Controlled liquor chemistry for chalcopyrite leaching

Abstract

An improved process for leaching copper from copper sulphide containing feed materials by leaching in one or more acidic sulphate liquors containing ferric iron and ferrous iron where the ferric and ferrous iron concentrations are controlled to give ferric / ferrous ratios that target the copper sulphide mineralogy in the material being leached such that maximum copper extraction is achieved.

Description

Controlled Liquor Chemistry for Chalcopyrite LeachingDescriptionField of the Invention

[0001] This invention relates to a novel process for producing high purity copper products from chalcopyrite containing feed materials by leaching in an acidic sulphate liquor containing ferric iron and ferrous iron where the ratio of ferric iron to ferrous iron is controlled to maximise the leach rate and then recovering the copper from the liquor to produce copper oxide and / or copper metal and / or copper sulphate.

[0002] The current dominant process for producing copper metal is from sulphide ores where a copper concentrate is produced via comminution and flotation and this is then smelted at high temperatures to make an impure blister copper which is then electrorefined to give high purity metal and to recover other valuable components especially gold and silver. The economics of the process are very dependent on the grade of copper in the ore and penalties associated with impurity elements present.

[0003] Acidic sulphate liquors are commonly used for leaching metals from copper ores such as in engineered heaps, in run of mine ore dumps, in tailings dams and from in situ leaching. This technology is well established and gives acceptable recovery for copper minerals where the copper is present in an oxidised form and / or in secondary sulphides such as chalcocite but is less effective where the copper is present in chalcopyrite.

[0004] The difficulty in leaching copper from chalcopyrite is well known in the industry and has been the target of considerable research over the past 30+ years but there has been limited success. There are numerous publications and patents but very little commercial implementation. The work has targeted both low grade ore deposits and higher copper level copper sulphide concentrates.

[0005] There is a need for a new leaching process for these applications. This invention provides an improved means of leaching the copper from chalcopyrite through the use of two or more liquor compositions where the liquors are specifically used to target selected reactions occurring within the minerals present in the ore.Summary of the Invention

[0006] The novel process uses two or more acid sulphate liquors with controlled concentrations of ferrous and ferric ions and of acid levels where these are added sequentially to the copper minerals in a cyclic manner to carry out desired reactions. The oxygen levels present in the liquor are also varied from having air injection to give significant levels through to anaerobic conditions where there is minimal oxygen present. These conditions are matched to the liquor compositions.

[0007] The chemistry involved in copper sulphide leaching is complex because of the range of possible reactions and solubility limits for some of the species present. The inclusion of active bacteria, and the use of air injection add further complexity.

[0008] This invention is based on individually controlling the concentrations of the ferric ion and ferrous ion within the liquor to match the copper mineralogy and its history to maximise the copper leach rate and overall extraction. In the simplest system this makes use of a liquor with ferric and ferrous ions present such that their ratio is in the range of 0.15-1.0 and most preferably in the range of 0.2 to 0.6. For this liquor the total iron content is limited by the pH as the ferric ion solubility is strongly pH dependent. The pH is preferably <2 and more preferably <1.5 and most preferably in the range of 0.8 - 1.2 such that the total iron content is in the range l-25g / l.

[0009] This liquor can react with both primary and secondary copper sulphide minerals present to dissolve copper and convert most of the sulphur present in the sulphide to elemental sulphur. Under these conditions pyrite present mostly does not react and most of the sulphur does not form sulphate. The reactions occurring are mildly exothermic but only contribute a small amount of heat to the system. This reaction can be carried out without the need to regenerate ferric ions through oxidation of the ferrous ions present provided the ferric ionconcentration in the liquor is sufficiently high to drive the reactions occurring without the ratio becoming too low such that the leaching rate slows to where the copper extraction is too low for commercial recovery.

[0010] This reaction is best carried out under conditions where there is limited oxygen present to avoid oxidising too much of the ferrous ions to ferric and moving the ferric / ferrous ratio outside the desired range. This can be achieved by carrying the reactions out in a sealed configuration through using barriers and / or by using flooded situations in heaps or dumps and / or by carrying out in situ leaching below the water table and / or by carrying the leaching out in stirred reactors where the amount of air injection can be controlled directly with instruments.

[0011] The reaction to form elemental sulphur in preference to sulphate is also advantageous in that it requires much less ferric iron to carry out the reaction. The reaction to form sulphur as shown is CuFeS? + ZFezfSC h = CUSO4 + 5FeSC>4 + 2S° and requires only around 25% as much ferric iron as the reaction CuFeS? + 8Fe2(SO4)3 +6H2O = CUSO4 + 17FeSO4 + 6H2SO4 where the sulphur is converted to sulphate.

[0012] This lower requirement for ferric iron is particularly important in situations such as with in situ leaching where regeneration of the ferric iron is difficult. For these situations addition of air / oxygen to oxidise some of the ferrous iron to ferric is difficult and the use of other methods such as electrolytic oxidation is complex and expensive so ideally is only used for the minimum amount of ferrous oxidation required.

