NZ508419A

NZ508419A - Process for recovering a precious metal from an ore by adding an ionic strength modifier then conducting a leaching process

Info

Publication number: NZ508419A
Application number: NZ508419A
Authority: NZ
Inventors: Michael Stoychevski
Original assignee: Michael Stoychevski
Priority date: 1999-11-25
Filing date: 2000-11-24
Publication date: 2002-04-26
Also published as: AUPQ427999A0

Abstract

A method of recovering a precious metal from a precious metal ore includes: a) adding a blanking agent such as a hydrocarbon to the ore bearing slurry; b) adding at lest one ionic strength modifier such as sodium hydroxide, sodium cyanide or calcium carbonate to the ore bearing slurry and then c) conducting a metal leaching process.

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number 508419 TECHNICAL FIELD This invention relates to the recovery of metals from their host materials In particular it relates to the recovery of precious metals, such as gold from carbonaceous materials 5 BACKGROUND ART The invention will be preferably described in relation to the recovery of gold from carbonaceous materials However, it should be appreciated that the invention is also useful for the recovery of other metals from such materials Gold which cannot be physically removed from gold bearing materials 10 must be dissolved in order to separate it from its surrounding matrix This process generally requires the formation of an electrically charged gold complex which is soluble under the prevailing conditions In the gold mining industry, the dissolution of gold is commonly achieved using the CN" ion to form a [Au(CN)2]~ complex under alkaline conditions (le cyanidation) Since this process requires 15 contact between metallic gold and CN", the ore must first be crushed to a size which liberates most of the gold to the liquid phase Once dissolution has been achieved, gold recovery is relatively simple The majority of gold plants utilise carbon to adsorb [Au(CN)2]" from the ore slurry in what is known as carbon-in-pulp (CIP) or carbon-in-leach (CIL) processing Relatively large carbon 20 fragments can by physically separated from a slurry and eluted (washed) to remove [Au(CN)2]~ The carbon can then be roasted to reactivate its surface Although carbon is a very effective adsorbing agent, ore components can also bind [Au(CN)2]" to their surface These ore components are generally referred to in the mining industry as preg-robbers Preg-robbers effectively compete 25 with carbon for [Au(CN)2]~ Their competitiveness is dependent on their activity (tendency to adsorb gold) and their concentration In general, the adsorption of gold is based on the dynamic equilibrium S+[Au(CN)2] aqu ^ S[Au(CN)2] ads The amount of adsorbed [Au(CN)2]~ on the surface of the ore is therefore 30 proportional to the concentration of aqueous [Au(CN)2]~ ([Au(CN)2]~aqu) and the availability of active surface sites (S) Therefore during CIL or CIP, [Au(CN)2]" is in dynamic equilibrium with active sites If the activity of S is high, then the equilibrium strongly favours the right hand side and, therefore, the adsorption of "i r ..r r.ir ; Oi , of k z 1 2 4 irJ\/ Z'wiifl DECEIVED [Au(CN)2]" By maintaining high concentrations of carbon in the slurry, preg-robbing can be minimised However, in some ores the prevalence and/or activity of preg-robbing species is high enough to significantly reduce leach recoveries 5 In complex ore bodies, there exists a vast potential for preg-robbing agents These range from indigenous carbonaceous materials through to inorganic species with ion exchange properties Almost all ore types exhibit some capacity to adsorb charged species, hence the need for CIP or CIL Potential preg-robbing agents include oxide structures which are 10 inherently electrostatic and carry residual surface charges Structures such as alumina (AI2O3), silica (S1O2), and a host of transition metal oxides (eg , Fe203Ni0,Zn0,Mn02,Cr203,M003etc) are widely used in industry as adsorbents (structures which adsorb molecules) Analogous oxide minerals which occur naturally in ore bodies in the form of clays are also well known 15 preg-robbing agents Naturally occurring carbonaceous material such as graphite, decaying vegetation or other organics can also act as preg-robbers by reactions alike to, and in opposition to, those of activated carbon, added for the purpose of recovering the metal Thus for many processes relating to the recovery of metals there exists the potential for preg-robbing 20 The recovery of gold may also be limited by obstruction of the pores of the adsorbent by other very fine ore particles The effect of