AU9703801A - Leach reactor - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION STANDARD PATENT "Leach Reactor" The following statement is a full description of this invention, including the best method of performing it known to me: 39yd iVNd3d WOOWO 009L9886ET9+ T10: TOOZ/ZT/ItB LEACH REACTOR Field of the Invention This invention relates to apparatus and methods for recovering valuable metals, particularly gold using an in line leach reactor. In particular non-limiting aspects, the invention also provides apparatus for dewatering and leach reactors which may be suitable for carrying out the method of the invention.

Background of the Invention Processes for the recovery of gold from gold bearing feeds have typically involved the use of a cyanidation step to convert the elemental gold into a soluble ionic form. The gold in solution can then be separated from the bulk mineral material which stays in solid form by 15 a simple liquids/solids separation process (eg. sedimentation or filtration).

The solution containing dissolved gold is then subjected to a gold recovery process such as the carbon-in-pulp process. In this process the gold in solution is adsorbed on an activated carbon substrate in the form of carbon granules and the gold is subsequently recovered.

While such processes have been successful in retrieving a significant proportion of the gold embedded in certain minerals, they suffer from significant disadvantages. For example, if the gold is present as nuggets or flakes larger than microscopic pieces, the cyanidation process, because of the relatively low concentration of the reagents used in the process, will generally not succeed in dissolving the larger pieces of gold. As a result, these larger pieces may be lost with the waste minerals discarded following the cyanidation process.

Furthermore, it is often the case that the minerals associated with gold deposits also include a proportion of native carbon, Unfortunately, this carbon is generally in a form which cannot be readily recovered or separated from the minerals. During the cyanidation process, the native carbon can adsorb a proportion of the gold during the leaching process.

Depending upon the level of native carbon present in the mineral, the time taken for the 39Vid IVN1J VJOON 00SLSBBSSTS+ TO:Tt T30/ZT/P0 leaching process and the concentration of the leaching reagents (ic. sodium or potassium hydroxide and sodium or potassium cyanide) the amount of gold lost in this way can be quite significant.

Given the large volumes of mineral material which need to be treated using the cyanidation process, it is not practical to use high concentrations of reagents because of their cost, and also because of the environmental concerns associated with the use of large quantities of dangerous reagents. Thus, one is often faced with a situation where the relatively low concentrations of the reagents require high residence times for leaching. The longer the residence time the greater the proportion of gold which will be adsorbed by the native carbon. Thus the presence of native carbon in the minerals being leached means that a significant proportion, perhaps 25% or even 50% or higher of the gold which goes into solution as a result of the leaching reaction can be adsorbed by the carbon in the mineral and is ultimately lost when the leached mineral solids are discarded.

00 0:0 It is possible to ameliorate this problem to some extent by burning off the carbon in a 99 9 woasting operation prior to leaching. However, it has been found that roasting, whilst it can drive off a significant proportion of the carbon in the mineral as carbon dioxide, is not 9999* 000000totally effective in that a substantial quantity of the carbon can still survive the woasting 0*0 20 process and remain in solid form intimately admixed or bound with the mineral. Thus, 0: even alter roasting, a significant proportion of the gold may be adsorbed by the remaining 999990 native carbon in the mineral during leaching. Furthermore, because the process of roasting 0:e. is very energy intensive, the economics of the gold recovery process can be significantly *.0220 worsened. This is particularly in light of the fact that gold deposits generally include only extremnely small quantities of gold (of the order of' grams per taone) with the result that a huge amount of energy needs to be expended to roast tonnes of ore only to yield grams of gold.

Thus there is a need for a process and apparatus which avoids the need for a roasting step but which can yield high gold recovery rates notwithstanding the fact that the minerals with which the gold is associated may include significant amounts of native carbon and/or LO 39Vd IVNd3d WOD JOW £0 D~ 1N~Jd O~OW009L9886619+ 10:11 100Z/ZT/t2 pieces of gold of a size which are larger than a microscopic size ie. large enough to be captured by a screen of 5 00 microns or even 1000 microns.

It is also desirable that the process and/or apparatus have a broad range of applications such as the recovery of gold from suiphide bearing minerals and concentrates or any other minerals which do not give high recoveries with normal gravity processes. It is even more desirable that the process and apparatus be adaptable to recover other valuable materials such as copper.

