Gold Extraction

Effect of Cupric Ammine on Gold Dissolution Rate

The dissolution of gold in ammoniacal solutions cannot take place in the absence of oxidants. Cupric ammine can act as an oxidant in this system according to Equation 3.

The effect of cupric ammine concentration on the dissolution rate of gold was investigated in a solution of 0.6 M total ammonia concentration (0.1 M (NH4)2SO4 and 0.4 M NH3). The cupric ammine solution was prepared by adding known concentrations of copper sulfate (CuSO4.5H2O) and free ammonia in the ratio of 1:4. Figure 2 shows the Tafel polarization curves for the dissolution of gold at different cupric ammine concentrations. It can be observed from these curves that the dissolution potential of the system increases with the increase of the concentration of cupric ammine. Therefore, cupric ammine can be successfully used as an oxidant for the dissolution of gold in ammoniacal solutions.

ammoniacal solution effect of cupric ammine concentration

It can also be seen from the curves in Figure 2 that variation in the cupric ammine concentration had no effect on the anodic portion of the curve. This suggests that cupric ammine has no effect on the anodic reaction which is given by Equation 1. Hence, it ….Read more

Gold Pyrite, Pyrrhotite and Arsenopyrite Recovery

One of the more common classes of ores containing gold is when gold is associated with pyrite, pyrrhotite, and arsenopyrite. This is the area of gold recovery that has probably received the most research and plant optimization support especially in light of the long history of South African industrial practice. From a reagent viewpoint, charged water soluble collectors such as xanthates, dithiophosphates, some thiophosphate analogs including phosphinates, and some recent adaptations of nitrogen based collectors starting from either urea and/or amines, are the most successful reagents used, e. g. Klimpel (1994). Pyrite as it occurs in sulfide mineral systems requires a collector to float. There is a great deal of fundamental research currently going on in the flotation of pyrite with various chemical structures.

Experience has shown that in the acid pH range of 4 to 5, almost all standard thio collectors are effective as pyrite collectors. Xanthates are not stable at these acid pH’s, e. g. Harris (1988), so that they are used in pyrite flotations only at alkaline pH’s. Collectors such as mercaptobenzothiazole, dithiophosphates, monothiophosphates, thionocarbamates, and dialkly sulfides all have the capability of functioning effectively in neutral to acid side flotations.

Figures 8 and 9 show a recent data ….Read more

Carbonaceous Gold Ore Treatment Method

Flotation

The simplest method of treating a carbonaceous ore is the method described by R. W. Nice (1971) at the McIntyre Porcupine Mine where the carbon, which contains very little gold, is floated off and discarded. The remaining ore is then responsive to cyanidation. This does not work at Carlin because the carbonaceous compounds have a high gold content. A considerable amount of flotation work was done on Carlin ores, however, to produce a high grade concentrate for possible shipment to a smelter and a tailing which could either be discarded or directly cyanided. All of the concentrates contained both carbonaceous material and pyrite and showed low recoveries of gold and poor selectivity. This was because of insufficient liberation of carbonaceous material and sulfide from the gangue, even at 100 per cent minus 325 mesh.

In the treatment of an auriferous sulfide associated with carbonaceous shale from South Africa by American Cyanamid Company (1939), up to 77 per cent of the carbon was eliminated by depressing it with Cyanamid reagent 637 while floating the sulfides for 90.5 per cent gold recovery, and 20.4 to 1 ratio of concentration. Fortunately, the carbon in the Witwatersrand ores is in a form which ….Read more

Thiourea Silver Leaching

Unlike base metals which are readily soluble in mineral acids, noble metals like gold and silver require the presence of oxidizing and complexing agents for dissolution. Silver approaches base metal behavior in acidic thiourea solutions (Ag + 3Thio ↔ Ag(Thio)3+ + e, E° = 0.025 V) requiring only mild oxidizing conditions for dissolution. Accordingly, the following reactions characterize the dissolution of silver in acidic thiourea with various oxidants

thourea-leaching-au-ag-oxidants

Ferric sulfate and chloride have been frequently employed as oxidants. Other oxidants that appear compatible with acidic thiourea systems include Na2O2, O3, KBrO3, and K2Cr2O7.

Like the metallic form, certain silver minerals require oxidizing conditions for dissolution in acidic solutions. Argentite (Ag2S) in the presence of thiourea is leached by ferric ions according to the following overall reaction

thiourea-leaching-au-ag-reaction

It is reasonable to believe that refractory silver minerals like Hessite (Ag2Te) would respond to acidic thiourea leaching similar to the chemistry represented in Eq. (6).

