Which method is not practical for the removal of cadmium from water?

Reverse osmosis is often deemed less practical for the removal of cadmium from water due to certain limitations in its application compared to the other methods listed. While reverse osmosis is effective in reducing many dissolved substances, including heavy metals like cadmium, it typically requires high pressures and can be subject to membrane fouling, which reduces efficiency and increases operational costs.

In contrast, methods such as filtration, activated carbon, and ion exchange can effectively target the removal of cadmium with different mechanisms that can be more straightforward to implement in certain scenarios. For instance, ion exchange specifically involves exchanging cadmium ions with less harmful ions on a resin, making it particularly effective for heavy metal removal. Activated carbon can adsorb various contaminants and is suitable for removal processes where organics and certain metals are concerned.

While reverse osmosis has its merits in water purification, the operational challenges and costs associated with it may render it less practical as a standalone solution for cadmium removal in some cases, particularly at lower concentrations or in larger treatment volumes.