| HS Code | 530559 |
| Productname | Sodium Cyanide |
| Chemicalformula | NaCN |
| Casnumber | 143-33-9 |
| Ecnumber | 205-599-4 |
| Rtecs | VZ7525000 |
| Molarmass | 49.0072 g/mol |
| Appearance | White crystalline powder or granules |
| Odor | Odorless when dry; may emit faint bitter almond odor in moist air or with acids |
| Physicalstate | Solid |
| Meltingpoint | 563.7 °C |
| Boilingpoint | 1496 °C |
| Density | 1.595 g/cm³ at 20 °C |
| Solubilityinwater | 48 g/100 mL at 20 °C |
| Solubilityinothersolvents | Soluble in ammonia, methanol, ethanol |
| Ph | 11.1 (0.1 M aqueous solution) |
| Vaporpressure | Negligible at room temperature |
| Flashpoint | Non-flammable |
| Hazardclass | 6.1 |
| Unnumber | 1689 |
| Packinggroup | I |
| Storage | Store in a cool, dry, well-ventilated area away from acids |
| Toxicity | Extremely toxic if swallowed, inhaled, or absorbed through skin |
| Decomposition | Releases hydrogen cyanide gas when exposed to acids |
| Crystalstructure | Cubic (NaCl-type) |
As an accredited Sodium Cyanide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium cyanide is packaged in UN-approved, airtight 25 kg steel drums, clearly labeled with toxic hazard symbols and safety warnings. |
| Container Loading (20′ FCL) | Sodium Cyanide (UN1689, toxic Class 6.1 PG I) loaded into a 20′ FCL container with secure, compliant stowage and segregation. |
| Shipping | Sodium cyanide is shipped under UN 1689, Class 6.1, Packing Group I, as a highly toxic solid. Use UN-approved sealed packaging, toxic hazard labels, and comply with ADR/IMDG/IATA rules. Segregate from acids, oxidizers, and food; keep dry. Include emergency response information and use trained, authorized carriers. |
| Storage | Sodium cyanide must be stored in a cool, dry, locked, well-ventilated area, separate from acids, oxidizers, moisture, and food. Keep it in tightly sealed, clearly labeled containers with secondary containment. Access should be restricted to trained, authorized personnel. Never store with acids, as contact releases highly toxic hydrogen cyanide gas. Follow local regulations and keep spill-control measures available. |
| Shelf Life | Sodium cyanide is stable with indefinite shelf life if kept dry, sealed, and protected from acids, moisture, and carbon dioxide. |
Within mechanically agitated carbon-in-leach circuits, sodium cyanide is delivered as a 25–30 wt% aqueous stock from a central mixing station through double-walled distribution piping to the first leach tank. The dosing circuit is interlocked with pH and free-cyanide analysers so that the pulp is maintained between 0.010 wt% and 0.050 wt% NaCN equivalent, while hydrated lime slurry holds pH between 10.5 and 11.5. Low-pressure blowers and down-hole spargers keep dissolved oxygen above 6 mg/L because gold dissolution becomes oxygen-limited below that threshold in many oxide ores. Leach tanks are sized for hydraulic residence times of 24–48 h, with specific power input between 0.5 kW/m³ and 2.0 kW/m³ from hydrofoil impellers to maintain solids suspension and oxygen mass transfer.
The Elsner stoichiometry 4Au + 8CN⁻ + O₂ + 2H₂O → 4[Au(CN)₂]⁻ + 4OH⁻ defines a minimum sodium cyanide demand near 0.5 kg per kg Au, but plant consumption commonly exceeds 2.0–10.0 kg/t ore because chalcopyrite, pyrrhotite, and other sulfides consume cyanide via thiocyanate, ferrocyanide, and copper cyanide complexes. Copper-bearing ores are particularly aggressive: the conversion of dissolved copper to Cu(CN)₄³⁻ consumes approximately 4 mol CN⁻ per mol Cu, and free cyanide must be raised correspondingly to hold gold leaching rate constant. Lead nitrate is added at 25–200 g/t of dry ore to passivate sulfur surfaces and reduce cyanide consumption in high-pyrrhotite feeds. Carbon retention in CIL tanks uses vertical stationary screens with 0.6–0.8 mm wedge-wire apertures and mechanically swept guide plates to prevent carbon blinding.