this is two-fold Firstly it can physically limit the loading capacity of the adsorbent, and secondly, pore-blocking retards the rate of adsorption of dissolved gold In Stoychevski M and Williams L R , "Sodium sulfide - assisted gold 25 recovery from arsenopyrite and roasted arsenopyrite" Transactions of the Institution of Mining and Metallurgy (Section C Mineral Process Extr Metall), Volume 102, pp C179-183, the addition of sodium sulfide during the cyanidation process was investigated This study established that sodium sulfide addition during the cyanidation process effectively increased gold recovery by lowering 30 the solution potential It was, however, noted that the effectiveness of this process was limited as that as the S2" concentration was increased to sustain the solution potential at the lowest possible level, the recovery of gold was retarded possibly by the 2 formation of a passivating layer on the gold In conclusion, it was found that the effectiveness of S2" in enhancing gold cyanidation appeared to be limited to oxidising ore slurries at solution potentials which resulted in unfavourably high cyanide consumption 5 In Australia Patent Application No 50889/96 there is described a method of increasing the recovery of a precious metal (eg gold) from a metal-bearing ore by adding an anti preg-robbing solvating agent (eg a sulfur compound containing an S" or S2" functional group) The purpose of the anti preg-robbing agents being to minimise the formation of preg-robbing oxides and/or to 10 minimise the activity of the existing preg-robbing species This was achieved by deactivation of the active preg-robbing surface via reactions with sulfide to form passivating sulfur layers In other prior art methods the gold mining industry has trialed the addition of blanking agents to the ore-bearing slurry prior to conducting CIP or CIL 15 processing The purpose of the blanking agent being to deactivate the surface of any extraneous carbonaceous materials to minimise their ability to adsorb [Au(CN)2] In these methods a range of organic materials, whose affinity for carbon is well known, have been utilised Of these, only kerosene and diesel have had large scale commercial success Their application has undoubtedly 20 been greatly assisted by their availability and cost, particularly in view of the remote location of some mining operations A significant limitation in the use of kerosene and diesel as well as other organic compounds in gold processing is that these compounds increase the risk of adsorbent fouling Accordingly, any successful blanking process needs 25 to overcome the potential of the blanking agent used (eg kerosene or diesel) to deactivate the CIL adsorbent Carbon fouling in CIL circuits has a compound effect which severely compromises recovery time, and is exacerbated by the added costs of regeneration OBJECT OF THE INVENTION 30 It is an object of this invention to provide conditions to increase the recovery of metals from their host materials It is also an object of this invention to enhance the recovery of gold by providing conditions before a traditional gold leaching process to inhibit the 3 adsorption of [Au(CN)2] and/or to improve the dispersion of any hydrocarbons in the ore bearing slurry. DISCLOSURE OF THE INVENTION Applicant has surprisingly found that precious metal recovery can be 5 optimised by adding an ionic strength modifier to an ore bearing slurry According to a first aspect of the invention there is provided a method of recovering a precious metal from a precious metal bearing ore, wherein said method includes the following steps- (a) adding a blanking agent to the ore bearing slurry; 10 (b) adding at least one ionic strength modifier to the ore bearing slurry; and subsequently (c) conducting a metal leaching process The term "blanking agent' as used herein refers to a reagent which deactivates indigenous metal-adsorbing species and thereby reduces the 15 preg-robbing abilities of the ore. The blanking agent and the ionic strength modifier may be added to the ore bearing slurry in any order In a preferred embodiment, the blanking agent is added to the ore bearing slurry prior to adding the ionic strength modifier In another embodiment, the blanking agent and ionic strength modifier are added 20 to the ore bearing slurry simultaneously In yet another embodiment, the ionic strength modifier is added to the ore bearing slurry prior to adding the blanking agent Applicant has also surprisingly found that precious metal recovery can be further optimised by conducting an oxidation process prior to adding the ionic 25 strength modifier Thus, according to