Application of Noncrystalline Aluminosilicates and its Effect for Soil Amelioration

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Flocculation experiments for a smectitic soil clay showed that synthetic imogolite・allophane is superior as a flocculating agent to that separated from a Kuroboku-do B horizon. Noncrystalline Hydroxy-Aluminosilicate Polymer (HASP), allophane and imogolite with Si/Al molar ratio *0.5 were then synthesized and tested for flocculation with smectitic and kaolinitic soil clays in comparison with Hydroxy-Aluminum Polymer (HAP), AlCl_3 and CaSO_4. The flocculating agents containing Al and CaSO_4 were added at the rate of 20 mumol Al and 220 mumol Ca/100 mg clay, and the reacted clay was repeatedly washed with water till dispersion. The flocculating effect evaluated based on the electric conductivity of the equilibrium solution in which the clay started dispersion was the same for the two soil clays and increased in the order CaSO_4<AlCl_3<HASP, HASP<imogolite. Allophane showed no flocculating effect. Based on the differences in the content of exchangeable cations (Ca, Mg, K, Na) between the untreated and treated clays, it was estimated that parts of cation-exchange sites of the soil clays, i. e. about 20 and 10 % in the smectitic clay and 50 and 30 % in the kaolinitic clay, reacted with the positive charge carried by HAP and imogolite, respectively. No difference was found between imogolite and allophane in this respect. The followings were concluded : 1) Unlike monomer Al^<3+> and Ca^<2+>, polymer cations HAP, HASP and imogolite can flocculate smectitic and kaolinitic clays even in the solution with a very low electrolyte concentration (<10^<-3> M as NaCl), 2) the size and shape of the polymer cation as well as its positive charge play an important role in this flocculation, and 3) because the amount of the polymer required to flocculate the clay was about 1-2 % of the clay weight, the polymer cations can be used for amelioration of heavy clayey soils.