AU2022231806A1

AU2022231806A1 - Improved hydrometallurgical copper process

Info

Publication number: AU2022231806A1
Application number: AU2022231806A
Authority: AU
Inventors: Raymond Shaw
Original assignee: Minetometal Pty Ltd
Current assignee: Minetometal Pty Ltd
Priority date: 2021-03-12
Filing date: 2022-03-08
Publication date: 2023-09-28
Also published as: WO2022187893A1

Abstract

Copper metal is produced from copper containing ammonia - ammonium chloride liquor by precipitating copper containing crystals which are subsequently reduced to copper metal using hydrogen containing gas with the source of the copper in the ammonia ammonium chloride being leaching of copper containing ores and/or wastes and/or residues.

Description

Improved Hydrometallurgical Copper Process

Field of the Invention

[0001]This invention relates to a novel process for producing high purity copper metal from copper containing feed materials by first producing copper containing crystals and then reducing the copper present in the crystals to copper metal using a hydrogen containing gas where the feed material can be any one or a combination of ores, residues, metallic wastes, precipitates, concentrates and calcine including but not limited to those materials that contain copper present in sulphide minerals such as chalcopyrite, bomite, covellite or chalcocite and materials containing oxidized copper such as calcine from oxidative roasting and common copper minerals such as malachite and azurite.

Background of the Invention.

[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 electrorefmed 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 costs for building the smelter and the cost of transporting the concentrate to the smelter. The CAPEX of smelters is very high and these are invariably large installations which benefit from economies of scale.

[0003 ]The transport costs and penalties imposed by the smelters for impurities and low copper grade are restrictive on the miners and force them to produce high grade, high purity concentrates which may not be ideal for the overall deposits being mined. For this reason there have been many attempts over the last 50 years to find an alternative low temperature process capable of making copper metal from a range of ores and concentrates without the high CAPEX needed for building a large smelter. These processes have also been attempted to process ores and/or concentrates which are high in toxic heavy metals such as arsenic which many of the existing smelters will not accept as feed material.

[0004]Despite these concerted efforts none of the processes developed to date have achieved significant commercialization. There has been some success with two medium scale plants

Substitue Sheets (Rule 26) RO/AU being used to treat chalcocite which is the most readily leached of the copper sulphide minerals but most other semi commercial work especially for chalcopyrite minerals has only been a few small tonnage operations being established as demonstration plants.

[0005]The processes developed have mainly focused on using an oxidative acidic leach to dissolve the copper. A major drawback of these acid systems is that the iron also dissolves and has to be precipitated. Another drawback is that the sulphur present most commonly reports as a sulphate which needs precipitation with lime to form an insoluble calcium sulphate that can be separated into the residue and this precipitation step is difficult and often consumes far more than the stoichiometric lime requirement especially where the lime also precipitates acid required for the leach step.

[0006] Another very serious challenge facing these processes is that solvent extraction and electrowinning are used to purify the leach liquor and to recover the copper as metal. Solvent extraction and electrowinning have very high OPEX and CAPEX. Recovery of valuable precious metals such as gold and silver is also difficult with most processes struggling to achieve suitable recoveries.

[0007]Apart from the acid systems there have also been some attempts to use ammonia leaching over the past 100 years and a commercial plant was built using the Arbiter Process and also another using a variation of this for partially leaching chalcocite concentrate at Escondida but these were commercially unsuccessful presumably because they also included the high cost solvent extraction - electrowinning steps and also because of issues with ammonia recovery and managing sulphate build up in the system all of which made them uncompetitive with smelting.

Summary of the Invention

[0008] This invention provides a new way of producing copper metal from a wide range of materials using a novel low CAPEX and OPEX process. The invention first produces copper containing crystals and then reducing the copper present to copper metal using a hydrogen containing gas by heating them in the atmosphere to a temperature which is above 150C and more typically above 220C.

Substitue Sheets (Rule 26) RO/AU [0009]The copper containing crystals are obtained by precipitation from an ammonia - ammonium chloride liquor prepared by leaching the copper containing feed material and then precipitating out the copper in crystals which are either cupric oxide and/or copper hydroxy chloride.

[0010]The copper containing ammonia - ammonium chloride liquor is obtained by leaching the copper feed material under conditions where the copper is readily dissolved. For oxidised material the copper is readily leached without any pretreatment and/or without oxidation in the leach step but for sulphide material and metallic wastes it is necessary to assist the leach either by oxidation before leaching and/or by oxidising the material during the leaching.

