Gold Processing Methodology Using Sodium Cyanide
There have been many methods developed by the miners for extracting gold particles from the ore over the last many years.
Of these methods, ‘Cyanide Leaching Process’ or Cyanidation, is one main method that is highly and most often used for doing this procedure. As the name implies, the main component of this process is the sodium cyanide solution. Here we will give the general overview on how this age-old gold mining method works.
How This Extraction Process Exactly Works?
Cyanidation isn’t used for extracting the big size of gold nuggets from the ore because this process is deemed very slow and isn’t very cost effective. For mining operations that have larger and free milling gold deposits, traditional gravity separation and stamping methods are quite effective. Cyanide can be used for extracting gold from the ore where it’s spread all over the ore in good amounts. It’s generally done in the conjunction with the process like milling, grinding, or gravity separation, which increases the surface area of an ore to expose too much of gold if possible; it can be done because sodium cyanide solution does not have any effect on gold during this extraction process and if it doesn’t come in direct contact with gold particles. Remaining ore left after grinding, gravity separation or milling is known as ‘heap’.
There’re two common methods for the heap to process:
The controlled mill is known as a ‘vat leaching’ and often happens in the specialized mill, which is situated on the mining sites. The process works on by exposing the crushed ore surface to cyanide salt solution. When exposed to gold, this solution binds with the ions in gold that allows it to separate out in solution and get screened for collection. This is known that more oxygen can speed up this leaching process and it isn’t often done in the mill out of the cost concerns. Various elements in ore itself will wreak havoc on this process and hurt the effectiveness of this process.
This kind of gold separation method works similar to the mill extraction, however, is quite cost-effective; the drawback is that it is much harder to control on what happens to its toxic cyanide solution after doing the job. It has the benefit of adding oxygen to the mix naturally. This is often used in the lowest ore grade or reprocess ore, which is the byproduct of other extraction steps. Cyanide Leaching Process is one highly used and cost-effective way of extracting gold from the ore since the 1970’s. Most of the open-pit mining operations across the world make use of heap leaching for extracting ores from such kinds of deposits. It will be impossible to work beneficially for most of the ores without using cyanide.
Lots of commercial mining processes have found this profitable to rework the old mine from the last century. Some significant gold was actually left behind in the tailings because of ineffective mining processes during those days, but they now are reworked profitably. Until the researchers get the cost-effective process of extraction, this looks like it can continue to remain popular gold extraction technique for the foreseeable future.
Introduction to the Gold Leaching
The cyanide leaching procedure has been one important process ever developed to extract gold from the ores. Reasons for the widespread acceptance are metallurgical and economic. It generally gets, the higher gold recovery than plate amalgamation as well as is simpler to operate than chlorine and bromine process. This produces a final product in the form of pure metal. Therefore, production from the large cyanide mill can be represented by the small gold bar that is simple to transport. In the same way, the gold mines are located in inaccessible districts served just by mule train or airplane. But, gold metallurgist should be quite familiar with other processes of the gold treatment, like flotation and amalgamation, since they are often used as the auxiliary to this cyanide process.
Precious Metal Leaching Methodology
Before we go into the theory of this cyanide process, a brief review of chemical properties of the gold might be very beneficial.
Gold doesn’t oxidize (or tarnish) at the ordinary temperatures nor this is soluble in the sulphuric, hydrochloric or nitric acids. It dissolves in the aqua regia (a mixture of nitric & hydrochloric acid) in chlorine & bromine compounds. Gold is quite soluble in mercury and uniting with it to form an amalgam. But, the main property of the commercial interest is gold is quite soluble in the dilute cyanide solutions.
The basis of this cyanide process is weak solutions of potassium or sodium cyanide have the preferential dissolving action for small particles of silver and metallic gold over other materials mainly found in the gold ores. But, there are some minerals called as cyanicides, which have the deleterious effects that can be discussed later. The temperature of the solution can be important for maintaining the efficient dissolving action. Thus, these are some of the popular gold processing methodology used quite often.
Safety of using Sodium Cynanide
Safety & Environmental Issues
Yes, we’re talking about same chemical well-known as the deadly toxin in its solid and its gaseous form. With this being said, the content of cyanide in an extraction solution is actually kept at a very low level (100 - 500 parts every million); it is actually done for the safety, economic and environmental reasons. Mining industry takes good care while handling sodium cyanide and also there has been no death to the mine employee till now. Lots of people don’t realize that the cyanide is naturally found in many of the foods that we eat daily, but our body tolerates this very well in smaller doses. The biggest health effect of using cyanide in the mining industry is the effect that it will have if this leaches into the surface water. Compared to humans, fish are more sensitive towards cyanide, and pollution will have a detrimental effect on the native ecosystems when used improperly. Thus, a reasonable amount of analysis of this method to make sure the right use of the chemical is justified.