brown and sharpe

[Harold_V]

Pete,
I likely should have been more specific. The use of cyanide for low grade ore is typically done by heap leaching, where only harvesting and stacking of the ore is accomplished. It is also important that the ore does not contain cyanicides, which tend to consume the cyanide. The ore is placed on huge, impervious pads, then low concentration cyanide solution is pumped to the pile, with values extracted when the solution is collected. Activated carbon is often used to recover the values, although there are other methods. Such ore typically has such low value that other methods do not apply, nor would they be effective. Without some kind of gathering medium (copper does that), the values would be lost in the slag were such ores processed by furnace. Ores that lend themselves to the cyanide process have gold deposited in microscopic bits, way too small to be recovered by other means.

Kennecott Copper (in Utah) recovers a huge array of elements with their process, which is by furnace. The precious metals report in the slimes when the copper is electrolytically parted.

H

[pete]

Hope Earl is understanding. Yep "some" types of copper ore processing is also done with the heap leach process. Seems like that's done far more in the South America region Harold. From how it's been explained to me by mining engineers it's used for highly oxidised ore bodys where the froth flotaion process doesn't work at all well for some reason. I don't know if cyanide is used for copper recovery though. A lot of the copper mines in SA have ore/waste cut off points that can be higher than what our high grade ore is here. So the time intensive heap leach process then gets much more cost effective. From the little I've read and the pictures I've seen the runoff from the heap leach has the copper removed by plating it onto large steel plates then that gets scrapped off.

[mcostello]

On "How it's Made," They said the ore was blended to keep the loads consistent from batch to batch, now I understand why.

[Harold_V]

Hope Earl is understanding.

Yep, me too! Although this topic does relate to the shop in some convoluted way. Besides, Earl is one hell of a good guy!

I don't know if cyanide is used for copper recovery though.

Typically, no, as it's considered a cyanicide. It will dissolve copper, but the cost makes it prohibitive. What is used is dilute sulfuric acid, which readily dissolves oxidized copper. The copper that is put in solution by the sulfuric acid is then recovered by displacement, using scrap steel. Kennecott, in Utah, did that, too. They ran (and likely still do run) a precipitation plant in Copperton, Utah, the only small town still remaining in the vicinity of the copper pit. All other towns have been displaced by the ever growing pit. An entire mountain has been removed, in fact. Curious? Take a look: https://en.wikipedia.org/wiki/Kennecott_Utah_Copper It's recognized as one of the largest open pit mines in the world.

From the little I've read and the pictures I've seen the runoff from the heap leach has the copper removed by plating it onto large steel plates then that gets scrapped off.

I used that very process when I refined precious metals. I ended up with a huge amount of copper in solution, as it was a constituent in red and yellow gold, as well as sterling silver, which I also refined. To add to the volume, I used copper to recover silver from solution. In that process, the sacrificial metal is displaced by the metal being recovered. Copper would displace silver, but leave other elements in solution unless they were more noble. I'd recover silver, palladium and the odd bit of platinum that would go in to solution in nitric acid (a phenomenon that is well recognized, in spite of the fact that nitric does not dissolve platinum). Scrap steel was used to recover copper and traces of nickel before the solution was discarded, At that point, it was no longer a hazardous waste.

For the record (and to make this post of value to the home shop----dilute sulfuric acid is an excellent pickle for copper. It restores copper to it's native appearance, dissolving any oxides that are present, but it does not dissolve native copper. It's a wonderful way to restore badly aged copper. Wear eye protection, and, especially with sulfuric, do not pour water in to the acid. Acid must be slowly poured to water while stirring vigorously, to avoid local heating.

H

[neanderman]

So far as I know, it's still being used extensively (here in the US) in the recovery of fine particles of gold in oxidized ores. It has no equal, and allows for recovery from extremely low grade ores (as little as 1/10 ounce/ton).

Silver, as well.

[Harold_V]

True. However, it may or may not result in great recovery for silver, unlike gold. That was true with the ore I processed many years ago. I achieved a recovery of over 99.5% gold, but scarcely hit 50% for silver. I had no idea why that was, however, but the volume of ore was relatively small, with the vast majority of value in gold (head assayed OVER 325 ounces/ton). The ore was crushed to 200- and run for over 140 hours in an agitation tank. A very rewarding and educational experience.

H

[earlgo]

Back to the OP topic.
So much for my touting "trust but verify". I was looking at my two screw pitch gages and guess what? BOTH, count 'em, BOTH have a 30tpi leaf. Must be that Oldtimer's Disease we hear about that made me miss them. At least I have a new gage, in case I misplace these two.

Screw pitch gages.

--earlgo

[pete]

I have a bridge for sale Earl if your willing to believe I've not done much the same before.