the invention there is also provided a method of recovering a precious metal from a precious metal bearing ore, wherein said method includes the following steps-a) oxidising a metal bearing ore, 30 b) adding a blanking agent to the ore bearing slurry, c) adding at least one ionic strength modifier to an ore bearing slurry, and d) conducting a metal leaching process. irn606027-amended-compNZ doc 4 In a preferred aspect of the invention the metal bearing ore slurry may be initially oxidised by any suitable method, the selection of the oxidation method being dependent on the properties and constituents of the ore In a particularly preferred aspect of the invention the metal bearing ore 5 slurry is oxidised by adding a peroxide oxidant Examples of suitable peroxide oxidants includes solutions that contain peroxomonosulfate ions (HS05~), or peroxide ions in the form of HOO" or 022" In a particularly preferred embodiment of the invention the metal bearing ore slurry is initially oxidised by adding a peroxomonosulfate ion to the slurry 10 under alkaline conditions The peroxomonosulfate ion can be supplied in powdered form (KHS05) or in the liquid state (HS05") - also known as Caro's acid The powder is the preferred reagent and is conveniently obtained from a triple salt with formula KHSO5 KHSO4 K2S04, manufactured by Du Pont under the name of Oxone. Alternatively the peroxomonosulfate may be manufactured 15 on site by using a chemical generator to which hydrogen peroxide (H202 ) and sulphuric acid (H2S04 ) are added. During the oxidation step, the solution potential (Eh) is preferably increased by about 100-250 mV for a minimum period of time. In practice the solution potential is initially determined by using a saturated calomel electrode 20 (SCE) and is then increased by about 100 - 250 mV for about 15-45 minutes, preferably 20 - 30 minutes In theory the main purpose of the oxidation step is to decrease the electron density from the aromatic ring system, thus irreversibly altering the carbon surface so that it binds less intimately to [Au(CN)2] during CIL 25 However, in some cases excessive oxidation has proved to be detrimental Accordingly, it is necessary to conduct a series of tests to select the optimum trn606027-amended compNZ doc 5 oxidation potentials and residence times for each specific ore Although, in general, applicant has noted that when Oxone is used the conditioning times should not exceed 60 minutes and the oxidant consumption should not exceed 2 0 Kg Oxone powder per ton of ore 5 Ideally, the oxidation phase is controlled in a bank of small conditioning tanks This allows for more precise control of solution potential (Eh) and retention time Short circuiting may become a problem if only 1 tank is employed The optimum Eh range will depend on the nature of the ore, but potentials should be set using automatic values controlled by a suitable redox 10 probe situated in the tanks Owing to localised concentration effects, and the instability of peroxomonosulfate under alkaline conditions, it has been found that Oxone powder is most effective when administered as a dilute acidic solution It should preferably not be applied in the solid form 15 The oxidation pH is also ore specific and preferably an optimum range is predetermined Generally though, peroxomonosulfate becomes increasingly unstable with increasing pH, decomposing to form molecular oxygen Thus, it has been found the pH range is preferably maintained at below 9 0 during the oxidation step 20 In the method of the invention any suitable ionic strength modifier or modifiers can be added to the metal bearing ore slurry The selection of ionic strength modifier(s) and the amount of modifier(s) to add is dependent on the nature of the ore Whilst not wishing to be bound by theory, Applicant believes that, the 25 addition of the ionic strength modifier serves three purposes Firstly, it assists with the emulsification of the organic materials, thus minimising their contact with the adsorbent, secondly, the presence of additional cations promotes the transport of [Au (CN)2] into CIL carbon, and thirdly it appears to reduce the amount of fouling of CIL carbon 30 Whilst not wishing to be bound by theory, Applicant believes that the addition of a blanking agent in combination with an ionic strength modifier reduces adsorbent fouling for two reasons Firstly, blanking agents have a greater tendency to micellise with surfactant particles present in the ore and the 6 resultant micelle droplets are smaller, more numerous and more stable resulting in a more stable emulsion, which limits contact of the blanking agent with the adsorbent, and