Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Involving measuring – analyzing – or testing during synthesis
Reexamination Certificate
1998-12-16
2001-01-23
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Involving measuring, analyzing, or testing during synthesis
C205S560000, C205S687000, C205S587000, C205S574000, C204S229800, C204S232000, C204S237000, C204S252000
Reexamination Certificate
active
06176997
ABSTRACT:
Heap-leaching, or dump-leaching, is a conventional technique for extracting metals such as copper from low-grade ore bodies. The metal is recovered from its oxide and/or sulphide ores in two stages. The first stage involves creating conditions in which the metal passes into solution. This is done by leaching the heap or dump of the ore with an appropriate solution, for example of weak sulphuric acid. Secondly, the metal is extracted from the pregnant leach liquor or lixiviant. This second stage, i.e the extraction of the dissolved metal from the lixiviant, can be done by chemical precipitation, or by electro-winning, for example.
The first stage of the process demands the provision of an aqueous environment in which the sulphide or other mineral in the ore breaks down to produce metallic (and other) species in solution. In the conventional heap-leaching techniques, an appropriate aqueous environment as been achieved by adding oxygen (atmospheric) to the lixiviant, together with acids, alkalies, or complexants, singly or in combinations. It is known that micro-organisms can play a significant role in producing the required environment.
The conventional second stage of the heap-leaching process receives the pregnant liquor from the first stage and extracts from it the required metal by chemical manipulation or by electro-winning. When chemical manipulations are performed, they are generally performed in a custom-built pond or container. When the metal is extracted from solution by electrolytic action, again such processing is generally performed in a custom-built pond or container.
It is emphasised that the electrolysis aspects of electro-winning the metal from solution are carried out upon the liquor into which the copper has already been caused to dissolve. Conventionally, the electrolysis takes place after the liquor has been withdrawn from the heap.
Typically, the pregnant leach liquor might contain up to 10 grams of copper per liter. Iron will also commonly be present in significant amounts as both ferrous and ferric ions. Other metals such as zinc, lead, cobalt, chromium, nickel, silver, gold and others, may also be present.
THE PRIOR ART
A general process for leaching of copper ores is described in U.S. Pat. No. 2,563,623 which illustrates a copper dissolution process as well as a precipitation process. Electro-winning of metal from solution is described in U.S. Pat. No. 3,103,474.
Summary Of The Prior Art Teachings:
the use of chemical and micro-biological manipulations in the first stage, to produce an aqueous environment conducive to the breakdown of e.g sulphide mineral ores;
the use of electrolysis in the second stage, i.e in the extraction of metal from the lixiviant drawn from the heap or dump.
The Prior Art Does Not Teach:
the use of electrolysis in the first stage, i.e the use of electrolysis actually in the heap, for the purpose of creating an aqueous environment conducive to the breakdown of sulphide mineral ores;
the use of electrolysis in the extraction of metal from lixiviant, in situ within the heap or dump;
the conversion in situ of the heap or dump of sulphide mineral ore itself into an electrochemical cell to accomplish these purposes.
SUMMARY OF THE INVENTION
The invention transforms the heap or dump of low-grade metal ore, being sulphides or the like, into an electrolytic cell. That is to say, the heap is caused to adopt an anode-cathode configuration by the imposition of an outside voltage. In practice, electrolyte is added to the heap in such a manner that the heap, if not totally saturated with electrolyte, is at least in a condition of overall electrolytic continuity.
The nature of the cell, as engineered, is such that at the anode of the cell the Eh (redox) voltage of the electrolyte is high enough, and the pH of the electrolyte is low enough, that the metal sulphide or other mineral breaks down, and the metal dissolves and passes into solution in the electrolyte.
Typically, in the case of copper, and in the case where iron is also present (iron is often present with copper), the designer might seek to engineer conditions at the anode in which, for instance, the Eh is +0.5 volts or more, and the pH is 2 or less. It depends, of course, on what else is present in the heap, but those levels will normally be enough to cause the copper to dissolve, and to pass into the electrolyte (as Cu
++
ions).
Generally, if the existing conditions of Eh and pH are not enough, because of other minerals that might be present, the designer of the system can cause the copper and other metals to pass into solution by adequately lowering the pH and raising the Eh; however, the prudent designer will seek to achieve breakdown, and dissolution of the metal, if possible, without going to the limits of acidity and voltage.
At the cathode, the electrolytic conditions are characterised by an increased pH, and a lowered Eh. As the metal cations approach the cathode, they will start to come out of solution, and indeed, if the cations reach the cathode, the cathode will become plated with the metal. But in the first stage of the heap extraction process, however, the desired effect is for the metal to pass into solution in the electrolyte (lixiviant), and to remain in solution therein until the time comes for the metal to be extracted from the liquid. As mentioned, the conventional manner of extracting the metal from the lixiviant might involve plating the cathode, or one of the electro-winning techniques, which involve removing the metal-laden lixiviant before it reaches the cathode.
Preferably, the high-Eh/low-pH conditions at the anode should obtain over a large portion of the whole heap. That is to say: the ideal would be for all the heap to be one large anode, whereby over the whole heap the ore would be breaking down, and the metal from the ore would be passing into solution. While it is rarely possible to ensure that the whole heap behaves like an anode, it is recognised that it is however possible to extend the anodic conditions into a substantial portion of the heap, i.e well beyond the immediate localised vicinity of the actual electrode.
The designer should preferably provide means for extending and augmenting the anodic conditions over large areas of the heap.
First, preferably, the designer should arrange that the anode electrode is itself large, whereby the anode occupies a large portion of the volume of the heap. This can be done by connecting several grids, placed at different levels in the heap, to the anode voltage, as will be described.
Second, preferably, the designer should arrange that the electrolyte has a physical movement or velocity that carries the electrolyte through the heap, in the direction away from the anode. The movement causes the anodic conditions to be extended away from the anode. One source of motion can be gravity, whereby the electrolyte falls down the heap from top to bottom. In this case, the anode should be at the top and the cathode at the bottom, so the electrolyte flows from anode to cathode. Alternatively, in a case where the electrolyte is pumped, the electrodes might be horizontally separated, for instance.
It is preferable also that the anode is located at a place in the heap where the heap is exposed to the atmosphere. The stronger the direct oxygen influence in the heap, and in the electrolyte, the naturally higher the Eh voltage. For this reason also, the designer should locate the anode at the top of the heap.
The designer, when providing for physical movement of the electrolyte through the heap, in order to ensure the electrolytic cell will function properly, must of course arrange that the disposition and extent of the moving electrolyte within the heap is such that electrolytic continuity is maintained between the anode and the cathode. But it is not necessary that the moving electrolyte containing the dissolved copper should actually reach the cathode—nor even that it should have a velocity directed towards the cathode, although usually that will be convenient.
If the configuration of the cell is such that
Chesworth Ward
Shelp Gene Sidney
Anthony Asquith & Co.
ENPAR Technologies Inc.
Valentine Donald R.
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