土壌溶液のアルミニウム種の形態に及ぼすpHとアルミニウム濃度の影響

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We aim to make clear the formation condition of aluminum (Al) species in relation to the pH and Al concentration in soil solution. Al species and their concentrations were calculated by applying the method of successive approximation reported by Adams (1971). In the present paper, as for the mass balance of Al species, the following four kinds of polynuclear Al species were programmed in addition to the mononuclear Al species: Alt'= [Al^<3+>] + [AlOH^<2+>] + [AI(OH)_2^+] + [Al(OH)_3^0] + [AlSo_4^+] + [AlH_2PO_4^<2+>] + [AlHPO_4^+] + 2 [Al_2(OH)_2^<4+>] + 3[Al_3(OH)_4^<5+>] + 6[Al_6(OH)_<15>^<3+>] + 13 [Al_<13>O_4(OH)_<24>^<7+>] The following results were obtained. 1 ) The Al^<3+> value exceeds about 60% of the Alt' value (total inorganic Al) when the pH value is lower than 4.5 and the pAlt' value is lower than 4. The ratio of Al^<3+> value to Alt' value decreased rapidly with increasing pH value and decreased gradually with decreasing the pAlt' value. The ratio of the concentration of Al(OH)_2^+ to that of Alt' becomes greater than 40% when the pH and pAlt' values are about 5, respectively. This suggests that AI(OH)_2^+ becomes the dominant species when the Alt' value is smaller than 10^<-5> mol L^<-1>. Based on this program, it is estimated that Al(OH)_3^0 becomes the dominant species when the pH value is higher than 6 (slight acidity) and the pAlt' value is lower than 10^<-5> mol L^<-1>. 2 ) The polynuclear species such as Al_2(OH)_2^<4+> and Al_3(OH)_4^<5+> are very low in concentration, and hence can be ignored in soil solution, whereas Al_6(OH)_<15>^<3+> becomes the dominant Al species if the value of the soil solution pH is around 4.5 or higher and the pAlt' value is lower than about 5. If the mass balance equation is based on the assumption that Al_6(OH)_<15>^<3+> and Al_<13>O_4(OH)_<24>^<7+> coexist at equilibrium, the Al_<13>O_4(OH)_<24>^<7+> calculated is very low in concentration, and hence can be ignored in soil solution.
社団法人日本土壌肥料学会の論文
1999-06-05

土壌溶液のアルミニウム種の形態に及ぼすpHとアルミニウム濃度の影響

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