Disclosure of the Invention The invention provides, a leach reactor comprising, an elongate cylinder, *drive means for rotating the elongate cylinder, *to an inlet and an outlet provided at opposite ends of the cylinder, in line with the axis to of the cylinder the inlet being of smaller size than the outlet to provide a gradient through the cylinder down which leach material may flow under gravity, and a plurality of baffles arranged to divide the cylinder into a plurality of zones.

t: 20 In another aspect the invention provides apparatus for the separation of a dense valuable material from a feed, including, concentrator means for concentrating dense material in the feed, a leach reactor as hereinbefore desribed arranged to receive the concentrated dense material from the concentrator, a solids/liquids separator aranged to receive leachant. from the leach reactor, return means arranged to recycle the solids from the solids/liquids; separator to the concentrator, and a recovery station for recovering dense valuable material from solution in the liquid separated by the solids/liquid separator.

The term concentrator includes any form of apparatus for concentrating dense material in a feed or for separating dense material from a feed. Thus it includes conventional jigs or 30Vd IVN83d WOONOW 80 D~d1V~I~ NO~O 9L9886S19+ 10:11 iOOg/Zi/t'O separators such as the "Harz Jig", "Hancock Jig" or a separator of the type described and claimed in Australian Patent No. 684153 hereinafter referred to as the "'In Line Pressure Jig". It also includes banks of two or more concentrators joined in parallel or series.

An In Line Pressure Jig is a pressurised concentrator which uses an agitated bed to separate dense particulates from a slurry. The slurry flows across the top of the bed with dense particulates from the slurry passing through the bed to be collected in a butch. The less dense tailings pass over the outer edge of the bed to be discharged via a tailings outlet.

The apparatus may be associated with a conventional gold recovery circuit such as a cyanidation circuit.

99999Suitably, the apparatus includes at least one concentrator which is an In Line Pressure Jig.

The apparatus may include more than one concentrator. Where there is more than one concentrator the concentrators may be in series or in parallel. More preferably they are in series.

-00004In a preferred form of the invention the, apparatus includes two In Line Pressure Jigs in 0"000 series.

The or each concentrator may include an inlet, an overflow and an outlet. Thus the inlet 9 may be arranged to receive incoming material contaiding the feed. The incoming material 0 0 0is most suitably mixed wit water. The outlet may constitute an outlet for material which has been concentrated by the concentrator. The overflow may be arranged to allow material rejected by the concentrator to flow out of the concentrator.

Means for crushing a feed, such as a gold bearing feed, may be provided in association with the apparatus. The means for crushing may include a grinding mill.

Primary separator means may be associated with the apparatus, The primary separator means may be arranged to receive crushed feed from, the means for crushing and to redirect it into a light fines stream, a heavy fines stream and a coarse material stream. Suitably the 30Vd IVNa3d WODZ OW 60 3~'d VN~Jd NOdOL' OGS986TS+ T011T pnimary separator means is arranged to redirect the coarse material stream into the means for crushing.

The light fines stream may be directed to a gold removal circuit.

The heavy fines stream may be directed to the or each concentrator.

Suitably the primary separator means includes a cyclone. It may include a plurality of cyclones. Most suitably the cyclones are, hydrocyclones.

The heavy fines stream from the primary separator means may be directed to a first concentrator via the inlet thereof Suitably the overflow of the concentrator may be arrnge to direct rejected material from the concentrator to the coarse material stream emanating from the primary separator means.

The outlet of the first concentrator may be directed to the inlet of a second concentrator.

Suitably the concentrate emanating from the outlet of the second concentrator is directed to the leach reactor.

In a particularly preferred farm of the invention a dewatering station may be provided to dewater concentrate prior to being fed to the leach reactor. The dewatering station may include a container having a conical base, a valve for metering the overflow of dewatered solids material from an outlet at the bottom of said base and weighing means for measuring the weight of material in said dewatering station, said valve being responsive to measurements of said weighing means to control rate of outflow of dewatered solids from the outlet of said dewatering station. Thus, in a further aspect the invention provides a dewatering station along the lines of that described herein above.

