DEPRESSION OF COPPER AND IRON SULFIDES IN MOLYBDENITE FLOTATION CIRCUITS

Abstract

A method of depressing copper sulfides and iron sulfides in a molybdenite floatation recovery process uses alkaline or alkaline earth polysulfides at high concentrate pH. The method of enriching molybdenite content from a slurry having molybdenite and at least one of iron sulfides and copper sulfides can include the steps of adding an effective amount of a depressing reagent selected from one or more alkaline poly sulfides, alkaline earth polysulfides, or a mixture thereof, to the slurry, wherein the pH of the slurry is greater than about 8.0; and passing a gas through the slurry to separate material by selective flotation, recovering the molybdonite from a froth.

Claims

1. A method of enriching a concentrate slurry comprising molybdenite and at least one of iron sulfides and copper sulfides, comprising the steps of: a) providing a slurry comprising molybdenite and one or more of copper sulfide and iron sulfide, wherein the pH of the slurry is greater than about 8.0 and less than about 10.5; b) adding an effective amount of a depressing reagent, wherein the depressing reagent is selected from one or more alkaline polysulfides, alkaline earth polysulfides, or a mixture thereof; c) passing a gas through the slurry to separate material; and d) recovering the molybdenite from a froth; wherein the polysulfide is effective at selectively depressing copper sulfide, iron sulfide, or both.

2. The method of claim 1 wherein the pH of the slurry before adding the depressing reagent is at or above pH 8.5 and less than 10.

3. The method of claim 1, wherein the polysulfides comprise calcium polysulfides.

4. The method of claim 3, wherein the calcium polysulfides have an average of between 4 and 4.5 sulfur atoms per molecule.

5. The method of claim 1, wherein the depressing reagent comprises an alkaline polysulfide selected from sodium polysulfide, potassium polysulfide, or a mixture or a combination thereof.

6. The method of claim 5, wherein the alkaline polysulfide has an average of between 2 and 4 sulfur atoms per molecule.

7. The method of claim 1, wherein the depressing reagent is substantially free of thiosulfates.

8. The method of claim 1, wherein the depressing reagent is added at a rate of between 0.003 to 0.0125 Kg of polysulfide(s) per Kg of concentrate (dry basis).

9. The method of claim 3, wherein the calcium polysulfides are added at a rate of about 0.003 to 0.006 Kg per Kg of concentrate (dry basis).

10. The method of claim 1, wherein the depressing reagent is sodium polysulfide and is added at a rate of about 0.005 to 0.008 Kg per Kg of concentrate (dry basis).

11. The method of claim 1, wherein the depressing reagent is potassium polysulfide and is added at a rate of about 0.003 to 0.055 Kg per Kg of concentrate (dry basis).

12. The method of claim 1, wherein the amount of the polysulfides is sufficient to maintain the Slurry Oxidation-Reduction Potential between 450 mV and 480 mV.

13. The method of claim 1, wherein the recovery of molybdenite in the froth is 95 weight % or greater based on molybdenite in the concentrate slurry.

14. The method of claim 1, further comprising the step of manufacturing the polysulfide depressing reagent selected from alkaline earth polysulfides, alkaline polysulfides, or a mixture thereof.

15. A method of enriching a concentrate slurry comprising molybdenite and at least one of iron sulfides and copper sulfides, comprising the steps of: a) providing a slurry comprising molybdenite and one or more of copper sulfide and iron sulfide; b) adding a depressing reagent, wherein the depressing reagent comprises at least 0.003 Kg of alkaline polysulfide(s), alkaline earth polysulfide(s), or a mixture thereof, per Kg of slurry (dry basis), wherein the pH of the resulting slurry is greater than 8 and less than 10.5; c) passing a gas through the slurry to separate material by selective flotation; and d) recovering the molybdenite from a froth; wherein the polysulfide is effective at selectively depressing copper sulfide, iron sulfide, or both.

16. The method of claim 15, wherein the pH of the slurry before adding the depressing reagent is at or above pH 8.0 and is less than 10.0.

17. The method of claim 15, wherein the depressing reagent comprises at least 0.004 Kg of alkaline polysulfides, alkaline earth polysulfides, or a mixture thereof per Kg slurry (dry basis).

18. The method of claim 15, wherein the depressing reagent comprises at least 0.0017 Kg calcium polysulfides per Kg slurry (dry basis).

19. The method of claim 1, wherein the pH of the concentrate slurry is between about 8 and 11, and wherein the oxidation reduction potential of the concentrate slurry is between 430 mV and 480 mV.

