Which reagent can be used to facilitate the removal of complexed metals in wastewater treatment?

The correct reagent for facilitating the removal of complexed metals in wastewater treatment is sodium sulfide. This compound is particularly effective because it reacts with various metal ions, forming insoluble metal sulfides. The formation of these insoluble precipitates allows for the easy removal of metals such as cadmium, lead, and mercury from the wastewater. By precipitating these metals out of solution, sodium sulfide effectively reduces the concentration of toxic metals, making the wastewater safer for discharge or further treatment processes.

In contrast, sodium bicarbonate primarily serves as a buffering agent and does not have the same capacity for metal complexation or precipitation. Calcium chloride can contribute to the treatment process by providing calcium ions, but it does not specifically target metal ions for removal. Barium sulfate is used in certain applications, but it is not suitable for the general removal of complexed metals in wastewater due to its specific reactivity and limitations in forming precipitates with a wide range of metals.