[0011] The copper is typically precipitated from the ammonia - ammonium chloride liquor by stripping off part of the ammonia using conventional ammonia stripping technology most commonly by either boiling the liquor and/or by stripping by blowing air through the liquor.

[0012] In another embodiment where the leaching is carried out above 40C the liquor is cooled to below 40C to precipitate some of the copper and also to provide a cooled liquor to recapture the ammonia from the vapour coming from the ammonia stripping step.

[0013] In another embodiment crystals are precipitated by stripping of part of the ammonia by boiling the pregnant liquor above 60C and the liquor is then cooled to below 40C to precipitate more copper crystals and the cooled spent liquor is then used to capture the gaseous ammonia which is boiled off.

[0014]The copper crystal composition depends upon the liquor composition being either cupric oxide or copper hydroxy chloride or a mixture of the two. Where the crystals contain some copper hydroxy chloride this can be converted to cupric oxide by removal of the chloride which is most commonly done in a hydrolysis step using either boiling water or more commonly by reacting the crystals with a dilute alkaline liquor containing a base such as ammonium hydroxide or sodium hydroxide. The dilute alkaline liquor also dissolves out trace impurities that coprecipitate and/or are entrained with the copper crystals.

[0015]The process relies on contacting the ammonia - ammonium liquor with the copper mineral where the copper is in an oxidized form either naturally in the mineral or by

Substitue Sheets (Rule 26) RO/AU oxidizing the copper in the feed material either by thermal treatment at elevated temperatures in an oxidizing atmosphere in advance of the leach and/or by oxidizing in situ during the leaching step itself by carrying out the leach with the addition of an oxidant such as oxygen gas and/or ozone and/or hydrogen peroxide to oxidise the copper present enabling the copper to dissolve in the ammonia-ammonium chloride liquor.

Detailed Description of the Invention

[0016] A pregnant liquor which typically contains between 0.1M/L and 1.25M/L copper and from 1-5M/1 of NH3 and 0.5-3M/1 of NH4C1 is obtained by leaching a copper containing material. Part of the ammonia is then stripped off this liquor to leave a liquor typically containing from 0.5M/1 to 2M/1 NH3 with part of the copper in the liquor precipitating as the NH3 is stripped off. Air stripping can be used to remove the ammonia, but the preferred method is to boil off the ammonia by heating the liquor to the boiling point and continually supplying heat to maintain the boiling.

[0017] The boiling point temperature depends upon the ammonia concentration and mainly on the pressure maintained in the system and can range from as low as 60C when the system is held under vacuum to above 120C when a positive pressure in maintained in the system. Most commonly the boiling point will be held in the range 65-lOOC. The ammonia depleted liquor is then cooled to between 20C and 40C to precipitate more of the copper and also to provide a cooled liquor which is used to recapture the ammonia which has been stripped off. The crystals are separated from the liquor by filtration and washed prior to further treatment. In some cases, it may be preferred to filter off some of the crystals from the ammonia stripping prior to cooling the liquor below 40C and then filter the crystal slurry again after the cooling stage.

[0018] The crystals can be cupric oxide or copper hydroxy chloride but most commonly are a mixture of the two and require treatment to hydrolyse any copper hydoxy chloride present to cupric oxide and also to dissolve out trace impurities present with the crystals. The treatment can be carried out by reacting the crystals in hot water but is more preferably carried out by reacting the crystals in a dilute solution of a base such as ammonium hydroxide or sodium hydroxide. During this hydrolysis other trace impurities dissolve in the hydrolysis liquor to give high purity cupric oxide crystals.

Substitue Sheets (Rule 26) RO/AU [0019] The cupric oxide crystals are separated from the hydrolysis liquor by filtration, washed with water to remove any entrained impurities and then passed to a reduction furnace to reduce the cupric oxide to copper metal. A number of furnace types can be used with one preferred option being to pass the crystals through a rotary kiln operating at around 250C with a continual flow of a hydrogen containing gas which preferably has over 10% hydrogen content to give efficient reduction. The preferred gas is either commercial grade hydrogen or syngas with over 10% hydrogen.

[0020] In another embodiment the washed cupric oxide and copper hydroxy chloride crystals are not hydrolysed but are fed directly to a furnace operating above 220C and preferably above 240C where a hydrogen containing gas is maintained such that any copper hydroxy chloride present decomposes to form copper oxide and hydrochloric acid gas and the copper oxide formed is reduced to copper metal. In this embodiment most other metallic impurities present are not reduced and these can be removed from the copper metal by dissolving them out in a suitable lixiviant in which they are soluble but where the copper metal is not dissolved.

