%0 Journal Article %T Binary K-Ca exchange on a clay separated from a soil with dominate illite (mica) mineralogy: 1- Effect of depletion-collapse of illite (mica) on the K-Ca selectivity %J Iranian Journal of Soil and Water Research %I University of Tehran %Z 2008-479X %A Towfighi, Hassan %A Khalilirad, Maryam %D 2017 %\ 04/21/2017 %V 48 %N 1 %P 149-163 %! Binary K-Ca exchange on a clay separated from a soil with dominate illite (mica) mineralogy: 1- Effect of depletion-collapse of illite (mica) on the K-Ca selectivity %K K-Ca exchange %K K-depleted illite %K Ionic strength %K NaTPhB %K Selectivity %R 10.22059/ijswr.2017.61349 %X Effects of K-depletion on K-Ca exchange equilibiria were studied in a clay separated from a soil with dominant illite (mica) mineralogy. Treatment of clay with NaTPhB+NaCl for periods of 6, 25 and 150 hours resulted in release of 22.1, 30.8 and 40.7% of total K, respectively. K release was much faster at first and then gradually decreased with the time. Cation exchange capacity (CEC) of the clay increased with K-depletion, indicating that at least some of the K was released from the interlayers of the clay. Mineral weathering contributed significantly to the total extracted Ca. Thus, exchangeable Ca values overestimated by 31.2 to 76.7% when weathering was neglected. Anion adsorption was found to be more than negative adsorption. Comparison of exchange isotherms of K-Ca with non-preference isotherm indicated that K was preferred over calcium up to ẼK≤0.8 in non-depleted clay and up to ẼK≤0.76 in depleted clays. Slight preference of Ca over K was observed on ẼK>0.8. Comparison of K-depleted clay’s exchange isotherms demonstrated that selectivities of exchangers were not affected by K-depletion. A study of XRD patterns of the K-depleted clays after treatment of the clay with a solution having 0.05 equivalent fraction of potassium showed that during the K-Ca exchange, layers were collapsed, but CEC values of these clays indicated that the layer collapse of the clays were not complete. Apparent K preference was increased with ionic strength, and with dilution of equilibrium solution, more Ca was absorbed. The difference between the two exchange isotherms at the two different ionic strengths was a result of valence-dilution effect. %U https://ijswr.ut.ac.ir/article_61349_2b46f7c089deff9844c1ac2eb3b831f2.pdf