AU719183B2 - Method of extracting metal from ore material - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor: Address for Service: KRUPP POLYSIUS AG DIPL.-ING. JOHANN KNECHT CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

METHOD OF EXTRACTING METAL FROM ORE MATERIAL .r Invention Title: The following statement is a full description of this invention, including the best method of performing it known to us Method of extracting metal from ore material The invention relates to a method of extracting metal, particularly precious metal, from ore material in which starting ore material is comminuted in a material bed roll mill and comminuted ore material is deposited on a heap and leached by the addition of leaching fluid.

It is already part of the general prior art that precious metals and other metals can be extracted from corresponding ore material by comminuting this ore material and depositing it on a heap, whereupon a suitable leaching fluid a cyanide solution) is distributed or sprayed over the heap so that this leaching fluid penetrates this ore material heap and in so doing breaks up the metal compounds, whereupon the laden leaching fluid is collected and drawn off for further processing.

Corresponding naturally occurring ores, residues in ore mining loll as well as any kind of industrial residues which contain the metals and in i" 15 particular precious metal to be extracted are regarded as ore material in this •context. In this case the expression "precious metal" includes principally gold, silver and platinum. Furthermore, other soluble valuable substances or metals, such as for example copper, can also be obtained by this heap leaching process.

A method of obtaining precious metal from corresponding ore material using material bed comminution and with heap leaching is known for i'.

example from US Patent No. 4,960,461. In this case it is preferred to add a binder to the starting ore material before the material comminution, by which fines from the comminution process should be bound to coarser particles so that the ore material heap can be made permeable to the leaching fluid. Thus the comminuted ore material coming from the material bed comminution has the shape of round flat agglomerates, so-called scabs, which can be deposited directly on the heap, but in many cases can also be broken up somewhat in a disagglomeration stage in order to limit the scabs to be deposited on the heap to a thickness of 10 to 30 mm and an edge length of to 90 mm. In any case, however, this scab material can or will contain a RA, very wide range of grain sizes, that is to say it may also contain relatively large particles which can have the maximum dimensions mentioned above.

2 In the practical execution of this known method it has been shown that extracting metal from the starting ore material is still most unsatisfactory.

The object of the invention, therefore, is to propose a method of extracting metal and in particular precious metal from ore material which permits an increased extraction or yield of precious metal and other metals from corresponding starting ore material.

According to a first embodiment of the present invention this is provided a method of extracting metal, particularly precious metal, from ore io material, in which starting ore material is comminuted in a material bed roll mill and comminuted ore material is deposited on a heap and leached by the addition of leaching fluid, wherein the comminuted ore material is deposited on the heap with a maximum grain size of approximately 12 to 15 mm.

In the tests on which the invention is based it has been 15 demonstrated that comminuted ore material is only insufficiently leached and thus the metals contained therein can only be insufficiently dissolved by the leaching fluid even when the comminution takes place in the form of material oo o bed comminution, that is to say in a material bed roll mill. It is known that in the material bed roll mill some of the brittle material can be completely S" 20 comminuted and some of it only scored by micro-cracks or partially comminuted by a combined individual grain loading and material bed loading.

SThe ore material thus comminuted leaves the material bed roll mill as more less severely compacted, round flat agglomerates, so-called scabs, which can normally be broken up or disagglomerated with relatively little exertion of force.

3 However, if these scabs are rendered more stable in shape by the addition of a corresponding binder to the starting ore material, as occurs for instance in the known method described above according to US Patent No. 4,960,461, then the relatively large scab pieces will also largely retain their shape and size in the leaching heap. Due to these relatively large scab pieces relatively large interstices are indeed created which favour the permeability of the heap to the leaching fluid; however, the scabs, which are round and flat or at least to some extent plate-shaped, can also often lie close above one another in layers in the heap, greatly reducing the permeability to leaching fluid. Overall, with this known method it has been shown that the rate of yield of Sprecious metal from ore material leaves a great deal to be desired, and moreover this known method can only be used with oxidic ore.

