from soils and colloidal clays, J. Amer. Soc. Agron., 34, 616, 10.2134/agronj1942.00021962003400070003x

Jackson, 1958, Soil Chemical Analysis, 498

Latimer, 1952, Oxidation Potentials, 392

10.2136/sssaj1937.03615995000100000013x

Tamm, 1922, Eine Method zur Bestimmung der anorganischen Komponenten des Gelkomplex in Boden, Medd. statens skogforsoksanst, 19, 385

10.1097/00010694-195612000-00005

10.1097/00010694-195905000-00001

10.1097/00010694-194412000-00001

10.2136/sssaj1947.036159950011000C0039x

Jackson, 1956, Soil Chemical Analysis—Advanced Course, 991

10.1097/00010694-194112000-00004

Mitchell, 1954, Removal of free-iron oxide from clays, Soil Sci., 77, 173, 10.1097/00010694-195403000-00001

10.1111/j.1365-2389.1954.tb02185.x

10.1111/j.1365-2389.1950.tb00733.x

Thông tin
Thông tin xuất bản

Cambridge University Press (CUP)

Tập 7

317-327

Thông tin tác giả