Question

Explain the permutit method for softening hard water.

Answer 1

Permutit is an artificial zeolite. Chemically, it is hydrated sodium aluminium orthosilicate with the formula Na₂Al₂Si₂O₈.XH₂O. For the sake of convenience, let us give it the formula Na₂P.

A tall cylinder is loosely filled with lumps of permutit. When hard water containing calcium and magnesium ions percolates through these lumps, ions exchange. Sodium permutit is slowly changed into calcium and magnesium permutit, and the water becomes soft with the removal of calcium and magnesium ions.

When no longer active, permutit is regenerated by running a concentrated solution of brine over it and removing calcium chloride formed by repeated washing.

\[\ce{CaP + 2NaCl -> Na2P + CaCl2}\]