The present invention likewise does utilise the advantages of material bed comminution on a material bed roll mill for the extraction of metal, particularly precious metal, from corresponding ore material However, this is done in such a way that the comminuted ore material is deposited on the heap with a maximum grain size of approximately 12 to 15 mm. Thus the ore material to be deposited on the heap or leaching heap is controlled after the material bed comminution and kept in a grain size range with a maximum grain size of 12 to 15 mm.

The previously mentioned tests on which this invention is based have also in fact shown that the yield of metals, and particularly of precious metals, from the corresponding starting ore material in heap leaching already deteriorates at a grain or particle size of over approximately 6 to 8 mm (maximum edge length), this deterioration in the metal extraction increasing particularly markedly above a grain or particle size of approximately 12 to 15 mrm.

The previous observations could also be confirmed by a series 4 of laboratory tests which were carried out with ore material containing gold, in each case with the same leaching fluid (cyanide solution) and the same ratio of leaching fluid to quantity of ore. Thus in a test example the ore material was comminuted to approximately 12.5 mm YV") mesh size and leached over a period of 120 hours; the yield of pure gold ore was 31.3%. Coarser test grain sizes lead to somewhat lower percentages in the gold extraction. With comminution of the ore to approximately 6.35 mm mesh size it was already possible to achieve a dramatic rise in the gold extraction, namely a percentage of 67,0% of the gold contained in the ore.

**oo Thus according to the invention it is particularly preferred to set the grain or particle size of the comminuted ore material to be deposited on the heap to smaller than approximately 8 mm and quite especially preferably to smaller than approximately 6 mm in the case of substantially powderfree grains. In this way an optimal yield of metal fractions S containing valuable substance from the corresponding starting S* ore material can be brought about. This advantage is all the more important if one considers that oxidic ore, i.e. ore which is directly leachable, containing metal or precious metal is available in ever decreasing quantities.

In this connection it should be explained that in this case oxidic ore is characterised in that with direct leaching of this ore general rates of yield of over 80X are achieved.

However, semi-refractory or refractory ores often require an intermediate treatment or at least still finer comminution, so that economically viable rates of yield of extraction can be achieved.

The maximum grain size proposed according to the invention for the comminuted ore material to be deposited on the leaching heap has also proved favourable with regard to the permeability to the leaching fluid within the heap. In fact, 5 with this grain size a particularly uniform distribution of the leaching fluid and thus to some extent a uniform washing round of all material grains or particles is achieved, which leads to the desired optimal release of the metals contained in the ore material particles comminuted in the material bed, that is it leads to an optimal extraction of precious metals.

Depending upon the mineralogical composition high clay fractions or the like) of the ore material to be treated, in the case of certain ore materials it is also important that the comminuted ore material to be deposited on the leaching heap is substantially powder-free in the said grain size Srange, i.e. no material particles in the form of dust or powder should be deposited on the leaching heap. This would clog the heap to some extent, so that the heap would lose its o:•o necessary permeability to the leaching fluid. Thus with this method according to the invention the optimal grain size range of the ore material to be deposited on the heap can be controlled or regulated quite deliberately.

In the simplest embodiment of the method according to the invention the procedure is such that the ore material which o ~has been comminuted in the material bed comminution to a maximum grain size of approximately 6 mm is deposited directly on the heap. However, this procedure is only reasonable when the ore material coming from the material bed comminution on the one hand does not exceed the aforementioned maximum grain size of approximately 6 mm and on the other hand is largely powder-free or contains few pieces of material which could cause partial blockage or uneven wetting of the entire heap.