secondly micellisation of ultra-fine ore particles enhances recovery by reducing physical pore-blocking of the adsorbent by such particles 5 As will be appreciated any known ionic strength modifiers may be added to the metal bearing ore slurry For example any compounds including any of the following anions may be added to the slurry OH", F", CI", Br", I", CO32", SO42", CN" and NO32" Compounds including, for example, any of the following cations may be added to the slurry H+, Li+, Na+, K+, Ca2+ and Al3+ 10 In a preferred embodiment of the invention the ionic strength modifier(s) are selected from any one or more of the following compounds, sodium hydroxide (NaOH), sodium chloride (NaCI), calcium hydroxide (Ca(OH)2), sodium cyanide (NaCN) and/or sodium carbonate (Na2C03) calcium carbonate (CaC03) 15 In general, sodium hydroxide is preferably used as the ionic strength modifier due to its ability to promote hydrocarbon dispersion Furthermore, it is readily available and relatively inexpensive However, if the ore rapidly consumes OH", then it is preferable to cease adding sodium hydroxide and add another ionic strength modifier For example, it may be beneficial to add 20 sodium chloride or sodium cyanide The preferred ionic strength modifier can be selected by conducting a series of standard leach tests to determine the optimum precious metal recovery In addition these standard leach tests can be used to determine the optimum modifier concentration and reaction conditions 25 When sodium hydroxide is used as the ionic strength modifier then approximately 2 to 10kg of NaOH, preferably 3 to 6 kg of NaOH per tonne of ore is added to the ore bearing slurry In a preferred embodiment, ionic strength modifier is added to the ore bearing slurry in multiple sequential tanks whereby the electrolyte concentration 30 in the first tank is elevated above that of the subsequent tanks Preferably, the number of sequential tanks is between two and four Preferably, the ionic strength modifier is added to the ore bearing slurry using an in-line mixing system This generates high diffusion of the ionic 7 strength modifier and reduces the residence time in which the pulp contacts the cyanide This provides a greater ionic strength effect and increases emulsification In the method of the invention any known blanking agent may be added to 5 the ore bearing slurry The selection of the blanking agent and the amount of blanking agent to add will depend on the nature of the ore In a preferred embodiment of the invention a long chain hydrocarbon compound can be used as the blanking agent For example any Cs toC2o hydrocarbon may be used Examples of suitable Cs to C20 hydrocarbon 10 blanking agents include octane, decane, 1-7 octadiene, dodecane, tetradecane, dodecene, chlorodecane, bromodecane, hexadecane, octadecane, eicosane or mixtures thereof In particular either kerosene or diesel may be used as the blanking agent as they are readily available and they are relatively inexpensive Other compounds that may be suitable as blanking agents include, for example, 15 nitropropane, nitrobutane, hexane, petroleum ether, chlorohexane, bromohexane, xylene, octanol, decanol, 2-heptanone, dioctylether, methylnapthalene, diethylsulfide or mixtures thereof The preferred blanking agent can be selected by conducting a series of standard leach tests to determine the optimum precious metal recovery In 20 addition these standard leach tests can be used to determine the optimum reaction conditions for adding the blanking agent When kerosene is used as the blanking agent then it is generally added to the ore bearing slurry such that overall concentration of kerosene in the slurry is within the range of 100 to 15,000ppm, preferably within the range 250 to 25 10,000ppm In a preferred embodiment of the invention the ionic strength modifier and blanking agent may be added to the ore bearing slurry simultaneously Following oxidation of the ore and adding an ionic modifier and blanking agent and ionic strength modifier to the ore any suitable leaching process may 30 be conducted The following examples illustrate some preferred embodiments of the invention and should not be construed as limiting the scope of this invention EXAMPLES Example 1 In these examples a range of different ore samples were obtained and gold was recovered there from by traditional leaching processes However, 5 prior to conducting the leaching process the ore slurry was treated by the following conditioning steps, a) addition of a blanking agent b) addition of a blanking agent and at lease one ionic modifier, and c) oxidising the slurry followed addition of blanking