Improvement of the NH₂OH-HCl-HOAc method for extracting manganese and iron oxides in Japanese Andisols and other soil types in Japan

Abstract

We evaluated the validity of Tessier's method as applied to the extraction of manganese (Mn) and iron (Fe) oxides in Japanese Andisols and other soil types in Japan. Using the original Tessier's extractant mixture, 0.04 mol L −1 hydroxylamine hydrochloride in 25% acetic acid (0.04 mol L-1 NH 2 OH-HCl in 25% HOAc), we found that substantial amounts of short-range-ordered Fe oxides were not extracted from allophanic Andisol samples and that considerable amounts of total Fe oxides were not extracted from all soil types. Relatively high extraction pH and large amounts of short-range-ordered Fe oxides in the Andisol samples might be responsible for incomplete extraction. Stoichiometric calculation indicated that the concentration of NH 2 OH-HCl might be insufficient for complete extraction of Fe oxides. The extracted amounts of Mn and Fe increased with increasing concentration of NH 2 OH-HCl in the extractant, and most of the Mn and Fe oxides in the soil samples, including samples with as much as 5.6% Fe, were extracted with 0.6 mol L-1 NH 2 OH-HCl in 25% HOAc. As judged from the simultaneous dissolution of aluminum (Al) and silicon (Si) minerals, extraction selectivity of Fe oxides with 0.6 mol L-1 NH 2 OH-HCl in 25% HOAc was comparable to that of the original Tessier's method and better than that of a modified Community Bureau of Reference (BCR) sequential extraction procedure or a method using an extractant consisting of a mixture of oxalate and ascorbate, especially for Andisol samples.

Wet-chemical extractions to characterise pedogenic Al and Fe species – a critical review

“…It was also used to extract Fe from 'amorphous oxides' and provided similar results to AOD (Chao and Zhou 1983). Qiang et al (1994) reported smaller amounts of Fe extracted by NH 2 OH-HCl than by AOD, and so did Suda et al (2013), who used a modification (NH 2 OH-HCl in acetic acid). Qiang et al (1994) explained this by incomplete reduction, hindered by SOM that covered or occluded the oxides, similar to that found for DCB (Eusterhues et al 2014a;Coward et al 2018).…”