Water purification is a necessary process for the water used in pharmaceutical manufacturing because it contains a lot of suspended material as well as in the form of ions. Turbidity and suspended solids can be removed by activated carbon filter but ions cannot be removed by ACF. This form of ions is called hardness of water. Hardness is denoted by Calcium and Magnesium ions. The process to remove this hardness is called softening and water is known as soft water.
Some resins are required to remove this hardness. Generally ion exchange resins are used for the process. These ions of hardness are taken by the resin. The resins are charged by chemicals to release this hardness.
Ion exchange resins are white to yellow colored synthetic polymers beads of small size ranging from 0.5-1.0 mm having the pores on their surface to trap and release the ions easily. Important – Resins are solids but measured in liter.
Two types of ion exchange resins are used in water systems - cation-exchange resins which release the hydrogen ions in water while trapping the ions from water and anion-exchange resins those release OH ions in exchange of hardness ions. Thus sodium ions are released in water and calcium and magnesium ions are attached with the resins. So the resins are required to regenerate before use again.
Anion is the negatively charged ion and anion exchanger is regenerated by 10-15% NaOH solution and water released from anion bed has pH between 7.5 and 9.5. Cation is positively charged ion and anion bed is regenerated by 8-12 % hydrochloric acid solution and pH of water released from the anion bed remains between 2 and 3.
By the process of regeneration sodium ions are attached again with the surface of ion exchange resin to get replaced by the calcium and magnesium ions of hard water.
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