Blockage should be understood here to mean that parts of the stockpile-like heap become impermeable to the applied fluids due to these fines, so that no or only insufficient yield of valuable substance can take place from these regions. A particularly good possibility for also binding the fine, approximately powdery material fractions can be that either 6 the fine material fraction from the classification stage before being deposited on the heap or also the comminuted ore material coming from the material bed roll mill is at least in part, preferably in total, first of all agglomerated in an agglomeration stage and then deposited on the heap. Such agglomeration can be carried out in an extremely controlled manner, so that approximately rounded or approximately spherical pellets, briquettes or the like can preferably be produced. In contrast to the flat round scab pieces described above, due to this agglomeration according to the invention of the ore material comminuted in the material bed roll mill the heap can be piled up particularly evenly with a correspondingly uniform permeability to the fluid to be applied to the heap, which in turn leads to optimum and uniform wetting of all material particles resulting in an o increased yield of valuable substance.

Whereas the previously described procedure can be used above all for leaching directly leachable oxidic ore materials by the addition of leaching fluid on the heap, there is also, however, the possibility of utilising this method according to the invention for processing of so-called refractory ores or ore materials, i.e. ore which is not directly leachable. In this case the procedure can be such that the ore material with a set grain size, that is to say in this case the refractory ore material, is first of all subjected on the heap to an oxidation treatment by the addition of a suitable oxidising agent, whereupon the ore material which has thus been rendered oxidic is then washed (and thus to a certain extent neutralised) and then leached on the heap by the addition of leaching fluid as described above.

In this way non-oxidic, that is to say refractory or semirefractory ore material can be economically leached on a stockpile. According to this embodiment of the method according to the invention this comminuted ore material 7 (typically above all gold and certain copper ores) is thus subjected to an oxidation treatment directly on the stockpile or heap. This oxidation can as is known per se be achieved by the action of certain bacteria or by corresponding chemicals. Following this oxidation treatment the ore material is then first of all set to the desired chemical properties in a washing process, i.e. is neutralised to a certain extent, before the valuable substances can then be extracted from this ore material by means of the said leaching process.

Thus in the processing of refractory ore materials the comminution of these types of ore in a material bed roll mill offers the advantage of micro-cracks in the comminuted ore particles, as a result of which the oxidation then also progresses in the manner described above more quickly and with higher degrees of oxidation, which overall can take place very economically. In this case it also proves particularly sensible in the case of the comminuted ore material coming from the material bed roll mill optionally after disagglomeration of scabs which have formed for the grain size of this comminuted ore material to be limited or set in the stated manner so as to favour the most complete oxidation possible of the individual particles.

There are various possible ways of using the method according to the invention in order to be able to regulate or control the optimum range of grain sizes with which the ore material coming from the material bed comminution is deposited on the leaching heap. This is explained in greater detail below with reference to some embodiments which are i 1 lustrated in the drawings, in which: Figure 1 shows a flow diagram (block diagram) of a first embodiment for carrying out the method according to the invention, in which a screen classifier is interposed between 8 the material bed comminution and the leaching heap; Figure 2 shows a flow diagram of a second embodiment with an agglomerating conveyor belt disposed between the material bed comminution and the leaching heap; Figure 3 shows a flow diagram for an embodiment in which a pelletising table is provided between the material bed comminution and the leaching heap; Figure 4 shows a flow diagram with variants of the embodiment according to Figure 1.

In all the embodiments described below with reference to Figures 1 to 4 it may be assumed that they are designed for carrying out the method according to the invention of which a far-reaching description has already been given above, particularly for extracting precious metal, such as for example gold, silver and platinum, from corresponding ore material. However, other suitable ore materials, e.g. in particular copper ores, can be processed in substantially the same way to give corresponding metals. For the sake of simplicity all machines or apparatus parts which are the same or of similar construction are provided with the same reference numerals, so that the corresponding apparatus parts essentially only have to be explained in detail once.

The first embodiment according to Figure 1 contains a material bed roll mill I which can be constructed in a manner which is known per se and accordingly is equipped with two rolls 3, 4 which are pressed against one another under high pressure and can be driven in opposite directions (cf. arrows 2) and between which a grinding gap 5 is constructed. The material bed roll mill 1 also has a material delivery shaft 6 in the region above the grinding gap 5. Downstream of the material bed roll mill 1 is provided a screen classifier 7 which for 9 example contains a top screen 7a with suitable screen hole size, and also a discharge 7b for the oversize material fraction as well as a discharge 7c for the product falling through or fine material fraction. Downstream of the discharge 7c for the fine material fraction of the screen classifier 7 there is provided a leaching heap 8 which can likewise be of a construction which is known per se and which accordingly has associated with it a delivery arrangement 9 for leaching fluid (broken arrows 10) which arrangement is optionally movable over the heap.