[0013] As well as the liquor chemistry the rate of the reaction depends on the physical nature of the material being leached especially the particle size and the amount of minerals exposed to the leach liquor. Another important factor is the temperature of the reaction. Typically this reaction takes along a long time to achieve close to full extraction of the copper under ambient temperatures and it can be advantageous to carry out the leach at temperatures above ambient with the preferred temperature being above 30C and more preferably above 35C.

[0014] The leaching reaction generating elemental sulphur does not provide sufficient heat to achieve this desired temperature and external heating can be used. The liquor has a muchhigher heat capacity than the solids and therefore requires more heat to reach the desired temperatures. This heat can be applied by passing the liquor through a suitable heat exchanger where heat can be supplied with the heat source being one or more of a liquor from a second reactor in which sulphate is forming to generate heat and / or from a thermal source such as a fossil fuel and / or electricity and / or most preferably using a solar heating arrangement.

[0015] The leach rate of the secondary sulphide minerals is not very dependent on the ferric / ferrous ratio provided there is sufficient ferric iron present to drive the reactions. To improve the overall efficiency of the process one or more other liquors can be used to drive different reactions. A more highly oxidising liquor where the liquor has a much higher ferric to ferrous ion ratio being preferably above 5:1 and more preferably above 10.1 can be used if there is a need to generate heat for heating the liquor and solids and also a need to generate some sulphuric acid to maintain the desired low pH.

[0016] This liquor leaches copper from secondary sulphides but surprisingly is not efficient at leaching copper from the primary sulphide mineral chalcopyrite. This liquor can react with elemental sulphur which resulted from the leaching carried out with the less oxidizing liquor to convert part or all of the sulphur to sulphate. This generates acid to help replace acid lost by reaction with gangue and most importantly generates substantial heat to increase the temperature of the chalcopyrite being leached. The preferred temperature of the leach is in the range 40-60C where the bacteria are highly efficient at driving the ferrous ion oxidation, the heat losses are lower and there is less tendency to form jarosite than occurs at higher temperature. There are also much wider range of bacteria capable of growing under these conditions as higher temperatures require extreme thermophiles which are less common.

[0017] This oxidizing liquor is best added in conjunction with the injection of air and with bacteria present as these help in the sulphur oxidation and also regenerate the ferric ions by oxidising ferrous ions that can form during the reactions. Some copper can also be leached with this liquor, but for chalcopyrite this is normally secondary to the leaching with the first liquor.

[0018] There is a serious drawback in adding this oxidizing liquor to ores and / or concentrates where there is unleached chalcopyrite present. We have found that not only does this liquor not leach the copper from the chalcopyrite but it also alters the mineral in such a way that itprevents leaching by the preferred less oxidizing liquor where the ferric / ferrous ratio is in the range 0.2-1. This alteration is commonly referred to as passivation although there is no single definitive explanation as to why it occurs.

[0019] This passivation is a particular problem where the ore and / or concentrate has been leached under conditions such as in biotic heaps used for secondary sulphides where oxygen and bacteria rare present as these oxidise ferrous iron present to ferric iron and push the ratio above 1 and as high as 5 -10. This is most probably the reason why copper leaching from chalcopyrite present in these type of heaps is reported to be low.

[0020] We have found that this passivation can be overcome by exposing the chalcopyrite to much more reducing liquor where the ferric / ferrous ratio is below 0.2 and more preferably below 0.1. This liquor is not efficient at leaching copper from the chalcopyrite but does alter the mineral such that it can now be more efficiently leached using the liquor with a ferric / ferrous ratio in the preferred range of 0.2-1.

[0021] This changing of the liquor between the ferric / ferrous ratios of 0.2-1, >1 and preferably >5 and <0.2 and preferably, 0.1 can be carried out more than once with the order, and duration, being dependent on the ore and / or concentrate being leached and on prior history such as where leaching of oxide copper and secondary sulphide minerals has previously been carried out.

[0022] For some materials such as those with secondary minerals and pyrite present a fourth liquor composition may be used with the ratio controlled in the range 1 to 5 to selectively leach the secondary copper minerals without attacking the chalcopyrite or most of the pyrite and without excessive formation of sulphate where under these conditions the copper leaching makes most efficient use of the available ferric ions in preference to their being consumed by the other minerals. This also avoids excessive buildup of sulphate and ferric iron in the liquor.

[0023] The leach liquors can be supplied sequentially with the cycle times being determined by the rate of reaction of the target minerals, and hence copper extraction, and the temperature achieved in the reaction zone. The sequence of the liquor additions depends on the mineralogy of the ore and the types of sulphide minerals present. The liquors can be added in a cyclic modesuch that each liquor is added more than once and the sequence used can be changed during the different cycles.

