Abstract

The K-Ca-Mg exchange selectivity on a synthetic aluminosilicate (Al-Si) was studied through ternary cation exchange equilibria. The effects of equilibrium temperature (4°C and 25°C), the equivalent fraction of K in solution (0-0.6), and sequential coatings of iron oxide and organic matter were considered. In general, the selectivity sequence K>Ca>Mg was observed. There is no temperature effect on exchange selectivity but the Cation Exchange Capacity (CEC) slightly increases when temperature changes from 4°C to 25°C. The iron oxide and organic matter coatings result in a 20 to 30% reduction of CEC and decreases the selectivity of Ca over Mg in relation to that of Al-Si. When the equivalent fraction of K in solution increases, the selectivity of Ca over Mg decreases in both samples (with and without coatings), and the CEC associated with Ca+Mg decreases. With these results, it is concluded that there are K selective exchange sites.