[0021] The invention requires a suitable leaching process to provide the copper containing ammonia - ammonium chloride liquor from which the copper is precipitated. For copper sulphide materials such as those containing common copper minerals such as chalcopyrite, bornite or chalcocite the sulphur requires oxidation to enable the copper to be leached.

[0022] In one embodiment the sulphur oxidation is achieved by roasting the sulphide containing material in an oxidizing atmosphere at temperatures from 570-720C and most preferably from 650-700C where the majority of the sulphur is converted to sulphur dioxide and/or sulphur trioxide gas which is then passed to an acid plant to produce sulphuric acid for sale. The temperature and atmosphere is controlled such that the majority of the sulphur reports to the gas and that any residual sulphur is present as sulphate and such that there is minimal formation of copper ferrite as this compound is quite refractory and difficult to leach.

[0023] In a variation of the above process where there is no commercial advantage in producing sulphuric acid and/or where the concentrate being treated has a low sulphur/copper ratio and the gas produced would be unsuitable for sulphuric acid production a calcium

Substitue Sheets (Rule 26) RO/AU source such as calcium carbonate and/or calcium oxide is added to the roast step such that the sulphur present reacts with the calcium and oxygen to form calcium sulphate in which case sulphur containing gases are largely not releasd and this removes the need for extensive gas handling and a sulphuric acid plant. The addition of a calcium source to the roasting step is particularly advantageous if the copper sulphide ore or concentrate contains harmful impurities especially arsenic which also reacts with the calcium to form insoluble compounds such as calcium arsenate which remain in the residue for disposal.

[0024] The roasted material is then leached in an ammonia - ammonium chloride which typically contains from 1-5M/1 of NH3 and 0.5-2.5M/1 of NH4C1 to selectively dissolve the copper and leave the iron and other gangue materials in the residue. Some calcium as an oxide or chloride is normally added to the leach liquor to precipitate any sulphate present in cases where the roasting has not fully removed the sulphur or fixed it as calcium sulphate and left some present as soluble sulphate such as copper sulphate or cobalt sulphate. This pregnant liquor typically contains from 0. lg/1 Ca to 2.5g/l Ca to ensure the majority of the sulphate is precipitated from the liquor. The pregnant liquor is then passed to the copper recovery section where the ammonia is stripped off to precipitate the required copper crystals.

[0025] In another embodiment the sulphide ore or concentrate is not roasted but is reacted directly in a leach reactor where the controlled oxidation is carried out during the leaching step by adding an oxidant such as oxygen gas, ozone or hydrogen peroxide to the leach step to convert the sulphide present to elemental sulphur and/or sulphate in parallel with the dissolution of the copper and the conversion of iron sulphides present to insoluble oxides.

The liquor used in this system is an ammonia - ammonium chloride solution with from 1- 5 M/1 NH3 and from 0.5 to 2.5 M/1 NH4C1.

[0026] The oxidation is most commonly achieved using injection of oxygen containing gas. This preferably uses oxygen from an oxygen separation plant but can use other oxidants such as hydrogen peroxide or ozone either as an alternative to the oxygen gas and/or to supplement the oxygen gas. The oxygen gas is normally injected into a well mixed reactor to achieve good dispersion and contact with the solid particles to give high usage efficiency.

[0027] The mixer can be a conventional type using high shear radial flow impellers but is more preferably a low energy type such as described in US Patent 6565070. The use of a

Substitue Sheets (Rule 26) RO/AU reactor capable of operating under positive pressure is preferred in that it assists in both maximizing the efficiency of the oxygen gas usage and also enables the leach to be carried out at elevated temperatures above the normal boiling point of the liquor at atmospheric pressure.

[0028] The selection between whether to predominantly form sulphur or sulphate is achieved by control of the temperature of the leach and the PH of the liquor with lower PH and lower temperatures favouring the formation of sulphur and higher temperatures and higher PH favouring the oxidation of the sulphide through to the sulphate.

[0029] Where the sulphide is oxidized to sulphur this remains in the residue from the leach with that residue typically being separated from the liquor by filtration. If economically justified the residue can be further processed to separate the sulphur for sale and/or for burning to produce sulphur dioxide gas suitable for converting to sulphuric acid.

