RECOVERY 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) contacting the material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and an alkali stable transition metal complex in order to form a leachate containing the precious metal and/or chalcophile metal; and (ii) recovering the precious metal and/or chalcophile metal from the leachate.

Claims

1. 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) contacting the material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and an alkali stable transition metal complex in order to form a leachate containing the precious metal and/or chalcophile metal; and (ii) recovering the precious metal and/or chalcophile metal from the leachate wherein the amino acid concentration is greater than 0.05 g/L and the concentration of alkali stable transition metal complex is a minimum of 0.05 g/L.

2. The process of claim 1, wherein the amino acid concentration is less than 250 g/L.

3. The process of claim 1, wherein the amino acid concentration is greater than 0.1 g/L.

4. The process of claim 1, wherein the amino acid concentration is less than 30 g/L.

5. The process of claim 1, wherein the alkali stable transition metal complex is an iron complex or a manganese complex.

6. The process of claim 1, wherein the pH of the leaching solution is at least 7.

7. The process of claim 1, wherein the pH of the leaching solution is at least 8.

8. The process of claim 1, wherein the temperature of the leaching process is between 5 and 90 degrees Celsius.

9. The process of claim 1, wherein the temperature of the leaching process is ambient temperature.

10. The process of claim 1, wherein the alkali stable transition metal complex includes ligands selected from carboxylic and dicarboxylic acid salts, pH-stable cyanide complexes, hydroxy-carboxylic acids and their salts, and ethylene diamine tetra-acetic acid (EDTA) and its salts.

11. The process of claim 1, wherein the alkali stable transition metal complex comprises one or more of chromate, permanganate, manganate, titanate, ferrate, and vanadate.

12. The process of claim 1, wherein the alkali stable transition metal complex comprises one or more of ferrocyanide, ferricyanide, ferro gluconate, fern gluconate, ferro citrate, fern citrate, ferro/ferri tartrate, ferro/ferri ethylene diamine tetra-acetic acid (EDTA) salt.

13. The process of claim 1, wherein the alkali stable transition metal complex comprises one or more of ferro/ferricyanide, ferric gluconate and ferric EDTA.

14. The process of claim 1, wherein the transition metal in the alkali stable transition metal complex is partially substituted by one or more of ammonium ions, alkali metal ions and alkali earth metal ions.

15. The process of claim 1, wherein the concentration of alkali stable transition metal complex is less than 50 g/L.

16. The process of claim 1, wherein the concentration of alkali stable transition metal complex is a minimum of 0.1 g/L.

17. The process of claim 1, wherein the concentration of alkali stable transition metal complex is less than 10 g/L.

18. The process of claim 1, wherein the alkaline solution further includes an oxidant, preferably selected from the group comprising air, oxygen, hydrogen peroxide, calcium peroxide, sodium peroxide, ammonium peroxide manganese dioxide or permanganate.

19. A leaching solution comprising an amino acid lixiviant and an alkali stable transition metal complex.

20. The leaching solution of claim 19, wherein the alkali stable transition metal complex is one or more of ferrocyanide, ferricyanide, ferric gluconate and ferric EDTA.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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:

[0047] FIG. 1 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using three different leaching solutions at room temperature: Fe complex only (diamonds), glycine only (circles) and Fe complex plus glycine (squares).

[0048] FIG. 2 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using Fe complex plus glycine leaching solutions at 3 g/L glycine (diamonds) and 7.5 g/L glycine (circles).

[0049] FIG. 3 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using Fe complex plus glycine leaching solutions at 3 g/L ferricyanide (diamonds) and 1.5 g/L ferricyanide (circles).

[0050] FIG. 4 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using three different leaching solutions at 50 C.: Fe complex only (diamonds), glycine only (circles) and Fe complex plus glycine (squares).

[0051] FIG. 5 is a graph of gold and copper recovery (%) versus time (hours) for leaching gold-copper containing ore using a leaching solution containing glycine and ferricyanide.

[0052] FIG. 6 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using a leaching solution containing glycine and potassium permanganate.

[0053] FIG. 7 is a graph of gold recovery (%) after leaching gold ore at 72 hours and 120 hours using solutions containing glycine and sodium chromate.

[0054] FIG. 8 is a graph of gold recovery (%) after 72 hours and 120 hours for leaching gold ore using solutions containing glycine and cerium nitrate.

[0055] FIG. 9 is a graph of gold recovery (%) versus time (hours) for leaching gold ore using solutions containing ferricyanide only (triangles), ferricyanide and NaCN (diamonds), and glycine, ferricyanide and NaCN (squares).

