- Cadmium nitrate is an inorganic salt with the molecular formula Cd(NO₃)₂, most commonly encountered in its tetrahydrate form Cd(NO₃)₂·4H₂O.
- In anhydrous form, it has a molar mass of 236.43 g/mol, while the tetrahydrate has a molar mass of 308.48 g/mol.
- The compound consists of divalent cadmium cations (Cd²⁺) coordinated by nitrate anions (NO₃⁻) in an ionic lattice. Each nitrate group contains one nitrogen atom covalently bonded to three oxygen atoms in a trigonal planar arrangement, with a net negative charge balanced by the cadmium ion.
- Cadmium nitrate typically appears as colorless, transparent crystals that are highly deliquescent. The tetrahydrate crystallizes in the monoclinic crystal system, with cadmium ions octahedrally coordinated by oxygen atoms from nitrate groups and water molecules. It is highly soluble in water, producing a slightly acidic solution due to partial hydrolysis. Solubility in ethanol and other polar organic solvents is also significant, though less than in water. The melting point of the tetrahydrate is around 59 °C, at which dehydration begins, eventually leading to decomposition before reaching a clear liquid phase.
- Industrial and laboratory production of cadmium nitrate is typically achieved by the reaction of cadmium metal, cadmium oxide, or cadmium carbonate with nitric acid:
- CdO + 2 HNO₃ → Cd(NO₃)₂ + H₂O
- Cd + 4 HNO₃ → Cd(NO₃)₂ + 2 NO₂ + 2 H₂O
- CdCO₃ + 2 HNO₃ → Cd(NO₃)₂ + CO₂ + H₂O
- Purification is usually accomplished by controlled crystallization from aqueous solution, followed by drying under reduced pressure to yield the desired hydrate form.
- As an oxidizing salt, cadmium nitrate can accelerate the combustion of combustible materials. Upon heating to about 150 °C, it begins to decompose, releasing nitrogen dioxide (NO₂), oxygen, and cadmium oxide (CdO):
- 2 Cd(NO₃)₂ → 2 CdO + 4 NO₂ + O₂
- This decomposition makes it a source of both cadmium oxide and nitrogen oxides in thermal processes. In aqueous solutions, cadmium nitrate dissociates completely into hydrated cadmium cations and nitrate anions, and the nitrate ion does not undergo hydrolysis, but the cadmium ion can hydrolyze slightly in neutral to basic solutions.
- Cadmium nitrate is used as a precursor in the synthesis of cadmium sulfide (CdS), a bright yellow semiconductor material used in pigments, photovoltaic cells, and photocatalysts. It is also employed in the ceramics and glass industry to impart specific optical properties and to manufacture specialty glasses. In some chemical processes, cadmium nitrate solutions act as catalysts or as nitrating agents for organic substrates. Additionally, it is sometimes used in electroplating baths and in the preparation of cadmium-containing coatings, though these applications are declining due to environmental and health concerns.
- Cadmium nitrate is classified as highly toxic and carcinogenic. Acute exposure can lead to severe irritation of the respiratory tract, nausea, vomiting, diarrhea, and in severe cases, pulmonary edema or kidney failure. Chronic exposure to cadmium compounds is associated with kidney damage, bone demineralization (osteomalacia, osteoporosis), and an increased risk of lung and prostate cancers. Absorption can occur via inhalation of dusts or aerosols, ingestion, or through skin contact with solutions. Because cadmium accumulates in the body with a biological half-life of decades, even low-level exposure over time is dangerous.
- Cadmium nitrate is highly toxic to aquatic life, with long-lasting effects. Its release into soil and water can lead to bioaccumulation in plants, fish, and other organisms, potentially entering the food chain. Many countries classify it as a hazardous substance subject to strict storage, transport, and disposal regulations. Waste containing cadmium nitrate must be collected for hazardous waste treatment and never released into municipal sewage systems. Handling requires personal protective equipment (PPE) including gloves, goggles, and fume hoods, and any spills should be neutralized and absorbed with appropriate materials.
- Internationally, cadmium nitrate is classified under the UN number UN 1477 (Nitrates, inorganic, n.o.s., oxidizing solid) for transport purposes, and it is assigned to hazard class 5.1 (oxidizer) with additional toxicity warnings. It is included in many hazardous substance lists such as the European REACH Regulation and the U.S. EPA’s list of toxic pollutants. Occupational exposure limits are very low—often less than 0.01 mg/m³ for cadmium dusts and compounds.
