Applicability of selective dissolution of manganese oxide by acidified 0.1 M NH2OH–HCl in Japanese soils

We investigated the extraction of manganese (Mn) oxides and iron (Fe) oxides from samples of three Andisols and seven other major Japanese soils with acidified 0.1 M NH2OH–HCl in order to evaluate this method's applicability to selective dissolution of Mn oxide. The temporal changes in the amounts of Mn and Fe extracted revealed the following: 1. Mn oxides in non-volcanic-ash soil (low Alo + 1/2Feo) could be dissolved semi-completely upon extraction for 30 min, which is the customary extraction time. 2. Mn oxides in volcanic ash-containing soils (moderate or high Alo + 1/2Feo) continued to dissolve substantially after 30 min of extraction; 3. Fe oxides in all soils gradually dissolved throughout 4 h of extraction, although dissolution rates in volcanic ash-containing soils were much lower than in other soils. These results indicated that the solubility of Mn and Fe oxides in volcanic ash-containing soils were low, suggesting characteristic state of the oxides in these soils, and that the method is therefore unsuitable.

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► Mn oxide in soils which contain high Alo+1/2Feo was dissolved slowly in NH2OH-HCl.
► Soils which contain high Alo+1/2Feo had low solubility of Fe oxide with NH2OH-HCl.
► Selective dissolution method for Mn oxide in soils cannot apply to volcanic ash soils.