[0056] FIG. 10 is a graph of gold and silver recovery (%) versus time (hours) for leaching high silver gold ore using solution containing glycine, ferricyanide and NaCN.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0057] FIGS. 1 to 4 show the results of leaching gold ore under various leaching conditions. All of the tests were performed using gold ores ground to a particle size of 100% passing 75 micron. Some tests were performed at room temperature (RT=20 C.), and in bottle rolls and others in stirred vessels at mildly elevated temperature. The maximum leach time was 48 hours in all cases.

[0058] Referring firstly to FIG. 1, a graph is shown for gold recovery (%) versus time (hours) for leaching gold ore using three different leaching solutions at room temperature. All three solutions have a pH of 11.0 and a solids content of 33.3%. The circles represent a solution containing glycine (without Fe complex) at a concentration of 7.5 g/L. The diamonds represent a solution containing an Fe complex, namely 1 g/L ferricyanide, without glycine. The squares represent a solution containing both 7.5 g/L glycine and 1 g/L ferricyanide.

[0059] It is evident that in the absence of moderate heating (ie, to >40 C.), and catalysts such as copper, leaching of gold ore using glycine alone yields very low gold recovery at room temperature. The recovery from leaching with a solution containing ferricyanide is slightly higher. However, there a significant improvement in recovery (around an order of magnitude) when the ore is leached with a solution containing both glycine and the ferricyanide together. The gold recovery increased to approximately 76% after 48 hours of leaching.

[0060] FIG. 2 shows gold recovery versus time for leaching gold ore at room temperature, a pH of 11.0 and a solids content of 33.3% (by weight) using Fe complex plus glycine leaching solutions at 3 g/L glycine (diamonds) and 7.5 g/L glycine (circles). It can be seen that doubling the glycine concentration at a given concentration of Fe complex increases the gold recovery by around 15% after 48 hours leaching.

[0061] FIG. 3 shows gold recovery versus time for leaching gold ore at room temperature, a pH of 11.0 and a solids content of 33.3% (by weight). using Fe complex plus glycine leaching solutions at 3 g/L ferricyanide (diamonds) and 1.5 g/L ferricyanide (circles). It can be seen that doubling the ferricyanide concentration at a given concentration of glycine increases the gold recovery by around 15% after 48 hours leaching.

[0062] FIG. 4 is a graph of gold recovery versus time for leaching gold ore using three different leaching solutions at an elevated temperature of 50 C., a pH of 11.0 and a solids content of 40% (by weight). The respective solutions contained Fe complex (4.5 g/L Ferric gluconate) only (diamonds), 7.5 g/L glycine only (circles) and Fe complex (4.5 g/L Ferric gluconate) plus 7.5 g/L glycine (squares). While the elevated temperature did improve gold recovery for solutions containing glycine or Fe complex only, there was a significant improvement in gold recovery when leaching was conducted with a solution containing both glycine and Fe complex. It is also evident that the overall gold recovery using glycine and ferricyanide at room temperature (see FIG. 1) is greater (75%) than using glycine and Ferric gluconate at elevated temperature (33%) for comparative leach times of 48 hours.

[0063] FIG. 5 is a graph of gold and copper recovery from gold-copper ore containing chalcopyrite and chalcocite as the main source of copper in the ore. The leach solutions containing 2 g/L glycine and 1.8 g/l ferricyanide. The leaching was conducted at 45% solids, pH 10.5 and room temperature. The results demonstrate that both copper and gold may be effectively leached using the present process. Under the conditions of this test, it is noted that the initial leaching rate for copper was higher than for gold, with the rate decreasing over time. In contrast, the leaching rate for gold was generally higher than for copper after approximately 48 hours leaching time.

[0064] FIG. 6 is a graph of gold recovery versus time for leaching gold ore using solutions containing 15 g/L glycine in the presence of 2.0 g/L potassium permanganate at pH 11.0 and 55 C. and a solids content of 30% (by weight). Upon comparison with FIG. 1, it can be seen that gold dissolution is also enhanced when the ore is leached with a solution containing both glycine and a permanganate (potassium permanganate). Under the conditions of this test, gold dissolution reaches approximately 77% after 96 hours of leaching. Therefore, under the respective process conditions of FIGS. 1 and 6, the rate of gold recovery is higher in the presence of ferricyanide than in the presence of permanganate.

[0065] FIG. 7 is a graph of gold recovery after 72 hours and 120 hours for leaching gold ore using solutions containing 15 g/L glycine in the presence of 2.0 g/L sodium chromate at pH 10.5 and 23 C. and a solids content of 30% (by weight). The results indicate that gold dissolution may be enhanced by leaching with a solution containing both glycine and an alkaline-stable transition metal complex comprising sodium chromate. Under the conditions of this test, the rate of gold dissolution using a solution containing sodium chromate is generally lower than that achieved using solutions containing any of ferricyanide, ferric gluconate and potassium permanganate.