[0030] The sulphur separation can be achieved by flotation where the naturally hydrophobic sulphur can be floated away from the hydrophilic gangue in the leach residue. The conditions for the leach reaction may also be set to enhance this separation such as by carrying out the leach at temperatures above the melting point of sulphur (115C) where the sulphur is present as a liquid which enables it to coalesce into larger particles more suited to flotation. To further enhance this coalescence chemicals such as lignosulphonates may be added to change the surface chemical behavior of the sulphur.

[0031] Another alternative for separating the sulphur is to have the residue at temperatures sufficiently above the sulphur melting point that the sulphur is liquid with a viscosity low enough that it can be separated from the gangue by filtration.

[0032] Where the sulphide is oxidized through to sulphate this can be removed from the liquor typically by precipitation as calcium sulphate (gypsum) through either including a calcium source in the leach stage and/or subsequent treatment of the liquor with a calcium source. The calcium source can be any one, or a combination of, calcium chloride, calcium oxide, limestone, dolomite or calcium containing smithsonite ore. In some cases where calcium oxide is used this may be added to the leach liquor prior to it entering the leach such that the calcium dissolves in the liquor and this can improve the efficiency of use of the

Substitue Sheets (Rule 26) RO/AU calcium as it avoids a known issue of the calcium sulphate forming coating the calcium oxide particles and hence reducing the reaction efficiency.

[0033] Where the feed material contains carbonate such as with the malachite ore calcium is added to precipitate out the carbonate as calcium carbonate to prevent it building in the liquor and interfering with the process.

[0034] Where calcium is added to control the sulphate and/or carbonate it is preferable to add a small excess such that some calcium is present in the pregnant liquor with a preferred concentration of between 0.2g/l and 2.5g/l.

[0035] After the liquor from the leach is separated from the solid residue, normally by filtration, this gives a pregnant liquor typically containing from 0.2 to lM/1 Cu, from 1-5M/1 NH3 and from 0.5 to 2.5 M/1 NH4C1. The liquor is then passed to the copper recovery section where the ammonia is stripped off to precipitate out copper containing crystals.

[0036] In carrying out this invention the ammonia stripping can be carried out in any one or a combination of different systems ranging from vacuum assisted stripping in bubble cap columns to stirred reactors operating under pressure with direct steam injection through to membrane distillation. The common features are that some heat input is required, either directly by steam injection or indirectly via heat exchanges, to provide the heat required to evaporate off ammonia and associated water, and that the crystallization temperature is largely set by the operating pressure with a lesser contribution from the liquor composition.

[0037] Where the crystals precipitated are cupric oxide or cupric hydroxide or after these are obtained after hydrolysis these can be converted to copper metal by direct reduction with a suitable reducing gas at elevated temperature or by dissolving in a sulphuric acid solution to provide a suitable electrolyte for electrowinning of the copper. The preferred embodiment is for the reduction to be carried out by gas where the preferred gas is a hydrogen containing gas such as commercial grade hydrogen or syngas which is a mix of hydrogen and carbon monoxide.

[0038] Where the crystals are precipitated as copper hydroxy chloride the crystals can either be dried and sold for applications such as in agriculture or more commonly are converted to

Substitue Sheets (Rule 26) RO/AU cupric oxide by hydrolysis in either hot water or in a basic solution such as dilute caustic soda and/or ammonium hydroxide.

[0039] The crystallisation and liquor compositions are controlled such that unwanted low copper high chloride compounds such as copper diammine chloride are not precipitated and the crystals are substantially ammonia free and have a high copper content of over 55% and a low chloride content of less than 20%.

[0040] For copper containing materials which also contain commercially valuable amounts of other metals such as cobalt, nickel and/or precious metals such as gold and silver additional steps can be included in the process to also recover these. The gold and silver are typically recovered by further processing the residue from the ammonia - ammonium chloride copper leach in a conventional gold process where either cyanide or thiosulphate is used to separate the gold and silver from the residue.

[0041] In the embodiment where cobalt is present it can be advantageous to carry out a first leach step to dissolve the majority of the cobalt whilst leaving the copper in the solid form. When the copper and cobalt are present in oxide form either naturally as minerals and /or from roasting of the sulphides where the copper sulphides form a mix of copper oxide and copper sulphate and the cobalt sulphide all reacts to cobalt sulphate the oxidised cobalt readily dissolves in water and/or dilute ammonia or ammonium chloride liquors. For these liquors the cobalt can then be separated from any dissolved copper by adjusting the liquid PH as the cobalt and copper have quite different solubility - PH curves. At PH above 5.5 the solubility of copper is quite low and reaches a minimum around PH6.5 whereas cobalt has quite high solubility at these PH's.