agent at least one ionic 10 modifier In addition for each ore sample gold was recovered without any conditioning process The results of these tests are provided in Table 1 The Ores The ores used in the tests were, 15 Ore A - Carbonaceous sulfide flotation concentrate Ore B - Carbonaceous sulfide flotation tailing Ore C - Autoclaved carbonaceous sulfide flotation concentrate Ore D - Carbonaceous sulfide Ore E - Carbonaceous sulfide flotation concentrate 20 Ore F - Bio-oxidised flotation concentrate, and Ore G - Carbonaceous oxide Addition of Blanking Agent In the examples where a blanking agent was added this was achieved by adding Kerosene and moderately agitating the slurry for 30 minutes 25 Addition of Ionic Modifier For each ore processed a different ionic modifier was added to the slurry and the selection, concentration and amount of ionic modifier are provided in table 1 Oxidation Step 30 In the examples where an initial oxidation step was conducted this was achieved by adding oxone powder to the ore bearing slurry As the optimum recovery is dependent on the solution potential (Eh) and the pH while the ore is being oxidised these values are also provided in Table 1 9 Results The results shown in Table 1 clearly indicate that when the ore slurry was conditioned either by a) addition of blanking agent and at least one ionic modifier, or by b) oxidising the slurry followed by addition of blanking agent and 5 at least one ionic modifier that a significant increase in gold recovery was achieved Example 2 In this example a range of different organic compounds were tested for blanking efficiency on a highly carbonaceous sulfide Gold was recovered from 10 the carbonaceous sulfide using a traditional leaching process Prior to conducting the leaching process the ore slurry was treated in individual treatments with the blanking agents listed in table 2 A summary of the blanking efficiencies of each blanking agent is provided in table 2 The results collected from a highly carbonaceous sulfide reveals that 15 an effective blanking agent should be 1) Immiscible with water and not subject to hydrogen bonding 2) Limited to intermolecular (van der Waal's) bonding 3) Lighter than water 4) Linear in configuration 20 5) Dense enough to support solid phase adhesion Example 3 In this example, the ability of the method of the invention to improve gold recovery from a number of different ore types was tested Kerosene conditioning was conducted for a period of 30 minutes under moderate agitation 25 followed by electrolyte addition for a further 30 minutes under moderate agitation The results of treatment of a variety of commercial gold ores is shown in table 3 'Au rec' denotes increased Au recovery in comparison to standard plant conditions Note that ores 3 and 4 were treated by RIP using a strong base quaternary amine It was noted that these positively charged amines were 30 extremely resilient to hydrocarbon fouling Primary consideration was given to cost effectiveness of the electrolyte addition 10 Example 4 In this example, the process by which ionic strength adjustment is conducted on the conditioned pulp prior to CIL and on the adsorbent, is schematically represented below Blanking agent Feed Electrolyte Electrolyte Adsorbent CIL Tailing CIL ore flow Adsorbent flow 10 15 20 25 Blanking agent = kerosene, deisel, etc. Electrolyte = NaCl, NaCN, NaOH, H2S04, Na2C03, etc. This process is applicable when it is necessary to use low volumes of ionic strength modifier For example, Applicant has found that NaCN is a highly effective ionic strength modifying electrolyte However, its disadvantages are its toxicity, reactivity, and cost Nevertheless, CN" addition using the above scheme can be used to effectively facilitate emulsification prior to CIL By dosing of CN" in tanks of reduced size, the residence time is decreased and the instantaneous concentration of CN" in the primary tank is increased This scenario applies to any ionic strength modifier, but is particularly applicable to NaCN Ideally, two to four tanks are used, thus the electrolyte concentration in the first tank is significantly elevated with respect to that which would normally be achieved in one large-volume tank It is also possible to add kerosene, then NaCN and other ionic strength modifiers using in-line mixing systems which generate high diffusion The shorter the residence time during initial pulp contact with cyanide, the greater the ionic strength effects and the greater the extent of emulsification Such a regime depends on the nature of the ore involved In the event that the pre-robbing/pore-blocking mechanisms are 11 </div>