Coconut-shell activated carbon of 6×12 mesh is loaded at 10–25 g/L of pulp, and carbon advance moves countercurrent to pulp flow. Loaded carbon is separated, eluted by the Zadra or AARL process, and electrowon in rectangular cells with stainless-steel anodes and carbon-steel cathodes at 60–80 °C. Cathode smelting produces doré bullion. Analytical control of leach liquor uses silver nitrate titration with rhodanine indicator or automated WAD cyanide analysers. Tailings are detoxified with SO₂/air or Caro’s acid to achieve site-specific WAD cyanide discharge limits, with verification by ASTM D2036-09 or Standard Methods 4500-CN. Operations are managed under the International Cyanide Management Code, which requires cyanide-specific training, emergency response plans, and audit verification of cyanide transport, storage, and effluent treatment.
Electrolyte control on return-type rack machines depends on maintaining the NaCN:Zn weight ratio between 2.0 and 3.0 rather than holding a single sodium cyanide concentration. A typical cyanide zinc bath contains 10–40 g/L NaCN, 7–15 g/L zinc oxide, 75–100 g/L sodium hydroxide, and 15–40 g/L sodium carbonate. The free cyanide component is titrated with silver nitrate using potassium iodide indicator; zinc metal is determined by EDTA titration; carbonate is monitored by acid titration because accumulation above 60 g/L produces rough dark deposits and narrows the bright range. Carbonate concentrations greater than 60 g/L are reduced by cooling the electrolyte to 0–5 °C, then filtering the crystallized carbonate sludge from the working tank.
Operating conditions on a rack line are normally set at 1–4 A/dm² cathode current density and 20–30 °C, with rectifier output adjusted to the total wetted area of the rack. Air agitation at 0.2–0.5 m³/min per metre of tank length is applied to prevent zinc depletion at the cathode boundary layer. Under these conditions, cathode current efficiency ranges from 65% to 85%, with hydrogen evolution accounting for the balance. Excessive current density or low free cyanide shifts the cathode reaction toward hydrogen embrittlement of high-strength steel substrates. The terminal parts are electrodeposited with zinc coatings of 5–25 µm thickness for ferrous fasteners, stampings, and conduit fittings.
Coating thickness and adhesion are verified under ASTM B633-19 or ISO 2081:2018; high-strength parts above 1000 MPa tensile strength require post-plate hydrogen embrittlement relief baking at 190–210 °C for 4–24 h in accordance with ASTM B850. Cyanide-bearing rinsewater is segregated and oxidized by alkaline chlorination or electrochemical oxidation, with final effluent monitoring by ASTM D2036-09. Drag-out tanks and floor sumps are kept alkaline above pH 10 to suppress hydrogen cyanide release before oxidation.
Table 1 summarizes the working envelope for a general-purpose cyanide zinc bath on rack and barrel lines.
