NaCN — Sodium Cyanide

Sodium cyanide (NaCN) is an inorganic salt composed of sodium (Na⁺) and cyanide (CN⁻) ions. It is a highly toxic, colorless, and water-soluble crystalline compound known for its potent chemical reactivity and industrial importance. Sodium cyanide is primarily used in the extraction of precious metals like gold and silver, as well as in electroplating, chemical synthesis, and metallurgy.

The compound is infamous for its toxicity, as it readily releases hydrogen cyanide (HCN) when exposed to acids or moisture. Despite its hazardous nature, sodium cyanide plays a crucial role in many industrial applications, particularly in hydrometallurgy, where it helps dissolve and recover metals from their ores.

Its production and use are tightly regulated worldwide due to environmental and safety concerns, but it remains indispensable in several chemical and manufacturing processes.

Sodium cyanide is composed of one sodium cation (Na⁺) and one cyanide anion (CN⁻). The cyanide ion itself is a diatomic species with a triple bond between the carbon and nitrogen atoms:

The C≡N bond consists of one sigma (σ) bond and two pi (π) bonds, making it very strong and short. The carbon atom bears a partial negative charge, while nitrogen carries a slight positive charge, contributing to the polarity of the cyanide ion.

In the solid state, sodium cyanide forms a face-centered cubic lattice similar to sodium chloride (NaCl), with alternating Na⁺ and CN⁻ ions. The compound is ionic in nature and highly soluble in polar solvents like water, where it dissociates completely into its constituent ions.

When dissolved in water, sodium cyanide undergoes hydrolysis to form small amounts of hydrogen cyanide and sodium hydroxide, making the solution strongly basic:

Sodium cyanide can be produced through several industrial and laboratory methods. The most common commercial process is the Castner process or the hydrogen cyanide neutralization method. The major preparation routes include:

• 1. Reaction of Hydrogen Cyanide with Sodium Hydroxide:

  \( HCN + NaOH \rightarrow NaCN + H_2O \)

  This is the most straightforward laboratory method. It must be conducted under controlled, dry conditions to avoid toxic HCN vapors.

• 2. Castner Process (Industrial Method):

  \( Na_2CO_3 + C + N_2 \xrightarrow{1000°C} 2NaCN + CO_2 \)

  This high-temperature process involves heating sodium carbonate, carbon, and nitrogen gas to produce sodium cyanide.

• 3. By Ammonia and Carbon Reaction (Old Method):

  \( 2NH_3 + 3C + Na_2CO_3 \rightarrow 2NaCN + 3H_2 + CO_2 \)

Modern production methods are optimized for higher yields and reduced toxic emissions, with HCN often generated in situ and immediately neutralized with sodium hydroxide.

Physical Properties:

• White, crystalline solid that is odorless when pure, but may emit a faint almond smell due to trace hydrogen cyanide release.
• Highly soluble in water, forming strongly basic solutions.
• Hygroscopic in nature, absorbing moisture from the air.
• Nonvolatile under dry conditions but releases toxic vapors when heated or moistened.

Chemical Properties:

• Basic Nature: Dissolves in water to form sodium hydroxide and hydrogen cyanide.
• Reaction with Acids: When treated with acids, sodium cyanide liberates hydrogen cyanide gas, which is extremely poisonous:

\( NaCN + HCl \rightarrow HCN + NaCl \)

• Reaction with Metals: Forms metal cyanide complexes used in electroplating:

\( NaCN + Au \rightarrow Na[Au(CN)_2] \)

• Decomposition: At high temperatures, it decomposes into sodium and cyanogen gas.
• Oxidation: When exposed to air and moisture, NaCN slowly oxidizes to sodium cyanate (NaOCN).

Due to its reactivity, sodium cyanide is a vital reagent in metallurgy and organic synthesis but must be handled with utmost care.

Sodium cyanide has a broad range of industrial and chemical applications:

• 1. Gold and Silver Extraction: The most significant use of NaCN is in the cyanidation process for extracting gold and silver from ores. The metal reacts with cyanide ions to form soluble complexes:

\( 4Au + 8NaCN + O_2 + 2H_2O \rightarrow 4Na[Au(CN)_2] + 4NaOH \)

• 2. Electroplating: Used to coat metals like gold, silver, and copper by forming stable metal-cyanide complexes.
• 3. Organic Synthesis: Serves as a cyanide source in the synthesis of nitriles, pharmaceuticals, and intermediates such as adiponitrile (used in nylon production).
• 4. Chemical Manufacturing: Utilized in producing chelating agents, pigments, and dyes.
• 5. Laboratory Applications: Acts as a reagent for preparing other cyanide compounds and metal salts.

Its versatility makes it a cornerstone of metallurgical and chemical industries, but strict safety protocols are essential during handling.

Sodium cyanide is extremely toxic and can be fatal even in small doses. The toxicity arises from the release of hydrogen cyanide gas, which inhibits the cytochrome oxidase enzyme in mitochondria, preventing cellular oxygen utilization and leading to asphyxiation.

Symptoms of poisoning include dizziness, rapid breathing, nausea, confusion, and loss of consciousness. Immediate medical treatment with antidotes such as amyl nitrite, sodium thiosulfate, or hydroxocobalamin is required in case of exposure.

Safety Measures:

• Handle only in well-ventilated areas or fume hoods.
• Store in airtight, moisture-proof containers to prevent HCN formation.
• Avoid contact with acids and heat sources.
• Use protective gear like gloves, goggles, and respirators.
• Dispose of waste cyanide through alkaline chlorination or hydrogen peroxide oxidation methods.

Due to its hazards, sodium cyanide is strictly controlled under international chemical safety laws, including REACH and OSHA guidelines.