METHODS OF BASE METAL RECOVERY WITH APPLICATIONS OF OXYGEN VECTORS

Abstract

In described embodiments, a process for recovery of a metal from a grounded ore comprises leaching the grounded ore with a leaching reagent, an oxidant and an oxygen vector. In particular, a process for recovery of gold from a grounded gold ore, comprises leaching the grounded gold ore with a cyanide salt, an oxidant and an oxygen vector. The oxygen vector is selected from dodecane, decane, hexadecane, or the like.

Claims

1. A process for recovery of a metal from a grounded ore, comprising the step of leaching the grounded ore with a leaching reagent, an oxidant and an oxygen vector.

2. The process of claim 1, further comprising the steps of floating the grounded ore to obtain an ore concentrate; and feeding the ore concentrate to the leaching step.

3. The process of claim 2, further comprising the steps of pre-oxidizing the ore concentrate and the grounded ore using the oxidant and the oxygen vector to obtain a slurry; and feeding the slurry to the leaching step.

4. The process of claim 1, wherein the metal is gold, copper, lead, nickel, zinc or cobalt.

5. The process of claim 1, wherein the leaching reagent is a cyanide salt or an alkaline.

6. The process of claim 5, wherein the cyanide salt is selected from one or ore of KCN, NaCN or Ca(CN).sub.2.

7. The process of claim 3, wherein the oxygen vector is dodecane, decane or hexadecane, wherein a weight percent of the oxygen vector in the pre-oxidation and/or cyanide leaching mixtures ranges from 1% to 6% by weight.

8. The process of claim 3, wherein the oxidant is a mixture of air, O.sub.2 and H.sub.2O.sub.2.

9. The process of claim 1, wherein a temperature of operation ranges from 10° C.-70° C.

10. The process of claim 3, wherein a pH of the leaching process and/or pre-oxidation process ranges 1-4 and 8-11.5.

11. A process for recovery of gold from a grounded gold ore, comprising the step of leaching the grounded gold ore with a cyanide salt, an oxidant and an oxygen vector.

12. The process of claim 11, further comprising the steps of floating the grounded gold ore to obtain a gold ore concentrate; and feeding the gold ore concentrate to the leaching step.

13. The process of claim 12, further comprising the steps of pre-oxidizing the gold ore concentrate and the grounded gold ore using the oxidant and the oxygen vector to obtain a slurry; and feeding the slurry to the leaching step.

14. The process of claim 13, wherein the oxygen vector is dodecane, decane or hexadecane, wherein a weight percent of the oxygen vector in the pre-oxidation and/or cyanide leaching mixtures ranges from 1% to 6% by weight.

15. The process of claim 11, wherein the cyanide salt is selected from one or more of KCN, NaCN or Ca(CN).sub.2.

16. The process of claim 13, wherein a pH of the leaching and/or pre-oxidation is >9.

17. The process of claim 11, wherein a temperature of operation ranges from 10° C.-70° C.

18. The process of claim 13, wherein the oxidant is a mixture of air, O.sub.2 and H.sub.2O.sub.2.

19. A process for recovery of a gold from a grounded gold ore, comprising the steps of floating the grounded gold ore to obtain a gold ore concentrate; pre-oxidizing the gold ore concentrate and the grounded gold ore using the oxidant and an oxygen vector and a mixture of air, O.sub.2 and H.sub.2O.sub.2 to obtain a slurry; and leaching the slurry, the gold ore concentrate and the grounded gold ore with NaCN, the oxygen vector and the mixture of air, O.sub.2 and H.sub.2O.sub.2, wherein the oxygen vector is selected from dodecane, decane or hexadecane.