[0042] In one embodiment where there is both some copper sulphate and cobalt sulphate present in the feed material the liquor from the cobalt leach has the PH increased from the natural PH of copper sulphate in solution of around 3.5 up to 6-6.5 by adding a suitable base such as lime, limestone, caustic soda or ammonium hydroxide. The copper precipitates as cupric oxide and/or cupric hydroxide and is filtered off leaving a cobalt rich stream.

Increasing the PH further to around PH8 using a base such as ammonium hydroxide or sodium hydroxide then precipitates the cobalt as cobalt hydroxide and/or cobalt oxide.

Substitue Sheets (Rule 26) RO/AU [0043] In another embodiment a base such as lime and/or ammonium hydroxide is added to the first leach step such that the leaching is carried out at a PH of from 5.5-6.5 such that the copper has very low solubility while the majority of the cobalt dissolves. The liquid is then filtered off and th PH increased as in the first embodiment to precipitate the cobalt as cobalt hydroxide and/or cobalt oxide.

[0044] In another embodiment where the cobalt and copper are leached directly as sulphides wih oxygen injection a first leach is used with low concentrations of ammonia and ammonium chloride such that the copper solubility is kept below 0.5M/L while dissolving substantially all of the cobalt. The liquor from this leach step is separated from the solids and acidified using hydrochloric acid to decrease the PH such that almost all of the copper precipitates. The cobalt is then recovered from the liquor either by precipitation or more commonly using ion exchange. The hydrochloric acid used can be provided commercially but preferably is captured from thermal decomposition of copper hydroxy chloride crystals.

[0045] The ammonium chloride leach described for cobalt can also be used to recover gold and silver which can dissolve in this liquor and can be recovered by including a suitable adsorption media such as activated carbon and/or a gold and/or silver selective resin in the leach which is capable of being physically separated from the leach slurry. The precious metals can then be recovered from the media using known technology.

[0046] An alternative embodiment of the invention is to include a separate leach step for extracting the precious metals from the residue from the copper leach stage. The presence of elemental sulphur and/or residual copper is detrimental to cyanide which is most commonly used for gold and where the leach residue contains these the preferred leach liquor is a thiosulphate such as ammonium thiosulphate, or a high strength chloride liquor. For a residue containing subtantially all of the sulphur as calcium sulphate with very low levels of copper the preferred leach system for recovering the gold and silver is cyanide. Both the thiosulphate and cyanide leach systems are practiced commercially and are well known technology.

Examples

[0047] Example 1. lOOgram of copper sulphide concentrate containing 45.4% copper and 18.5% sulphur was mixed with 30.5 gram of lime (CaO) and roasted for 3 hours in air at

Substitue Sheets (Rule 26) RO/AU 650C. 50gram of the calcine from the roast was then leached in 350 ml of a solution containing approximately 50g/l NH3 and 50g/l NH4C1 for 1.5 hours at 50C. After leaching the liquor contained 29.4 g/1 copper confirming that the majority of the copper was being leached out of the calcine into the liquor.

[0048] Example 2. 50gram of copper sulphide concentrate containing 45.4% copper and 18.5% sulphur was placed into a stirred reactor with 500ml of liquor containing approximately 50g/l NH3 and 50g/l NH4C1, 6 gram of lime (CaO) was added and the reactor heated to 80C and oxygen gas injected to maintain an oxygen pressure of ~5KPa. After 2 hours the liquor contained 20.4g/l copper showing that the copper was being leached into the liquor. The concentrate and residue were both analysed by XRD to show the minerals present and the XRD results showed that the bomite content of the material decreased from 33.1% to 10.8% and the chalcopyrite content decreased from 33.5% to 24.7% confirming that both these copper minerals were reacting under the conditions used and that the copper sulphides could be leached in this manner.

[0049] Example 3. A solution containing approximately 30g/l copper in liquor with approximately 40g/l NH3 and 50g/l NH4C1 was heated to drive off part of the NH3 and precipitate copper containing crystals and then cooled to ~25C to precipitate more copper crystals. These were filtered off and analysed by XRD and found to be 100% Atacamite (Copper hydroxy chloride). 7 gram of these crystals were then placed in 350ml of hot water containing 5g/l NH3 for 1 hour and then filtered off and analysed using XRD. The crystals were found to contain 85% tenorite (CuO) and only 15% Atacamite showing that the copper hydroxy chloride was being hydrolysed to cupric oxide under these conditions.