| Parameter | Working range | Control method |
| NaCN | 10–40 g/L | AgNO₃ titration with KI indicator |
| Zinc oxide | 7–15 g/L | EDTA titration |
| NaOH | 75–100 g/L | Acid-base titration |
| Na₂CO₃ | 15–40 g/L | Acid titration after BaCl₂ precipitation |
| NaCN:Zn ratio | 2.0–3.0 | Calculated from titrations |
| Cathode current density | 1–4 A/dm² | Rectifier ammeter |
| Temperature | 20–30 °C | Immersion sensor with PID heat exchanger |
Molten salt cyaniding uses a carrier of sodium cyanide, sodium carbonate, and sodium chloride, with sodium cyanide typically maintained at 20–50 wt% of the bath. The salt is melted in a nickel-alloy or mild-steel pot heated by external gas or electric elements to 760–870 °C. Case depth in low-carbon steel such as AISI 1018 is controlled primarily by immersion time, with 15–90 min producing a hardened case of 0.05–0.75 mm. The bath generates active carbon and nitrogen at the steel surface; the cyanate intermediate concentration controls the carbon-to-nitrogen activity ratio and therefore the resulting hardness profile. Sodium cyanide replenishment is based on titration of quenched salt samples, and the bath is periodically corrected with fresh NaCN to maintain the specified operating band.
Temperature uniformity is monitored by multi-thermocouple survey in accordance with AMS 2750E class 2, with control by PID loops on the immersion heater banks. Quenching is normally conducted in agitated oil or water containing a caustic hold to prevent release of hydrogen cyanide from drag-out. Cyanide drag-out from the bath gradually contaminates the quench; continuous filtration and alkaline chlorination of the quench blowdown prevent accumulation of free cyanide. Hardened parts include gears, pawls, cams, and wear plates requiring a surface hardness of 55–62 HRC after quenching and low-temperature tempering.
Case depth is verified by microindentation hardness traverse in accordance with ASTM E384-22, with effective case depth defined as the distance to 550 HV unless otherwise specified by drawing. Cyanide salt bath processing is confined to enclosed, ventilated hoods with wet-packed scrubbers and restricted work zones. Workpiece baskets are preheated to eliminate moisture carryover into the molten salt, which would rapidly generate steam and entrain cyanide aerosol.
In pharmaceutical and agrochemical intermediate reactors, sodium cyanide is metered as a 30 wt% aqueous solution into glass-lined vessels charged with a benzyl halide, water, toluene, and a quaternary ammonium phase-transfer catalyst. The addition rate is controlled to keep the aqueous-phase pH between 9.5 and 11.5 and the temperature at 75–95 °C; the reflux condenser vents to a packed-column caustic scrubber that converts liberated hydrogen cyanide back to sodium cyanide solution. The molar ratio of benzyl chloride to sodium cyanide is held at 1.0:1.05–1.10 to ensure complete conversion while leaving a small residual cyanide inventory that is destroyed before phase separation.
Under these biphasic conditions, benzyl chloride converts to phenylacetonitrile at an organic-phase selectivity above 98%, with dibenzyl ether and benzyl alcohol as minor side products. The organic layer is separated, washed with water, and distilled under vacuum at 10–20 kPa absolute to recover phenylacetonitrile at assay above 99.5%. Residual cyanide in the aqueous phase is oxidized with sodium hypochlorite to cyanate and then to ammonia and carbon dioxide, with discharge monitoring by ASTM D2036-09. Phenylacetonitrile is hydrolyzed to phenylacetic acid or reduced to phenethylamine in subsequent steps; both intermediates enter beta-lactam and fine chemical supply chains.
The process is operated under REACH cyanide handling requirements, and residual solvent limits in the isolated phenylacetonitrile are specified by ICH Q3C. Glass-lined distillation columns with structured packing are commonly selected because residual cyanide species accelerate corrosion at flange surfaces if acidic steam is introduced during cleaning. Batch records include cyanide mass balance reconciliation from dispensing, conversion, phase separation, and waste destruction to satisfy site permitting requirements.
Pulp potential and free cyanide residual jointly determine sphalerite depression in differential lead–zinc flotation. Sodium cyanide is added to the grinding circuit or first conditioner at 5–50 g/t of dry ore, while soda ash or lime maintains pH between 8 and 11. The cyanide ion complexes iron and zinc species on sphalerite and pyrite surfaces, preventing adsorption of xanthate collectors and reducing zinc misclassification into the lead concentrate. Excess free cyanide, however, can depress chalcopyrite and reduce precious metal recoveries. The measured pulp free cyanide is therefore maintained within a circuit-specific band, often 10–100 mg/L in the lead rougher feed, depending on feed mineralogy and collector dosage.
