EXCHANGE OF ALKALINE-EARTH CATIONS IN SOIL ORGANIC-MATTER

We conducted batch equilibration ion exchange experiments to determine selectivity of peat for various alkaline earth ions with calcium as the resident cation. Two levels of Ca-neutralized peat (100 and 33%) were prepared from acid-washed samples (CEC=2.72 mol(+) kg-1) by equilibration with equivalent amounts of CO2-free satureated Ca(OH)2. The pH and concentrations of Ca2+ and the exchanging ion were determined at the end of each equilibration period. Both the 100 and 33% Ca-neutralized peat showed the preferential sequence Mg<Sr<Ca<Ba. Considering the Eisenman model, we suggest that this exchange behavior is due to the widely separated fixed carboxylate sites. The formation of (RCOO Me)+ ion pairs is thus suggested to predominate in such systems.