Hiroshi Ikeda

Bio: Hiroshi Ikeda is an academic researcher from Yamaguchi University. The author has contributed to research in topics: Oxalate & Allophane. The author has an hindex of 1, co-authored 1 publications receiving 76 citations.

Allophane and imogolite: role in soil biogeochemical processes

Abstract: The literature on the formation, structure and properties of allophane and imogolite is reviewed, with particular emphasis on the seminal contributions by Colin Farmer. Allophane and imogolite occur not only in volcanic-ash soils but also in other environments. The conditions required for the precipitation of allophane and imogolite are discussed. These include pH, availability of Al and Si, rainfall, leaching regime, and reactions with organic matter. Because of their excellent water storage and physical properties, allophanic soils can accumulate large amounts of biomass. In areas of high rainfall, these soils often occur under rain forest, and the soil organic matter derived from the forest biomass is stabilized by allophane and aluminium ions. Thus the turnover of soil organic matter in allophanic soils is slower than that in non-allophanic soils. The organic matter appears to be derived from the microbial by-products of the plant material rather than from the plant material itself. The growth of young forests may be limited by nitrogen supply but growth of older forests tends to be P limited. Phosphorus is recycled through both inorganic and organic pathways, but it is also strongly sorbed by Al compounds including allophane. When crops are grown in allophanic soils, large amounts of labile P are required and, accordingly, these soils have to be managed to counteract the large P sorption capacity of allophane and other Al compounds, and to ensure an adequate supply of labile P. Because of their physical and chemical properties, allophanic soils are excellent filters of heavy metals and pathogens.

Comparison of an oxalate-extraction methon and an infrared spectroscopic method for determining allophane in soll clays

Abstract: The day fractions of nine New Zealand soils and an andesitic pumice, separated using minimal prctreatment, were examined by infrared spectroscopy (IR) and by dissolution in acid oxalate and pyrophosphate reapnts. Allophane, with an Al/Si ratio dose to 2/1, was prcsent in most samples and was estimated quantitatively for acid-oxalate extraction of Si and from the IR absorbance at 348 cm−1. These two methods pvc quantitative results wbich were in good agreement not only for clays formed from volcanic ash but also for clays lormed from basalt and clays formcd in podzolizcd soils. The hipt allopbane contents in the soil clays occurred in the cJays from the Mairoa Ash soil and from the Addison and One Tree Point podzolized soils.

Surface Properties of Allophane, Halloysite, and Imogolite

Abstract: The adsorption of sodium, chloride, and phosphate ions by allophane, imogolite, and halloysite has been studied in relation to the surface structure of the mineral samples. The high adsorption of phos- phate (>200/zmole/g) and chloride (10-30 meq/100 g at pH 4) by allophane is ascribed to the small particle size of allophane, its high surface area (-800 m2/g), and the presence at the surface of A1-OH-A1 groups and defect sites. In contrast, halloysite has a relatively large particle size and a Si-O-Si surface. Accord- ingly, the adsorption of phosphate (5-10/xmole/g) and chloride (1 meq/100 g) by halloysite is very much lower as compared with allophane. Phosphate adsorption by halloysite is also related to particle mor- phology and the number of edge sites. Thus, a sample consisting entirely of spheroidal particles adsorbed only 5/xmole/g at a solution concentration of 1  10 4 M, whereas the tubular types of comparable surface area adsorbed 7-10/zmole/g at the same concentration. This is because spheroidal halloysite particles have few, if any, edge sites at which phosphate can adsorb. The relative degree of order and hydration of hal- loysite, as indicated by infrared spectroscopy, also affects phosphate adsorption. However, this factor is apparently less important than particle morphology and surface structure. Although imogolite also has an A1-OH-A1 surface, it contains relatively few defect sites where phosphate can adsorb. Consequently, much less phosphate (120/zmole/g) was adsorbed as compared with allophane.