[0024] The cyclic leaching technology described in this invention can be applied to a range of leach systems. It is ideally suited to heap leaching and run of mine dump leaching but can also be used for in situ and in place leaching and in vat or stirred reactor systems. Most commonly it will be applied in a system where there are two or more separate leach reactors with the different liquors being applied in parallel to the different reactors. In more complex situations there can be four or more reactors operating simultaneously with different liquor compositions in each.

[0025] In the context of this invention the generic term reactor refers to any arrangement where chalcopyrite mineral is being exposed to an acidic sulphate liquor to undergo reaction. This includes conventional heap leaches, run of mine dump leaches, in situ and / or in place leaches and vat or stirred reactors. The reactors can be physically separated such as with stirred reactors or can be zones within a reactor such as a heap where the liquor flows are controlled to keep the different liquors separate. This most commonly would be done through having impermeable barriers between zones but may also be done just by controlling the liquor flow such as could occur with in situ leaching. The preferred configuration for any operation can include the use of a mix of different reactor types such as having a mix of surface heaps and underground in situ or a mixed of stirred reactors and static heap / dump systems.

[0026] In one embodiment the leaching using the four liquors sequentially. A chalcopyrite containing ore that also contains some pyrite and secondary copper minerals is initially leached with an oxidising liquor to react the pyrite which generates heat and acid and to leach the less refractory secondary copper sulphide minerals. The pyrite can be present in the ore with the chalcopyrite or can be added from a separate source such as a higher pyrite or and / or even as a concentrate where it can be mixed with the chalcopyrite ore and / or added to the coarse particles as a coating such as is done in the Geocoat process.

[0027] This leaching is carried out with bacteria present and air injection to ensure the ferric / ferrous ratio is kept above 10. The temperature of the heap increases and can reach 60C if there is sufficient pyrite present as this is the main source of heat generation. For ores withlittle or no pyrite it can be advantageous to add some pyrite rich material to provide the heat, acid and some ferric ions. The leach liquor can also be heated externally prior to supply to the leach reactor using any suitable fuel, and external bacterial oxidation step and is also particularly suited to solar heating.

[0028] The rate of copper leaching decreases as the secondary sulphides are reacted and the rate of leaching of chalcopyrite is slow under these conditions. The liquor composition is then changed by stopping circulating the high ferric ion liquor and replacing it with a ferrous ion dominated liquor. The system is operated in a flooded mode without air injection such that the oxidation of ferrous to ferric ions no longer occurs. The ferric to ferrous ratio of the liquor decreases through the reaction of the liquor with copper sulphides present and the dilution effect of the added ferrous ions. The presence of sulphur reducing bacteria under these anaerobic conditions can be used to assist in reducing the ferric ions present to ferrous ions. During this transition stage some copper leaching continues especially of any secondary sulphides but there is limited leaching of copper from the chalcopyrite. The sulphur present reports as a mix of elemental sulphur, sulphide and sulphate.

[0029] With continued addition of the high ferrous ion liquor under substantially anaerobic conditions the ferric to ferrous ion ratio moves into the high leach rate zone with a ferric to ferrous ion ratio of around 0.4. The liquor is held at this ratio for a substantial time by controlled oxidation of ferrous ions back to ferric ion as the ferric ions are consumed by the leach reaction. This oxidation can be managed by limited air injection but more preferably is managed by external oxidation of part or all of the high ferrous liquor. The chalcopyrite reacts with the copper and part of the iron going into solution and part of the sulphur in the chalcopyrite forming elemental sulphur with limited formation of sulphate.

[0030] If the ferric / ferrous ratio becomes too high and the chalcopyrite leach rate decreases too far the liquor conditions can be changed by having fully anaerobic conditions such that any ferric ions present are reduced to ferrous ions to give a liquor with a Fe3+ / Fe2+ ratio of <0.2 and more preferably <0.1. This also converts part of the sulphate present to elemental sulphur. During this stage there is little leaching of copper from the chalcopyrite but chemical changes occur on the chalcopyrite surface that assist with leaching during the subsequent more oxidising leach stages.

[0031] These systematic changes of the liquor composition can be repeated such that a cyclic leach system is used. The time which each liquor is in contact with the chalcopyrite mainly depends on the mineralogy and the temperature of the reactor. The order of the liquor changes can also be changed dependent on the leach performance of the system.

[0032] The copper containing liquor from the leach is processed to recover the copper in a marketable form. The copper can be recovered from the acidic sulphate liquor using any one, or combination, of processes. One conventional means is to use solvent extraction -electrowinning which is well established technology. An alternative is to use ion exchange -electrowinning or a further alternative is to use cementation with iron.

[0033] Where the copper concentration in the leach liquor is low a further alternative is to use a novel process which forms part of this invention as it also assists in controlling the liquor composition especially where a reducing liquor is applied. The novel process uses the solubility properties of common compounds of the metals and of magnesium coupled with known biological reactions of sulphur compounds to recover the metals as oxides and / or hydroxides without excessive consumption of reagents. The ferric iron can be selectively removed to maintain the desired ratio and also to bleed iron to keep the total iron level around the desired level.