Suitably the leach reactor is arranged to receive concentrate continuously or intermittently for continuous or intermittent leaching of the concentrate. Most suitably the reactor is in the form of a cylinder closed off at each end. It may include drive means for rotating the OT 39VJ IVN Bd WOONOW 01 D~dlVd~dNO~ON008L9886S19+ 10:11 I00Z/ZT/'2 reactor. It may include flow control means for controlling flow through the leach reactor.

Most preferably it includes a plurality of baffles for controlling the flow of leach material through the leach reactor. Most suitably there are two baffles. The baffles may separate the reactor into three or more zones. One or more openings will be provided in each of the baffles to allow communication between the zones. The openings are most suitably provided in proximity to the wall of the leach reactor to control the flow of leach mnaterial therethrough as the reactor rotates. Openings on adjacent baffles are most suitably provided on diametrically opposite sides of the cylinder.

An inlet may be provided at one end of the leach reactor and an outlet at the other end.

Most suitably the inlet is provided in line with the axis of the cylider. Similarly the outlet may be provided at the other end in line with the axis of the cylinder. Most suitably, the inlet is of smaller size tha the outlet in order to provide a gradient down which the leach material travels as it moves through the leach reactor.

A second dewatering station may be provided to receive leach material from the leach reactor. It suitably includes an inclined linear action dewatering screen, The second dewatering station may be arranged to provide a solids stream and a pregnant liquor stream.

The solids stream may be recycled to the first concentrator. The overflow from a second 20 concentrator may also be recycled to the first concentrator via the inlet.

The pregnant liquor stream may be directed to a gold recovery facility. The gold recovery facility may include an electrowinning station. It may also include a settling tank for 000. settling of any solids in the pregnant liquor prior to electrowinning.

Recycling means may be provided to recycle spent liquor from the electrowinning facility to the settling storage tank. The -recycling means may also be arranged from the overflow liquid from the settling storage tank to the inlet of the first concentrator.

The apparatus of the invention may be used in a method for the separation of gold from a feed which method comprises the steps of: It BDVd JVNd3d WNOWV 003L9886819+ 10:11 T0RZ/ZT/P0 crushing the feed; (ii) concentrating a mixture of the crushed feed and water to form a concentrate stream containing gold wherein at least 80% of the particles in the concentrate stream have a particle size less than 2,000 microns; (iii) dewatering the concentrate stream; (iv) leaching the dewatered concentrate stream continuously'in a rotating leach reactor with aqueous reagent to form a pregnant liquor; controlling the residence time of the dewatered concentrate in the reactor by controlling the rate of rotation of the leach reactor, and (vi) recovering gold from the pregnant liquor.

The leachant liquid may be a mixture of a sodium or potassium hydroxide and sodium or potassium cyanide. The concentration of the cyanide is preferably at least 0.5% by weight of cyanide in the leachant/solid mix. Most suitably the cyanide concentration is at least 15 1.50/.

Preferably the rotation rate of the leach reactor is such as to produce a peripheral speed of rotation of at least 3 metres per minute, more preferably at least 8 metres per minute. The residence time of the leach material in the reactor is preferably less than 10 hours, most 20 preferably less than two hours.

9eego Oxygen may be introduced into the leachant mixture in the leach reactor to facilitate leaching. The oxygen may be obtained from an electrowinning facility for recovering gold from the leachant liquid. Most suitably the oxygen is added by recycled spent leachant liquid after electrowinning to the leach reactor. Oxygen may also be added through bubbling air and/or oxygen into the leach mix.

The leach reaction may be carried out at relatively low temperatures ie. below 50'C, more preferably below 400C and most preferably at ambient temperature.

Most suitably at least 80% of the concentrate fed to the reactor will have a particle size less than 2000 microns, more preferably less than 1000 microns.

Z I 39Vd IVNd3d WOOWO0W 009L88619+ 10:11 1800/1?0/P Most suitably the residence time for leaching is adjusted so that at least 70% of gold, more preferably 85% and most preferably at least 90% or even 95% is taken into solution.

Preferably gold recovery fromn the leachant is by way of electrowinning, or by carbon adsorption or by zinc precipitation processes.

