Question

Draw a neat diagram showing the Permutit process of softening hard water and label the following: (a) Zeolite layer (b) Soft water layer.

Answer 1

Hint: Try to identify the Zeolite layer in which zeolite is regenerated by passing a brine solution. The soft water layer will be above this zeolite layer which is free from impurities. Calcium and Magnesium zeolites settle at the bottom.

Complete step by step answer:
We know that in the Permutit process salts which cause hardness of water are replaced by salts of sodium. Zeolites are made of aluminates and silicates which can attract many cations. In the Permutit process, we use sodium zeolites for softening hard water. The formula of sodium zeolite is ${ Na }_{ 2 }{ Al }_{ 2 }{ Si }_{ 3 }{ O }_{ 10 }.2{ H }_{ 2 }O$.
This sodium zeolite reacts with salts of magnesium and calcium and converts them to magnesium and calcium zeolites.
\[{ Na }_{ 2 }Pm\quad +\quad CaSO_{ 4 }\quad \longrightarrow \quad CaPm\quad +\quad Na_{ 2 }SO_{ 4 }\]
\[{ Na }_{ 2 }Pm\quad +\quad Ca\left( HCO_{ 3 } \right) _{ 2 }\quad \longrightarrow \quad CaPm\quad +\quad 2NaHCO_{ 3 }\]
Here Pm stands for Permutit or zeolite. Similar reactions occur with magnesium salts.
After sometime sodium zeolite is completely converted to calcium and magnesium zeolites so reactions stop. Then, we pass a 10% brine solution through these calcium and magnesium salts to regenerate back sodium Permutit. And we can reuse this Permutit in softening hard water.
\[CaPm\quad \left( or\quad MgPm \right) \quad +\quad 2NaCl\quad \longrightarrow \quad Na_{ 2 }Pm\quad +\quad CaCl_{ 2 }\quad \left( or\quad MgCl_{ 2 } \right)\]

The zeolite layer is below the soft water layer.

Note: If there are some transition metal impurities they need to be removed first. In this reaction as there is no precipitate formation, hard water has no obstruction to come into the chamber. It is a fast process and can be easily managed.