Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Reexamination Certificate
1999-04-08
2001-04-03
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
C423S027000, C423S029000
Reexamination Certificate
active
06210648
ABSTRACT:
FIELD OF THE INVENTION
The present invention involves a method for processing gold-bearing refractory sulfide ores, including refractory auriferous sulfides, to facilitate recovery of gold. In particular, the present invention involves flotation processing of refractory sulfide ores in a manner that reduces problems associated with conventional flotation of refractory auriferous sulfides in the ore to produce an ore concentrate that is concentrated in the refractory auriferous sulfides and, accordingly, also in the gold within the refractory auriferous sulfides.
BACKGROUND OF THE INVENTION
Significant amounts of gold occur in ores that are often referred to as refractory sulfides. The gold in these ores is often referred to as being refractory because it cannot be recovered by direct cyanidation. That is because the refractory gold is bound in the mineral lattice of the sulfides, and is therefore unavailable for recovery by traditional gold recovery techniques, such as direct cyanidation of the ore. Therefore, these refractory sulfide ores are commonly treated to chemically destroy the sulfide mineral lattice in which the gold is located and to release the gold for dissolution, such as by cyanidation, during subsequent gold recovery operations.
One technique for destroying the sulfide mineral lattice is to subject the ore to an oxidative treatment to oxidize sulfide sulfur, thereby releasing the gold for subsequent recovery. One method for oxidatively treating a refractory sulfide ore is pressure oxidation, in which a slurry of the ore is subjected to oxygen gas in an autoclave at elevated temperature and pressure to decompose the sulfide mineral, freeing the gold for subsequent recovery. Other oxidative treating methods include roasting and bio-oxidation of the ore in the presence of air or oxygen gas.
Treating whole ores by pressure oxidation or by oxidative roasting is expensive. Part of the expense is due to energy consumed in heating gold-barren gangue material in the whole ore, and especially the energy required to heat water in which the gangue material is slurried in the case of pressure oxidation. Also, process equipment for treating a whole ore must be sized to accommodate the throughput of gangue material, in addition to the throughput of refractroy auriferous sulfides, thereby significantly adding to the cost of process equipment. Moreover, side reactions may occur involving gangue material which can detrimentally affect the oxidative treating or can produce hazardous materials which require special handling.
One way to reduce the high energy and process equipment costs associated with oxidative treating of a whole ore, as well as the potential for problems associated with side reactions, would be to remove gangue material from the ore prior to the oxidative treatment. For example, one method that has been used to remove gangue material from refractory sulfide ores is flotation. In flotation, air is bubbled through a slurry of ore particles which have been treated with reagents and the particles of the ore which are less hydrophilic tend to attach to and rise with the air bubbles, thereby permitting separation of the ore into two fractions. Flotation has been used to prepare concentrates of sulfide minerals from refractory sulfide ores in an attempt to concentrate the gold into the flotation concentrate, thereby avoiding the expense of processing the gangue in subsequent oxidative treating. One problem with flotation of refractory sulfide ores, however, is that a significant amount of refractory gold often reports to the wrong flotation fraction, even when a high percentage of sulfides minerals is recovered in the concentrate.
There is a significant need for an improved method for processing refractory sulfide ores that avoids the high costs associated with oxidatively treating whole ores without the significant loss of refractory gold associated with concentrating sulfide minerals by conventional flotation.
SUMMARY OF THE INVENTION
The present invention involves a method for processing refractory sulfide ores to facilitate gold recovery without the burden of pressure oxidizing or roasting a whole ore and without the substantial loss of gold value associated with preparation of an ore concentrate by conventional flotation. With the present invention, it has been found that much of the refractory gold in refractory sulfide ores is contained in sulfide species referred to herein as refractory auriferous sulfides. Although these sulfide species may represent only a small fraction of the sulfides in a refractory sulfide ore, they typically contain a majority of the refractory gold.
As used herein, refractory auriferous sulfides are sulfides containing gold that is not amenable to direct cyanidation except by destruction of the sulfide mineral lattice, which is usually accomplished by oxidation of the refractory auriferous sulfide. Typically, these refractory auriferous sulfides are auriferous arseno ferrous sulfides, having a composition according to the formula Fe
x
As
y
S
z
.Au, with x,y and z being in any relative proportions. The gold contained in the refractory auriferous sulfides is in solid solution in the sulfide mineral lattice and is refractory gold in that it is not amenable to recovery by direct cyanidation except by destruction of the sulfide mineral lattice, which is typically accomplished by oxidation of the refractory auriferous sulfides. Such solid solution gold is also sometimes referred to as atomic gold or structural gold.
It has been found that the largest occurrences of refractory gold in refractory sulfide ores occur in these refractory auriferous sulfides. Little, if any, refractory gold occurs in other, more classically recognized pure iron-sulfur containing sulfide species, such as pyrite (FeS
2
), marcasite (FeS
2
), and pyrrhotite (Fe
(1-x)
S, with x ranging from 0 to 0.17).
This distinction is important because traditional flotation, involving the use of air as a flotation gas, is often effective for recovering a large fraction of the more traditionally recognized iron-containing sulfide species. It has been found with the present invention, however, that the traditional flotation is not effective for flotation of refractory auriferous sulfides, which contain most of the refractory gold. Therefore, it is often possible with traditional flotation to recover a high percentage of sulfide minerals in the concentrate, and at the same time experience a low recovery in the concentrate of refractory gold. This is because an unacceptably large fraction of the refractory auriferous sulfides, which contain most of the refractory gold, reports to the flotation tails.
The refractory auriferous sulfides should not be confused with non-refractory sulfides. Gold in non-refractory sulfides occurs as particulate gold that is amenable to direct cyanidation without destruction of the sulfide mineral lattice. This non-refractory, particulate gold may be exposed, to the extent necessary, for direct cyanidation by mechanical processing, such as comminution to a very fine particle size, prior to direct cyanidation. It should be noted, however, that although gold from non-refractory sulfides may be recovered by direct cyanidation, it is not always economic to do so. For example, particulate gold inclusions are often found in copper and other base metal sulfides. The copper in many copper sulfides, however, has varying degrees of solubility by direct cyanidation. Therefore, cyanide consumption becomes prohibitively large for economic gold extraction by direct cyanidation because of the concurrent cyanide dissolution of the copper.
It has been found with the present invention that air, which is used as the flotation gas in conventional flotation, detrimentally affects flotation of refractory auriferous sulfides. According to the present invention, significantly enhanced flotation performance may be obtained by maintaining the ore in an environment substantially free of air until a desired final flotation concentrate has been obtained.
It is believed that refractory
Gathje John C.
Simmons Gary L.
Bos Steven
Marsh & Fischmann & Breyfogle LLP
Newmont Mining Corporation
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