20. The method of claim 19, wherein the polysulfides are effective at selectively depressing copper sulfide, iron sulfide, or both, and wherein the pH of the concentrate slurry is between pH 9 and pH 10.

21. The method of claim 1, wherein the pH of the slurry before adding the depressing agent is between pH 9 and pH 10.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 shows results of headspace gas analysis for hydrogen sulfide over liquids containing both inventive and comparative depressing agents versus liquid pH.

DESCRIPTION OF EMBODIMENTS

[0040] These chemicals have been laboratory tested successfully using concentrates from three different Cu/Mo operations in the Southwest U.S. and Mexico. A list of typical test parameters is shown below; [0041] Conditioning Time: 1 to 30 Minutes as necessary [0042] Float time: 12 to 30 minutes as necessary. [0043] Froth removal rate: Slow to moderate for good selectivity. [0044] ORP value in Conditioning and Flotation [0045] CaPS: 430 to 580 mV; at 3.4 to 8 #/T dosage rate [0046] NaPS: 450 to 560 mV; at 9 to 15 #/T dosage rate [0047] KPS: 450 to 560 mV; at 6 to 11 #/T dosage rate
NOTE: #/T=pounds reagent per ton of Cu/Mo concentrate feed, dry basis.

[0048] A typical testing protocol that simulates plant operations was used for the testing with some variations depending on the specific plant location and desired parameter optimization. A typical Mo flotation process which is the basis of the simulated testing has Cu/Mo Concentrate flow passing sequentially through a Thickener (60% Solids) to a stirred Conditioner, where polysulfide and other optional ingredients were added, then to a Rougher (where additional polysulfide might be added), a stirred conditioner, followed by a Cleaner and filtration. An example of the testing protocol is as follows: [0049] a) Cut sample of thickener underflow (60% solids) and adjust to 30% solids after the Conditioner. [0050] b) Transfer sample to a 1.2 L or larger to a Denver (or similar) flotation cell. [0051] c) Add reagent to achieve desired ORP range. Amount added is in pounds per US don (dry weight), where 1 pound per ton is equivalent to 0.0005 Kg polysulfide per Kg concentrate (dry basis). [0052] d) Condition for 1 to 30 min as necessary. [0053] e) Float for 12 to 20 min as necessary with a slow to moderate froth removal rate for good selectivity, where air, nitrogen, or CO2 could be used for flotation. [0054] f) (OPTIONAL STEP) during flotation; Stop flotation floatation, add additional reagent to bring ORP back to desired range. [0055] g) (OPTIONAL STEP) during flotation; Add small amount of frother/collector if necessary.

[0056] ORP, pH and reagent additions were recorded during the testing. The typical temperature and pH ranged for the starting thickener underflow samples were between 60 deg. F (15.6 degrees C.) and 80 deg. F (26.6 degrees C.) and pH of 10.0-11.0. Again, these were conditions tested in the lab, but wide variations in temperature are to be found in the various separation plants and such temperatures will not cause issues.

[0057] Results from three representative tests and one comparative example, which are averages of multiple series of testing at each condition, are tabulated below. This data shows the effectiveness of these polysulfide reagents in the Mo separation process in comparison to the comparative test with the NaHS reagent. In a typical Cu/Mo concentrate, Mo content ranged between 0.8-3.5% with Cu content ranging between 25-35%. The ore bodies tested also range in mineralogy containing primarily Chalcopyrite with smaller amounts of Chalcocite, Covellite and Bornite with Cu/Mo contents of 0.3-0.5% and 0.02-0.04%, respectively.

TABLE-US-00001 De- Conc., Mo Tail pres- Test Wt Cu Fe Mo Rec Mo sant # % % % % % % K CaPS 1 8.8 18.9 17.9 15.9 95.8 0.07 11.3 NaPS 2 11.5 13.1 7.3 36.6 97.0 0.15 8.7 KPS 3 9.4 17.3 18.9 14.9 96.8 0.05 10.6 NaHS Comp. 9.5 16.6 18.6 15.2 97.6 0.04 10.5 4

[0058] In the above data, Conc. Wt % is weight percent floated compared to the feed weight, the Cu %, Fe %, and Mo % are assays of the concentrate. Mo Rec % is the molybdenum recovery in percent, and the Tail Mo % is the tailing (not separated) molybdenum assay. Generally, acceptable tailings content is 0.2% or less, but this is highly dependent on feed (concentrate) molybdenite content as well as other process factors. The final column K is the ratio of Mo concentration removed, as K=[% Mo in concentrate% Mo in tail]/[% Mo in feed% Mo in tail].

