Methods of ion exchange and their applications in water treatment

What is Ion Exchange Method?

The ion exchange method is the process of removing unwanted ions from a solution and replacing them with other ions. It is operated to remove salts, nitrates, color, soften water, and eliminate heavy metals. This method is crucial to help the subsequent wastewater treatment process run more efficiently.

The ion exchange process can be understood as separating unwanted ions from water and replacing them with other ions. This process takes place in a specialized device containing an ion exchange column. This is a chemical interaction process between liquid-phase ions and solid-phase ions (ion exchange resin beads).

The ion exchange reactions, also known as displacement reactions, involve solid-phase ions absorbing liquid-phase ions, thereby replacing the ions on the ion exchange resin matrix (the ion exchange resin beads). The substances involved in ion exchange are usually inorganic and organic compounds.

During the process, metals such as Pb, Zn, Cu, Hg, compounds like As, P, CN, radioactive liquid substances, etc., are separated from wastewater to ensure that the treated water meets standards before being discharged into the environment.

Advantages and Disadvantages of Ion Exchange Method

This method is commonly used in wastewater treatment processes.

Advantages

• Environmentally friendly.
• Does not require the use of any chemicals to treat wastewater.
• Provides high-quality treated water that meets standards before discharge into the environment.

Disadvantages

• Relatively high investment and operational costs. Therefore, large-scale projects rarely use this method.
• It can increase the salt concentration in water.

Applications of Ion Exchange Methods

The ion exchange method with its flexible operating mechanism is commonly used for treating water containing metal ions, water softening, and also for recovering citric acid and wash wastewater. Next, we will explore the recovery applications of each type.

Recovery of Citric Acid

The treatment of electroplating wastewater also uses this method because the components in this wastewater contain a lot of chromic acid. This method is used to treat heavy metals.

In electroplating tanks, chromic acid wastewater is passed through a strong cation exchange resin column (RH) to remove heavy metals such as Fe, Cr3+, Al, etc. The wastewater after passing through the cation resin column can be recirculated back to the electroplating tank or a reserve tank.

Since the Chromium content passing through the electroplating tank is relatively high, about 105 - 120kg CrO3/m3, it is advisable to dilute the wastewater containing chromic acid for the exchange process to be effective.

For Wash Wastewater

When implementing this method, the wash wastewater is passed through a strong cation resin column to remove heavy metals present in the water. Subsequently, the treated water source will pass through a strong anion resin column to completely recover demineralized and chromate water.

Next, a solution of Na2CrO4 along with NaOH is used to pass through a cation exchange column to recover H2CrO4 back to the electroplating tank. Finally, the regenerated solution will recover chromic acid with an average concentration of 4 to 6%. The treated solution will be neutralized with alkaline substances. Heavy metals in the solution will precipitate and settle in a settling tank before being discharged.

Especially, impurities in ion state in water can be completely removed. The treated water quality is very good. Therefore, this method is also commonly used for treating and supplying water to boilers.

Ion Exchange Methods

The commonly applied ion exchange methods today:

Using Ion Exchange Resin Columns

Ion exchange resin columns are used to separate ion compounds from a solution. They are widely used in desalination plants, industrial processes, and drinking water. They have been developed over time to improve their operational efficiency by making them more compact and less costly to operate.

An ion exchange column is used to separate ions from a solution containing them. The process using this type of column is quite simple: an ion compound enters the top of the column where it reacts with any cations in the solution.

Ion Exchange with Moving Resin Bed

Ion exchange with a moving resin bed operates continuously and is regenerated continuously.

Ion Exchange with Static Resin Bed

Ion exchange with a stationary resin bed operates intermittently and is regenerated intermittently.

Among these, ion exchange with a static resin bed is the most common.

A material is needed to act as an ion exchange substance and treat when this material comes into contact with water. It uses its own ions to exchange with other ions of the same charge in the water. If the exchange material is in the form of NaR, encountering water containing Ca2+ will result in the following exchange reaction:

2NaR + Ca => CaR2 + 2Na => Ca2+ and Na+

Finally, Ca2+ has been absorbed onto the ion exchange material. This material will release Ca2+ and Na+ into the water. Ca2+ has been removed.

In general, ion exchange methods are crucial in the wastewater treatment process. It helps remove and treat metals in water, providing cleaner water sources. Contact Toan A JSC now via hotline: 0913.543.469 for assistance.