INTRODUCTION

Specific gravity, liquid

1560 F, 850 C

Heat of formation (AH°)

1.19

Du Pont sodium cyanide (NaCN) is available in two convenient all-purpose forms: a briquette form (CYANOBRIK sodium cyanide) and a granular form (CYANOGRANR sodium cyanide). The briquettes of CYANOBRIK are of uniform size, average 13 grams or about 1⁄2 ounce in weight and have overall dimensions of approximately 3.5 x 3.5 x 1.3 cm or 1% x 18 x 1⁄2 in. They are resistant to breakage and dusting, easy to scoop up, and readily soluble in water. The white granules of CYANOGRAN are also of uniform size so they flow better and generate a minimum of dust. The crystalline solid passes 99% through USS Sieve No. 2; 10% maximum through USS Sieve No. 50. Also available is a granular compounding grade which will pass 100% through USS Sieve No. 8, and a reagent grade meeting A.C.S. Specifications.

The Chemical Abstract Service Registry Number for NaCN is 143-33-9.

SPECIFICATIONS AND TYPICAL ANALYSIS

The metal, chemical and mining industries are the principal consumers of sodium cyanide. Typical uses include

Electroplating

Cyanide brass, cadmium, copper, gold, silver, and zinc baths deposit decorative and/or functional metal coatings on a variety of substrates. The good throwing power of the electrolyte causes relatively uniform deposition of the metal on intricately shaped parts. Small amounts of special additives in the baths give bright metal deposits even on recessed surfaces of the work. Cyanide electroplating baths are versatile: they are capable of high production rates whether the work consists of massive or minute parts.

Ore Extraction and Ore Flotation

The cyanide process for extracting gold and silver from low-grade ores uses aqueous solutions of sodium cyanide with oxygen (air) to convert the noble metal (M) to soluble NaM (CN)2, from which M can be recovered

either by precipitation with zinc dust or aluminum powder, carbon absorption, or by electrowinning.

In the flotation of galena (lead sulfide) to separate it from mixed ores containing sphalerite (zinc sulfide) and pyrite (iron sulfide), sodium cyanide acts as a depressor; that is, it reduces the tendency of gangue materials to travel along on the froth and so impair the separation. Sodium cyanide finds similar use in the separation of pentlandite from pyrrhotite and molybdenite from copper concentrates by flotation. It is also used to purify the molybdenite by extraction of copper impurities.

Case Hardening Steel

Molten salt baths containing 10-30% sodium cyanide find extensive use for case hardening steels at temperatures below 1600 F (870 C). The molten bath process is fast, easy to operate, and yields mixed carbon-nitrogen cases that have excellent wear resistance and uniformity. The addition of activators or accelerators to the bath results in deeper cases than those obtained with

plain cyanide baths, but nitrogen pickup is usually less The life of keen-edged tools improves when the highspeed steel is cyanide-nitrided in molten cyanide baths at about 1050 F (565 C).

Metal Cleaning

Aqueous solutions of sodium cyanide are effective metal cleaners, especially for smut removal after acid pickling.

Chemical Manufacture

Sodium cyanide is used to make other chemicals that lead to such diverse products as drugs and vitamins, dyes and pigments, insecticides, sequestrants, polymers, and catalysts. (See CHEMICAL REACTIONS SECTION).

In any synthesis or formulation involving sodium cyanide, no cyanide compound should survive in the final product as an impurity. This is especially important with regard to consumer products.