The invention is particularly suitable for recovering gold sulphide and free gold from sulphide and free gold concentrates especially when the gold containing materials will not to give high recoveries using normal gravity based processes. Where sulphide bearing concentrates are involved, high recoveries may not be readily achievable using low level cyanide leaching conditions. However, more intense conditions such as higher temperatures and/or more concentrated leachant liquid and/or higher leach residence times can increase overall recovery particularly in instances where particles of valuable minerals or metals are partially locked in to other less valuable particles.

Whilst a major application of the. invention is the recovery of gold it is to be understood that the invention is also applicable to other valuable minerals, such as copper bearing minerals.

**:The invention will now be described with reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 shows a flow chart for carrying out a process using the apparatus of the invention; Figure 2 is a sectional elevational view of a dewatering device in accordance with one aspect of the invention; and Figure 3 is a sectional elevational view of a leach reactor in accordance with a further aspect of the invention.

61 39Vd iVNd3d W006OW El S~ 1N~id OOON009L9B86619+ 10:11 l037/ZT/t'0 Detailed Description of the Preferred Embodiments Referring to Figure 1, the leach circuit for gold containing ores generally designated 1 includes a grinding mill 2 arranged to receive and crush ore and to dump it in the hopper 3.

A pump 4 connected to the hopper 3 serves to pump the slurry in hopper 3 via the pipe 6 to a series of hydrocyclones 9. These hydrocyclones are arranged to discharge coarse and large heavy material into the holding bin which is itself arranged to recycle this material to the grinding mill 2.

The hydrocyclones are provided with two outlets connecting with a pipe 10 and a bleedline The pipe 10 directs light and fine material from the circuit into a conventional gold .recovery process and the bleedline 15 takes a denser fraction from the hydrocyclone circuit to form an inlet for a concentration stage.

The concentration stage includes a first and a second concentrator 16 and 17 connected in series. The first and second concentrators are In Line Pressure Jigs. They are constructed substantially along the lines of the concentrator shown in the drawings of Australian patent No. 684153 and the disclosures in that patent are by this cross reference incorporated 20 herein. The second concentrator is arranged to direct concentrate and rejected material to 0: the dewatering station 32 and overflow tank 28 via the lines 23 and 24 respectively.

The dewatering station 32 is shown in more detail in Figure 2, *o Referring to Figure 2, the dewatering station includes a cylinder 84 having a conical base and an outlet for dewatered concentrate A circumferential mounting flange 86 is provided on the cylinder 84 and is mounted on a support 87 and load cell 88.

The valve 89 is controlled by signals from the load cell 88. It is arranged to control the discharge of the solid dewatered material 91 when it has reached the level 92 shown at the VT 30Vd iVNdBd WODHW 009L9886E19+ 10:TT 1003/31/P0 side of the cylinder 84. The liquid 90 in the cylinder extends to the level 93 where it overflows into the excess liquid line 33.

Referring to Figure 1, the dewatered solid 35 from the dewatering station is taken up in the inlet 44 to the leach reactor The leach reactor is shown in more detail in Figure 3.

It includes a rotating drum 100 provided with an inlet 44 and an outlet 46 arranged at each end of the drum in the region of the drum axis.

Baffles 10 1 and 102 are provided in the drum to control the flow of leach liquid/solid in association with the openings 104 and 105 provided in the baffles.

15 The openings 104 and 105 are provided near the cylindrical walls of the drum and on opposite sides thereof in order to limit the rate of flaw of the leach slurry through the drum., The leach slurry level 108, 109 and 110 in the different parts of the drum forms a gradient across the drum as the outlet 46 is of greater diameter than the inlet 44.

:20 Referring to Figure 1, a dewatering station 50 is arranged to receive the outflow from thle **:leach reactor and to split it into a dewatered solid stream 51 and a pregnant liquid stream The dewatered solid stream 51 is directed to a solids separation station 52.

The solid separation station includes a vibrating screen which is slightly inclined to the horizontal, the screen having a mesh size of about 300 microns. Excess liquid 54 is directed to the flocculation tank 62 and the solids recycling line 53 is arranged to direct solids which are balled and separated from the screen into the overflow tank 28.

The pregnant liquor recirculation pump 69 is arranged to direct the pregnant liquor to the settling storage tank 71 from which the pregnant liquor is pumped via the pumnp 80 to the 9 1 3DVd iVN83d WOMIOW 91 D~d.LVd~ WOdONOOLSBBESTS+ 10:11 109Z/MT/t'0 12 electrowin station 83. A tap 82 controls the flow of pregnant liquor to the electrowin station.