Rougher and cleaner banks use mechanically agitated flotation cells with rotor-stator dispersion, and sodium cyanide dosage is split between the rougher conditioner and the first cleaner to account for declining cyanide demand as sphalerite surface area declines. Xanthate collector addition is typically 10–50 g/t, and the interaction between collector and depressant is monitored by oxidation-reduction potential and free cyanide titration. The terminal output is a separate lead concentrate, zinc concentrate, and pyrite-bearing tailings, with concentrate quality verified by fire assay and X-ray fluorescence. Sampling and moisture determination of shipped concentrates follow ISO 12743:2021.
Tailings water from cyanide-added circuits is retained in thickeners and treated with ferrous sulfate to precipitate stable ferrocyanide complexes before release, with final WAD cyanide limit compliance tested by ASTM D2036-09. Because cyanide dosage interacts with oxidation-reduction potential, milling operations trend ORP against lead-zinc grade and manipulate collector addition in closed-loop mode. Cyanide addition is stopped when flotation feed contains secondary copper minerals above a threshold set by metallurgical testwork, because copper cyanide complexes can alter pulp viscosity and depress copper recovery in the cleaning circuit.
Sodium cyanide is converted to sodium thiocyanate by reaction with elemental sulfur in a jacketed stainless-steel reactor blanketed with nitrogen. A 25–30 wt% NaCN solution is heated to 80–90 °C while sulfur powder is introduced as a slurry; the reaction NaCN + S → NaSCN is exothermic, so cooling water is applied to hold the set point within ±2 °C. Residual cyanide is monitored by ion-selective electrode until below 1 wt% of the reaction mass before the batch is filtered through a plate filter to remove unreacted sulfur.
The clarified liquor is concentrated under vacuum and crystallized to sodium thiocyanate dihydrate or anhydrous product. Acrylic fiber producers use sodium thiocyanate as a wet-spinning solvent at 51–55 wt% concentration in the dope; the recovered solvent is purified by ion exchange and evaporation. Sodium thiocyanate is also used in corrosion inhibition admixtures and as a tracer in concrete, where chloride-free specification requires assay above 98% and iron below 20 mg/kg. Product grade is verified by iodometric titration for NaSCN content and by AAS or ICP-OES for heavy metals.
The process sewer is routed through alkaline chlorination to destroy residual cyanide before discharge, and feedstock handling follows closed-loop transfer, double-walled pipe, and scrubber interlocks. Reactor headspace is monitored continuously for hydrogen cyanide and interlocked with the caustic scrubber dampers. Sodium thiocyanate batches intended for solvent-grade use are filtered through 0.45 µm membranes to control insoluble particulates before bulk loading.
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Sodium cyanide (NaCN; CAS 143-33-9) is supplied as a white hygroscopic solid with a molecular weight of 49.0072 g/mol and a crystal density of 1.595 g/cm³ at 20°C. Commercial product models are differentiated by physical form and NaCN concentration: solid briquette at ≥ 98.0% w/w, solid granular at ≥ 98.0% w/w, and aqueous solution at 30.0% w/w NaCN. Briquette and granular products differ chiefly in dusting propensity, dissolution rate, and compatibility with closed-loop dosing equipment. Solid sodium cyanide has a melting point of 563.7°C and decomposes before boiling at ambient pressure; liquid product is handled exclusively as an aqueous process stream rather than as molten NaCN.
