Process for the selective removal of copper compounds and other impurities with respect to molybdenum and rhenium, from molybdenite concentrates

Abstract

Disclosed is a process for the selective removal of copper compounds, and other impurities with respect to molybdenum and rhenium, from concentrates of molybdenite (MoS.sub.2) with a copper content that is higher than 0.5% in dry weight.

Claims

1. An industrially scalable process for the selective removal of copper compounds and other impurities with respect to molybdenum and rhenium from a molybdenite (MoS.sub.2) concentrate with a copper content of more than 0.5% by dry weight, comprising the following steps: (a) mixing a concentrate of impure MoS.sub.2 (1) with process water and/or a leaching solution of dilute sulfuric acid in water (2), in which the concentration of sulfuric acid is up to 20 g/l, in a repulping stage (3), to obtain a first pulp (4) with a solid content in the pulp of 50% to 20% by weight, maintaining a ratio of liquid to solid in the range of 1/1 to 4/1, volume/weight; (b) leaching the first pulp (4) inside a pressure reactor, in a pressurized leaching stage (6) under an oxidizing atmosphere, with an oxygen-bearing gas (5), at a leaching temperature between 110° C.-180° C. with a partial pressure for the oxidizing gas inside the reactor between 20-150 psig (0.1-1.0 MPa) to obtain a second pulp (7) containing a cleaned molybdenite concentrate and a mother liquor containing dissolved impurities, including sulfuric acid that was generated in situ by the selective oxidation of sulfur contained in the sulfides that initially comprised the impurities in the molybdenite concentrate; (c) carrying the second pulp (7) to a cooling tank (8), to obtain a third pulp (7a) with a temperature of at most 60° C.; and (d) carrying the third pulp (7a) to a solid/liquid separation stage (9) to obtain a clean molybdenite concentrate (10) with a percentage of copper of less than 0.5% by weight and a liquor (11) containing the copper and impurities in solution produced by chemical reactions in the pressurized leaching stage (6).

2. The process according to claim 1, wherein the clean molybdenite concentrate (10) is carried to the following steps, comprising: (e) carrying the clean molybdenite concentrate (10) to a washing stage (12) with washing water (13), to extract the mother liquor that is impregnated in the clean molybdenite concentrate (10), to obtain a washed clean molybdenite concentrate (14); and (f) carrying the washed clean molybdenite concentrate (14) to drying, packing and storage; or (g) carrying the washed wet or dry clean molybdenite concentrate (14) to roasting to obtain technical grade molybdenum trioxide.

3. The process according to claim 2, wherein the technical grade molybdenum trioxide obtained in stage (g) is used in the manufacture of other molybdenum products, or is used as a precursor for the manufacture of pure molybdates from molybdenum.

4. The process according to claim 1, wherein the liquor (11), rich in copper and impurities obtained in step (d) of the solid/liquid separation (9), contains molybdenum and rhenium in solution, the liquor (11) is carried to a solvent extraction stage for separating the molybdenum and the rhenium.

5. The process according to claim 1, wherein the liquor (11) rich in copper and impurities is treated by consecutive stages of solvent extraction and electrodeposition, or cementation, to obtain the copper.

6. The process according to claim 1, wherein the liquor (11) rich in copper and impurities is recirculated to the pressurized leaching stage (6).

7. The process according to claim 1, wherein the copper compounds present in the solid material (1) to be removed correspond to primary sulfides and secondary sulfides.

8. The process according to claim 7, wherein the primary sulfides correspond to chalcopyrite (CuFeS.sub.2) and the secondary sulfides correspond to chalcocite (Cu.sub.2S) and covellite (CuS).

9. The process according to claim 1, wherein the oxygen-bearing gas (5) is selected from pure oxygen, oxygen-enriched air, or air.

10. The process according to claim 1, wherein the pressure reactor is a horizontal or vertical autoclave, with one or more paddles, and having one or more compartments separated by baffles, with submerged gas injection, or injection on top, or both.

11. The process according to claim 1, wherein the residence time of the pulp inside the pressure reactor is between 15 and 240 minutes.

12. The process according to claim 1, wherein the second pulp (7) resulting from the leaching stage (6) has a pH between 0 and 2 and a potential for oxidation/reduction between 0.2 and 0.5 volts vs Ag/AgCl.