[0034] The solubility of the common metals is very PH dependent as is shown in Figure 1 and therefore it is possible to selectively precipitate out some of those by adjusting the PH by addition of a basic compound to react with acid present. The economics of this are very dependent on the cost of the basic compound and being able to recover the base and then recycle it within the process is important.

[0035] The invention uses the difference in solubility of magnesium sulphate and magnesium carbonate. Magnesium sulphate is highly soluble in water whereas magnesium carbonate has very low solubility. Magnesium differs from the other common neutralising agents such as lime where both calcium sulphate and calcium carbonate have low solubility and sodium hydroxide where both sodium sulphate and sodium carbonate are highly soluble.

[0036] The first step in the process is to neutralise the acidic solution with magnesium oxide and / or magnesium carbonate and raise in stages to precipitate out the dissolved metals. The first stage removes aluminium and ferric iron by raising the PH to ~4. Where ferrous iron is also present the liquor may be reacted with air in either a separate stage or as part of the precipitation stage to oxidise the ferrous iron to ferric iron to increase the amount of iron being precipitated. This oxidation can be carried out using a conventional sparged tank or alternatively using a venturi reactor system such as described in patent applications WO 94 / 0120 and WO 2018 / 102850 Al.

[0037] The PH is then raised to around 6 to precipitate out copper that is present. This is commonly done using a magnesium compound such as magnesium carbonate and / or magnesium hydroxide and / or magnesium oxide but other common bases such as lime or sodium hydroxide can also be used. The copper typically precipitates as copper hydroxide and / or copper oxide and can be further processed to reduce to metal using hydrogen and / or Syngas and / or dissolved in sulphuric acid and reprecipitated as copper sulphate.

[0038] A third stage precipitation with further additions a suitable base such as magnesium carbonate and / or magnesium hydroxide may then be used to precipitate out zinc, ferrous iron and cobalt if these are present in sufficient concentrations to warrant separation.

[0039] The solid precipitates are separated using conventional solid - liquid separation such as filters. The liquor which contains magnesium sulphate is then processed to recover the magnesium as magnesium carbonate and the sulphur as elemental sulphur and / or dilute sulphuric acid. This processing uses two stage bio reactors where in the first stage the sulphate is reduced to a sulphide such as hydrogen disulphide gas in an anaerobic reactor and a second aerobic reactor where the sulphide is oxidised to elemental sulphur and / or sulphuric acid. The bioreactors generate carbon dioxide as part of the reaction which reacts with the magnesium present to precipitate it as magnesium carbonate.

[0040] When sulphuric acid is produced in the aerobic bioreactor this is recycled to leach more metal from the ore before being reprocessed. For leaching ores where the copper is present as sulphides ferric iron is required as an oxidant and, in this case, precipitated ferric iron from the Stage 1 PH adjustment is dissolved in the acid to give the desired amount of ferric iron. Themagnesium carbonate generated in the bioreactors is recycled to the neutralisation stages to give PH control.

[0041] Where the ore being leached generates sulphate in the leach stage the aerobic reactor is operated with a controlled amount of oxygen present such that part of the sulphide is not fully oxidised to sulphate but remains as elemental sulphur which can be separated and sold as an additional product. In cases where the ore being leached consumes the acid through reactions with other minerals present such as calcite and / or dolomite a sulphur source such as elemental sulphur is added to the aerobic bioreactor to generate additional sulphuric acid to carry out the leach step.

[0042] The invention minimises the consumption of reagents while recovering valuable metals in the liquor and providing a leach liquor for recovering more metals. The main consumable input is the nutrient required to feed the bacteria which carry out the sulphate reduction and oxidation. In some cases where there is a net consumption of sulphuric acid elemental sulphur is also required to maintain the sulphur balance. This method of treating the copper containing acidic sulphate liquor can also be applied to liquor from natural leaching of copper sulphide materials such as occurs with Acid Mine Drainage formation.Examples

[0043] Example 1. A leach test was carried out where 250.5 g of a mixed bornite chalcopyrite copper ore containing 0,25% copper of which ~40% is present as chalcopyrite was mixed with 999g of acidic sulphate liquor with a pH of ~1 and 5.81g of ferric sulphate and 18.2g of ferrous sulphate to give a starting ferric / ferrous ratio of ~0.4. The sample was continuously stirred in a rolling bottle at 50C for 3 days after which the copper content of the solid residue was 0.01% showing that >95% of the copper had been extracted.

