The long-term alteration rate of Na-smectite in natural bentonite formation

Alteration of the natural bentonite in Kuroishi ore deposit located in the north Japan was estimated by the vertical element profiles of Na, Ca and Mg in the drilled core samples. Th exchangeable Na depleted from the ground s urface to 20 m in depth and the total loss of Na coincided with the accumul ation of Ca and Mg. This suggests the Na depletion was caused by the ion ex change reactions. A simple analytical calculation using the steady state ap proximation indicated the average alteration rate was about 1 cm/1000 years . This value is equivalent to that by geomorphological studies. (C) 1998 El sevier Science B.V. All rights reserved.