20. The process of claim 19, wherein a total percentage (%) increase of a gold recovery is 0.2%-1.6% with oxygen and oxygen vector versus oxygen injection only.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0054] For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0055] FIG. 1 is a flow chart of an exemplary embodiment of a gold leaching process.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] Disclosed are methods of a base metal recovery with applications of oxygen vectors. More specifically, the disclosed are the methods of using oxygen vectors (i.e., organic solvents) in a leaching process to increase oxygen mass transfer (OMT) in a real metal-based hydrometallurgical system. The disclosed methods may include a pre-oxidation process in which the oxygen vector is added to an oxidant. A flotation process may be included to obtain an ore concentrate before pre-oxidation process. A comminution process may be applied to get a crushed and grounded ore for the flotation process. The base metal includes gold, copper, lead, nickel, cobalt or the like. The oxygen vector may be a higher carbon chain organic solvent, such as dodecane, decane and hexadecane.

[0057] The applications of the oxygen vectors in existing metal leaching and pre-oxidation reactors have the following benefits: [0058] Larger mineral liberation for the same oxygen utilization, which could extend existing comprehensive metal leaching systems for additional mineralogies. For example, gold does not present on the surface, but presents inside resistant sulfide minerals, like Arsenopyrite. [0059] Reduced residence time in process systems that could imply an increase in existing process throughput. [0060] Enhancement of the OMT in existing reactors.

[0061] In one embodiment, the disclosed method is applied to extract gold from a gold ore concentrate. Commercially, the gold ore/concentrate is treated by employing a hydrometallurgical leaching process to dissolve gold into a solution phase. The solution phase is then subjected to additional concentration and stripping of gold. The final product after all the back end processing is a gold doré. A generalized flowchart for gold extraction of the disclosed method is shown in FIG. 1, a flowchart of an exemplary embodiment of a gold-cyanide leaching process. As shown, a gold ore is mined from open pit or underground mining operations and then crushed. The crushed gold ore is subjected to a series of crushing and grinding operations, i.e., comminution operation at step 102 to obtain a fine ground gold ore. The objective of the comminution operation is to reach a desired gold ore particle size suitable for further downstream processing. At step 104, the fine ground gold ore is optionally treated by flotation. The flotation is a physical separation technique used to concentrate the gold bearing sulfidic minerals in lieu of their surface specificity by adding a flotation reagent. The flotation reagent may be aerofloat series or xanthates. The flotation technique is applied to certain ore mineralogies amenable for surface assisted separation. A product of the flotation is called as an ore concentrate or a flotation concentrate. A slurry tails from the flotation process is discharged. Here the ground ore from comminution or the flotation concentrate from flotation is then subjected to pre-oxidation with an oxidant injection at step 106. The oxidant may be a mixture of air, O.sub.2 and H.sub.2O.sub.2. The pre-oxidation could include any one of the techniques described in the background. The pre-oxidation is optional and dependent on the amount and quantities of oxygen consuming compounds (e.g., sulfides) and the shape and size of gold particles and the association of the gold bearing particles in the oxygen consuming compound matrix. In this step, an oxygen vector may be add to the oxidant to increase OMT. The oxygen vector may be dodecane, decane, hexadecane, or the like. The pre-oxidation treatment prior to cyanide leaching (step 108) liberates or frees the locked gold and contributes to cyanide reagent savings in the subsequent cyanide leaching operation. The product of the pre-oxidation is a pre-oxidation slurry. The ground ore, flotation ore concentrate, pre-oxidized slurry (i.e., precursor) and combinations thereof are then subjected to cyanide leaching to selectively dissolve the gold at step 108. Cyanide salts addition and air/O.sub.2/H.sub.2O.sub.2 injection are performed on the precursors. The cyanide salts may be potassium cyanide (KCN), sodium cyanide (NaCN) and calcium cyanide (Ca(CN).sub.2). The cyanide salt may be selected from one or more of KCN, NaCN or Ca(CN).sub.2. The gold particles in the precursors is complexed to form a gold cyanide complex selectively leaving undissolved gangue (impurities) in a residue. In this step, the oxygen vector may be add to the cyanide salt and the oxidant to increase OMT, The oxygen vectors may be dodecane, decane, hexadecane, or the like. The leach liquor from the leaching process is then subjected to downstream processing and refining operations to produce a gold doré (e.g., 80% Gold). The gold dorés are subsequently refined in protected government facilities (i.e., mints) to produce a gold bar. A solid tail from the leaching process may be recycled back to the pre-oxidation slurry.

