Talk:Gold cyanidation

From Wikipedia, the free encyclopedia

Gold reacts with sulfides to form thiocyanates, renderring the cyanide useless to gold leaching. Thiosulfate is all together different chemistry, and not nearly so interesting to cyanide consumption.

Sometimes thiocyanate is written as SCN-.

Contents

[edit] The Effect of pH

Lime (calcium hydroxide) or soda (sodium hydroxide) is added to ensure that the pH during cyanidation is maintained over pH 10.5.

why 10.5? Josh Parris # 03:35, 22 September 2005 (UTC)

cause it's very low Klonimus 07:19, 19 September 2005 (UTC)

Okay, I get that, but why not 11? Or 10.73? What is the special magic about 10.5? Josh Parris # 03:35, 22 September 2005 (UTC)

The reason that the pH is maintained above 10.5 is because as the pH gets lower, cyanide in solution reacts to form hydrogen cyanide (HCN) gas! 10.5 is considered a safe pH for operating with a relatively comfortable margin, preventing the exposure of operators working around the leaching solution. From memory, the leaching reactions forming the gold-cyanide complexes are actually favored at lower pH. But operationally it's unsafe to go there.BSMet94 18:18, 12 January 2007 (UTC)

[edit] Effect of Lead Nitrate

Lead nitrate can improve gold leaching speed and quantity recovered, particularly in processing partially oxidized ores.

how? why? Josh Parris # 03:35, 22 September 2005 (UTC)

probably some sort of reduction reaction

Tell me more. Josh Parris # 03:35, 22 September 2005 (UTC)

This is a complex process that is not fully understood. There are some electrochemical aspects to the lead nitrate participation in the process. You should be able to dig up some papers on the subject (it's been written about quite a bit). What is meant by partially oxidized ores? Most cyanide processing takes place when the ore is highly oxidized because sulfides tend to increase cyanide consumption and interfere generally in the leaching process.


[edit] Revert of 61.68.199.162

From Cyanide: "Cyanide is highly reactive; it decomposes rapidly in sunlight." which gells with 61.68.199.162's entry of "While cyanide is toxic, it breaks down rapidly in nature. This fact has allowed its safe use over many decades at hundreds of mine sites without adverse side effects to workers at the mines."

Is there any reason why I shouldn't reinstate that text, perhaps reworked? Josh Parris # 03:44, 4 November 2005 (UTC)

I suppose that would be OK. As long as it's accurate. Perhaps I "rolled back" too fast.

dino 04:05, 4 November 2005 (UTC)

[edit] Cyanide detoxification

That reference for "over 90 mines" is not definitive, as the figure is unsourced in the reference document. If I had to guess, it's ultimately from some Inco SO2/Air sales literature, which means they've put in over 90 systems. It doesn't necessarily mean that all of them are still operating, or operated well. Also, no mention is made to the main competition for the SO2/Air process, which is the hydrogen peroxide based methods. They're just as commonly used. DeGussa is one supplier of this technology. Someone should come up with a more definitive source, and the article should not plug only one specific cyanide destruction technology (NPOV). BSMet94 20:07, 15 February 2007 (UTC)

[edit] Bulk leach extractable gold

Is this article related to this one?--134.76.234.75 (talk) 15:13, 23 November 2007 (UTC)

[edit] Bias much?

"It should be noted that destruction caused by such toxic releases cannot be easily washed away, and attempts to trivialize the environmental effects by citing the growth of plankton after two weeks are merely whitewashes by an industry tarnished by a horrendous environmental record." —Preceding unsigned comment added by 70.73.53.88 (talk) 04:03, 24 March 2008 (UTC)

[edit] Patent

The google patent [1] might be a good addition?--Stone (talk) 07:47, 18 April 2008 (UTC)