PROCESS FOR ACIDIC LEACHING OF PRECIOUS AND CHALCOPHILE METALS

Abstract

A process for recovery of one or more elements, selected from precious metals and chalcophile metals as herein defined, from materials containing precious and/or chalcophile metal/s, said process including: (i) a leaching step comprising contacting the material with an acidic solution containing a lixiviant comprising an aqueous amino acid-thiourea compound formed from an amino acid (as herein defined) and thiourea (as herein defined), in order to form a leachate containing the precious metal and/or chalcophile metal; and (ii) a recovery step comprising recovering the precious metal and/or chalcophile metal from the leachate.

Claims

1-51. (canceled)

52. A process for recovery of one or more elements, selected from precious metals and chalcophile metals as herein defined, from materials containing precious and/or chalcophile metal/s, said process including: a leaching step comprising contacting the material with an acidic solution containing a lixiviant comprising an aqueous amino acid-thiourea compound formed from an amino acid (as herein defined) and thiourea (as herein defined), in order to form a leachate containing the precious metal and/or chalcophile metal; and (ii) a recovery step comprising recovering the precious metal and/or chalcophile metal from the leachate.

53. The process of claim 52, wherein the amino acid concentration in solution is between 0.01 to 250 grams per litre and the thiourea concentration in solution is between 0.01 to 250 grams per litre.

54. The process of claim 52, wherein the amino acid-thiourea compound is glycine-thiourea, preferably produced by dissolving glycine in thiourea solution at a minimum 1:1 molar ratio of Glycine:Thiourea.

55. The process of claim 52, wherein the amino acid-thiourea compound is formed in situ in solution.

56. The process of claim 52, wherein the leaching step is performed in the presence of an oxidant, preferably selected from air (gaseous and dissolved states), oxygen (gaseous and dissolved states), hydrogen peroxide, ferric ions, cupric ions, chromic ions, stannic ions, cobaltic ions, manganese dioxide, hypochloride, hypobromide, chlorite, chlorate, perchlorate, chlorine, bromine, bromate, perbromate, nitrate, permanganate, chromate and dichromate.

57. The process of claim 56, wherein the oxidant is dissolved oxygen provided via aeration or oxygenation and is preferably between 0.1 and 100 mg/L in solution, more preferably between 2 and 30 mg/L in solution.

58. The process of claim 56, wherein the oxidant is selected from: (a) hydrogen peroxide at a concentration from 0.01%, to 5%, (b) ferric ions, and (c) metal ions and the lixiviating solution comprises a stabilizing reagent to increase the stability of the metal ions.

59. The process of claim 58, wherein the stabilizing reagent is selected from hydroxyl-carboxylic acids (e.g. gluconic acid, citric acid and tartaric acid), di- and polycarboxylic acids (e.g. oxalic acid) and EDTA and any ferric chelating reagents.

60. The process of claim 58, wherein the stabilizing reagent comprises excess amino acids.

61. The process of claim 52, wherein the acidic solution has a pH range of between 0 and 6, preferably between 2 and 6, more preferably between 1 and 3.

62. The process of claim 52, wherein the lixiviating solution further comprises a pH modifier which is preferably sulfuric acid.

63. The process of claim 52, wherein the material containing the precious metal and/or chalcophile metal comprises one or more of: (a) an ore or an ore concentrate, (b) is a waste material, such as electronic or electrical scrap or mining waste for example tailings, (c) a mining or metallurgical process intermediate, (d) metal-contaminated soils.

64. The process of claim 52, wherein the precious metal and/or chalcophile metal is in the form of one or more of sulfides, oxides, arsenides, sulfo-arsenides, native metals, tellurides, sulfates, carbonates, chlorides, silicates, hydroxylated-salts and hydroxide minerals.

65. The process of claim 52, wherein the leaching step takes place in situ or in place.

66. The process of claim 52, wherein the leaching step is selected from: (i) dump leaching, which preferably comprises leaching blasted but uncrushed particles, preferably smaller than 200 mm, (ii) heap leaching, which preferably comprises leaching coarse crushed particles, preferably smaller than 25 mm, (iii) vat leaching, which preferably comprises leaching fine crushed, particles, preferably smaller than 4 mm, (iv) agitated tank leaching, which preferably comprises leaching milled material having particles preferably smaller than about 0.1 mm/100 micrometre, or (v) leaching takes place in a pressure leaching autoclave, and comprises leaching particles that are preferably smaller than 100 micrometres.

67. The process of claim 52, wherein the recovery step is conducted at a temperature where water remains in the liquid state at a given system pressure, preferably the recovery step is conducted at an ambient or mildly elevated temperature.

68. The process of claim 52, wherein the recovery step is conducted from 10 C. to 200 C., preferably from 0 C. to 100 C., more preferably between 20 C. to 65 C.

69. The process of claim 52, wherein the recovery step is conducted at atmospheric pressure, an elevated pressure or a pressure below atmospheric pressure.

