Commonwealth of Australia 2010
Manufacture, Importation and Use
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- 4.2Manufacture, formulation and transport
- 4.2.2Formulation and transport of products
- 5.Liquid form
4.Manufacture, Importation and Use4.1Sodium cyanide in AustraliaSodium cyanide is introduced into Australia through importation and manufacture. Sodium cyanide has been manufactured in Australia since the late 1980s. There were three dedicated sodium cyanide manufacturing facilities in Australia, one located in WA (the Australian Gold Reagents Pty Ltd [AGR] plant at CSBP’s chemical and fertiliser complex at Kwinana) and two in Qld (the Orica Chemicals and Ticor Chemical Company plants at Yarwun, near Gladstone), but the Ticor plant closed in 2004. Total Australian production has continued to be approximately 100 000 tonnes per annum since 2000 despite this plant closing, with increased plant capacity added at both sites. This is a significant proportion of world sodium cyanide production, which is of the order of 500 000 tonnes per annum. 4.2Manufacture, formulation and transport4.2.1ManufactureWorldwide, almost all sodium cyanide is manufactured by reacting hydrogen cyanide (HCN) with sodium hydroxide (NaOH), a process sometimes referred to as the neutralisation-wet process (i.e. HCN + NaOH NaCN + H2O). The HCN may be obtained from purpose-built HCN plants or may also be sourced as a by-product of an acrylonitrile manufacturing process (Mills, 2001). In general, the most popular processes for manufacturing HCN include the Shawinigan Process (3NH3 + C3H8 3HCN + 7H2), the Andrussaw Process (CH4 + NH3 + 1.5O2 HCN + 3H2O), and the BMA Process (CH4 + NH3 HCN + 3H2). Sodium cyanide is also sometimes prepared by melting sodium chloride with calcium cyanamide or by heating sodium amide salt with carbon (IPCS, 2004). Australian sodium cyanide manufacturing facilities use the Andrussaw process, reacting methane and ammonia to produce hydrogen cyanide gas (HCN), and then absorbing the cyanide into a solution of sodium hydroxide. The result is an aqueous solution of sodium cyanide (NaCN). Sodium hydroxide is introduced into the process as a 50% w/w solution, at a rate that maintains the system pH at or above 12.5. A high pH maximises the absorption of cyanide into solution, and stabilises the product while in storage, limiting HCN evolution. A liquid product containing approximately 30% w/w sodium cyanide is marketed from this, or the solution is further treated to arrive at a solid form of sodium cyanide. The solid sodium cyanide process involves evaporating a significant proportion of the water from the cyanide solution to yield a slurry. The slurry is then centrifuged, and the crystals put through a series of drying stages, before being compressed to form the final product, such as briquettes (J. Fozdar, CSBP Chemicals, pers. comm. 2005). 4.2.2Formulation and transport of productsSolid form Sodium cyanide is manufactured as solid briquettes, tablets (‘cyanoids’) or granules/flakes containing approximately 96%-99% NaCN (refer Table 4.), or in a liquid form containing approximately 30% NaCN. The majority of sodium cyanide manufactured in Australia is sold in the solid form, including all exports of the substance. Table 4.. Typical constituents of formulated solid sodium cyanide
Solid sodium cyanide may be formed into uniform briquettes, with dimensions and weight varying between manufacturers. In Australia, briquettes are typically pillow shaped, weigh ~20-30 g each and have approximate dimensions of 40 x 35 x 20 mm to 47 x 37 x 20 mm. Alternatively, solid sodium cyanide may be provided commercially as granules or flakes. These are irregularly shaped particles typically sized to generate a minimum of dust (e.g. granules with 80% passing a 9.5 mm screen and 3% passing a 0.3 mm screen). All solid sodium cyanide currently manufactured in Australia is produced in briquette form, whereas imports may be in the granular form. Within Australia, sodium cyanide is transported mainly by road and rail. The two current manufacturers supply solid forms of sodium cyanide in bulk quantities packaged either in:
StoL isotainers are tanks which are typically purpose-built for rail or road transportation. Solid cyanide is added to the containers at the manufacturing facility and transported to the customer’s site in this form. Upon delivery, the cyanide is dissolved in the isotainer by addition of water at the mine site and the liquid drained into on-site storage tanks. This reduces the requirement for manual handling of solid as well as minimising possibilities of spillage during transfer and handling at the minesite storage facility (Environment Australia, 1998). Neither factory in Australia has facilities for filling smaller containers, hence all product sold in smaller quantities (~50 kg to <1 kg) is imported. Much of this is sold in the containers in which it is imported, but several companies in Australia reformulate solid sodium cyanide into smaller, more manageable quantities for specialist uses. 5.Liquid formLiquid sodium cyanide is supplied for use in reasonable proximity (< ~1000 km) to production plants, with transport by road and rail in specially designed isotainers. The isotainers used in Western Australia are filled with 20.6 tonnes of solution, which translates to ~17.5 kL, containing ~6.25 tonnes of NaCN in the loaded solution (Fozdar, pers. comm. 2005). Those in Queensland are similar, holding ~18 000 L, equivalent to 6 tonnes NaCN (J. Cowan, Orica Australia Pty Ltd, pers. comm. 2005). Approximately half of the NaCN produced in Western Australia is sold in the liquid form, but the majority of product from the Queensland factory is sold in the solid form. The liquid form is preferred by some mines because of handling advantages over solid NaCN at the mine site (i.e. when supplied in CIBCs) and/or where supply already dissolved in water is an advantage because of local water quality problems. However, transport in liquid form becomes uneconomical over larger distances. Table 4. describes the typical constituents of liquid sodium cyanide. Table 4.. Typical constituents of liquid sodium cyanide
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