Extractability of manganese and iron oxides in typical Japanese soils by 0.5 mol L⁻¹hydroxylamine hydrochloride (pH 1.5)

Abstract

We investigated the extractability of manganese (Mn) and iron (Fe) oxides from typical Japanese soils (Entisols, Inceptisols, and Andisols) by 0.5 mol L À1 hydroxylamine hydrochloride (NH 2 OH-HCl) extraction (pH 1.5; 16 h shaking at 25 C; soil:solution ratio 1:40), referred as to HH mBCR , which is Step 2 (used for the reducible fraction) of the modified BCR (Community Bureau of Reference) sequential extraction procedure. The HH mBCR procedure extracted almost all Mn oxides from the non-Andisol samples, but failed to extract a part of the Mn oxides from some Andisol samples. The procedure extracted most short-range ordered Fe oxides from non-Andisol samples, but it extracted only 7.5% and 13% of the short-range ordered Fe oxides from allophanic and non-allophanic Andisol samples, respectively. This remarkably low extractability of Fe oxides suggests that the HH mBCR method is not suitable for extracting oxide-occluded heavy metals from Andisols. Since the extraction rate of short-range ordered Fe oxides from various soils with the extractant was negatively correlated with the amounts of oxalate-and pyrophosphate-extractable Al even when the variability of the extraction pH was reduced by increasing the soil:solution ratio from 1:40 to 1:500, the extractability of Fe oxides would be negatively affected by the presence of active Al, including allophane/ imogolite, amorphous Al, and Al-humus complexes. Because these Al constituents are abundant in Andisols, they would be at least partially responsible for the lower extractability of Fe oxides by HH mBCR from Andisols.

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

“…The results for the nonallophanic Andisol samples indicate that substantial amounts of Al were extracted from the Al-humus complex, although this extraction has been carried out before organically bound heavy metals are extracted in the modified BCR SEP. In contrast, HH mBCR extracted very small amounts of Fe from the Andisol samples, resulting in remarkably high Al/Fe ratios in these samples, being consistent with the results of Suda et al (2012). Oxa-Asc extracted large amounts of Fe except for the allophanic Andisol samples.…”

“…A common method is extraction with acidified 0.5 mol L -1 hydroxylamine hydrochloride (NH 2 OH-HCl), the second-step fraction in the modified Community Bureau of Reference (BCR) sequential extraction procedure (SEP) (Sahuquillo et al 1999). However, Suda et al (2012) reported that this method was not suitable for Japanese Andisols, especially allophanic Andisols, which showed poor extraction selectivity and low rates of extraction of short-range-ordered Fe oxides such as ferrihydrite.…”

“…In Japanese agricultural fields, Andisols are among the most common soil types containing high amounts of Mn and Fe (Takeda et al 2004). Mn oxides and short-range-ordered Fe oxides in Andisol samples are hardly extracted by 0.1 mol L -1 NH 2 OH-HCl (pH 2.0) and 0.5 mol L -1 NH 2 OH-HCl (pH 1.5), respectively (Suda et al 2011(Suda et al , 2012. Inceptisols, classified as Brown Forest Soils in the Japanese soil classification system, are also widely distributed in Japan and generally contain abundant highly crystalline Fe oxides such as goethite.…”

Iron Speciation of Natural and Anthropogenic Dust by Spectroscopic and Chemical Methods

“…According to XAS results, the residual fraction of SH_Dec2014 may be ascribed to aluminosilicates and iron oxy(hydr)oxides, whereas the AST_E45 residue is attributable to spinel-type non-reducible iron oxides. In fact, well-crystalline (e.g., hematite and goethite) and short-range-ordered (e.g., ferrihydrite) iron oxides could be not completely extracted by hydroxylamine hydrochloride -depending on the sample type, the sample mass/solution volume ratio, and the reagent concentration [52,53] and hence remain in the residual fraction.…”

Iron Speciation in Different Saharan Dust Advections and Effect of the Procedural Blank on the Results From X-ray Absorption Spectroscopy and Selective Leaching Experiments

“…This percentage is much lower than what reported by Formenti et al [20], who observed the iron oxides contribution in Saharan dust being in the range 38-72%, and apparently not in accordance with XAS results, which point towards the presence of Fe(III) oxides in determining the observed spectral features. However, it has to be considered that some iron oxides identified in Saharan dust by XAS speciation analyses (e.g., hematite, goethite, ferrihydrite) could not be completely extracted in step II, hence contributing to the residual insoluble fraction ( [33]; [34]; [35]), which accounts for about 70% for all the Saharan dust samples considered in this study.…”