Ion Exchange Water Treatment Studies
Membrane Works now offer extensive Ion-exchange (IX) resin testing services in our Sydney laboratory.
What is an ion exchange study?
In our treatment studies, we generally focus on testing a number of different resins and conditions to validate and optimise the treatment process. There are two main ways of doing this:
- Equilibrium isotherms are designed to test the resin’s capacity and are a good way of quickly selecting and optimising treatment conditions such as resin type, pH, flow-rate, water blends etc
- Column tests are designed to mimic the scaled-up plant and are more focused on the kinetics of the water treatment system
There are also a wide range of computer modelling softwares that provide very good design and performance prediction for normal water treatment plants. However, for systems that have complex waters with competing ions or trace removal requirements, there is no substitute for laboratory work.
So, let’s have a look in a bit more detail.
Equilibrium adsorption isotherms
Equilibrium Adsorption Isotherms…what a mouthful!
These types of experiments focus on the removal capacity of the resin by discounting kinetic factors. This is tested in experiments where the adsorption is allowed to come to equilibrium, and by changing the water to resin ratio from low (where the resin will be out of capacity) to high (where the resin is under saturated). The result gives a measure of the total capacity, as well as the strength of the adsorption. This simplifies the analysis by taking kinetic (reaction rate) factors out of the calculation and focusing only on capacity. Adsorption isotherms are generally a good way of screening resins and conditions such as pH, temperature, ionic strength and solution concentration.
Figure 1: Equilibrium isotherm plots showing favourable and unfavourable adsorption profiles.
Ion Exchange Resin Column tests
Column tests are performed to both assess the real-world application as well as part of an optimization process. We focus optimising conditions to maximise the time until breakthough (and thus the operating capacity), as well as minimise the Mass Transfer Zone (MTZ). Minimizing the MTZ means that the resin is removing as many of the ions as possible before the water passes further down the bed. If the flow rate is too high then you will see bleed though the bed as the resin isnt able to adsorb the ions fast enough. If the flow-rate is too low, then the ion exchange resin is effectively being under-utilized. This shows that the resin is maximizing its adsorption until it reaches capacity and allows minimal bleed through. A theoretical breakthrough curve is shown below.
Figure 2: Theoretical breakthrough curve
Laboratory scale trials are generally carried out with a 12.5 mm diameter glass column with a sintered glass bottom.
|Column aspect ratio
|Resin loading (g/L of resin)
|From the equilibrium testing
|Service flow rate
Laboratory regeneration studies are usually conducted to improve an existing cleaning program when it’s found that a resin isn’t regenerating properly. This is frequently due to the precipitation of fouling material that requires a more specialised cleaning program to bring it back into optimal performance.
Appropriate regeneration chemicals, their concentration and quantities are generally adopted from the manufacturer’s recommendation or from the available literature. However, there are occasions where more novel cleaning programs may be required.
Who should be doing column testing?
In general, water treatment testing is suited to more complex systems such as mining applications, trace contaminant removal, high fouling environments, PFAS removal, and similar systems.
Benefits to lab testing
The benefit to lab testing incudes:
- Increased design confidence by validating performance
- Save money and optimise performance by comparing resins across multiple manufacturers
- Improve system performance by optimising water treatment before implementing in the plant
- Decrease system down-time by stress testing different operational conditions