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6. Structure of the 1:1 minerals kaolinite/serpentinite and the 2:1 mineral mica (illite). From Brindley and Brown, 1980. Legend see 7.
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Currently, there is a tendency to develop chemical and chemical-technological processes that consume as little energy as possible. Recently, ionizing and microwave radiation began to be used for these purposes in the chemical industry, since conventional heating can be slow and inefficient, which increases energy consumption. Polymer sulfur, which...
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... Since the Fe concentration of typical soil is considerably higher than that of Mn, NO 3 − and SO 4 2− , morphological changes in the Fe due to the redox process have a significant influence on the chemical properties of the soil (Neubauer et al. 2007). For the reduction from trivalent Fe [Fe(III)] to divalent Fe [Fe(II)] in the soil, a few conditions are required, i.e., (1) the presence of organic matter; (2) the absence of oxygen, NO 3 − and easily reducible Mn oxides; (3) the presence of anaerobic bacteria and an environment suitable for their growth (Breemen and Buurman 2002). Most of the Fe(II) in the anoxic soil is in the state of an exchangeable and solid form, while the movable Fe(II) ion occurs only slightly in a soil solution (Breemen and Buurman 2002). ...
... For the reduction from trivalent Fe [Fe(III)] to divalent Fe [Fe(II)] in the soil, a few conditions are required, i.e., (1) the presence of organic matter; (2) the absence of oxygen, NO 3 − and easily reducible Mn oxides; (3) the presence of anaerobic bacteria and an environment suitable for their growth (Breemen and Buurman 2002). Most of the Fe(II) in the anoxic soil is in the state of an exchangeable and solid form, while the movable Fe(II) ion occurs only slightly in a soil solution (Breemen and Buurman 2002). However, Fe(II) ion in the soil solution accumulates at the boundary near the oxidative environment, and specific nodules and mottles are formed with specific characteristics affected by changes in the water management or water table (King et al. 1990;Kyuma 2004). ...
Siderite (FeCO3), a type of carbonate mineral, is very occasionally recognized as a nodule in anoxic soils and sediments. During siderite formation, elements are expected to be accumulated or excluded between siderite and bulk soil. Therefore, we verified the affinity of 40 elements for siderite found in the gley horizon of a smectite-rich paddy field in northeastern Japan from the elemental concentration of the soil and the siderite dissolved in 2.88 mol L⁻¹ hydrochloric acid (10% HCl). The concentration ratio of the target element of the soil to the siderite was expressed by the product of the dimensionless R0 value and ratio of titanium (Ti) concentration of the soil to the siderite (Csiderite /Csoil) = R0 (Tisiderite /Tisoil). The affinity of each element for the siderite was analyzed by comparing the R0 values. In comparison with Ti used as the reference element, P, Cr, Co and Mo were accumulated (R0 > 1.0), and alkali metals, such as Li, Na and K, and chalcophile elements, such as Cu, Zn, Cd and Pb, tended to be equal or excluded from the siderite (R0 ≦1.0). Of the group 2 elements, Ca, Sr and Ba were accumulated, while Mg was excluded. The affinity of Mn for siderite exceeded that of Fe as the main component of the siderite, which reflects the fact that siderite was formed in a fresh water condition. The siderite size did not influence the elemental affinity. Observation of micromorphology using a scanning electron microscope showed that the siderite nodules were aggregations of siderite particles and clays, suggesting that the siderite grew by taking in clay around it. The rare earth element (REE) distribution pattern showed a tendency not to increase linearly but to increase with forming a concave curve at the intervals of the four elements with the increase of atomic number (i.e. tetrad effects). Although these findings are from the lower horizons of anoxic soils, the elemental affinity for siderite of this study is useful in order to elucidate the complex elemental dynamics in the anoxic environment.
