Method of cyanide salt production

Details Method of cyanide salt production Method of cyanide salt production

2001-03-27

2003-11-18

Langel, Wayne A. (Department: 1754)

Chemistry of inorganic compounds

Nitrogen or compound thereof

Carbon containing

C210S681000, C210S683000, C423S379000

Reexamination Certificate

active

06649136

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to methods and/or apparatuses for production of cyanide salts and by product salts from hydrogen cyanide or Group IA or Group IIA cyanide salts without the use of sodium hydroxide.
Sodium cyanide production has become increasingly important since the late 19
th
century when a process using cyanide to extract gold and silver from ores was patented. The Beilby process for producing NaCN was predominant in 1891 and produced significant industrial quantities of sodium cyanide until about 1900 when the Castner process superceded it. The Beilby Process consisted of reacting fused carbonates of potassium and sodium with ammonia and carbon:
Na
2
CO
3
+K
2
CO
3
+4NH
3
+2C→2NaCN+2KCN+6H
2
O
The Castner process produced a much higher purity sodium cyanide product by reacting molten sodium metal with ammonia and charcoal. The process became preferred because reagent costs were reduced (sodium is less expensive than potassium).
2Na+2NH
3
+2C→2NaCN+3H
2
Wet processes that react hydrogen cyanide with sodium hydroxide solution superceded both of the above methods. One process (U.S. Pat. No. 2,993,754, Jenks and Linder, Jul. 25, 1961) reports reacting high purity liquid hydrogen cyanide with a concentrated sodium hydroxide solution.
HCN+NaOH→NaCN+H2O
The resulting solution or slurry from this neutralization can be sold as a solution or evaporated, crystallized, dried, and briquetted. Another process (U.S. Pat. No. 3,619,132, H. J. Mann, Nov. 9, 1971) reports directly absorbing HCN containing gas into a sodium hydroxide solution. The resulting slurry or solution can be evaporated and crystallized. The wet processes represent improvements in reagent costs and product purity from the earlier processes.
There remains a need for a process to produce sodium cyanide or other cyanide salts that does not involve the use of caustic soda (sodium hydroxide) as a reagent.
BRIEF SUMMARY OF THE INVENTION
Provided is a method of preparing sodium cyanide and other Group IA and Group IIA cyanide salts. Generally, there are four main embodiments of the disclosed process. These include a two step process using anion exchangers to metathesize cyanide salts; a two step process using cation exchangers to metathesize cyanide salts; a one step process using anion exchangers to directly metathesize cyanide salts; and a one step process using cation exchangers to directly metathesize cyanide salts. “Two step” processes first convert Group IA or Group IIA cyanide salts, or ammonium cyanide, to an alkali salt using a base such as lime (calcium hydroxide) or other bases, preferably other than NaOH. The subsequent basic cyanide salt is then reacted in an anion or cation exchange apparatus, such that the desired cyanide salt product is formed. “One step” or “single step” processes directly produce cyanide salt products without first being converted to a basic salt.
More specifically, a method is provided of making a compound selected from the group consisting of: Group IA and IIA cyanide salts comprising: (a) contacting a reacting substance comprising cyanide ion and a first exchangeable cation with an ion-exchange media containing a second exchangeable ion wherein either the cyanide ion or the first exchangeable cation exchanges with the second exchangeable ion; and (b) if the cyanide ion is exchanged, contacting the ion-exchange media with a composition selected from the group consisting of: Group IA or IIA metal ions and a third exchangeable ion, wherein the third exchangeable ion is exchanged with cyanide ion and whereby Group IA or IIA cyanide salts are formed; provided that if the first exchangeable cation is exchanged, the second exchangeable ion is a Group IA or Group IIA metal. The method may further comprise the step of reacting said reacting substance with a pre-reacting material which contains one or more Group IA or Group IIA elements or ions, or ammonium, producing a reacting substance comprising cyanide and either ammonium or at least one Group IA or Group IIA element, before contacting said reacting substance with said ion-exchange media.
The reacting substance may be one or more of hydrogen cyanide, Group IA cyanides, Group IIA cyanides, or ammonium cyanide. It is preferred that hydrogen cyanide is the reacting substance. The pre-reacting material is preferably calcium hydroxide or calcium carbonate. The Group IA or Group IIA cyanide salt product is preferably sodium cyanide.
The disclosed process may proceed through anion exchange or cation exchange. In the anion exchange process, hydrogen cyanide or some neutral or alkaline cyanide feed solution comprising cyanide anions and one or more Group IA or Group IIA cations is contacted with an anion exchange media; cyanide anion displaces the anion from the anion exchange media and forms a cyanide loaded ion exchange media; the solution containing the feed cation and the displaced anion that was originally present on the ion exchange media is preferably removed; the cyanide loaded resin is contacted with a solution containing a second cation and an anionic counter-ion which displaces the cyanide, forming a solution containing the second cation and the cyanide ions.
The disclosed process may also proceed through cation exchange. In the cation exchange process, hydrogen cyanide or some neutral or alkaline cyanide salt feed solution comprising cyanide anions and one or more Group IA or Group IIA cations is contacted with a cation exchange media; the Group IA or Group IIA cation displaces the cation from the cation exchange media and forms a Group IA or Group IIA loaded exchange media; and a solution comprising the cyanide anion and the displaced cation from the exchange media is formed. The ion exchange media may be regenerated, as known in the art.
A two-step process using anion exchangers is provided, wherein a cyanide gas or liquid composition comprising one or more Group IA or Group IIA cations is contacted with a basic salt solution having a first exchangeable cation. The first exchangeable cation exchanges with the Group IA or Group IIA cation to form a basic cyanide solution. This solution is contacted with an ion exchange media that is loaded with a first exchangeable anion. Cyanide ions exchange with the first exchangeable anion to form a cyanide-loaded ion exchange media. A solution containing a second exchangeable anion that can exchange with the cyanide ions and a second exchangeable cation that can combine with the cyanide to form a desired salt is contacted with the media. Cyanide is displaced from the media and the desired salt solution is formed.
A two-step process using cation exchangers is also provided, wherein a cyanide liquid or gas composition comprising one or more Group IA or Group IIA cations is contacted with a basic salt solution having a first exchangeable cation. The first exchangeable cation exchanges with the Group IA or Group IIA element to form a basic cyanide solution having the first exchangeable cation. This solution is contacted with an ion exchange media that has a second exchangeable cation. The first exchangeable cation exchanges with the second exchangeable cation, forming a cyanide salt solution comprising cyanide and the second exchangeable cation. The media may be returned to its original state by means known in the art.
A one-step process using anion exchangers is also provided, wherein a cyanide gas or liquid comprising one or more Group IA or Group IIA cations is contacted with an anion exchange media containing a first exchangeable anion. The first exchangeable anion exchanges with the cyanide, forming a cyanide-loaded media. The cyanide is removed from the media, if desired, by contacting the media with a solution containing a second exchangeable anion which exchanges with the cyanide ions and a cation which combines with the cyanide to form a desired salt.
A one-step process using cation exchangers is also provided, wherein a cyanide gas or liquid comprising one or more Group IA or Group IIA

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