[0059] Comp example 4 is a comparative example.

[0060] It is seen that the K value is substantially the same using the polysulfide reagents as with the comparative NaHS reagent. This shows that the polysulfides tested provided recovery comparable to that provided by NaHS, but without the safety and health issues (H2S release, toxic agents, and the like) present when using NaHS. Hydrogen sulfide release is extremely important in the industry, as potentially fatal concentrations can readily accumulate. Greater recovery and K than is seen with NaSH seems possible with calcium polysulfide. Note Test 2 with NaPS was performed on a higher grade feed material than the other tests, so the numbers are somewhat different in comparison.

[0061] Some testing was conducted at higher temperatures using hot dilution water, which showed improved separation and recoveries due to the dispersion effect achieved with the higher temperature. These tests were not deemed relevant as this is not a typical or feasible operation at all plant sites and due to this effect being equivalent for all reagents. The depressing agents and methods of this invention are applicable over the range of temperatures found in the industry.

[0062] Plant Scale testing with CaPS as the depressant, was conducted successfully at a mine site with a copper molybdenum orebody. This testing showed that the polysulfides used in the invention are useful even at a wide range of Mo content of the feed, in this case less than 1% by weight, and at widely varying feed rates. The important operating and metallurgical parameters of the test are shown below: [0063] Operating Parameters [0064] Conditioning time 12 minutes [0065] Flotation Time 29 minutes [0066] Depressant Dosage 7#/T to 30#/T [0067] pH=10 to 12 [0068] ORP Range 430 mV to 470 mV [0069] Flotation Medium Nitrogen [0070] Pulp Density 30% Solids [0071] Metallurgical Information [0072] Feed Content 0.335% Mo [0073] Concentrate 48.0% Mo [0074] Tailing 0.092% Mo [0075] Molybdenum Recovery 74.4%

Tests of Polysulfide H2S Evolution vs. pH

[0076] The H2S evolution due to the decomposition of depressant reagents during storage, handling and application presents the highest associated hazard with regards to health and safety (HSE). Testing of TKI's Alkaline Polysulfide products against the standard (NaHS reagent) was conducted in a simulated flotation process using lab apparatus to determine the amount of H2S evolved at various pH's. The tests were conducted using the following testing protocol; [0077] All tests were ran at ambient temperatures using tap water. Add 500 ml of tap water to 1000 L glass apparatus, check pH and temp, start and maintain stirring throughout test. [0078] Add Ca(OH)2 to raise pH to approximately 10.5 [0079] Add 5 mL of reagent. [0080] Allow to stabilize for 2 min, with cracking of stopper to equilibrate at 1 min. [0081] Check pH, temperature and H2S in VP using analyzer. [0082] Add H2SO4 to decrease pH to 9. [0083] Allow to stabilize for 2 min, with cracking of stopper to equilibrate at 1 min. [0084] Check pH, temperature and H2S in VP using analyzer. [0085] Repeat last three Steps for pH 9, 8 and 7 if applicable.

[0086] Test results are summarized in FIG. 1, which shows the ppm hydrogen sulfide (H2S) evolved versus the pH of the liquid. At pH greater than 10 to 10.5, the samples with calcium polysulfide (CaPS), potassium polysulfide (KPS), and sodium polysulfide (NaPS) showed low (less than 200 ppm) H2S in vapor phase, as did the concentration of H2S in the vapor phase above comparative examples using NaHS. However, when the pH was adjusted to between 9 and 9.5, the hydrogen sulfide in the vapor phase above the NaHS samples spiked to 1500 ppm, while the concentration of H2S in the vapor phase above the samples of CaPS, NaPS, and presumably KPS remained low. Note the H2S in the vapor phase above the polysulfide samples increased to 1500 ppm at pH near 8.2, while this 1500 ppm level was reached by NaHS samples at pH 9.1 to 9.3. The polysulfide products show significantly less H2S evolution than the standard NaHS as pH is reduced. This would translate into a less hazardous environment in applications where the process is run ran at lower pH's (9) utilizing for example CO2 as a flotation medium or modifying agent.

[0087] Values above 1500 ppm are lower limits, as the H2S meter maximum reading was 2000 PPM. The maximum PPM readings for Polysulfides were significantly less than that for NaHS samples, however, based on the time required for the meter to return back to a zero baseline. Therefore, this invention may show significant health and safety benefits even at pH near 8.

[0088] The invention is meant to be illustrated to, but not limited by, the Examples. There were additional tests performed, but the Examples are representative of and consistent with the other tests.