13. The process according to claim 1, wherein in step (d), the solid/liquid separation stage (9) is carried out by filtration, sedimentation, clarification, thickening, centrifugation, dewatering, or decantation.

14. The process according to claim 13, wherein the solid/liquid separation stage (9) is carried out by filtration in a plate or diaphragm filter, with a washing liquid-solid ratio between 0.2 and 1.0 volume/weight.

15. The process according to claim 3, wherein said other molybdenum products comprise ferromolybdenum.

16. The process according to claim 3, wherein said precursor for the manufacture of pure molybdates from molybdenum comprises ammonium dimolybdate (ADM), ammonium heptamolybdate (AHM), or other molybdates.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a flowchart of the process of invention.

SUMMARY OF THE DISCLOSURE

(2) This invention is a purification or cleaning process for a molybdenite concentrate. In this process, the concept of purification or cleaning mainly refers to the extraction, removal or leaching of copper sulfide compounds, however, it also extracts other impurities, particularly iron, zinc, nickel, sodium, calcium and manganese, from the molybdenite concentrate. The process comprises a stage where the molybdenite concentrate is mixed or repulped with water that has been acidified with sulfuric acid (in the range of 0 to 20 g/l) to form a pulp, which is fed into an autoclave where a pressurized leaching stage is developed by injecting oxygen or an oxygen-bearing gas for the entire residence time, thus producing a pulp composed of a clean or purified molybdenum concentrate and a liquor that is rich in impurities dissolved in a sulfuric acid medium. The process is developed under auto-thermal conditions, mainly using the heat from the reaction of the oxidation of the copper sulfides and iron. This pulp is carried to a solid/liquid separation stage, where a clean molybdenum concentrate is obtained together with a liquor containing the copper compounds and other elements extracted from the original concentrate, which are recovered through later industrial processes, such as solvent extraction, ion exchange, electrodeposition or others.

(3) The process is efficient for (primary and secondary) copper sulfides, iron, zinc, nickel, sodium, calcium, manganese and other metals. And as long as a control is kept over the main variables of the process, such as oxygen overpressure and temperature, the molybdenum sulfides and rhenium, particularly rhenium, will not dissolve.

(4) The cleaning process in the autoclave is, consequently, a purification process that enables an optimum quality of concentrate for feeding the roasting furnaces to be obtained, achieving increases in production capacity and the recovery of rhenium.

DETAILED DESCRIPTION

(5) The process of the invention is a process for the efficient removal of copper compounds, and other elements (except molybdenum and rhenium), from dirty molybdenite concentrates. The copper compounds and other elements present in this concentrate are of the sulfide type that came about thanks to the inefficiencies of the flotation process from which the molybdenite concentrate is obtained.

(6) The copper sulfide compounds that are present in the molybdenite concentrate preferably are primary sulfides, such as chalcopyrite (CuFeS.sub.2), and secondary sulfides, such as covellite (CuS) and chalcocite (Cu.sub.2S). In addition to these sulfide compounds, this invention is also capable of leaching Cu, Fe, As, P, Na, Co, F, Cl, Ca, Mn, Zn and Ni compounds.

(7) The process of the present invention comprises the selective removal of the copper compounds and other impurities with respect to the molybdenum and rhenium from the molybdenite concentrate with a higher copper content than 0.5% in dry weight, according to the following stages:

(8) mixing a concentrate of impure MoS.sub.2 (1) with process water and/or a leaching solution that is diluted with sulfuric acid (2), with a concentration of sulfuric acid is in the range of 0 to 20 g/l, in a repulping stage (3), to obtain a first pulp (4) with a solid content in the pulp of 50 to 20% in weight, maintaining equivalently a ratio of liquid to solid in the range of 1/1 to 4/1, volume/weight;
leaching the first pulp (4) inside a pressure reactor, in a pressurized leaching stage (6) at an oxidizing atmosphere, with an oxygen-bearing gas (5), at a leaching temperature between 110° C.-180° C. with a partial pressure for the oxidizing gas inside the reactor between 20-150 psig (0.1-1.0 MPa) to obtain a second pulp (7) containing the clean molybdenite concentrate and a solution or mother liquor containing the dissolved impurities, including the sulfuric acid that was generated in situ by the selective oxidation of the sulfur contained in the sulfides that initially formed the impurities (particularly copper sulfide and zinc sulfide) in the dirty molybdenite concentrate;
carrying the second pulp (7) to a cooling tank (8), to get a third pulp (7a) with a temperature of at most 60° C.;
carrying the third pulp (7a) to a solid/liquid separation stage (9) to obtain a clean molybdenite concentrate (10) with a percentage of copper of less than 0.5% in weight and a liquor (11) containing the copper and impurities in solution produced by the chemical reactions of the leaching stage (6).

