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 NH₂OH-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 NH₂OH-HCl might be insufficient for complete extraction of Fe oxides. The extracted amounts of Mn and Fe increased with increasing concentration of NH₂OH-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 NH₂OH–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 NH₂OH-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.

Key words:

• Fe oxide
• heavy metals
• hydroxylamine hydrochloride
• Tessier

ACKNOWLEDGMENTS

We acknowledge Dr. S. Ono, Dr. T. Ito (Tohoku University), Dr. K. Kamewada, Dr. A. Aoki (Tochigi Prefecture Agricultural Experiment Station) and Dr. Y. Nagasaki (National Agricultural Research Center for the Western Region) for soil sampling. We also thank Dr. S. Wakabayashi (Agricultural Research Center) and Dr. J. Takahashi (University of Tsukuba) for providing some of the soil samples used in this study and for providing physicochemical data for some of the samples. We also thank Dr. Y. Maejima and Dr. I. Akahane (National Institute for Agro-Environmental Sciences) and Dr. K. Tamura (University of Tsukuba) for helpful comments. This work was supported by a Grant-in-Aid for Research Fellows of the Japan Society for the Promotion of Science (No. 23-444).