Dear Mr. Elbady,

Fe and Mn may decouple under certain circumstances as shown in the Eh-pH plot for Fe and Mn in oxisols and hydromorphic soils. In this case the Fe and Mn phases for paleosols are used.

Manganese is chemically related to iron. Due to the redox-related variation, oxidic Fe and Mn minerals have stability fields not very much different from each other with regard to their shape (a ,b). Oxidic manganese minerals precipitated from meteoric waters of a higher alkalinity than those of iron (a, b). Decoupling can be achieved by lowering of the pH value from > pH 7 to slightly acidic. By and large the change in the pH value may be crucial. In some cases on calcareous parent rocks the Mn content in the topstratum is increased for reasons of pH changes. The two diagrams may visualize why there is a splitting apart of two elements otherwise very closely related with each other.

Best regards

H.G.Dill

Thanks alot Dr. Dill, your explanation was very helpful to me. I wonder if you sir could support me with some papers in this point if it possible. I'd be so grateful.

Sincerely,

E. Elbadry

Dear Mr. Elbady,

The chemical similarity between Mn and Fe as the dominant redox-sensitive elements present in soil is reflected in their common association in the Fe-Mn concretions and nodules. The significant negative relationship between Fe and Mn in soil concretions in many studies have shown that that while Fe may deposit on the Mn accumulations as well as on the purer Fe concentrations, Mn tends to deposit at sites where both Mn and Fe concentrations already exist (Sullivan and Koppi 1992 ; Gasparatos et al. 2005 ). Mn compounds oxidize Fe 2+ and infuence its site of deposition (White and Dixon 1996 ) . Because Mn is mobilized at higher pH’s and under less reductive environments compared with Fe it seem to concentrates at a faster rate than Fe as the concretion formation progresses. Thus at the late stage of concretion development the Mn supply is largely exhausted and the smaller concretions, which have formed more recently than the large ones, showed a higher Fe and lower Mn composition.

These trends indicate that the formation and the development of concretions are a dynamic process that controls the translocation and transformation of Fe and Mn in the soil system.

Please find as attached files the appropriate references

Best regards

D. Gasparatos

Many thanks Dr. Gasparatos for your informations, and for the papers you provide me with.

Sincerely,

E. Elbadry

Dear Mr. Elbady,

Explanation for weak Mn and Fe correlation can also be explained by thermodynamic equations. For example, ΔG for ferrous  and Mn(II) oxidation with O at pH 7 is -21.0 and -7.2 Kcal/equivalent, respectively. You can find more  ΔG values for various elements and Eh/pH values. Also microbial activity is another important factor for Mn and Fe distribution in soils. Chemistry of soils  (Sposito, G.,1989) is a good summary book for starting.

Best regards,

E. Kakouros

Thanks alot for your notes, I shall keep this in mind.

Sincerely,

E. Elbadry

  Dear Elbadry

Soil is formed by the erosion (breakdown by water and wind) of rocks and bedrock. The deposition of organic material increases the disintegration of the rock and allows an environment for microorganisms and plants to colonise the soil. 

Please form a scaling soil horizones and  determine soil zones. If elements (Fe-Mn) have different ionic-potential values they have vary mobilization in soil. Between Fe and Mn correlation coefficient become is negative in organic-acids rich soil due to their different ionic potential values. Fe3+ can be precipitated in soil B-Zone before Mn.

best regards

No correlation between total Fe and Mn contents  and any soil properties of present day soils may exist when Fe and Mn are formed in  pH  conditions much different than that of the present  day  soil pH.Possibly such soils may have polygenetic  history and much of Fe and Mn compounds are of relict in nature.

Dear Dr. Kalender, I thank you for your clarification and your advice which is very helpful to me,  but unfortunately I didn't form a scaling soil horizons and determin them. Although the geochemistry of Mn is similar to that of Fe, but their ionic potential values different (as you said) according to pH and Eh conditions which control their deposition. Thanks alot to all of you.

Sincerely,

E. Elbadry