Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing single metal
Reexamination Certificate
2001-01-23
2003-03-25
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing single metal
C205S581000, C204S233000, C423S027000, C423S658500
Reexamination Certificate
active
06537440
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to processes for recovering copper from copper containing feeds.
BACKGROUND OF THE INVENTION
A number of alternative process routes exist for the treatment of copper ores, particularly ores in which the copper is present as copper sulphides such as chalcocite Cu
2
S, covellite CuS, bornite Cu
5
FeS
4
and enargite Cu
3
AsS
4
. These routes include in-situ leaching, heap leaching and agitated tank leaching. Each route can incorporate different methods of regenerating ferric ion, the principal leach agent—bacterial oxidation, gaseous oxygen oxidation or chemical oxidants. The choice of route is influenced by factors such as resource tonnage and grade, mineralogy of both copper minerals and gangue, climate and environmental considerations.
These alternative methods are discussed in more detail below:
In-Situ Leaching
This technique has major environmental draw backs because of the difficulty in containing the leach solutions within the ore zone. Other difficulties arise from variable permeability of the ore, inability to control the leach reaction and the high likelihood of quite low overall recoveries. In-situ leaching is generally only considered for high permeability, low grade material which cannot be processed by other means and for resources where the leaching agent is quickly neutralised by waste rock surrounding the ore zone.
Heap Leaching
Heap leaching is commonly used to treat chalcocite ores in Australia e.g. Mt Gordon, Girilambone, and in other properties worldwide. However the effectiveness of this technique is highly dependent on the nature of the ore being treated. For some ores using medium height heaps, long leach times would be required for moderate recoveries. The rate of leaching is less dependent on the actual mineral leach rate than on those factors which will promote or inhibit leaching—oxygen supply, heap permeability, liquor percolation and ore grade variability. Many heap leach mine sites, experience continuing difficulty in attaining satisfactory stability in these factors with the result that heap leach performance often falls well below expectations which seemed theoretically reasonable at the time of the performance of trial leach tests.
Furthermore, where the ore contains high levels of pyrite there is a likelihood of a reaction of pyrite with ferric ion leading to increased acid production and conditions unsuitable for bacterial leaching.
Agitated Tank Leaching
Agitated tank leaching has the potential to maximise recoveries under controlled leach conditions. Leach times for either ground ore or a concentrate can be reduced to several hours. Pyrite reactions can be monitored and parameters such as oxygen supply and temperature adjusted to ensure the reaction is controlled. The process involves leaching ground ore in the presence of an acidic leachant containing ferric ion. The ferric ion oxidises the copper to form soluble copper ions and is itself reduced to ferrous ions. The ferrous ion is then converted back to ferric ion for further copper mineral attack. The ferrous ion oxidation can occur by a number of methods. The leachant can be separated from the solids and ferric regenerated bacterially or by reaction with acid and finely dispersed oxygen (or air). Alternatively ferric can be regenerated directly in the slurry by injection of finely dispersed oxygen or air. This can occur in the leach tank or by removing a small stream and passing it through a side-stream air/oxygen injection device. The process can be closely controlled so that the scale up to a full size plant is well understood and accurate estimates of final recoveries and operating and capital costs can be made. However there is significant effort and expense involved in regenerating the leachant. Furthermore the rate of leaching can decrease as ferric ion is used up in the leaching step. With some minerals e.g. covellite and enargite the leach rate is more dependent on the Eh which is strongly influenced by the ferric/ferrous ratio. Highest leach recoveries are often obtained by having an elevated ferric/ferrous rates at the end of the leach. This is difficult to attain in an atmospheric leach as the rate of oxygen dispersion in the pulp is limited.
Thus there is a need for a process which is suitable for treatment of a range of copper ores which deals with the disadvantages of the conventional processes described above.
DISCLOSURE OF THE INVENTION
A method for extracting copper from a mineral feed containing copper sulphide mineral including the steps of:
(a) leaching the feed with an acidic solution containing ferrous and/or ferric ions at a temperature above ambient in the presence of oxygen at superatmospheric oxygen pressure to produce a leachant solution containing copper ions;
(b) selectively extracting copper ions from the leachant solution by solvent extraction to form an extract solution containing copper ions and an acidic raffinate containing ferrous, ferric and low levels of copper ions;
(c) recycling some of the raffinate to be included in the acidic solution of step (a); and
(d) recovering copper from the extract solution.
Suitably the feed does not include significant quantities of soluble or leachable chloride. It should include less than 5% by weight of chloride more preferably less than 1% by weight. The presence of significant quantities of chloride ions makes for a very aggressive environment and thus requires the use of expensive equipment. This in turn leads to increased costs. Hence the preference for feeds low in chloride. Similarly the acidic solution should be kept substantially free of chlorides.
The copper sulphide mineral may include chalcocite Cu
2
S, covellite CuS, bornite Cu
5
FeS
4
or enargite Cu
3
AsS
4
and/or mixtures of two or more of these. The copper sulphide mineral may include iron mineralization. The iron mineralization may be pyrite. It may include 15% to 95% pyrite. The copper sulphide mineral may be from the Esperanza deposit in Australia. Esperanza ore typically contains about 70% pyrite in association with chalcocite. After mining dilution the ore will average 60% pyrite i.e. the feed to the autoclave will be 30% to 70% pyrite averaging 60%.
By comparison an ore concentrate from the Mammoth deposit in Australia, after flotation may typically contain about 30% by weight of pyrite. This concentrate is also suitable for treatment to recover copper by the process of this invention.
To facilitate more rapid leaching the feed may be ground. After grinding the majority of particles in the feed have a size generally less than 150 microns more preferably less than 100 microns. Preferably after grinding the feed will be 80% by weight passing 150 microns and more preferably 80% by weight passing 75 to 106 microns.
In step (a) the acidic solution will contain sulphuric acid. The sulphuric acid is suitably generated in-situ in step (a) by the oxidation of sulphides contained in the feed and by transfer via solvent extraction from electrowinning. Suitably the concentration of the acidic solution falls within the range 10 to 60 g/l H
2
SO
4
.
Ferric ions in step (a) may be generated in-situ by the leaching of iron in the feed to produce ferrous ions and by the oxidation of ferrous ions in the feed and recycled raffinate to ferric ions by oxygen. The ferric ions promote the dissolution of the copper minerals to produce copper ions (mostly divalent cupric ions Cu
2+
) and in the process are themselves reduced to the ferrous Fe
2+
state. Thus the acidic solution will contain both ferric and ferrous ions. It is preferred that the ratio of ferric to ferrous is at least 1.0 and is more preferably in excess of 2.0 at the end of the autoclave stage. Suitably the concentration of iron in solution is maintained in the range 10 to 40 g/l during leaching.
Suitably the leaching step (a) is carried out at a temperature in the range 50° C. to 105° C., more preferably 65° C. to 95° C. The oxygen partial pressure used for carrying out step (a) is generally maintained in the range 1 to 10 Bar more suitably 2 to
Dreisinger David B
Richmond Geoffrey
Intellectual Property Law Group LLP
Jackson Juneko C.
Lee Otto O.
Valentine Donald R.
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