Question

Q.

A) Write an ion exchange reaction that shows how zinc is retained by an anion exchange resin

B) Explain why nickel ions are not retained by the same anion exchange resin

C) What flow rate is specified for solutions passing through the ion exchange column, in terms of mL/min and in drops/sec?

Answer 1

A) and B)

Ion exchange resins are insoluble substances containing loosely bound ions which are able to be exchanged with other ions in solution. Ion exchange resins are insoluble acids or bases which have salts which are also insoluble, and this enables them to exchange either positively charged ions (cation exchange) or negatively charged ones (anion exchange).

The affinity of sulphonic acid resins for cations varies with the ionic size and charge of the cation. Generally the affinity is greatest for large ions with high valency.

Suppose a resin has greater affinity for ion C than for ion D. If the resin contains ion D and ion C is dissolved in the water passing through it, then the following exchange takes place, the reaction proceeding to the right (R represents the resin):

DR + C^n± = CR + D^n±

For the queston above the C is Zn²⁺ .THe Ni ion has the greater affinity for the sulphonic acid resin than Zn²⁺ due to the large size of Ni relative to Zn cation.

C) Resins can operate over a range of flow rates, but the design of ion exchange columns is often very basic and in many cases cannot accommodate very low flow rates. Poor distribution / collection is encountered at low flow rates leading to channelling and very poor performance of the resin.