70. The process of claim 52, wherein the recovery step is conducted at a pressure between 0.01 bar to 1000 bar, preferably between 0.5 and 1.5 bar.

71. The process of claim 52, wherein the recovery step comprises recovering the metal in a solid state, such as by zinc cementation, or by using one of: ion-exchange (IX) resins, solvent extraction (SX), organic solvents, activated carbon, molecular recognition (MR) resins, or coated adsorbents (CA's).

72. The process of claim 52, wherein the recovery step includes regeneration of the amino acid-thiourea lixiviant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Notwithstanding any other forms which may fall within the scope of the apparatus and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0062] FIG. 1a is a graph showing gold extraction (mg/L) versus time (minutes) in solutions containing as lixiviants Thiourea only (squares) and Glycine-Thiourea (circles). Both solutions use ferric ions as oxidants;

[0063] FIG. 1b is a graph showing gold extraction rates mol/m.sup.2.s versus time (minutes) in solutions containing as lixiviants Thiourea only (squares) and Glycine-Thiourea (circles). Both solutions use ferric ions as oxidants;

[0064] FIG. 2a a graph showing gold extraction (mg/L) versus time (minutes) in solutions containing as lixiviants Thiourea only (squares) and Glycine-Thiourea (circles). Both solutions use cupric ions as an oxidant;

[0065] FIG. 2b is a graph showing gold extraction rates mol/m.sup.2.s versus time (minutes) in solutions containing as lixiviants Thiourea only (squares) and Glycine-Thiourea (circles). Both solutions use cupric ions as an oxidant;

[0066] FIG. 3 is a graph showing gold extraction (%) versus time (hours) from gold PDX residue in solutions containing as lixiviants Thiourea only (diamonds) and Glycine-Thiourea (triangles);

[0067] FIG. 4 is a graph showing silver extraction (mg/L) versus time (minutes) in Glycine-Thiourea and excess glycine in the presence of ferric ions as oxidant;

[0068] FIGS. 5a and 5b are graphs showing Gold recovery from acidic glycine-thiourea solutions by activated carbon (a) gold concentration (mg/L) versus time (minutes) and (b) log [Au]c/[Au]s vs log time;

[0069] FIG. 6 is a graph of Gold Elution (%) versus time (minutes) from loaded activated carbon by acidic thiourea and sulphuric acid; and

[0070] FIG. 7 is a graph of Gold Elution (%) versus time (minutes) from loaded activated carbon by sulfide and caustic solutions.

[0071] FIG. 8 is a graph of gold recovery (%) versus time (hours) for leaching of a BIOX gold bearing flotation concentrate under different reagent concentrations.

[0072] FIG. 9 is a graph of gold recovery (%) versus time (hours) for leaching of a pressure oxidised gold bearing ore under different reagent concentrations.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Examples

[0073] Non-limiting Examples of a process for the recovery of one or more elements, selected from precious metals and chalcophile metals, are described below. The following abbreviations are used for lixiviants: GT is used for the system Glycine-Thiourea, Tu is used for Thiourea on its own, Gly refers to Glycine, AA refers any Amino acid and AAT refers to any amino acid-thiourea combination. GT or AAT may either be prepared beforehand as a distinct compound or in-situ as a GT/AAT complex in solution from its components. The pressure and temperature of all examples were 1 atmosphere and room temperature (20 deg C.), respectively.

Example 1

[0074] In a solution containing 1 g/L of glycine-thiourea (GT), 2 g/L glycine (Gly) and 1 g/L ferric sulfate at pH 2.5, gold ore was leached more rapidly than in the traditional leaching system (1 g/L Thiourea (Tu) and 1 g/L Ferric sulfate). It can be seen that gold leaching kinetics (FIG. 1a) and gold leaching rate (FIG. 1b) are much higher in the GT system than in the conventional thiourea leaching process. The new system presents two advantages, namely that glycine can carry/complex with both thiourea and the ferric ions.

Example 2

[0075] In a solution containing 0.4 g/L of glycine-thiourea (GT), 0.4 g/L glycine, 0.65 g/L cupric sulfate at pH 3.0, gold ore was leached at close to twice the rate than the leaching system using thiourea only (0.4 g/L Tu and 0.65 g/L Cupric sulfate). It can be seen that gold leaching kinetics (FIG. 2a) and gold dissolution rate (FIG. 2b) is much higher when leaching with GT than leaching with Tu only. Note that B in FIGS. 2a and 2b refers to glycine and that cupric ions are used as an oxidant in both leaching systems.

Example 3

[0076] In Example 3, the residue arising from acidic pressure oxidization of a refractory gold ore (hereinafter called acidic PDX residue) was subjected to leaching by thiourea and by glycine-thiourea solutions respectively. A slurry of acidic PDX residue was filtered, washed and dried. The acidic PDX filtrate contained ferric ions arising from the pressure oxidation process which were taken advantage of during the subsequent leaching steps.