Description of Drawings

[0050] Figure 1 shows a plot of the solubility of copper in liquor containing ~50g/l NH4C1 and from approximately 1-3M/L NH3 at different temperatures. At 3M/1 NH3 and 50C the solubility is .. and this decreases to ..g/1 at lM/1 NH3 at 23C. This shows that the copper solubility can be controlled by altering the NH3 concentration and the temperature.

[0051] Figure 2 shows a process for the crystallisation, hydrolysis and reduction steps for producing copper metal. Copper pregnant liquor is fed to an ammonia stripping -

Substitue Sheets (Rule 26) RO/AU crystallization step where the ammonia is stripped off by heating the liquor to boiling point. The pregnant liquor continues to boil as it is heated and this drives off ammonia gas in an ammonia - water gas. As the ammonia concentration drops the copper solubility decreases and copper containing crystals which contain some copper hydroxy chloride precipitate. The crystal containing liquor is then cooled to 25C to precipitate more crystals and filtered to separate the crystal from the spent liquor. The ammonia - water vapour gas passes into an absorption column where it is contacted with the cooled spent liquor from the crystallisation stage and the ammonia and water are recaptured for recycle to the leaching stage. The crystals are filtered and washed and hydrolysed by mixing with a dilute ammonium hydroxide solution to hydrolyse the copper hydroxy chloride present to cupric oxide. The dilute ammonia solution also dissolves traces of unwanted impurities that are precipitated with, or more generally entrained, in the crystals. The pure cupric oxide crystals are then filtered of, washed in pure hot water and passed to the reduction stage. In the reduction stage the crystals pass through a rotary kiln held at a temperature of -250C with hydrogen gas continually fed into the rotary kiln to reduce the cupric oxide to copper metal which is the desired product.

[0053] Figure 3 shows a modified process for copper metal production where any copper hydroxy chloride present in the copper crystals is decomposed thermally during the reduction step. In the flowsheet in Figure 3 copper pregnant liquor is fed to an ammonia stripping - crystallization step where the ammonia is stripped off by heating the liquor to boiling point. The pregnant liquor continues to boil as it is heated and this drives off ammonia gas in an ammonia - water gas. As the ammonia concentration drops the copper solubility decreases and copper containing crystals which contain some copper hydroxy chloride precipitate. The ammonia - water vapour gas passes into an absorption column where it is contacted with cooled spent liquor from the crystallisation stage and the ammonia and water are recaptured for recycle to the leaching stage. The crystals are filtered washed in pure hot water and passed to the thermal decomposition and reduction stage. In the thermal decomposition and reduction stage the crystals pass through a rotary kiln held at a temperature of -250C with hydrogen gas continually fed into the rotary kiln to reduce the cupric oxide to copper metal which is the desired product and to remove the chloride from the copper hydroxy chloride as hydrochloric acid vapour.

Substitue Sheets (Rule 26) RO/AU [0054] Figure 4 shows an overall process for recovering copper and cobalt from a sulphide concentrate. In this version of the process the copper concentrate is fed directly to a roasting stage where a calcium source such as calcium oxide or more preferably calcium carbonate is added mixed with the copper sulphide such that as the material is roasted in an oxygen containing gas at -650C the sulphur present oxidises and reacts with the calcium to form calcium sulphate. This removes the need for an acid plant. The roasted material is then fed to a hot water leach where the PH is maintained at ~6.5 by having sufficient calcium present to react with copper sulphate as it dissolves in the liquor but not so much as to raise the PH above 6.5 which would cause cobalt containing crystals to precipitate. The slurry from this hot water leach is filtered to give a cobalt rich liquor and a copper rich residue. An ammonia solution is mixed with the cobalt containing liquor to raise the pH to around 8 and precipitate the cobalt as cobalt oxide and/or cobalt hydroxide. The copper rich residue is fed to an ammonia - ammonium chloride leach stage to dissolve the copper away from the gangue material in the residue. The slurry is then filtered to give a copper depleted solid residue and a copper rich pregnant liquor. The residue is washed using conventional means and then fed to a conventional gold circuit where gold and silver are recovered using cyanide technology.

The copper pregnant liquor is fed to an ammonia stripping - crystallization step and copper metal is produced as described in Figure 2.