The electrowin recirculation pump 84 is arranged to pump spent liquor from the electrowin station to the leach reactor inlet 44.

A reagent supply station 40 is provided for the supply of fresh reagents such as caustic soda and sodium cyanide via the dosing pump and the feed line 42 to the inlet 44 of the leach reactor.

Similarly a flocculant supply station 56 is arranged to deliver flocculant via the dosing pump 57 and flocculaut delivery line 58 to the flocculation tank 62.

A return pump 29 is arranged to return material from the overflow tank 28 via the return line 30 to the inlet of the concentrator 16.

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The settling storage tank has an overflow line 72 which also connects with the overflow 0 tank 28.

20 The bottom of the settling storage tank 71 is also provided with a solid liquid line 73 and tap 74 for directing settled solids back into the overflow tank 28 as well.

During operation of the apparatus described with reference to Figures 1 and 3, the raw ore is directed to the grinding mill 2 where it is crushed and mixed with water to form a slurry.

Following comminution it is dumped in the hopper 3.

The pump 4 pumps the resultant slurry via the pipe 6 to the hydrocyclones 9 which separate the slurry into three streams namely, a stream of light fine material which is directed by the pipe 10 to a conventional gold reclamation circuit, a stream of coarse and/or heavy material which goes via the holding bin 7 back into the grinding mill and a bleed stream which goes via the bleed line 15 to the concentration circuit.

91 3S'Vd lAN3d HOONOW 809L9886ES9+ 10:11 102,/ZT/VO The bleed 15 contains the heavier particulates including large and/or flaky particles of gold which are difficult to recover by conventional gold recovery processes. This is because the concentration of reagents in conventional recovery processes, because of the very large volume of material which needs to be treated, has to be kept low and as a result, the larger gold particles tend to pass through a conventional gold leaching circuit without going into solution and are lost to waste.

The first concentrator 16 has a first concentrator overflow line 21 which recycles lighter material rejected by the concentrator to the holding bin 7 and hence grinding mill 2. A water line 18 controlled via taps 19 to both the first and second concentrator is used to maintain pressure in the two concentrators in the manner described in Patent No. 684153.

The concentrate from the first concentrator is directed via the first concentrate line 20 to the second concentrator 17 where the concentration process is repeated with the overflow from the second concentrator being returned to the overflow tank 28.

The concentrate from the second concentrator is directed via the second concentrate line 23 to the dewatering station where the major part of the liquid is separated from the solids. In order for the process to proceed efficiently, it is generally important to ensure that the amount of liquid mixed with solid entering the leach reactor is kept to a minimum. Thus it 20 is anticipated that the dewatered "solid" exiting the dewatering station will be at least and preferably at least 60% by weight of solids.

The dewatering; station is run so that there are sufficient solids in the cylinder 84 to completely cover the outlet at the bottom of the conical base 85. This generally means that the solids will represent about 30% by volume of the solids/liquids mixture in the dewatering unit 32.

As the solids are denser than the liquid contained therein, the proportion of solids can be sensed by a load cell 88 which simply measures the total weight of the assembly. When the weight exceeds a predetermined figure, the valve 89 may be opened preferably on a pulsating basis, until sufficient of the solids have been allowed to drain out as to return the LT 30Vd IVNd3d W0060H £1 S~dIV~~d O~dN 9L9886813+ 10:11 ieegi/iT/PO overall weight of the assembly to within a prescribed range. Thus the dewatering station may be effectively operated continuously.

The dewatered solids are mixed with spent solution from the electrowin process fed by the electrowin recirculation line 85 and additional reagents in the form of caustic soda and sodium cyanide prior to being fed to the leach reactor via inlet 44. It is noted that because the electrowin process is run at ambient temperatures, the spent liquor recycled to the leach reactor will have large amounts of dissolved oxygen forned by the electrowin process.

Additional air/oxygen may also be introduced into the reactor via a sparge line.

The residence time in the leach reactor will depend upon the particular qualities of the ore being treated. However it is to be appreciated that preg-robbing ores require as short a *0 residence timne as is reasonably practicable in order to minimise the amount of gold 0 adsorbed by the preg-robbing carbon in the native ore body.

