Arrange the following steps in the correct chronological order to illustrate how water har… — JAMB UTME

Arrange the following steps in the correct chronological order to illustrate how water hardness is removed using the zeolite (permutit) ion-exchange method and how the column is subsequently regenerated.

1Hard water containing dissolved calcium ions ( $\text{Ca}^{2+}$ ) and magnesium ions ( $\text{Mg}^{2+}$ ) is passed into the zeolite column.
2The $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions displace sodium ions ( $\text{Na}^+$ ) from the sodium aluminum silicate matrix.
3Softened water containing soluble, non-hardness-causing sodium salts is collected at the outlet.
4A concentrated sodium chloride solution (brine) is passed through the exhausted column to replace captured $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions with $\text{Na}^+$ ions.

Answer

The correct sequence for removing water hardness and regenerating the ion-exchange bed is: first, passing hard water into the column; second, exchanging calcium and magnesium ions for sodium ions; third, collecting the softened water; and fourth, regenerating the exhausted column with concentrated brine.

Hard water softening via the permutit process begins by feeding water containing hardness-causing cations (

\text{Ca}^{2+}

\text{Mg}^{2+}

) into the zeolite column. As the water percolates, an ion exchange occurs where

\text{Ca}^{2+}

and

\text{Mg}^{2+}

bind to the matrix while

\text{Na}^+

is released. The softened water free of calcium and magnesium is then collected. Finally, once the column becomes exhausted, a concentrated brine solution (

\text{NaCl}

) is flushed through to regenerate the zeolite bed for repeated use.

Step-by-Step Solution

Introduce hard water containing calcium and magnesium ions into the column.

Untreated water makes contact with the active sodium zeolite matrix.

Ion exchange requires direct contact between the dissolved divalent metal ions and the exchanger bed.

Execute the cation exchange reaction.

Calcium and magnesium ions bind to the zeolite structure, releasing sodium ions into solution.

Sodium zeolite (

\text{Na}_2\text{Z}

) trades its

\text{Na}^+

ions for

\text{Ca}^{2+}

\text{Mg}^{2+}

due to structural affinity.

Collect the effluent water.

Water free of

\text{Ca}^{2+}

and

\text{Mg}^{2+}

ions is obtained.

Sodium salts left in solution do not react with soap to form scum or cause scale build-up.

Regenerate the exhausted exchanger with concentrated sodium chloride (brine).

The column is converted back to active sodium zeolite (

\text{Na}_2\text{Z}

High concentration of

\text{Na}^+

ions forces the reverse reaction, removing bound

\text{Ca}^{2+}

and

\text{Mg}^{2+}

ions.

Key Concept

Ion-Exchange Softening and Permutit Regeneration

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