[0055] Figure 5 shows the process for recovering copper and cobalt from a sulphide concentrate. In this version of the process the copper concentrate is fed directly to a roasting stage where a calcium source such as calcium oxide or more preferably calcium carbonate is added mixed with the copper sulphide such that as the material is roasted in an oxygen containing gas at -650C the sulphur present oxidises and reacts with the calcium to form calcium sulphate. This removes the need for an acid plant. The roasted material is then fed to a hot water leach where the PH is maintained at ~6.5 by having sufficient calcium present to react with copper sulphate as it dissolves in the liquor but not so much as to raise the PH above 6.5 which would cause cobalt containing crystals to precipitate. The slurry from this hot water leach is filtered to give a cobalt rich liquor and a copper rich residue. An ammonia solution is mixed with the cobalt containing liquor to raise the pH to around 8 and precipitate the cobalt as cobalt oxide and/or cobalt hydroxide. The copper rich residue is fed to an ammonia - ammonium chloride leach stage to dissolve the copper away from the gangue material in the residue. The slurry is then filtered to give a copper depleted solid residue and a copper rich pregnant liquor. The residue is washed using conventional means and then fed to

Substitue Sheets (Rule 26)

RO/AU a conventional gold circuit where gold and silver are recovered using cyanide technology.

[0056] Figure 6 shows the process for recovering copper from a sulphide concentrate. In this version of the process the copper concentrate is fed directly to a roasting stage where calcium carbonate is added mixed with the copper sulphide such that as the material is roasted in an oxygen containing gas at -700C the sulphur present oxidises and reacts with the calcium to form calcium sulphate. This removes the need for an acid plant. The roasted material is then fed to an ammonia - ammonium chloride leach stage to dissolve the copper away from the gangue material in the residue. The slurry is then filtered to give a copper depleted solid residue and a copper rich pregnant liquor. The residue is washed using conventional means and then fed to a conventional gold circuit where gold and silver are recovered using cyanide technology. The copper pregnant liquor is fed to an ammonia stripping - crystallization step and copper metal is produced as described in Figure 3.

[0057] Figure 7 shows the process where the copper concentrate is fed directly to an oxidative ammonia - ammonium chloride leach stage where oxygen is injected to provide the oxidizing power. Lime is added to the ammonia - ammonium chloride liquor either prior to the leach and/or in the leach reactor to react with the sulphate being formed to precipitate it as calcium sulphate. The leach is carried out at a PH of >9.5 and a temperature of >70C under which conditions the sulphur oxidises to sulphate rather than remaining as elemental sulphur. The copper present in the concentrate dissolves into the liquor. The slurry is then filtered to give a copper depleted solid residue and a copper pregnant liquor. The residue is washed using conventional means and then fed to a conventional gold circuit where gold and silver are recovered using cyanide and/or thiosulphate technology. The copper pregnant liquor is fed to an ammonia stripping - crystallization step and copper metal is produced as described in Figure 3.

[0058] Figure 8 shows an overall process for recovering copper from a copper sulphide concentrate which also contains valuable amounts of cobalt, gold and silver. The concentrate contains around 35% copper mainly as bomite and chalcopyrite with 20g/t gold, 206g/t silver and 0.23% cobalt. The copper concentrate is fed to a leach reactor along with a concentrated ammonium chloride liquor which is low in free ammonia and oxygen is injected at sufficient

Substitue Sheets (Rule 26) RO/AU rate to maintain the redox potential high enough to break down the sulphide minerals but not so high as to promote excessive sulphate formation. The temperature is also controlled to be low enough that elemental sulphur formation is preferred to oxidation to the sulphate. The cobalt is selectively leached by the liquor whilst the majority of the copper remains in the solid residue. The solids and liquids are separated using conventional filters and liquor which is high in cobalt is treated to recover cobalt as a marketable compound either by Ion Exchange or by PH adjustment. The cobalt depleted ammonia - ammonium chloride liquor is then mixed with high ammonia liquor and the leach residue in another oxidative leach step carried out at moderate (<80C) temperature and the copper present in the residue dissolves into the liquor. The slurry is then filtered to give a copper depleted solid residue and a copper pregnant liquor. The residue is washed using conventional means and either disposed of directly or further processed to recover any residual precious metals and if warranted to separate out elemental sulphur for sale or for burning to make sulphuric acid. Calcium oxide and/or calcium chloride is added to the copper pregnant liquor to precipitate out dissolved sulphates. The copper pregnant liquor is fed to an ammonia stripping - crystallization step and copper metal is produced as described in Figure 2.