Claims

<div class="application article clearfix printTableText" id="claims">



extremely rapid, then leaching of gold in the absence of adsorbent may preclude an in-line system In such cases, dosage into low volume tanks containing the adsorbent is the preferred option 

Finally, it is to be understood that various alterations, modifications and/or additions may be made to the process of the invention as previously described without departing from the spirit or ambit of the invention 

12 

f I 

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS. 

1 A method of recovering a precious metal from a precious metal bearing ore wherein said method includes the steps a) adding a blanking agent to the ore bearing slurry; 5 b) adding at least one ionic strength modifier to the ore bearing slurry; 

and subsequently c) conducting a metal leaching process
2 The method of claim 1 wherein the amount of ionic strength modifier added to the ore bearing slurry is between 2 and 10 kg per tonne of ore 

10 3. The method of claim 2 wherein the amount of ionic strength modifier added to the ore bearing slurry is between 3 and 6 kg per Tonne of ore. 4. The method of any one of claims 1 to 3 wherein the ionic strength modifier is selected from one or more compounds having an ion selected from OH", F", CI", Br", I", C032", S042", CN", N032", H+, Li+, Na\ K+, Ca2+ or Al3+ or mixtures 15 thereof. 

5 The method of claim 4 wherein the ionic strength modifier is selected from one or more of sodium hydroxide, sodium chloride, calcium hydroxide, sodium carbonate, calcium carbonate, sodium cyanide or mixtures thereof. 

6 The method of claim 5 wherein the ionic strength modifier is sodium 20 hydroxide. 

7. The method of claim 5 wherein the ionic strength modifier is sodium cyanide. 

8 The method of any one of claims 1 to 7 wherein the ionic strength modifier is added to the ore bearing slurry in multiple sequential tanks whereby the ionic 

25 strength modifier concentration in the first tank is higher than that of subsequent tanks. 

9 The method of any one of claims 1 to 8 wherein the ionic strength modifier is added to the metal bearing slurry prior to adding the blanking agent. 

10. The method of any one of claims 1 to 9 wherein the blanking agent is 30 added to the metal bearing slurry prior to adding the ionic strength modifier. 

11 The method of any one of claims 1 to 10 wherein the blanking agent and ionic strength modifier are added to the metal bearing ore simultaneously. 

irn606027-amended-compNZ doc 

13 

12 The method of any one of claims 1 to 11 wherein the resulting concentration of blanking agent added to the ore bearing slurry is between 100 and 15,000 ppm. 

13 The method of claim 12 wherein the resulting concentration of blanking 5 agent is between 250 to 10,000 ppm 

14 The method of any one of claims 1 to 13 wherein the blanking agent is a hydrocarbon selected from the group comprising Cs to C20 hydrocarbons, nitropropane, C6-C7 alkane, chlorohexane, bromohexane, xylene, alcohol immiscible in water, ketone, ether, methylnaphthalene, diethyl sulfate or 

10 mixtures thereof. 

15. The method of any one of claims 1 to 14 wherein the blanking agent is a linear hydrocarbon being immiscible in water, limited to intermolecular bonding, less dense than water, and having a density to support solid phase adhesion. 

16. The method of claim 15 wherein the blanking agent is dodecane, 15 tetradecane or mixtures thereof. 

17 The method of claim 15 wherein the blanking agent is kerosene or diesel. 18. The method of any one of claims 1 to 17 wherein said method further comprises the step of oxidising the metal bearing ore prior to adding the blanking agent and ionic strength buffer. 

