Which method is not practical for the removal of cadmium?

The most appropriate method for the removal of cadmium that is considered impractical in this context is reverse osmosis. While reverse osmosis is generally effective for removing a wide range of dissolved contaminants from water, including some heavy metals, it may not be the best choice for cadmium specifically due to operational challenges such as fouling of the membranes and the cost associated with system maintenance and energy requirements. The effectiveness can also be influenced by the concentration and presence of other impurities.

In comparison, methods like ion exchange and lime softening can selectively target cadmium ions and remove them from water more effectively. Ion exchange utilizes resins that can bind to metal ions, including cadmium, effectively lowering its concentration in water. Lime softening works by increasing pH to precipitate cadmium as insoluble compounds.

Iron coagulation also serves as a practical method where iron ions can bind with cadmium, forming a floc that can be removed from the water. Each of these options demonstrates a practical approach to addressing cadmium contamination, which is why reverse osmosis is seen as less practical compared to the other methods listed.