- Cadmium hydroxide (Cd(OH)₂) is an inorganic compound composed of cadmium and hydroxide ions, belonging to the family of cadmium(II) compounds.
- In its pure form, it appears as a white, odorless, crystalline or amorphous solid. Cd(OH)₂ is sparingly soluble in water, and its solubility decreases further in alkaline solutions due to the common ion effect.
- It dissolves readily in acids, forming cadmium salts, and in strong bases, producing cadmates such as [Cd(OH)₄]²⁻. The compound’s low solubility and amphoteric nature make it chemically versatile, while also influencing its behavior in environmental and industrial contexts.
- Cadmium hydroxide can be prepared by adding a hydroxide source, such as sodium hydroxide or potassium hydroxide, to an aqueous solution of a soluble cadmium salt (e.g., cadmium nitrate, cadmium sulfate, or cadmium chloride). This precipitation method yields Cd(OH)₂ as a gelatinous or crystalline product, which can then be filtered and dried. Another preparation method involves electrolysis of cadmium solutions, where cadmium hydroxide forms at the cathode. Upon heating, Cd(OH)₂ readily decomposes to cadmium oxide (CdO) and water vapor.
- In industrial and technological applications, cadmium hydroxide is most notably used as an active material in the positive electrodes of nickel–cadmium (Ni–Cd) rechargeable batteries. In these cells, Cd(OH)₂ participates in the reversible redox reaction between cadmium metal and cadmium hydroxide during charge and discharge cycles. It is also used as a precursor for the synthesis of other cadmium compounds, including cadmium salts, pigments, and semiconductors. Due to its relatively stable and non-volatile nature, it serves as a convenient intermediate for cadmium chemistry in both laboratory and manufacturing processes.
- Although less acutely hazardous than some soluble cadmium salts, cadmium hydroxide remains toxic and must be handled with care. Cadmium is a heavy metal that bioaccumulates in living organisms, causing long-term health issues such as kidney damage, bone demineralization, and cancer. Inhalation of Cd(OH)₂ dust or prolonged skin contact can be harmful, and ingestion poses serious systemic risks. Handling should always be conducted with appropriate safety measures, including gloves, eye protection, and ventilation or fume hoods.
- Environmental concerns regarding cadmium hydroxide are significant. If improperly disposed of, Cd(OH)₂ can enter water systems, where it may transform into more soluble cadmium species under acidic conditions, increasing its mobility and bioavailability. Cadmium contamination can persist for decades, impacting aquatic life and entering the human food chain through bioaccumulation in fish and crops. As a result, cadmium hydroxide waste is regulated as hazardous material, and its disposal must follow strict environmental protection protocols.