Cerargyrite (AgCl) is a silver mineral that will dissolve in acidified thiourea solutions under nonoxidizing conditions. This mineral proceeds to solution by simple complexation dissolution. The following reaction represents the dissolution of AgCl in thiourea

….Read more

Where to Find Gold

So tonight’s topic of interest is kind of near and dear to me, I’m going to start with the first slide; Rocks and Gold Clues. What rocks tell you about where to find gold, there are clues that they give and those are very important if you’re going to find gold and that’s what we’re here for; right? Hi, I’m Prospector Jess; this is another hangout regarding gold prospecting and how to find gold. I just want to make sure that everybody is in tune with where were going. The adventure for tonight is about rocks and gold and how the two are connected together. I have a background in geology and engineering, primarily from UCSD. I have been an engineering manager for a number of years and then more recently I’ve been doing work helping with gold prospecting. The gold prospecting part I started it as a family adventure but actually it’s deep in my roots, my great-grandfather was a prospector in 1849. So it’s one of those things where I learned about it as a child and then learned again when I had children. And I think it’s important to recognize that a certain amount of excitement and ….Read more

How to Pan Gold

I told you I wanted to do a panning video. So what you’re going to do is, I’m going to break this down a little bit differently. I’m not going to get real scientific on this; I’m just going to put it in plain terminology. Now unfortunately we are probably going to listen to gunshots down the road because its deer season and everyone is getting sighted in. But I am going to show you this, I am going to try and keep it simple but it really is hard to keep panning simple, I am going to warn you about that now. So if you don’t want to watch a pretty in depth panning video, go away, shut this off, and don’t watch it. But I figured I would show you a couple different tricks, I am going to show you some techniques, I am going to show you some things that I like to do. And panning is not something really you can just pick up a book and read on it’s something that comes with practice, so you really need to practice. And of course you can practice with cons.

Now the nice thing about practicing with our ….Read more

Zinc Box Gold Precipitation

The simplest precipitation equipment for a small mine is what is known as a zinc-box (Fig. 150). This consists of a long, narrow, sloping, wood or painted sheet-iron box divided into wide compartments or cells which are separated by baffle-boards and narrow compartments. The bottom of the box slopes to one side to facilitate the clean-up through plug-holes which discharge into a small launder. Near the bottom of each large compartment is a ledge on which is supported a heavy wire screen-tray. These compartments are filled firmly yet are springy with zinc shavings or filament. The gold- and silver-bearing solution is turned into the first narrow compartment, and the baffle, which does not reach the bottom, deflects the solution under the tray holding the zinc. The solution flows upward through the zinc, over the side of the compartment, down by the next baffle to the next lot of zinc, and so on, through 6 to 10 cells to the discharge, whence the solution flows to a sump or storage-tank. At this point it should be practically barren of precious metals. One cubic foot of filament will serve 6 to 10 tons of solution a day.

From time to time during a ….Read more

Mercury Amalgamation

Mercury or quicksilver fed into stamp mortar-boxes and riffles or applied to copper plates has been for ages the method of catching free gold. Many millions of ounces of gold have been saved thereby, and the mercury has been returned to circulation with small loss. Amalgamation is still practiced, but the recovery of gold by traps, jigs, cells, and cloth is lessening the amount so saved, although gold from these appliances is amalgamated for cleaning up.

Amalgamation is affected more or less by some pyrite minerals, especially if decomposed, also by antimony, bismuth, and copper.

If such is the case, tabling could precede amalgamation or corduroy should be substituted.

Mortar-box. If a mine has a stamp-mill and inside amalgamation is desirable, mercury is added to the mortar-box in quantity enough to form a spongy amalgam therein and not enough to work out on to the copper plates and make them sloppy with mercury.

mineral processing hydraulic gold trap

Copper Plates. Pure copper, 7/64 inch thick, is rolled into plates or sheets for the amalgamation of gold; 2 to 4 square feet is used per ton of ore per day. New or used plates are procurable, but care should ….Read more

Magnetic Black Sand Separator

During the past 50 years or more there has been a great waste of money, energy, and time in devising, building, and trying many machines to recover gold and platinum, also gemstones, from black sand. Volumes have been written on the subject, and many inquiries have been made by prospectors and others who thought that although they could not save the precious metals, which most likely were never there, some process must be suitable. Near Nome, Alaska, the black sand was rich, and some on the west coast of the South Island of New Zealand is being worked at a profit at the present time. A few spots along the California- Oregon coast were worth handling, as have several along the rivers in the western United States and Canada. The black sands from sluicing and dredging operations are worth careful treatment because they are from the concentration of thousands of yards of gravel daily. By-product black sand from inland placering is often richer than beach sand. But generally, black sand, unless a concentrate, is not worth much effort. In any case, it is worth spending a dollar or two to have an assay made for gold of a carefully taken ….Read more

Cyanidation

As coarse gold is not dissolved by cyanide, it must be removed from an ore by one of the methods already described. Weak solutions of sodium cyanide (or potassium cyanide, seldom used) will dissolve the fine, untarnished gold and silver in ores and tailings, provided the latter have been ground fine enough and do not contain any material, such as acid compounds or minerals, that would affect the cyanide. The gold and silver are recovered or precipitated from the solutions by means of zinc shavings or zinc dust. Melting of the dried precipitate with fluxes yields marketable bullion. An entire ore may be slimed and cyanided, or it may be divided into sand and slime and then cyanided. Tailings may be sand or slime or a mixture of such. Barren solutions, when strengthened with more cyanide salt, can be used again. The strength of solutions must be known, but this is easily determined, as described later.

Cyanide

Two types of cyanide are used in treating gold and silver ores and tailings, also in the flotation of ores: sodium cyanide, which contains 98 per cent NaCN, and calcium cyanide (Aero brand), which contains up to 50 per cent NaCN equivalent. The wholesale price ….Read more

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