[0044] Example 2 A leach test was carried out as per example 1 except that in this case 18.50g of ferric sulphate and 2.53g of ferrous sulphate were added to give a starting ratio of ~10. After leaching for 3days the copper content of the solid residue was 0.10% indicating ~60% of the copper present was leached. The liquor was removed and replaced by fresh acidic liquor with a pH of ~ 1 with 5.81g of ferric sulphate and 18.2 g of ferrous sulphate added to give aferric / ferrous ratio of ~0.4, After another 6 days of leaching the copper content was 0.11% indicating that no further leaching occurred suggesting that only the bornite and other secondary copper minerals leached and that the refractory chalcopyrite present did not leach under these conditions and that the high ferric / ferrous ratio liquor had stopped the chalcopyrite being leached by the lower 0.4 ratio liquor.

[0045] Example 3. A leach test was carried out as in example 2 where this case 18.50g of ferric sulphate and 2.53g of ferrous sulphate were added to give a starting ratio of ~10 except that in this case the leach was carried out at 40C. After leaching for 6days the copper content of the solid residue was 0.12% indicating ~50% of the copper present was leached. The liquor was removed and replaced by fresh acidic liquor with a pH of ~ 1 with 1.82g of ferric sulphate and 22.6g of ferrous sulphate to give a ratio of 0.1 and then after a further 4 days of leaching this liquor was replaced by liquor having 5.81g of ferric sulphate and 18.2g of ferrous sulphate to give a ratio of ~0.4. 81g of ferric sulphate and 18.2 g of ferrous sulphate added to give a ferric / ferrous ratio of ~0.4. The leach was stopped after a further 7 days and the solid residue analysed and found to have 0.01% copper showing that under these conditions >95% of the copper was leached.Description of the Drawings[Fig. 1]

[0046] [Fig. 1] shows the relationship between the rate of reaction of a primary copper sulphide (chalcopyrite) secondary copper sulphides such as chalcocite, covellite and bornite, and pyrite and the ratio of ferric to ferrous ions in an acid sulphate liquor. The compositions of the four liquors that are the basis of this invention are shown on the figure.[Fig. 2]

[0047] [Fig. 2] shows the relationship between the redox potential and the ratio of ferric to ferrous ions in the liquor. The position of the line shown does depend on the temperature and acidity of the liquor but retains the same basic shape. This shows that it is difficult to obtain Eh potentials above around 800mV in this system without the addition of a strong oxidant such as hydrogen peroxide and / or sodium nitrate.[Fig. 3]

[0048] [Fig. 3] shows the simplest version of applying the technology to fresh ore containing chalcopyrite. In this system the leaching is carried out using two heaps where one operates with an average ferric / ferrous ratio of around 0.4 and the other operates at a much higher ferric / ferrous ratio. A liquor with a ferric / ferrous ratio of ~0.6 is fed to a heap operating in a flooded mode under abiotic conditions at a temperature of ~40C. The leaching reaction consumes some of the ferric iron and the liquor coming out of the heap has a lower ferric / ferrous ratio of around 0.2 and a copper content of over 500mg / l and preferably over 1.5g / l. This liquor is split into two streams with one stream being passed through a heat exchanger to increase the temperature above 40C before being recycled to the abiotic heap to leach more copper. The heat for the heat exchanger is supplied by externally heating liquor using a solar thermal heat plant. The second stream is passed to a solvent extraction plant where most of the copper is extracted for recovery via electrowinning. After the copper is removed the liquor is fed to a second heap operating under a much higher ferric / ferrous ratio where the presence of bacteria and oxygen consume the ferrous iron to push the ratio up to the target of around 10. Minimal copper is leached in this heap but the reaction also converts sulphur to sulphate to provide acid for the leaching reactions and also generates heat which can be used to provide heat to the abiotic leaching heap. The liquor from this oxidizing heap can be split into two streams where one is mixed with the low ferric / ferrous ratio liquor from solvent extraction and fed to the abiotic heap and the other can be treated to remove iron if this is building up from the leach reactions. The oxidizing heap can be fresh ore especially if there is significant reactive pyrite but is more typically would be a heap where the copper has been leached using the abiotic leach step leaving unreacted pyrite and elemental sulphur both of which are reacted under the oxidizing conditions.[Fig. 4]

[0049] [Fig. 4] - shows a similar arrangement to Figure 3 except that in this case the ore is present in an existing heap that has been leached under biotic conditions where the ferric / ferrous ratio was above 1 and the secondary copper sulphides and any copper oxide minerals present have been leached but the primary copper sulphide is mostly unleached. In this figure a liquor with a ferric / ferrous ratio of ~0.05 is passed though the heap to activate the chalcopyrite present such that it is suitable for leaching with a liquor with a ferric / ferrous ratio in the range 0.2-0.6 where the liquor is fed in at ~0.6 and the ratio decreases as the copperleaching reaction proceeds. The liquor from this and the leach system then operates as described in Figure 3.[Fig. 5]

