What is the exact procedure to determine free iron oxides in soil? Does it work in estimating available iron because I did by shaking but the results were not satisfying.
Dear Dr. Hassan,
The procedures and extracting agents for determing free iron oxides and available iron in soil are different. The former is extracted by sodium sulfite, sodium citrate and sodium bicarbonate, and then measured by using Phenanthroline spectrophotometric method; the latter is extracted by ammonium acetate (acidic soil) or DTPA solution (neutral and alkaline soil), and then measured by using atomic absorption spectrometry.
Detailed protocal should be available in the Mannual for Soil Analysis, and if nacessary, I could post the link or send you related file. Good luck!
Regards,
Ping
"Free" iron oxides (both well crystalline and amorphous) are extracted with a well-established protocol, i.e., sodium dithionite. You may find it in any soil methods book, or even over the internet.
Free iron is usually considered to include non-crystalline forms of iron plus crystalline iron oxihydroxides. It is usually determined by extraction with sodium dithionite and citrate, either buffered or not by sodium bicarbonate. A rapid procedure can be found in: Holmgren G G S 1967 A Rapid Citrate-Dithionite Extractable Iron Procedure Soil Sci. Soc. Am. J. 31, 210–211.
Free iron is different from available iron, which is usually determined by extraction by a complexing agent (EDTA, DTPA, Mehlich 3 reagent). We have compared DTPA and Mehlich 3 for extracting Fe and other elements from mine soils in NW Spain (Monterroso C, Alvarez E, Fernández Marcos, M L 1999 Evaluation of Mehlich 3 reagent as a multielement extractant in mine soils Land Degradation & Development 10, 35-47).
Thanks a lot for all your helpful comments I am grateful for your cooperation.
Dear Dr.
free iron oxides, amorphous iron oxides and total iron and manganese were extracted using citrate dithionate bicarbonate (CDB) (Mehra and Jackson, 1960), ammonium oxalate in the dark (Mckeage and Day, 1966) and 4 N nitric acid (Richards et al, 1998) in respective.
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