(9) Preferably the sulfuric acid concentration of the leaching solution (2) for the repulping (3), in order to get the first pulp (4) of molybdenite concentrate, it is found in the range of 0 to 20 g/l.

(10) As an option, the clean concentrate (10) can be carried to the following stages, comprising:

(11) carrying the clean molybdenite concentrate (10) to a washing stage (12), with washing water (13), to drag the mother liquor that is impregnated in the clean molybdenite concentrate (10);

(12) carrying the washed clean molybdenite concentrate (14) to drying, packing and storage; or

(13) carrying the washed wet or dry clean molybdenite concentrate (14) to roasting to obtain technical grade molybdenum trioxide.

(14) Technical grade molybdenum trioxide is used in the manufacture of other molybdenum products, such as ferromolybdenum, or is used as a precursor for the manufacture of pure molybdates from molybdenum, such as ammonium dimolybdate (ADM), ammonium heptamolybdate (AHM) and other molybdates.

(15) Eventually, the liquor (11) obtained from the solid/liquid separation stage (9) might contain molybdenum and rhenium in solution as a consequence of poor control of the process variables, such as pressure and temperature, in which case the liquor rich in copper and impurity (11) is carried to a solvent extraction stage to recover the molybdenum and rhenium. Copper is also recovered from the raffinate from this solvent extraction stage.

(16) As an option, the liquor rich in copper and impurity (11) is treated in consecutive solvent extraction and electrodeposition or cementation stages for obtaining the copper.

(17) Optionally the liquor rich in copper and impurity (11) is recirculated to the pressurized leaching stage (6).

(18) The solid content in the pulp from 50 to 20% in weight (according to the liquid to solid ratio in the range of 1/1 to 4/1, volume/weight), reached in the repulping stage (3) promotes auto-thermal process, which condition can be achieved because of the exothermic nature of the chemical reactions that occur in the system.

(19) The oxidizing atmosphere that is maintained in the leaching stage (6) is achieved due to the presence of an oxygen-bearing gas, as pure oxygen, air enriched with oxygen or air, with oxygen preferably being used.

(20) During the leaching stage (6), the copper compounds and other elements from the MoS.sub.2 concentrate are dissolved to produce the second pulp (7) that contains a mother liquor with copper and other impurities in solution (particularly the sulfuric acid generated in situ by the selective oxidation of the sulfur of the sulfides that said impurities formed in the dirty molybdenite concentrate) and a solid material (that contains the clean molybdenite concentrate) with a low content of copper and other impurities, whose concentrations are within the specifications of a commercial molybdenite concentrate.

(21) The second pulp (7) that results from the leaching stage (6) has a pH between 0 and 2 and a potential for oxidation/reduction between 0.2 and 0.5 volts vs Ag/AgCl electrode.

(22) The leaching process needs the continuous feed of the oxidizing gas (5) for the occurrence of the chemical reactions that allow to transform the copper sulfide compounds and other elements into soluble compounds. The chemical reactions of interest during the leaching stage, which are thermodynamically spontaneous within the indicated temperature range, are the following:
CuFeS.sub.2+H.sub.2SO.sub.4+5/4O.sub.2+½H.sub.2O═CuSO.sub.4+Fe(OH).sub.3+2S°  [1]
CuFeS.sub.2+5/2H.sub.2O+17/4O.sub.2═CuSO.sub.4+2H.sub.2SO.sub.4+Fe(OH).sub.3  [2]
CuS+H.sub.2SO.sub.4+½O.sub.2═CuSO.sub.4+H.sub.2O+S°  [3]
Cu.sub.2S+2H.sub.2SO.sub.4+O.sub.2═2CuSO.sub.4+2H.sub.2O+S°  [4]

(23) In chemical reaction [1], the sulfur (CuFeS.sub.2) is oxidized into elementary sulfur (S°). Chemical reaction [2] indicates that the sulfur (CuFeS.sub.2) is oxidized into sulfate (in the form of copper sulfate and sulfuric acid), reaching its maximum state of oxidation with the consequent oxygen consumption. This latter aspect is important for the economy of the process.