In the apparatus according to Figure 1 starting ore material •ago containing precious metal is delivered according to the arrow 11 to the material bed roll mill 1 via the material delivery shaft 6 thereof. This starting ore material 11 is subjected to material bed comminution in the grinding gap 5 between the two rolls 3, 4. The comminuted ore material according to the arrow 12 is then first of all delivered to the screen classifier 7, the top screen 7a of which is constructed so that only comminuted ore material with a grain size of smaller than approximately 8 mm to 12 mm, preferably smaller than approximately 6 mm to 10 mm, fal Ils through downwards, so that this product falling through the screen or the fine material fraction formed thereby can be deposited and distributed uniformly on the heap 8 according to the broken line 13 where it can be leached by means of leaching fluid 10. The retained product or the oversize fraction of the classification stage formed by the screen classifier 7 is drawn off at the discharge 7b and returned to the material feed shaft (feed arrangement) 6 of the material bed roll mill 1 according to the dash-dot line 14, so that it is again subjected to material bed comminution with the fresh starting ore material 11. In the processing of the ore material in the material bed roll mill 1 it may be mentioned that it is comminuted without the addition of binder and thus the scabs obtained can be disagglomerated relatively easily, at least partially on the 10 top screen 7a of the screen classifier 7. Therefore the maximum grain size of the comminuted ore material to be deposited on the heap 8 can easily be set in a very controlled manner.

In the second embodiment of the apparatus illustrated in Figure 2 an agglomeration stage in the form of a conveyor belt or agglomerating conveyor belt 15 is interposed between the material bed roll mill 1 and the leaching heap 8. In this way at least part but preferably all of the ore material 12 comminuted in the material bed roll mill 1 can be shaped into pellets of any suitable size on this agglomerating conveyor 000* belt 15. In this case a suitable binder can then be added to *.0 the comminuted ore material on the conveyor belt 15 above all when the component consisting of very fine particles or .o powdery particles is relatively large, so that these powdery particles can then be incorporated into the pellets and cannot impair the permeability of the heap.

As regards the resulting agglomerates in pellet form, it may also be mentioned that due to the production on the agglomerating conveyor belt 15 or another suitable pelletising 0 0 arrangement these agglomerates can be at least somewhat rounded, but generally can be approximately spheroidal or spherical. Moreover, they can also be somewhat larger than the maximum grain size of the ore material particles, that is to say for example larger than 6 to 8 mm. In contrast to the depositing of larger round flat scab pieces as in the known method explained above the desired quality and size of the pellets to be deposited on the heap, in which the grain size of the comminuted ore material in each case is kept to the maximum grain size explained above or set to that size, can be set in a very control led manner by this agglomeration of the ore material which has already been comminuted. When the pellets or agglomerates produced in this way are deposited on the heap, optimum preconditions are created for the fluid 11 (leaching fluid) delivered to the heap to be very evenly distributed and for the individual pellets and thus also the ore particles incorporated therein to be optimally wetted, so that a particularly high degree of leaching and consequently a very high rate of yield of valuable substances can be achieved.

The embodiment according to Figure 3 to some extent represents a variant of the example previously explained with reference to Figure 2. In this case (Figure 3) the agglomeration stage is formed by a pelletising table 16 which is known per se, to which all of the comminuted ore material from the material bed roll mill 1 is also delivered, so that it can be agglomerated to the optimum grain size (that is to say with the optimum pellet size) and can then be deposited on the heap.

o.

