Problem 107 - Chemistry: An Atoms-Focused Approach

Question

Explain how a mixture of anion and cation exchangers can be used to deionize water.

Step-by-Step Solution

Answer

Answer: Deionization using a mixture of anion and cation exchangers works by simultaneously removing both anions and cations from the water. Anion exchangers bind to negatively charged anions, while cation exchangers bind to positively charged cations. As the water flows through a mixed bed ion exchange column, it becomes deionized, with the removed ions being collected by the exchangers. After a period of use, the exchangers are regenerated by washing with a concentrated solution of the ions they exchange, allowing them to be used again for deionization.

Step 1: Understand ion exchange

Ion exchange is a process where ions are exchanged between a solid, the ion exchanger (resin), and an aqueous solution (water), resulting in the removal of unwanted ions from the solution. Ion exchangers consist of a porous medium, such as resin beads, with fixed charged groups that attract and bind to oppositely charged ions. Anion exchangers have positively charged functional groups, which attract and bind anions (negatively charged ions), while cation exchangers have negatively charged functional groups, which attract and bind cations (positively charged ions).

Step 2: Anion and cation exchangers work together for deionization

In a deionization process, anion and cation exchangers are mixed together to remove both anions and cations from the water. The anion and cation exchangers work simultaneously, with the anion exchanger binding to the negatively charged anions in the water and the cation exchanger binding to the positively charged cations. As a result, the water becomes deionized, meaning it contains no dissolved ions.

Step 3: Regeneration of the ion exchangers

Over time, the ion exchangers will become saturated with the anions and cations they remove from the water. They will need to be regenerated by washing with a concentrated solution of the ions they exchange. For example, to regenerate an anion exchanger, a solution with high concentrations of hydroxide ions (OH-) can be used. Similarly, for a cation exchanger, a solution with high concentrations of hydrogen ions (H+) can be used. The ions in these solutions displace the bound anions and cations from the exchangers, allowing them to be used again for deionization.

Step 4: Deionization using mixed bed ion exchange columns

A practical and highly efficient way to achieve deionization is by using mixed bed ion exchange columns. These columns contain a homogeneous mixture of both anion and cation exchange resins. As water flows through the column, the anions and cations in the water bind to their respective exchangers. The deionized water then passes through the column and is collected for use. These mixed bed ion exchange columns can be regenerated in the same way as described in step 3. In conclusion, deionization of water can be achieved using a mixture of anion and cation exchangers that work together to remove both anions and cations from the water. This process is effective and can be carried out in practical settings, such as mixed bed ion exchange columns, to achieve deionized water for various applications.