[0062] The disclosed methods use oxygen vectors, such as, dodecane, decane and hexadecane, in atmospheric leaching processes for metal recoveries. The oxygen vectors increase the mass transfer of oxygen from gas phase to liquid phase. The oxygen vectors are added in-situ into the leaching step and are recovered back into the process using gravity. The metal recovery is not limited to gold but may be applied to any metal leaching using oxygen as one of the reactants/oxidants. The metals of interest could be extended to copper, lead, nickel, cobalt or the like. In particular, referring to gold leaching, the above mentioned oxygen vectors may be applied in the pre-oxidation and/or cyanide leaching unit operation. The associated benefits of using oxygen vectors in gold leaching may be envisaged in terms of increased gold recovery and decreased cyanide consumption.

[0063] The ranges of parameters and benefits, which could be employed for this application in reference to gold in pre-oxidation and cyanide leaching, include: [0064] Wt % of oxygen vector addition: 1%-6% w/w % of the pre-oxidation and/or cyanide leaching mixtures; [0065] Temperature of operation: 10° C.-70° C.; [0066] pH: 8-11.5; preferably pH>9; [0067] Dissolved oxygen in liquid in range of: 5 ppm to 40 ppm; [0068] Total % increase of gold/metal recovery: 0.2%-1.6% with oxygen and oxygen vector versus oxygen injection only; [0069] Leaching reagent sodium cyanide (kg NaCN/t of ore) savings: 8%-33% with oxygen and oxygen vector versus oxygen injection only; [0070] Oxygen consumption reduction (kg of O.sub.2/t of ore): 10-26% on the application of oxygen and solvent versus oxygen addition only.

[0071] Here, the pH in pre-oxidation and leaching may vary depending on the leaching reagent that is applied. For example, for some metals, an alkaline may not be used as a leaching reagent; the pH may range from 1 to 4. Thus, the overall pH for metal recoveries may range from 1 to 4 and 8 to 11.5.

EXAMPLES

[0072] The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the inventions described herein.

Example 1. Gold Recovery

[0073] A gold ore concentrate chosen for this example has significant oxygen demands, which may not be sustained using air. A set of 5 tests were performed for pre-oxidation and cyanide leaching using air, O.sub.2 and O.sub.2+ each of the selected oxygen vectors in a reactor shown in Table 1. The selected oxygen vectors have a higher boiling point compared to the desired temperature of operation (e.g., 25-35° C.), high oxygen capacity, lower density and a lower water solubility (facilitates separation and reuse of solvents after unit operation).

TABLE-US-00001 TABLE 1 Properties of Different Oxygen Vectors Solubility V. P. in water O.sub.2 (Pa) B.P. M.P. Density (ppm) solubility @ 11.5 (° C.) (° C.) (g/cc) 25° C. (xL*10{circumflex over ( )}3) 25° C. Hazards n-Hexane 69 −95 0.6603 9.5 1.96 Flammable (Colorless) 1.1%-7.5% Toluene 110.7 −95 0.866 526 0.922 Flammable, (Colorless) Corrosive n-Heptane 98.38 −90 0.6795 0.0034 1.94 Highly flammable, corrosive, toxic n-Decane 173 −30 0.73 0.052 2.2 195 Flashpoint 46° C., Flammable (LFL 0.7 vol %, UFL 5.4 vol %) n-Dodecane 218 −9.55 0.749 0.0037 1.86 18 Flammable, Flashpoint 7l° C., (LFL 0.6 %, UFL no data) n- 287 18 0.77 0.000021 1.74 0.3 Not flammable, Hexadecane health hazard Octanol 195 −16 0.83 1120 1.132 Corrosive, irritant Hexanol 157 −45 0814 5900

[0074] Increase in oxygen mass transfer is known to increase gold recovery and reduce the consumption of sodium cyanide. Total five sets of batch experiments were carried out as the preliminary tests: only air, only O.sub.2, decane+O.sub.2, dodecane+O.sub.2 and hexadecane+O.sub.2.