The leach reactor will typically be rotated at a peripheral speed of about 10 metres per minute. For a one metre diameter drum this involves a rotational speed of about 3 rotations per minute.

20 The baffles combined with the openings 104 and 105 in the leach reactor serve to limit the rate of progress of the leach mixture through the reactor in a controlled manner.

Furthermore, the construction is such -that the ratio of liquid reagent to solid material being leached can be adjusted to reflect the requirements for a particular solid. Thus, if the solid contains a high proportion of native carbon, the amount of reagent added by comparison to the volume of solid can be significantly increased and the residence time required for leaching can be correspondingly decreased. Where shorter residence times are required, it is a simple matter to increase the rate of reagent delivery and also the rate of rotation of the leach reactor to speed up the overall process. T7hus the Process is particularly suitable where ores of variable quality are being treated as it is possible to continuously monitor and adjust the rate of the leach reaction as is necessary.

81 39Vd iVN83d WOOHOW ST D'i lVd~dVJOdOW009L98866T9+ TOUTT TOOZ/ZT/tO Upon discharge from the leach reactor via the outlet 46, the leachant 47 is directed to a further dewatering station 50 which may be constructed in a similar manner to that described in relation to the first dewatering station 32.

The pregnant liquor 55 from the further dewatering station is directed to the flocculation tank 62 whereas the solids component 51 is directed to a further dewatering operation through the solids separation station 52.

The solids separation station includes a screen having a mesh size of about 100 microns which is inclined to the horizontal. The screen is driven to vibrate and cause the solids to ball up and "walk" uphill to be dropped off at the end into a receptacle and eventually returned via the solids recycling line 53 to the overflow tank 28. The pregnant liquor 54 separated by the screen as excess liquid, is also directed to the flocculation tank 62 where the liquid is mixed with flocculant delivered from the flocculant supply station 56 via the dosing pump 57 and flocculant delivery line 58.

The bottom of the flocculation tank is provided with an outlet for tapping solids which are recirculated via the solids recirculation pump 63 and solids recirculation line 64 to the dewatering station Similarly, pregnant liquor is taken from the upper part of the dewatering station via the pregnant liquor line 70 and pumped via the pump 69 to a further settling storage tank 71.

This settling storage tank 71 is again used to control off take of pregnant liquor via the pregnant liquor line 81 and the pump 80 using the tap 82 to control supply to the electrowin station 83 which recovers gold from the pregnant liquor. Alternative gold recovery processes include the zinc precipitation or carbon based processes. Solids from the settling storage tank are directed to the overflow tank 28 via the line 73 after being mixed with liquid overflow from the tank 71 and excess liquid coming from the first dewatering station 32 via the excess liquid tine 33.

GT 3D d 1VN63d WOOW 009L9886619+ rO:TT TO0/Z1/VO 16 A mixture of recycled solids and liquids fromn the overflow tank 28 is returned to the inlet of the first concentrator.

Similarly, the spent pregnant liquor solution is recycled to the leach reactor after going through the electrowin station.

The process and apparatus of the invention have particular advantages over the prior art in that they can be operated continuously, and they can cope with a range of different ore types with adjustments made to the rate of leaching and treatment in accordance with the io properties of that ore type, In particular, because the volumes of concentrate treated are much smaller than the volume of feed initially introduced into the process, reagents may be economically used at high concentration. Furthermore, because of the high reagent concentrations, the rate of leaching is substantially increased wit consequent decrease of leaching residence times and corresponding opportunity for native carbon to adsorb gold 1s during leaching. Thus, the invention is particularly suitable for treatment of preg-robbing ores. It also has major security advantages in that the gold in the circuit is not in a form which can be readily stolen, the only major security precautions required being in relation to the final electrowin process where solid gold is produced. However as this only represents a small part of the overall process it can be far more readily subjected to security conditions.

Operating Results The results below show the average daily recoveries of the in line leach reactor described with reference to the drawings operating at 80 100 kg/br of gravity (<2mm) concentrates.

These recoveries are total recoveries and do not reflect free gold recoveries. No free gold was visible in the reactor solids tailing.