[0059] Figure 9 shows the process where the copper in the feed material is present in oxidised state such as in precipitates obtained from neutralising acid mine drainage and/or heap leach and/or insitu leach liquors or from carbonate ores such as malachite or from slags from copper smelting. The feed material is fed to an ammonia - ammonium chloride leach stage to leach the copper. If there are carbonates and/or sulphates present lime is added to the ammonia - ammonium chloride liquor either prior to the leach and/or in the leach reactor to react with any sulphate present o precipitate it as calcium sulphate and to react with carbonate to precipitate it as calcium carbonate. The slurry is then filtered to give a copper depleted solid residue and a copper pregnant liquor. The residue is washed using conventional means and if there is sufficient gold and/or silver present is then fed to a conventional gold circuit where gold and silver are recovered using cyanide and/or thiosulphate technology. The copper pregnant liquor is fed to an ammonia stripping - crystallization step and copper metal is produced as described in Figure 3.

Substitue Sheets (Rule 26) RO/AU

Claims

1. A process for producing high purity copper metal where a copper containing pregnant liquor with between 0.2M/1 Cu to lM/1 Cu and 1-5M/L NH3 and 0.5 - 3 M/1 NH4C1 is obtained by leaching a copper containing feed material and copper containing crystals are precipitated from the liquor and then reduced to copper metal by heating to above 150C in a hydrogen containing gas atmosphere.

2. A claim according to claim 1 where the leaching is carried out with oxygen being injected to assist the reaction.

3. A process according to claim 1 where the copper containing feed material is calcine resulting from roasted copper containing materials where the roasting is carried out in an oxygen containing atmosphere at a temperature in the range 570 -720C.

4. A process according to claim 1 where the copper containing pregnant liquor is obtained by leaching oxidised copper ores such as malachite and azurite.

5. A process according to claim 1 where the copper containing pregnant liquor is obtained by leaching secondary oxidised copper materials such as precipitated copper oxide or copper hydroxide or waste materials from smelting operations such as slag or furnace dust

6. A process according to any of the preceding claims where the leaching is carried out at a temperature above 40C.

7. A process according to claim 1 where the crystals are precipitated by stripping off part of the NH3 from the copper containing pregnant liquor.

8. A process according to claim 1 where the copper containing pregnant liquor is cooled to below 40C to precipitate copper containing crystals.

9. A process according to Claim 1 where part of the NH3 is stripped from the pregnant liquor by boiling after which the liquor with a lower NH3 concentration is then cooled to below 40C.

Substitue Sheets (Rule 26) RO/AU

10. A process according to any of the preceding claims where the copper content of the crystals is over 55% and the chloride content is less than 20%.

11. A process according to any of the preceding claims where the copper containing crystals are contacted with a dilute alkaline liquor which contains a suitable base such as ammonium hydroxide or sodium hydroxide.

12. A process according to any of the preceding claims where the copper containing crystals are heated to above 220C in a hydrogen containing gas.

13. A process according to claim 1 and claim 11 where the copper containing crystals are reduced to copper metal by heating in a hydrogen containing gas.

14. A process according to any of the preceding claims where the hydrogen containing gas contains greater than 10% hydrogen.

15. A process according to any of the preceding claims where calcium is added to precipitate sulphate or carbonate impurities either present in the feed material or resulting from reactions during the leach as calcium compounds.

16. A process according to claim 1 and claim 3 where a calcium containing material such as lime or limestone is added to the roaster with the copper material such that the calcium reacts with the sulphur in the copper material and oxygen from the gas atmosphere to form calcium sulphate.

17. A process according to claims 1, 13 and 14 where sufficient calcium is added for the copper containing pregnant liquor to contain from 0.2g/l to 2.5g/l calcium.

18. A process according to claim 1 and claim 3 where the copper containing material contains cobalt and the calcine is leached to dissolve cobalt before leaching the copper in the ammonia - ammonium chloride liquor.

Substitue Sheets (Rule 26) RO/AU

19. A process for producing high purity cupric oxide where copper containing crystals are precipitated from a copper containing liquor with between 0.2-1M/1 Cu and 1-5M/L NH3 and 0.5

- 3 M/1 NH4C1 and separated from the liquor by filtration and then washed to remove trace impurities and then heated in a hydrogen containing gas at a temperature above 220C to produce copper metal.

20. A process according to claim 19 where the copper containing crystals are hydrolysed after washing to convert copper hydroxy chloride present to cupric oxide prior to being heated in the hydrogen containing gas.

Substitue Sheets (Rule 26) RO/AU