Effect of Addition of Al Hydroxides on Changes in Dispersibility and Charge Characteristics of Soils |
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| Authors: | Katsuhiko Itami Yasuo Kitagawa Kazutake Kyuma Takashi Kosaki |
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| Institution: | 1. Faculty of Bioscience , Fukui Prefectural University , Matsuoka-cho, Fukui , 910-11 , Japan;2. School of Environmental Sciences, The University of Shiga Prefecture , Hikone , 522 , Japan;3. Faculty of Bioscience , Fukui Prefectural University , Matsuoka-cho, Fukui , 910-11 , Japan;4. Faculty of Agriculture , Kyoto University , Sakyo-ku, Kyoto , 606 , Japan;5. School of Environmental Sciences, The University of Shiga Prefecture , Hikone , 522 , Japan |
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| Abstract: | Using a soil from a newly reclaimed area where high dispersibility of fine particles had led to poor physical properties in the field, changes in dispersibility and charge characteristics after artificial precipitation of Al hydroxides onto the soil were investigated. Al hydroxides were precipitated by neutralization with NaOH of an acidic A1C13 solution in which the soil samples were placed. When the titration rates were changed, no significant differences in dispersibility were observed in the resultant soils. In the systems with the addition of 2 g kg-1 or less of A1(OH)3, dispersion ratios of clays were almost identical with those of blank samples although the specific surface areas were reduced. In the systems with 5 g kg-1 or more of A1(OH)3, considerable effects of Al hydroxides on reduction of clay dispersibility were recognized (e.g. 10 g kg-1 addition yielded less than one-third of the original ratio of the clay dispersion). A slightly larger decrease in dispersion was observed by the addition of 15 g kg-1 or more. As the amount of added Al increased, the amount of negative charges of the soil decreased while that of positive charges increased. The charge characteristics of the system with the addition of 20 g kg-1 of A1(OH)3 were closer to those of the adjacent forest soil which was characterized by a very low dispersibility. It was inferred that added Al hydroxides polymerized to form Al polycation species that were not readily exchangeable, neutralizing negative charges of clays, and acting as interparticle bonding between the clays. On the other hand, forest soils were considered to have acquired a physical stability against the dispersion of fine particles as free Al oxides had been accumulated in the process of natural weathering. It was concluded that charge characteristics primarily determined the dispersion and flocculation behavior of soils and that Al hydroxides were important modifiers of charge characteristics of soils. |
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| Keywords: | Al hydroxides charge characteristics dispersion ratio reclaimed area weathering |
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