(24) The covellite (CuS) and chalcocite (Cu.sub.2S), found, depending on their source, in variable quantities in the molybdenite concentrates, are oxidized according to chemical reactions [3] and [4].

(25) The above reactions constitute a simplification of the oxidation complex process of the sulfides using pressurized oxygen. In particular, the formation of sulfuric acid in situ from elementary sulfur obtained in said reactions and gaseous oxygen is important, given the spontaneity of the next reaction to the process temperatures during the leaching stage (6) and the percentage of solids in the pulp that promote the formation in situ of sulfuric acid and its exothermic nature:
S°+1.5O.sub.2(g)+H.sub.2O═H.sub.2SO.sub.4

(26) Because of the high temperatures and pressures of the leaching stage (6), the use of a pressure reactor is required, particularly one that has been conditioned for such purpose, this may be one of the autoclave type that withstands high pressures, high temperatures and the acidity of the process. The basis for the operation of the autoclave(s) process of the invention may be in batch or continuous form. The autoclave itself can have different designs, such as horizontal or vertical, however in all these designs, the autoclave can have one or more paddles, with one or more compartments that are separated by baffles, with submerged gas injection or injection on top or both.

(27) The residence time of the pulp inside the reactor must be sufficient for the correct development of the chemical reactions. Good leaching results are found to be obtained for residence times in the range from 15 to 240 minutes.

(28) Regarding the solid/liquid separation stage (9), any separation process can be used to separate the clean molybdenite concentrate (10) from the liquor with the dissolved impurities (11). Commonly used techniques include: filtration, sedimentation, clarification, thickening, centrifugation, dewatering and decantation. The selection of the solid/liquid separation technique is not critical for the success of this invention.

(29) The solid/liquid separation stage (9) is preferably carried out by filtration in a plate or diaphragm filter, with a washing liquid-solid ratio between 0.2 and 1.0 volume/weight.

(30) In the washing stage (12) a washing water to solid product ratio in the range of 0.2 a 1.0 volume/weight is used.

EXAMPLES

Example N° 1: Oxidation Kinetics of Molybdenite Concentrates

(31) In this example, the process of removing copper with respect to molybdenum from molybdenite concentrates is carried out with the following operating conditions: pulp temperature of 160° C., a partial pressure of O.sub.2 of 80 psig (0.6 MPa), a ratio of liquid to solid of the first pulp of 2/1, volume/weight, and an initial acidity of 10 g/l de H.sub.2SO.sub.4.

(32) Tables 1 and 2 show the chemical analysis and mineralogical composition of the six molybdenite concentrates from different sources that were tested.

(33) TABLE-US-00001 TABLE 1 Chemical analysis of the concentrates (% in weight) Element Concentrate % N°1 N°2 N°3 N°4 N°5 N°6 Mo 50.10 49.12 50.12 55.08 47.35 49.11 Cu 3.62 3.93 3.11 0.90 3.62 3.36

(34) TABLE-US-00002 TABLE 2 Mineralogical composition mineral base (% in weight) Concentrate Mioneral N°1 N°2 N°3 N°4 N°5 N°6 Chalcopyrite 8.08 11.27 2.37 2.38 4.71 8.53 Chalcocite 0.08 0.23 0.05 0.06 0.85 0.01 Covellite 1.14 0.18 1.86 0.03 0.79 0.15 Bornite — 0.05 0.05 0.02 0.40 0.41 Enargite — — 0.83 — 1.12 — Gray — 0.13 — — — 0.07 Copper Pyrite 0.18 0.82 2.35 1.80 6.35 2.37 Molybdenite 85.96 82.17 84.09 91.19 78.64 83.65 Gangue 4.54 5.14 8.40 4.53 7.15 4.81 TOTAL, % 100 100 100 100 100 100

(35) Table 3 shows the results obtained for the residence time of the pulp inside the reactor, using the six MoS.sub.2 concentrates.