20 19. The method of claim 18 wherein the solution potential of the ore bearing slurry is increased by between 100mV to 250mV during the oxidising step 20 The method of claim 18 or 19 wherein the pH of the ore bearing slurry is maintained below pH 9 during the oxidising step 

21. The method of any one of claims 18 to 20 wherein the oxidising step 25 comprises adding a peroxide oxidant to the ore bearing slurry. 

22 The method of claim 21 wherein the peroxide oxidant includes a peroxomonosulfate ion 

23. The method of claim 22 wherein the peroxomonosulfate ion is in a powdered form. 

30 24 The method of claim 22 wherein the peroxide oxidant is a salt having the formula KHSO5. KHS04. K2S04. 

25. The method of claim 22 wherein the peroxomonosulfate ion is in a liquid form. 

irn606027-amended-compN2 doc 

14 

26. A method according to claim 1 substantially as hereinbefore described with reference to any one of the examples 

DATED: 31 January 2001 

5 

PHILLIPS ORMONDE & FITZPATRICK Attorneys for MICHAEL STOYCHEVSKI 

irn606027-amefided-compNZ doc 

15 

TABLE 1 

ORE 

OXIDATION STEP 

ADD IONIC STRENGTH 

ADD BLANKING AGENT 

ADDITIONAL 

MODIFIER 

Kerosene, ppm 

GOLD RECOVERED 

Increase Eh 

PH 

Electrolyte 

Conc'n grams/tonne 

+mV 

g/L 

A 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

A 

N/A 

N/A 

N/A 

N/A 

250 

09 

A 

N/A 

N/A 

NaCI 

5 

250 

1 75 

NaF 

1 

A 

200 

7 5 

NaCI 

5 

250 

22 

NaF 

1 

B 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

B 

N/A 

N/A 

N/A 

N/A 

500 

0 65 

B 

N/A 

N/A 

NaCI 

4 

500 

1 4 

Na2(C03) 

2 

B 

200 

10 5 

NaCI 

4 

500 

1 9 

Na2(C03) 

2 

C 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

C 

N/A 

N/A 

N/A 

N/A 

700 

1 0 

C 

N/A 

N/A 

NaCI 

3 

700 

2 43 

Na2(C03) 

2 

NaF 

1 

C 

150 

5 5 

NaCI 

3 

700 

33 

Na2(C03) 

2 

NaF 

1 

D 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

D 

N/A 

N/A 

N/A 

N/A 

2000 

03 

D 

N/A 

N/A 

NaCI 

6 

2000 

07 

D 

150 

9 5 

NaCI 

6 

2000 

09 

E 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

E 

N/A 

N/A 

N/A 

N/A 

5000 

28 

16 

h 

TABLE 1 

ORE 

OXIDATION STEP 

ADD IONIC STRENGTH 

ADD BLANKING AGENT 

ADDITIONAL 

MODIFIER 

Kerosene, ppm 

GOLD RECOVERED 

Increase Eh +mV 

PH 

Electrolyte 

Conc'n g/L 

grams/tonne 

E 

N/A 

N/A 

NaCI 

10 

5000 

85 

E 

250 

7 0 

NaCI 

10 

5000 

100 

F 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

F 

N/A 

N/A 

N/A 

N/A 

1000 

06 

F 

N/A 

N/A 

NaCI NaF 

6 

2 5 

1000 

32 

F 

200 

2 5 

NaCI NaF 

6 

2 5 

1000 

4 8 

G 

N/A 

N/A 

N/A 

N/A 

N/A 

0 

G 

N/A 

N/A 

N/A 

N/A 

500 

0 8 

G 

N/A 

N/A 

NaCI NaF 

3 1 

500 

32 

G 

150 

8 0 

NaCI NaF 

3 1 

500 

3 5 

17 

Table 2 Blanking efficiency of various hydrocarbons on a highly carbonaceous sulfide 