[0075] For homogenizing the gold ore concentrate samples, the homogenizing technique was used. Percent solids and percent moisture determinations were made for each sample. The ore was processed in a 2.3 liter glass vessel with the following capabilities: temperature control (at 25° C.) via a heating jacket and cooling loop, pH control (at 10.5) with Ca(OH).sub.2 pumped in, dissolved oxygen control using optical DO (dissolved oxygen) probe, inlet gas (O.sub.2 and N.sub.2) control. Here N.sub.2 is used to maintain a dissolved oxygen concentration. For example, a ratio of N.sub.2 and O.sub.2 was 50% N.sub.2 versus 50% O.sub.2. The pH probe and the two DO probes were calibrated prior to the start of each run. A leak test was performed after the reactor and all of its parts were assembled. The oxygen vector solvent was then added through a port in the lid at 2 volume % of the slurry volume.

[0076] Referring to FIG. 1, pre-oxidation (step 106) started when the desired pH (10.5) and temperature (25° C.) were reached. A sample was taken and the oxygen and nitrogen flow was started to achieve the desired DO concentration (10 mg/L), Here nitrogen is used to maintain a dissolved oxygen level in the process along with oxygen. Oxygen Uptake Rates (OUR) were taken at 0.25 hr, 1 hr, 2 hr, 4 hr, 8 hr and 13 hr. During the OUR measurements, the gas in and gas out were turned off, the reactor was isolated and the mixing rpm (rotation per minute) was reduced. An additional sample was taken at 13 hr at the end of pre-oxidation.

[0077] Before the cyanide leaching (step 108) was started, the volume of the slurry was estimated and the temperature (25° C.), DO (15 mg/L) and pH (11.25) were adjusted. The free cyanide concentration was controlled to 1000 ppm by adding 10% NaCN based on slurry volume. OUR measurements and samples were taken at 1 hr (OUR only), 2 hr, 5 hr, 12 hr, and 24 hr times. During the OUR measurements, the gas in and gas out were turned off, the reactor was isolated and the mixing rpm was reduced. After measuring CN in the filtered samples by an ion sensitive electrode (ISE) CN probe, the residual CN in the reactor was adjusted to 800 ppm by adding the 10% NaCN solution through a port in the lid, After 24 hours, the slurry from the reactor was filtered (and washed with 2.5 L of DI water) and the dried solids were collected and sent for assaying. The unused Ca(OH).sub.2 was collected and weighed to estimate the CaO consumption.

[0078] Summary or the reaction parameter used for this example are: [0079] a. Oxygen vector solvent addition: in experiments with solvent, 2 vol % of solvent is added. [0080] b. Pre-oxidation: 25° C., 45% solids, pH 10.5, DO 10 ppm and 13 hour reaction time. [0081] c. Cyanide Leaching: 25° C., 45% solids, 800 ppm free CN concentration, DO 15 ppm, 24 hour reaction time.

[0082] At the completion of every experiment, the solid residues and leach liquors are weighed and collected. The solids were assayed for gold, sulfur (total sulfur, sulfide sulfur and sulfate) and silver. The liquids were analyzed for gold, silver and anions (thiosulfate, sulfate and thiocyanate) respectively.

