Mono-divalent and mono- trivalent exchange:

The apparent selectivity coefficient for the exchange of a divalent ion with a monovalent ion is K^A2+_B+(C^r/C) and for the exchange of a trivalent ion with a monovalent ion it is K^A3+_B+(C^r/C)². This means the concentration term of the exchanging ion figures. In the first case, it is inversely related to the concentration in solution and in the second case, it is inversely related to the square of the total concentration. This implies that for such types of exchange to take place, the solutions of the exchanging ions should be very dilute.