[0066] FIG. 8 is a graph of gold recovery after 72 and 120 hours for leaching gold ore using solutions containing 15 g/L glycine in the presence of 2.3 g/L cerium nitrate at pH 10.5 and 23 C. and a solids content of 30% (by weight). The results indicate that gold dissolution may be enhanced by leaching with a solution containing both glycine and an alkaline-stable transition metal complex comprising cerium nitrate. Under the conditions of this test, the rate of gold dissolution using a solution containing cerium nitrate is generally lower than that achieved using solutions containing any of ferricyanide, ferric gluconate, potassium permanganate and sodium chromate.

[0067] FIG. 9 is a graph of gold recovery versus time for leaching gold ore using solutions containing ferricyanide only (triangles), ferricyanide and NaCN (diamonds), and glycine, ferricyanide and NaCN (squares). Where present, the concentrations of the various components in solution are 2 g/L glycine, 1.0 g/L ferricyanide and 10 ppm NaCN. The solutions each had a pH of 10.5, ambient temperature (23 C.) and a solids content of 40% (by weight). The results show that while moderate levels of gold are recovered using a solution containing ferricyanide and NaCN, the recovery is significantly enhanced when glycine is also added to the solution. The overall recovery is approximately 85% after 48 hours leaching. The results indicate that neither ferricyanide nor NaCN are themselves present in sufficient concentration to achieve economic extraction of the precious or chalcophile metals in the absence of additional lixiviant (ie amino acid).

[0068] FIG. 10 is a graph of gold (circles) and silver (triangles) recovery versus time for leaching high silver gold ore using solutions containing 7.5 g/L glycine in the presence of 1.5 g/L ferricyanide and 200 ppm NaCN at pH 10.5, ambient temperature (23 C.) and a solids content of 40% (by weight). The rate of gold dissolution was very high, with maximum gold recovery of greater than 95% achieved after only 6 hours of leaching. Silver recovery was also very good, with a maximum recovery of about 76% achieved after 6 hours of leaching. The leaching rate was enhanced by the presence of a low concentration of NaCN which acted as a leaching catalyst.

EXAMPLES

[0069] Non-limiting Examples of a process for recovery of one or more precious metal and/or chalcophile metal will now be described.

Example 1

[0070] A gold ore was leached in an aqueous pulp containing 33.3% solids at room temperature (20 degrees Celsius) at a pH of 11. Leaching was conducted in three solutions containing: (a) glycine only, (b) Fe complex only and (c) glycine and Fe complex. The following was noted during bottle roll tests: [0071] (a) For the case of using glycine only (using 7.5 g/L), in the absence of any alkali-stable transition metal complex, the gold extraction into solution is only about 1% after 48 hours leaching. [0072] (b) For the case of the alkali-stable transition metal complex only (potassium ferricyanide in this case, at a concentration of 1 g/L) the gold extraction into solution is only about 5%) after 48 hours leaching. [0073] (c) However, when 7.5 g/L glycine and 1 g/L ferricyanide are used in combination, the gold extraction/leaching into solution is around 75% after 48 hours leaching.

[0074] Thus the combination of the two reagents gives an outcome that is not just the sum of the effects, but a multiple of 15-75 times the effect of any single reagent when used on its own, all other conditions being the same.

Example 2

[0075] An ore material containing gold, nickel, copper, cobalt and zinc was leached in a solution containing 15 g/L glycine in the presence of 2.0 g/L permanganate at pH 11.0, a temperature of 55 C. and a solids content of 30% (by weight). Table 1 lists the concentrations of elements in the leachate after 120 hours leaching. These results indicate that the recovery of gold, nickel, copper, cobalt and zinc was 77, 30, 55, 25 and 40% respectively.

TABLE-US-00001 TABLE 1 Sample Au Cu Co Fe Si Al Ni Zn UNITS mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L Glycine- 0.894 3 2.2 BDL 8 BDL 3.8 2.5 permanganate Extraction, % 77.0 55.0 25.0 <BDL <0.02 <BDL 30.0 40.0 *BDL = below detection limit

[0076] The data indicates that under the specified leaching conditions, the process results in very high recovery of precious metal (gold) and moderate to high recovery of the chalcophile elements copper, cobalt, nickel and zinc. However, the dissolution of the undesirable non-chalcophile elements, iron, aluminium and silicon was very low, indicating the preferential leaching of target metals over the undesirable elements using this process.

[0077] 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.