Supplier certificates of analysis for solid sodium cyanide are commonly structured around GB 19306-2003 industrial-grade requirements. The primary assay is determined by argentometric titration following acid distillation of hydrogen cyanide into sodium hydroxide solution; the result is reported as NaCN mass fraction on an as-received basis. Batch-to-batch variance in production-scale shipments is typically below 0.2 percentage points for the main assay when product is drawn from continuous neutralization and crystallization operations.
| Parameter | Typical briquette/granular value | Test basis |
|---|---|---|
| NaCN content | ≥ 98.0% w/w | Argentometric titration after HCN distillation |
| Sodium hydroxide (NaOH) | ≤ 0.5% w/w | Acid-base titration |
| Sodium carbonate (Na2CO3) | ≤ 1.0% w/w | Acidimetric method |
| Water | ≤ 0.5% w/w | Karl Fischer titration |
| Water-insoluble matter | ≤ 0.2% w/w | Gravimetric filtration |
Aqueous sodium cyanide solution is supplied at 30.0% w/w NaCN with sodium hydroxide content generally held at 0.5–1.0% w/w to suppress hydrolysis. Liquid deliveries are monitored by density, refractive index, and total cyanide titration rather than by dry solids assay.
Within the solid product class, pillow-shaped briquettes of 30–40 mm nominal width are used to reduce airborne dust during open transfer and to provide controlled dissolution in makeup tanks fitted with eductor mixing. Granular product is preferred in facilities using screw feeders and closed hoppers because it flows under gravity with lower bridging tendency; however, it generates a larger proportion of respirable fines in open bag-dump stations. Process engineers frequently select briquettes for remote mining applications because the larger particle mass limits dust liberation in vendor-conducted enclosure tests, although site-specific published dust data is limited.
In carbon-in-pulp and carbon-in-leach circuits for free-milling gold ores, published metallurgical balances place sodium cyanide consumption at 0.10–0.60 kg per metric ton of ore. Leach pH is maintained at 10.5–11.5 by lime addition to shift cyanide speciation toward free CN⁻ and to suppress hydrogen cyanide volatilization. Dissolved oxygen is maintained above 5 mg/L in mechanically agitated tanks; below this concentration, cyanide leach kinetics slow and reagent consumption rises without proportional recovery gain.
Production-scale circuits typically use six to eight agitated leach tanks with a total residence time of 24–48 h. Sodium cyanide is added as a 10–15% w/w aqueous solution through ring-main dosing headers. Dissolved oxygen is supplied by radial impellers and air spargers. Published design guidance for oxygen mass transfer in high-solids cyanidation tanks recommends impeller tip speeds above 3 m/s, but pilot testing at site ore pulp densities of 45–50% w/w solids is necessary because published data for specific impeller and sparger combinations is limited.
The leach rate for free gold in milled ore follows a diffusion-controlled shrinking-core model. Above approximately 0.1 g/L free cyanide, dissolved oxygen concentration exerts a stronger influence on the rate than further increases in free cyanide. Therefore, raising NaCN addition from 0.2 kg/t to 0.6 kg/t without increasing dissolved oxygen does not generate proportionally higher recovery. Bottle roll tests and leach-versus-time curves are used to quantify ore-specific cyanide-consuming minerals such as pyrrhotite, chalcopyrite, and secondary copper salts.
Tailings from sodium cyanide-based leaching are routed through cyanide destruction circuits before discharge. The sulfur dioxide-air process and Caro’s acid oxidative process are used in full-scale operations; residual weak acid dissociable cyanide is monitored to ≤ 50 mg/L or lower under site-specific permits and International Cyanide Management Code certification. Analysis of free, weak acid dissociable, and total cyanide in process water is performed using ASTM D2036-09 Method D for distillation and colorimetric or ion-selective electrode finish.
Alkaline electroplating baths use sodium cyanide to sequester metal cations and produce fine-grained deposits. In copper strike formulations, free sodium cyanide is held at 10–25 g/L, copper metal at 10–20 g/L, and bath temperature at 40–60°C; typical cathode current density is 1–5 A/dm². The free cyanide-to-copper ratio, rather than total cyanide, controls anode dissolution and deposit adhesion on steel and zinc die-cast substrates. Bath filtration through depth cartridges at 5–10 µm nominal retention removes precipitated salts, and oil-free air blowers provide agitation without organic contamination.