(36) TABLE-US-00003 TABLE 3 Leaching kinetics with pressurized oxygen. The residual copper is shown in the concentrate (% in weight) the dissolved molybdenum with respect to the initial amount in the concentrate (% in weight). Concentrate N°1 N°2 N°3 N°4 N°5 N°6 Elements Cu Mo Cu Mo Cu Mo Cu Mo Cu Mo Cu Mo Time, min 0 3.75 0.00 3.93 0.00 3.11 0.00 0.90 0.00 3.62 0.00 3.36 0.00 15 0.34 0.00 2.21 0.00 0.36 0.80 0.38 0.02 0.94 0.02 2.72 0.00 30 0.13 0.60 1.64 0.00 0.12 3.53 0.27 0.03 0.67 0.14 2.40 0.00 45 0.11 1.90 1.45 0.00 0.16 4.84 0.16 0.27 0.38 1.30 2.13 0.00 60 0.09 2.60 1.07 0.00 0.07 10.54 0.06 1.16 0.31 1.86 1.84 <0.01

(37) This example leads to the conclusion that good results are obtained for the extraction of copper with a leaching time between 15 and 60 minutes, except for concentrates N° 2 and N° 6. With these last two concentrates, good leaching results were only obtained (a result for Cu of less than 0.5% in weight) either by re-milling or mixing with molybdenite concentrates containing chalcocite and/or covellite in its mineralogy.

Example N° 2: Tests with Concentrate that Only Contains Chalcopyrite (Concentrate N° 6)

(38) In this example, two tests were performed with concentrate N° 6, varying the granulometry of the sample (results given in table 4), varying the temperature (results given in table 5) and varying the oxygen pressure (results given in table 6).

(39) These tests were performed considering, if said variables are not part of the test, an initial acidity of 10 g/l, a pulp temperature of 175° C., an oxygen overpressure of 80 psig (0.6 MPa) and a liquid to solid ratio equal to 2/1, volume/weight.

(40) TABLE-US-00004 TABLE 4 Influence of the decreased particle size on the copper leaching. The residual copper in the concentrate (% in weight) and the dissolved molybdenum are shown with respect to the initial amount in the concentrate (% in weight). Variable Not Milled Milled Elements Time, min Cu Mo Cu Mo 0 3.36 0.00 3.36 0.00 30 1.69 0.05 0.15 19.8

(41) The results in table 4 lead to the conclusion that the increased reaction area obtained by remilling the concentrate allows to achieve the objective of obtaining less than 0.5% in weight of copper in the clean concentrate through the increase of reaction kinetics.

(42) TABLE-US-00005 TABLE 5 Influence of the temperature on the copper leaching. The residual copper in the concentrate (% in weight) and the dissolved molybdenum are shown with respect to the initial amount in the concentrate (% in weight). Variable 160 ° C. 175 ° C. Elements Time, min Cu Mo Cu Mo 0 3.36 0.00 3.36 0.00 30 2.40 0.00 1.69 0.05

(43) The results show a significant increase in reaction kinetics as the process temperature rises, indicating a possible chemical or electrochemical control of the overall reaction.

(44) TABLE-US-00006 TABLE 6 Influence of the oxygen overpressure on the copper leaching. The residual copper in the concentrate (% in weight) and the dissolved copper are shown with respect to the initial amount in the concentrate (%). Variable 80 psig (0.6 MPa) 150 psig (1.0 MPa) Elements Residual Dissolved Residual Dissolved Time, min Cu Cu Cu Cu 0 3.36 0.00 3.36 0.00 30 1.69 50.7 1.27 66.1

(45) The results show an increase in the reaction kinetics increasing the oxygen overpressure.

(46) These examples lead to the conclusion that the decreased of the granulometry and the rise of the pressure and temperature in the system have favorable effects on the reaction rate of the copper leaching.

(47) The process of this invention can be efficiently controlled in an industrial plant through the control of the following variables: temperature of the pulp in the autoclave and oxygen overpressure, basically.

(48) The reaction kinetic of the process that is the subject matter of this invention is fast thus enabling the achievement, in industrial practices, of very high cleaning capacities for the molybdenite concentrate in relation to the useful volume of the autoclave.

(49) The oxidation reactions of sulfides permit the efficient use of the heat from the reaction (exothermic process) to set the process temperature and obtain an auto-thermal operation, on condition that the liquid/solid ratio is set as indicated in the present invention, This is a huge advantage with respect to the cleaning processes for molybdenite concentrates that are known at the present time (for example, leaching with chlorides).