Blanking agent 

Description 

Blanking Efficiency 

C3-C5 halide dichloropropane,chlorobutane ineffective 

C3 nitro nitropropane moderate 

C5 alkane pentane ineffective 

C6-C7 alkane hexane, petroleum ether mild chloride chlorohexane superior to hexane bromide bromohexane comparable to chlorohexane 

C8-C10 alkane octane, decane moderate 

C8 alkene 

1-7 octadiene comparable to C8 alkane 

C12-C14 alkane dodecane, tetradecane high 

C12 alkene dodecene comparable to C12 alkane 

C12 halide chlorododecane comparable to C12 alkane 

bromododecane* 

inferior to C12 alkane 

C16 alkane hexadecane slightly inferior to C12-C14 

C18-20 alkane octadecane, eicosane problems associated with solidification aromatic xylene inferior to linear C8 

cresol* 

ineffective 

chlorobenzenes* 

ineffective 

nitrobenzene* 

ineffective miscible alcohol ethanol, methanol ineffective immiscible alcohol octanol, decanol, 

mild 

cyclohexanol, phenol* 

ineffective ketone 

2-heptanone mild ether dioctylether moderate naptha methylnapthalene* 

mild sulfide diethylsulfide mild surfactant sodium lauryl sulfate ineffective 

alkylbenzenesulfonates ineffective surfactant/alkane lauryl sulfate (dilute)/dodecane moderate 

lauryl sulfate (excess)/dodecane ineffective 

alkylsulfonate/dodecane moderate 

*Denser than water 

18 

Table 3 Gold recoveries from samples obtained from gold processing plants 

Ore-type kerosene ppm 

Electrolyte 

PH 

Increased Au rec 

% 

Autoclave discharae 1 Carbonaceous 

500 

NaOH 2 5 g/L NaCI 1 0 g/L Na2C03 0 5 g/L LiCI 

2 0-2 5 >7 0 

5-7 

2 Non-carbonaceous 

250 

NaOH 2 0 g/L NaCI 1 5 g/L Na2C03 0 5 g/L LiCI 

>7 0 

2-3 

Carbonaceous sulfide
3 Flotation conc
4 Cyclone overflow A 

6000 2500 

3 5 g/L NaCI 

1 5 g/L NaOH 

0 5 g/L NaF 

2 0 g/l Na2C03 

1 0 g/l NaCI 

1 0 g/L NaOH 

9 0-9 5 7 0-7 5 7 5-8 0 

15-20 10-15
5 Cyclone overflow B 

500 

3 g/L NaCI 1 0 g/l NaOH 

8 0-8 5 

5-10
6 Cyclone overflow C 

750 

2 5 g/L NaCI 1 0 g/L NaOH 1 0 g/L Na2C03 

8 0-8 5 

7 5-10 

0 

5 0 g/L NaCI 3 0 g/L Na2C03 2 0 g/L NaOH 1 0 g/L NaF 

4-6 

19 

Bio-oxidised 7 Carbonaceous 

1000 

NaOH 4 0 g/L NaCI 0 5 g/L NaF 

1 5-2 0 >7 0 

3-5 

8 Non-carbonaceous A 

300 

NaOH 3 0 g/L NaCI 

100 

3-4 

9 Non-carbonaceous B 

400 

NaOH 1 5 g/L NaCI 1 5 g/L Na2C03 

>7 0 

2-3 

Roasted 10 Carbonaceous & Non-carbonaceous 

500 

2 5 g/L NaCI 1 0 g/L NaOH 1 0 g/L LiCI 

8-9 

2-4 

20 

ABSTRACT 

The invention relates to a method of recovering a metal from a metal bearing ore wherein said method includes the steps of adding at least one ionic strength modifier to an ore bearing slurry, and subsequently conducting a metal leaching process 

INTlL! CK'AL P'OTRTY Of FICC OF NZ. 

2 4 NOV 2000 



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