In batch organic synthesis, sodium cyanide in dipolar aprotic solvents such as DMSO or DMF is used for SN2 displacement of alkyl halides to nitriles. Reaction conditions are typically 60–90°C for 4–24 h with 1.1–1.5 molar equivalents of NaCN. Excess cyanide is destroyed in alkaline hypochlorite after workup. Granular NaCN is selected over potassium cyanide in DMF-based cyanation because sodium salts have lower tendency to precipitate in the reaction mixture.
Sodium cyanide is selected over potassium cyanide where cation mass and reagent cost per kilogram of cyanide ion are controlling variables. Theoretical cyanide content is 53.09% w/w for NaCN, 39.95% w/w for KCN, and 56.49% w/w for pure calcium cyanide. Technical calcium cyanide often contains variable cyanamide and chloride, reducing its effective cyanide delivery and complicating leach control.
| Property | NaCN | KCN | Ca(CN)2 |
|---|---|---|---|
| Molecular weight | 49.0072 g/mol | 65.1157 g/mol | 92.1128 g/mol |
| Theoretical CN⁻ content | 53.09% w/w | 39.95% w/w | 56.49% w/w |
| Typical industrial forms | Briquettes, granules, solution | Crystalline solid, powder | Powder, flakes; variable technical grade |
| Hydrolysis behavior | Moderate alkalinity; NaOH addition suppresses HCN release | Alkaline; similar pH control required | Releases HCN readily under acidic conditions; technical variability is higher |
| Dominant application | Gold leaching, electroplating | Silver electroplating, organic synthesis | Leaching where calcium ion is acceptable |
Solid NaCN at 98.0% w/w contains approximately 52.0% w/w cyanide ion; liquid NaCN at 30.0% w/w contains approximately 15.9% w/w cyanide ion. This difference changes freight mass, storage tank design, and dosing pump sizing when liquid is substituted for solid. Liquid product eliminates dissolution time but increases the volume of regulated hazardous material stored on site.
When a gold leach facility replaces solid briquette with 30.0% w/w liquid sodium cyanide, the main process changes occur in reagent storage, metering accuracy, and secondary containment. Liquid delivery systems use fiberglass-reinforced plastic or stainless steel storage tanks with secondary containment rated for 110% of tank volume. Metering pumps with pulsation dampeners are set to deliver the same free cyanide addition rate as the solid-dissolution circuit; conversion calculations use the density of 1.19–1.21 g/cm³ at 20°C for the 30.0% solution rather than the solid product’s 53.09% theoretical cyanide equivalence.
Operational boundaries for sodium cyanide are dominated by hydrolysis and hydrogen cyanide release. Sodium cyanide is hygroscopic; briquettes exposed to air above 60% RH absorb moisture and may cake. Contact with acids, carbon dioxide, or strong oxidizing salts must be prevented because HCN gas is released at pH below 8.0. Cyanide salts are incompatible with sodium hypochlorite, peroxides, and strong mineral acids. Warehouses are ventilated at 6–10 air changes per hour to keep HCN below detection limit, and emergency showers and cyanide antidote kits are positioned outside storage enclosures rather than inside contaminated atmospheres.
Occupational exposure to hydrogen cyanide vapor from NaCN is controlled below the ACGIH ceiling limit of 4.7 ppm. Electrochemical gas monitors are placed around mix tanks and leach tank perimeters. Personnel handling solid product wear full-body chemical protective clothing with positive-pressure supplied air where airborne cyanide may exceed 4.7 ppm. Sodium cyanide is subject to EU CLP classification as Acute Toxicity Category 1 with hazard statements H300, H310, and H330. International Cyanide Management Code certification includes design review of storage and mixing facilities, emergency response capability, and training audits; certified operations are audited at 3-year intervals.