OZ 3EV~d lVNd~d HOOdON 329L9886S19+ 10:11 TO0g/gT/'0 Day Feed (ppm) Tail (ppm) Recovery 1 819.00 13.00 98.41 2 381.00 10.50 97.24 3 686.00 3.25 99.53 4 1305.50 15.65 98.80 773.00 19.65 97.46 6 695.00 14.35 97.94 It is to be understood that the word comprising as used throughout the specification is to be interpreted in its inclusive form ie. use of the word comprising does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

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Claims (12)

1. A leach reactor comprising, an elongate cylinder, drive means for rotating the elongate cylinder, an inlet and an outlet provided at opposite ends of the cylinder, in line with the axis of the cylinder the inlet being of smaller size than the outlet to provide a gradient through the cylinder down which leach material may flow under gravity, and a plurality of baffles arranged to divide the cylinder into a plurality of zones. A leach reactor according to claim 2 wherein each of the baffles include one or more openings near the wall of the reactor defined by the cylinder to allow communication between zones.

3. Apparatus accordance to claim 1 or 2 wherein there are two baffles.

4. Apparatus according to any one of the preceding claims wherein the drive means *are set to rotate the elongate the elongate cylinder so that it has a peripheral speed of rotation of at least 3 metres per minute. 7*5. Apparatus according to claim 4 wherein the drive means are set to provide a peripheral speed of rotation of at least 8 mectres per minute.

6. Apparatus for the separation of a dense valuable material from a feed, comprising, concentrator means for concentrating dense material in the feed, a leach reactor according to any one of the claims 1 to 5 arranged to receive the concentrated dense material from the concentrator, a solids/liquids separator arranged to receive leachant from the leach reactor, return jneans arranged to recycle the solids from the solids from the solids/liquids separator to the concentrator, and ZZ 39Vd iVNd3d W00 10W BS~ JV~~d O~ON009L9886S19+ 10 :11 1003/Z1/n a recovery station for recovering dense valuable material from solution in the liquid separator

7. Apparatus according to claim 6 wherein the concentrator means is an In Line Pressure Jig.

8. Apparatus according to any one of claims 6 or 7 including crushing means for crushing the feed and mixing it with water to produce a solids/liquids mixture.

9. Apparatus according to claim 8 including primary separator means for removing a coarse material stream from the solids/liquids mixture and recycling the coarse material o stream to the crushing means. Apparatus according to claim 9 wherein the primary separator means includes one or more hydrocyclones and the primary separator means is adapted to split the solids/liquids mixture into a coarse material stream, and a light fines stream.

11. Apparatus according to claim 10 wherein, the concentrator means comprise two In Line Pressure Jigs arranged in series, the primary separator is arranged to direct the heavy fines stream to the more than one concentrator, and a dewatering station for dewatering concentrated dense material prior to delivery to the leach reactor.

12. Apparatus according to claim 11 wherein the dewatering station includes, a container having a conical base, a valve for metering the outflow of dewatered solids material from an outlet at the bottom of said base, and weighing means for measuring the weight of material in the dewatering station, the valve being responsive to measurements of the weighing means to control the rate of outflow of dewatered solids from the outlet of the dewatering station. CZ 30Vd 1VNd3d WOOdW 00G9L98B6ET9+ iO:TT TOi0/0T/t0

13. Apparatus according to any one of the preceding claims wherein the solids/liquids separator comprises, a dewatering station having an outlet provided near the bottom of a settling vessel to allow material containing a high proportion of settled solids to drain therethrough, a screen for separating solids and liquids making up the material, and recycle means for recycling solids to the concentrator and liquids to a settling storage tank.

14. Apparatus according to claim 13 wherein the settling storage tank comprises, means for recycling settled solids to the concentrator, and feed means for directing pregnant liquor from the settling storage tank to an electrowin station for recovering gold from the pregnant liquor and return means for returning spent liquor from the electrowin station.

15. Apparatus according to any one of the preceding claims including means for sparging the contents of the leach reactor with an oxygen containing gas. Dated this 4th day of December 2001 Alexander Hamilton Lewis-Gray and Elizabeth Beatrice Gail Lewis-Gray by their patent attorneys Morcom Pemat VZ 39VJ IVNN3d WOONW dOLSBB9EEE9+ 10:11 100I/I/t