[0050] [Fig. 5] shows a staged reactor system where 4 reactors are being exposed to liquors of different compositions simultaneously and the liquors are cycled between the reactors. A highly oxidising liquor is applied to reactor 1 and then after an appropriate time transferred to reactor 2 as part of cycle 2 of the leaching. The oxidising liquor is then transferred to reactor 3 (cycle3) and subsequently to reactor 4 before being returned to reactor 1. Air is injected to the reactors when the oxidising liquor is present and bacterial activity is encouraged to ensure the liquor remains highly oxidising by oxidising ferrous ions present to ferric. Some adjustments may be made to the liquor composition during the transfers between the reactors most notably to maintain the desired pH through acid addition or removal and the iron concentration most commonly through removing any excess. At the same time as the oxidixising liquor is being fed to reactor 1 a "transition" liquor with a ferric to ferrous ratio in the range of 1 to 5 is fed to reactor 2. This liquor is then transferred sequentially to reactor 3 and then reactor 4 and from there to reactor 1. This liquor leaches a small amount of copper and when this builds sufficiently a bleed stream is taken off to recover copper and the composition of the liquor can be adjusted by iron and / or acid additions if these are out of the preferred range. In parallel with the oxidising liquor being fed to Reactor 1 and the transition liquor to reactor 2 the leaching liquor with a ferric to ferrous ratio in the range 0.1 to 1 is fed to reactor 3 where it leaches copper from the chalcopyrite. The liquor from the reactor then passes to a copper recovery step before being transferred to reactor 4 to leach more copper. This step is repeated as the liquor moves sequentially through reactors 2 and 3. In parallel with the liquor movement above the fourth highly reducing liquor with a ferric to ferrous ratio of <0.1 passes through reactors 4, reactor 3, reactor 2 and reactor 1 which during these cycles are operated anaerobically to avoid oxidation of the ferrous present to ferric and changing the ratio. The system is operated continuously through numerous cycles until the majority of the copper is leached from the chalcopyrite.[Fig. 6]

[0051] [Fig. 6] shows a similar arrangement to that shown in Figure 5 except in this case only three leach liquors are circulated between the reactors being the oxidising, leaching and reduction liquors without any transition liquor being used.[Fig. 7]

[0052] [Fig. 7] shows a similar arrangement to that shown in Figure 5 except in this arrangement only three reactors are used and only the oxidising and leaching liquors are cycled between the reactors.[Fig. 8]

[0053] [Fig. 8] shows the solubility of a number of metals in sulphate solutions as a function of the PH. The most important features are that ferric iron and aluminium have little solubility above PH 4 and copper is soluble at PH 4 but has very low solubility above PH6.[Fig. 9]

[0054] [Fig. 9] - This drawing shows a flowsheet for recovering copper from an acidic sulphate stream containing copper and iron such as a bleed stream from a copper leach operation as shown in Figure 3 and / or an acid mine drainage generated liquor. The liquor is mixed with sufficient magnesium carbonate to neutralise the majority of the acid and raise the PH to ~ 4 to precipitate the iron as a ferric oxide / hydroxide compound such as ferric hydroxide and / or goethite. The precipitate is filtered off leaving a copper rich solution free of ferric iron. This solution is then mixed with more magnesium carbonate to raise the PH to ~6.5. At that PH almost all of the copper precipitates as copper oxide and / or copper hydroxide leaving a magnesium sulphate solution. The copper containing precipitate is filtered off and sold as a product or processed further to give copper metal. The magnesium sulphate solution is then fed to an anaerobic bioreactor which contains suitable sulphate reducing bacteria and a nutrient to feed the bacteria. The nutrient can be any commonly used low molecular weight compounds such as organic acids and alcohols or where available other organic materials such as molasses or waste organic material. The bacteria drive the reduction of the sulphate to sulphide and this is released as hydrogen disulphide gas which is transferred to a separateaerobic bioreactor. Sufficient air is added to the aerobic reactor to enable complete oxidation of the sulphide to sulphate and generate a dilute sulphuric acid liquor suitable for recycle to the leaching section to dissolve more copper. The reaction in the first bioreactor also generates carbon dioxide which reacts with the magnesium present to precipitate the magnesium present as magnesium carbonate. The fine magnesium carbonate particles are flushed from the reactor which allows them to be separated from the nutrients and they are then filtered to give wet magnesium carbonate solids which are then returned to the precipitation stages.[Fig. 10]