It should also be pointed out at this point that other suitable agglomeration arrangements can also be used for the agglomeration stage if the sizes and shapes or properties of the agglomerates or pellets as described above can be achieved and maintained thereby. Thus instead of an agglomerating conveyor belt and a pelletising table a pelletising drum can for example be used. Moreover, it may also be advantageous to carry out the agglomeration of the comminuted ore material in a conventional briquette press, in which case the agglomerates can advantageously also be passed to the briquette press in the desired briquette mould (in a similar manner to the pellets) without the addition of binders. As a result the operating costs can be reduced, and depending upon the leaching agent or the leaching fluid a better yield of valuable substance can be achieved.

Also in connection with the agglomeration stage 15 or 16) it should be pointed out that at the beginning of the agglomerating or pelletising operation the scabs from the material bed roll mill 1, which without binder are relatively 12loosely cohesive, can first of all be at least partially broken up and only after that brought in a quite controlled manner to the desired grain size.

Thus the two embodiments of apparatus according to Figures 2 and 3 are particularly suitable if the starting ore material 11 is comminuted relatively finely or largely comminuted in the material bed roll mill 1 and contains a relatively large amount of very fine material in the form of powder or dust.

Thus by the interposition of the agglomeration stage 15 or 16 it is possible to ensure in a reliably controlled manner that the comminuted ore material to be delivered to the heap a leaching is kept substantially powder-free in the desired grain size range.

Depending upon the nature or the properties of the starting ore material 1 1 to be comminuted as we ll 1 as the mode of operation of the material bed roll mill 1, there are yet further combinations or variants which are possible in apparatus for carrying out the method according to the invention.

Thus basically it may be helpful or necessary if the comminuted ore material to be delivered to the classification stage (Figure 1) or the agglomeration stage (Figures 2 and 3) is previously intentionally disagglomerated at least to some extent.

Accordingly Figure 4 shows a variant of the embodiment of the apparatus according to Figure 1 in such a way that a suitable disagglomeration stage 17 can also be disposed between the material bed roll mill I and the screen classifier 7 if need be. Thus if for example the comminuted ore material coming from the material bed roll mill 1 has been agglomerated in relatively large round flat scabs, then these scabs can first of all be at least partially or sufficiently broken up in the 13disagglomeration stage 17 so that afterwards a good classification of the comminuted ore material 12 can take place in the screen classifier 7. Also in this case the oversize material fraction (screen residue) 14 is thereupon returned to the material delivery shaft 6 of the material bed roll mill 1, whilst the screenings or the fine material fraction 13 can be deposited on the leaching heap 8.

As is indicated furthermore by a dash-dot line in Figure 4, however, an agglomeration stage in the form of a pelletising drum 18 or the like can also be disposed between the screen classifier 7 and the leaching heap 8. Thus this measure also provides the possibility that the fine material fraction 13 @0 from the classification stage or the screen classifier 7 can *00* be set in the agglomeration stage 18 to an optimum grain size for heap leaching before it is deposited on the heap 8. In this way as already described above very fine fractions of *00 the comminuted ore material which are in the form of powder or 0@ 00 dust can be incorporated into the ore material pellets or agglomerates, thus reliably preventing the pores or interstices between the material grains in the leaching heap from being clogged by powdery fractions.

The embodiments of apparatus or methods explained above with reference to Figures I to 4 are suitable in the described form above all for heap leaching of oxidic ore material. However, increasing efforts have been made recently to leach non-oxidic ore, so-called refractory or semi-refractory ore or ore material economically on a heap or a stockpile. As has already been explained above, this method according to the invention can also be designed so that it is suitable for heap leaching of non-oxidic or refractory ore materials, particularly for example gold and certain copper ores. In this case it must generally be ensured that the comminuted ore material to be leached on the heap is previously subjected in a suitable manner to oxidation treatment. This can preferably 14 take place for example in such a way that the refractory ore material, which has previously in a similar way been subjected to material bed comminution and set to a predetermined maximum grain size as described with reference to Figures 1 to 4, is subjected on the heap first of all to oxidation treatment by the addition of a suitable oxidising agent bacteria or other suitable oxidising agents). With this oxidation treatment too, the optimum preparation, i.e. material bed comminution and setting to an optimum maximum grain size of the ore particles, has an extremely advantageous effect on the distribution of the oxidising agent and thus on the entire oxidation of the ore material on the heap. This oxidation treatment is followed by a washing operation in which the residual oxidising agent is washed out and thereby the oxidised ore material is neutralised to a certain extent before the actual leaching can be initiated by delivery of leaching fluid and carried out in the aforementioned manner.