[0077] FIG. 3 shows that gold extraction reached 92.4% when leaching an acidic PDX residue by glycine-thiourea (triangles) whereas only 78.8% gold extraction was achieved when the lixiviant was Thiourea only (diamonds). Thiourea addition was 2.5 kg/t and 5 kg/t to GT and Thiourea systems, respectively. The advantages of mixing glycine with thiourea was 50% Thiourea saving with about 13.6% greater gold extraction. Table 1 summarizes the amounts of thiourea addition for each leaching system and the amount of gold present in the acidic PDX residue before and after leaching by glycine-thiourea (GT) and Thiourea (T).

TABLE-US-00001 TABLE 1 Summary of GT and Thiourea leaching of POX residue sample Crystalline UNITS T GT Head Grade g/t 4.51 4.51 Calc Head G g/t 5.15 5.1 Residue g/t 1.09 0.391 Thiourea kg/t 5 2.5 Glycine kg/t 2.5

Example 4

[0078] In solutions containing glycine-thiourea mixture and an excess of glycine in the presence of ferric as an oxidant, it was found silver can be easily leached from materials containing 4% silver. The pH and temperature of solution was 2 and ambient, respectively. The excess glycine acts as a stabilising complexing agent to maintain the ferric ions in solution. FIG. 4 shows silver extraction is continuously linear over the leaching time.

Example 5

[0079] Gold recovery from leachate arising from glycine-thiourea leaching has been conducted using activated carbon. The results in FIG. 5a show that activated carbon can effectively adsorb gold from an acidic glycine-thiourea solution at 10 g/L carbon and a pH of 3. The model of gold adsorption from glycine-thiourea solutions shown in FIG. 5b indicates that 2.24 kg of gold/tonne of carbon was adsorbed in 4 hours.

Example 6

[0080] The loaded gold on carbon has been eluted by two different elution solutions and the results are shown in FIGS. 6 and 7. FIG. 6 shows the gold elution from loaded activated carbon by an elution solution comprising acidic thiourea and sulfuric acid (50 g/L Tu and 50 g/L sulfuric acid). FIG. 7 shows gold elution from loaded activated carbon by 0.5 M sulfide and 0.5 M NaOH. The Figures show positive results of elution efficiency from both systems. The use of a proper elution column under optimized elution conditions can achieve a better elution recovery.

Example 7

[0081] Thiourea (Tu) and glycine (Gly)-thiourea leaching of a BIOX gold bearing flotation concentrate has been conducted under different reagent concentrations. The bulk mineralogy of the material is provided below:

TABLE-US-00002 TABLE 2 Mineralogy of the BIOX gold bearing flotation concentrate Mineral (%) BIOX (concentrate) Quartz 36 Mica 33 Pyrophyllite 0 Amphibole 14 Jarosite 5 Other clays 9 Gold (g/t) 140

[0082] The BIOX-concentrate is derived from an industrial BIOX pretreatment plant. Samples were bottle-rolled at 10% solids in 450 mL water at 140 rpm.

[0083] Very rapid gold dissolution was observed (FIG. 8) under all process conditions. The results show that leaching with a solution comprising 16 kg thiourea/tonne ore and 16 kg glycine/tonne ore gives the same total dissolution as using a solution containing 32 kg Thiourea/tonne ore. Accordingly, the quantity of thiourea, which is expensive, can be significantly reduced by instead using the amino acid-thiourea lixiviant of the present invention. Moreover, the lixiviant can be regenerated and recycled, thereby further reducing operational costs.

Example 8

[0084] Thiourea and glycine-thiourea leaching of a pressure oxidised gold bearing ore has been conducted under different reagent concentrations. The bulk mineralogy of the material is provided below:

TABLE-US-00003 TABLE 3 Mineralogy of the pressure oxidised gold bearing ore. Mineral (%) POX (ore) Quartz 59 Mica 0 Pyrophyllite 29 Amphibole 0 Jarosite 0 Other clays 11 Gold (g/t) 4.7

[0085] The samples were bottle-rolled at 40% solids in 600 mL water at 140 rpm. Reagents were added equally in stages at each data point.

[0086] Rapid gold dissolution was observed (FIG. 9) under all process conditions. The results show that leaching with a solution comprising Glycine+Thiourea was always more effective than using a solution containing the same quantity of Thiourea without amino acid. In addition, leaching using a solution containing as a lixiviant 12 kg Thiourea/tonne ore+12 kg Glycine per tonne ore, gave better results than leaching with a solution containing double the quantity (24 kg Thiourea (only)/tonne ore) of thiourea on its own. Again, the reduced need for and the ability to regenerate and recycle expensive reagents enables significant reduction in operational costs.

[0087] Whilst a number of specific process embodiments have been described, it should be appreciated that the process may be embodied in many other forms.

[0088] In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.