[0055] [Fig. 10] This drawing shows a flowsheet for recovering copper from an acidic sulphate stream containing copper and iron. The liquor is first passed through a venturi where it is intimately mixed with an oxygen containing gas most commonly air and passed to a stirred tank to which sufficient magnesium carbonate is added to raise the PH to ~4. The added oxygen oxidises any ferrous iron present in the liquor to ferric iron which has very low solubility and precipitates the iron as a ferric oxide / hydroxide compound such as ferric hydroxide and / or goethite. The precipitate is filtered off leaving a copper rich solution free of ferric iron. This solution is then mixed with more magnesium carbonate to raise the PH to ~6.5. At that PH almost all of the copper precipitates as copper oxide and / or copper hydroxide leaving a magnesium sulphate solution. The copper containing precipitate is filtered off and sold as a product or processed further to give copper metal. The magnesium sulphate solution is then fed to an anaerobic bioreactor which contains suitable sulphate reducing bacteria and a nutrient to feed the bacteria. The nutrient can be any commonly used low molecular weight compounds such as organic acids and alcohols or where available other organic materials such as molasses or waste organic material. The bacteria drive the reduction of the sulphate to sulphide and this is released as hydrogen disulphide gas which is transferred to a separate aerobic bioreactor. Sufficient air is added to the aerobic reactor to enable complete oxidation of the sulphide to sulphate and generate a dilute sulphuric acid liquor suitable for recycle to the leaching section to dissolve more copper. The reaction in the first bioreactor also generates carbon dioxide which reacts with the magnesium present to precipitate the magnesium present as magnesium carbonate. The fine magnesium carbonate particles are flushed from the reactor which allows them to be separated from the nutrients and they are then filtered to give wet magnesium carbonate solids which are then returned to the precipitation stages. The dilute sulphuric acid is mixed with part or all of the iron precipitate from the first precipitation stageto dissolve the ferric iron and provide a solution which is suitable for oxidative leaching of copper sulphide minerals such as are commonly found in ROM dumps, in heaps or in insitu and / or in mine leaching operations.[Fig. 11]

[0056] [Fig. 11] This drawing shows a flowsheet for recovering copper from an acidic sulphate stream containing copper and iron. The liquor is oxidised to ensure all of the iron is present as ferric iron and then passed to a stirred tank to which sufficient magnesium carbonate is added to raise the PH to ~4. The added oxygen oxidises any ferrous iron present in the liquor to ferric iron which has very low solubility and precipitates the iron as a ferric oxide / hydroxide compound such as ferric hydroxide and / or goethite. The precipitate is filtered off leaving a copper rich solution free of ferric iron. This solution is then mixed with more magnesium carbonate to raise the PH to ~6.5. At that PH almost all of the copper precipitates as copper oxide and / or copper hydroxide leaving a magnesium sulphate solution. The copper containing precipitate is filtered off and sold as a product or processed further to give copper metal. The magnesium sulphate solution is then fed to an anaerobic bioreactor which contains suitable sulphate reducing bacteria and a nutrient to feed the bacteria. The nutrient can be any commonly used low molecular weight compounds such as organic acids and alcohols or where available other organic materials such as molasses or waste organic material. The bacteria drive the reduction of the sulphate to sulphide and this is released as hydrogen disulphide gas which is transferred to a separate aerobic bioreactor. Additional sulphur is added to the Aerobic reactor to generate more sulphuric acid to ensure there is enough for continued leaching. Sufficient air is added to the aerobic reactor to enable complete oxidation of the sulphide and sulphur to sulphate and generate a dilute sulphuric acid liquor suitable for recycle to the leaching section to dissolve more copper. The reaction in the first bioreactor also generates carbon dioxide which reacts with the magnesium present to precipitate the magnesium present as magnesium carbonate. The fine magnesium carbonate particles are flushed from the reactor which allows them to be separated from the nutrients and they are then filtered to give wet magnesium carbonate solids which are then returned to the precipitation stages.

Claims

Claims1. A process for leaching copper from copper sulphide minerals using an acidic sulphate liquor which has controlled concentrations of ferric iron and ferrous iron such that their ratio remains in the range of 0.2-0.8 where the ratio is controlled by managing the ratio of the feed liquor and the subsequent amount of oxidation of ferrous iron which forms during the leach reactions.

2. A process as in claim 1 where the leach is carried out in a reactor configuration where the ore is fully saturated with liquor to prevent air ingress and hence the availability of oxygen and the ferric iron needed for the reaction is supplied in the feed liquor.

3. A process as in claims 1 and 2 where the leach reactor is a stirred tank and the copper containing material is a concentrate.

4. A process as in claims 1 and 2 where the reactor is an engineered heap such as is commonly used for leaching copper oxide ore and / or secondary copper sulphides where the copper containing material is ore.

5. A process as in claims 1 & 2 where the reactor is an underground ore body which lies below the water table as is commonly described as in situ and / or in place mining.

6. A process as in claim 1 where the reactor is an underground ore body which lies below the water table as is commonly described as in situ and / or in place mining and where an electrolytic cell is placed underground to oxidise a controlled amount of the ferrous iron which forms to ferric iron to provide sufficient ferric iron to oxidise the copper sulphide mineral but not so much as to raise the ferric / ferrous ratio above 0.8.

7. Carrying out the leach as in claim 1 using leach liquor at above ambient temperature and preferably in the range of 30-55C where the liquor is heated prior to being fed to the reactor by passing it though a heat exchanger and exchanging heat from a second liquor which is heated using any one or a combination of solar thermal heating and / or an external heat source such as a boiler heated by fossil fuel and / or electricity.