In this case the washing out of the oxidation agent can take place on the same heap. However, if a particularly intensive washing of the heap is necessary, then this can also take place due to the fact that the oxidised stockpile or the oxidised heap is built up and in the course of that subjected to a washing operation, whereupon the leaching of the valuable substances is carried out in a heap or stockpile to be newly erected. Accordingly the valuable substances can then also be extracted from refractory or semi-refractory ore materials by means of heap leaching with a high rate of yield.

With this method according to the invention there are also the possibilities of adding leaching fluid or an oxidising agent to the comminuted ore material as early as before or during the agglomeration or pelletising or briquetting operation, as is indicated by the arrow 19 for example in Figures 3 and 4 in the case of the pelletising table 16 or the pelletising drum 18 respectively. In this way depending upon the type of processing required or depending upon the type of ore material 15 to be treated (oxidic or refractory) the operation of leaching or oxidation of the ore material can already be initiated in the region of the agglomeration stage.

Claims (2)

16- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Method of extracting metal, particularly precious metal, from ore material, in which starting ore material is comminuted in a material bed roll mill and comminuted ore material is deposited on a heap and leached by the addition of leaching fluid characterised in that the comminuted ore material is deposited on the heap with a maximum grain size of approximately 12 to 15 mm. 2. Method as claimed in Claim 1, characterised in that the grain size of the comminuted ore material to be deposited on the heap is set to smaller than approximately 8 mm, preferably smaller than approximately 6 mm, with substantially powder-free grains. a. 3. Method as claimed in Claim 2, characterised in that the ore material comminuted in the material bed comminution to a grain size of a maximum of 6 mm is deposited directly on the heap. S 4. Method as claimed in Claim 2, characterised in that the maximum grain size of the comminuted ore material is set in a I classification stage, particularly a screen classifier from which a fine material fraction (13) is deposited on the heap and the oversize material fraction (14) is returned to a feed arrangement of the material bed roll mill Method as claimed in Claim 4, characterised in that the fine material fraction (13) from the classification stage (7) is agglomerated in an agglomeration stage (18) before being deposited on the heap 6. Method as claimed in Claim 2, characterised in that at least part, preferably all of the comminuted ore material coming from the material bed roll mill is agglomerated in

17- an agglomeration stage (15, 16) and is then deposited on the heap 7. Method as claimed in Claim 5 or 6, characterised in that the agglomeration of the comminuted ore material is carried out on an agglomerating conveyor belt a pelletising table in a pelletising drum in a conventional briquette press or the like. 8. Method as claimed in Claim 7, characterised in that the comminuted ore material is agglomerated with or without the addition of binder. **ee 9. Method as claimed in Claim 7, characterised in that S leaching fluid or an oxidising agent is added to the comminuted ore material before or during the agglomeration ,operation. Method as claimed in Claim 2, in which the during the material bed comminution in the material bed roll mill the starting ore material is agglomerated in round flat scabs, characterised in that the ore material in scab form coming from the material bed roll mill is first of all broken up at least partially in a disagglomeration stage (17). 11. Method as claimed in Claim 2, characterised in that in the processing of refractory ore material the ore material which has been set in its grain size is first of all subjected on the heap to oxidation treatment by the addition of an oxidising agent, whereupon the ore material which has been rendered oxidic is then washed and subsequently leached on the heap by the addition of leaching fluid. 18 12. A method of extracting precious metal from ore material substantially as herein described with reference to the accompanying drawings. DATED this 5th day of June 1997 KRUPP POLYSIUS AG By their Patent Attorneys CULLEN CO. S. S *o S