Effect of aluminum treatments on permeability and cation status of a smectitic clay.
Wada K. | Beppu Y.
Aluminum sulfate or Al2(S04)3 and CaCO3 mixtures were added to a smectitic clay in which Al3+, Al(OH)2+, Al(OH)+2, and Al(OH)3 formed when wetted with water. The treatment increased the permeability of the soil leached with distilled water. The permeability increased in the order of Al(OH)3 less than Al(OH)+2, Al(OH)2+ less than Al3+ and with the amount of Al, but its relative increase decreased with increasing addition of Al. The treatment with a relatively small amount of Al3+ (e.g., 5 cmol Al kg-1) was recommended to this soil having cation exchange capacity of 29 cmol kg-1 for its efficiency in increasing the permeability and permissible decrease of exchangeable Ca, Mg, and K. The acidity and exchangeable cation status as well as cation exchange capacity should, however, be considered in the choice of the treatment for a soil. There was a correlation between the permeability and the amount of Al retained by the soil. The contribution of exchangeable Al (monomeric Al3+) to the permeability was much higher than that of nonexchangable Al (polymeric hydroxy-Al cations) when evaluated in terms of molar quantities, indicating the importance of electric charge on an Al atom and the location of these Al cations on the bonding between clay particles.
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