8. Controlled ferric / ferrous ratio leaching of copper sulphide minerals where the leach liquor used is altered during the leach such that the minerals are contacted with two or more liquors with different ferric / ferrous ratios liquors at different times where the ratio used at any time is matched to the characteristics of the sulphide minerals in the material.

9. A process according to claim 8 where one of the liquors has a ferric / ferrous ratio of <0.2 and this liquor is typically used where the copper sulphide minerals being leached have previously been exposed to an oxidizing liquor with a ferric / ferrous ratio >1.

10. A process according to claim 9 where one of the liquors has a ferric / ferrous ratio in the range of 0.2 - 0.8 which is used where the copper minerals have not been exposed to oxidizing conditions and / or have previously been exposed to ferric / ferrous liquor with a ratio of <0.2 as described in claim 9.

11. A process according to claim 8 where one of the liquors has a ferric / ferrous ratio of >5 which is employed when the minerals being leached include secondary copper sulphides and iron sulphides such as pyrite and the liquor is used to dissolve the secondary sulphides and convert the iron sulphides to oxides and sulphates which also generates heat for heating the liquor and the material to be leached.

12. A process according to claim 8 where one of the liquors has a ferric / ferrous ratio in the range of 1-5 such that it leaches secondary copper sulphides present but substantially does not react with the primary copper sulphides and the iron pyrite present.

13. A process according to claims 8 and 10 where the leaching with a liquor having a ferric / ferrous ratio in the range 02. -0.8 has generated elemental sulphur and this liquor is replaced by a liquor with a ferric / ferrous ratio of >5 and this liquor reacts with the elemental sulphur to convert it to sulphate and generate heat and sulphuric acid and also reacts with any iron sulphides and / or secondary copper sulphides present to convert them to sulphates.

14. A process according to claim 8 where an ore containing a mix of primary and secondary copper minerals plus some pyrite is first leached with an oxidising liquor with the ferric / ferrous ratio above 5 to dissolve the secondary copper minerals and react the pyrite to form oxides and sulphates and generate heat and is then subjected to a reducing liquor with a ferric / ferrous ratio of <0.2 to activate the primary copper sulphide before then being leached with liquor with a ferric / ferrous ratio in the range of 0.2-0.8.

15. Carrying out the leach as described in claim 8 where the ferric / ferrous ratio is <0.2 and the leach is carried out in a reactor where the material is fully saturated with liquor to prevent air and / or oxygen ingress and therefore prevent any oxidation of the ferrous iron present.

16. Carrying out the leach as described in claim 8 where the ferric / ferrous ratio is maintained in the range 0.2 - 0.8 and the leach is carried out in a reactor where the material is fully saturated with liquor to prevent uncontrolled air and / or oxygen ingress and therefore prevent excessive oxidation of the ferrous iron present by gaseous oxygen or bacteria such that the ferric / ferrous ratio remains within the desired range.

17. Carrying out the leach as described in claim 8 where the ferric / ferrous ratio in liquor fed to the reactor has a ratio in the range 0.2-0.8 and an electrolytic cell is used to oxidise a controlled amount of the ferrous iron within the reactor to maintain the ferric / ferrous ratio in the range 0.2-0.8 such that there is sufficient ferric iron present to oxidise the sulphide minerals and leach the copper.

18. Carrying out the leach as described in claim 8 where the ferric / ferrous ratio in liquor fed to the reactor has a ratio in the range 0.2-0.8 and a controlled amount of oxygen is injected into the reactor to oxidise a part of the ferrous iron formed within the reactor through the leach reactions to maintain the ferric / ferrous ratio in the range 0.2-0.8 such that there is sufficient ferric iron present to oxidise the sulphide minerals and leach the copper.

19. Carrying out the leaching step as in claims 8-18 using leach liquor at above ambient temperature and preferably in the range of 30-55C where the liquor is heated prior to being fed to the reactor using a heat exchanger and exchanging heat from a second liquor which is heated using any one or a combination of solar thermal heating and / or an external heat source such as a boiler heated by fossil fuel and / or electricity.

20. Processing the copper containing acidic sulphate leach liquor as generated by any of the preceding claims by adding magnesium carbonate to the liquor in one or more stages to precipitate ferric hydroxide and copper hydroxide then processing the magnesium containing liquor through bioreactors to recover the magnesium carbonate.

21. A process according to claim 15 where one bioreactor is abiotic and the other is biotic and the products from these are magnesium carbonate and dilute sulphuric acid which can both be recycled.

22. A process according to claim 15 where the copper hydroxide is processed to convert the hydroxide to one or more of copper oxide, copper sulphate and / or copper metal.

23. Processing the copper containing acidic sulphate leach liquor generated by the leaching processes as described in claims 8-18 to recover the copper as copper metal using solvent extraction and / or ion exchange in conjunction with electrowinning.

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