Example 2: Gold Concentration

[0083] Gold concentration in solid residues were carried out using gold fire assay technique. Gold recovery presented in Table 2 was calculated using gold (g/t) remaining in the residue,

TABLE-US-00002 TABLE 2 Gold Recovery Table for Flextime Experiments Condition Au Recovery % Dodecane + O.sub.2 87.17% Hexadecane + O.sub.2 87.48% Oxygen 87.05% Air 86.63% n-Decane + O.sub.2 88.62%

[0084] As presented in Table 2, it can be seen that in experiments using n-Decane repeat experiment performed as an oxygen vector, about 1.5% (4 million $) increase in gold recovery was obtained compared to the no solvent (oxygen case). In general, an increasing trend for gold recovery was observed with a solvent addition viz: about 0.5% increase with Hexadecane, about 0.12% increase with dodecane. An increase in gold recovery was seen with the addition of a lowest carbon chain alkane (n-Decane) at about 1.5%. Here the gold recovery increase is calculated as a total increase.

Example 3: Cyanide Consumption

[0085] Free cyanide concentration was monitored in the gold leaching slurry at the following times in cyanide leaching: 2 h, 5 h, 12 h and 24 h. The measurement was conducted using ISE CN probe. 1000 ppm free Cyanide was maintained initially, followed by an 800 ppm free CN concentration for the remainder of the experiment. 10% Sodium Cyanide was used to adjust the cyanide content.

TABLE-US-00003 TABLE 3 Sodium Cyanide Consumption in Flextime Experiments Sodium Cyanide Experimental Case consumption (kg/t) 2 wt % Dedecane + O.sub.2 2.2 kg/t 2 wt % Hexadecane + O.sub.2 2.8 kg/t Oxygen 3.2 kg/t Air 4.4 kg/t 2 wt % Decane + O.sub.2 2.9 kg/t

[0086] From Table 3, there is a decrease of about 28% in sodium cyanide consumption in case of oxygen compared to air. The experiments with the oxygen vectors displayed a decrease in sodium cyanide consumption compared oxygen: about 31% in case of dodecane (savings of 700,000 $), viz 12.5% in case of hexadecane and about 10% in case of decane (savings of 200,000 $).

Example 4: Oxygen Consumption

[0087] The total oxygen consumption in experiments (pre-oxidation and cyanide leaching) was calculated using the Oxygen Uptake Rate studies performed as mentioned in section 2 under methodology and experimentation. Table 4 presents the Oxygen Consumption (kg of O.sub.2/t of ore) utilized in the experiments.

TABLE-US-00004 TABLE 4 Total Oxygen Uptake (kg of solids) Utilized in the Flextime Tests Total oxygen uptake Preox O.sub.2 CNL O.sub.2 (kg of O.sub.2/mt (kg of O.sub.2/mt (kg of O.sub.2/mt Test of solids) of solids) of solids) Dodecane + O.sub.2 3.82 3.7 0.12 Hexadecane + O.sub.2 3.47 3.33 0.14 Oxygen 3.9 3.8 0.1 Decane + O.sub.2 2.88 2.76 0.12

[0088] Majority of the oxygen used was consumed during the pre-oxidation stage of the reaction. The above observation could be correlated to the passivation of labile sulfides in the pre-oxidation stage as iron hydroxides. These hydroxides do not participate in the cyanide leaching. In general, compared to experiments with no solvent addition, a decrease in oxygen consumption was observed with the addition of oxygen vectors.

[0089] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

[0090] As used herein, the indefinite article “a” or “an” s used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0091] As used herein, “about” or “around” or “approximately” in the text or in a claim means±10% of the value stated.

[0092] The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviations (e.g., Au refers to gold, etc.).

[0093] Additionally, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations, That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances.

[0094] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

[0095] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0096] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

[0097] As used in this application, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion.

Although the subject matter described herein may be described in the context of illustrative implementations to process one or more computing application features/operations for a computing application having user-interactive components the subject matter is not limited to these particular embodiments, Rather, the techniques described herein can be applied to any suitable type of user-interactive component execution management methods, systems, platforms, and/or apparatus.

[0098] It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.