Method for processing mineral material containing acid-consuming carbonate and precious metal in sulfide minerals

Abstract

Processing of mineral material containing precious metal with one or more sulfide minerals and non-sulfide gangue minerals including acid-consuming carbonate may include preparation of a sulfide concentrate by flotation with the flotation or conditioning prior to flotation using a gas comprising carbon dioxide. Flotation may be at an acidic pH without prior decomposition of the acid-consuming carbonate and may be without addition of acid for pH adjustment.

Claims

1. A method for processing mineral material containing precious metal with one or more sulfide minerals and containing non-sulfide gangue minerals comprising acid-consuming carbonate, the method comprising flotation processing, wherein the flotation processing comprises: flotation of the mineral material in aqueous liquid medium at a pH less than pH 7 with flotation gas to prepare a flotation concentrate enriched in sulfide minerals and associated precious metal relative to the mineral material as fed to the flotation and a flotation tail enriched in non-sulfide gangue minerals relative to the mineral material as fed to the flotation; and prior to the flotation, conditioning the mineral material, comprising treating a slurry including the mineral material with a conditioning gas comprising at least 5 volume percent carbon dioxide; and wherein: the mineral material comprises at least 1 weight percent acid-consuming carbonate before and after the conditioning; the conditioning comprises reducing the pH of the slurry from greater than pH 7 to a range of from pH 5 to pH 6.2 due mostly or entirely to carbon dioxide in the conditioning gas; during the conditioning and the flotation no more than 10 percent of acid-consuming carbonate in the mineral material as fed to the conditioning is decomposed; the flotation is conducted at a pH in a range of pH 5 to pH 6.2; and the mineral material comprises at least 1weight percent acid-consuming carbonate when the mineral material is fed to the flotation and the flotation tail and the flotation concentrate together comprise at least 1 weight percent acid-consuming carbonate relative to the combined weight of the flotation tail and the flotation concentrate.

2. A method according to claim 1, wherein the flotation is conducted at a pH in a range of from pH 5 to pH 6.5.

3. A method according to claim 2, wherein the flotation gas comprises at least 5 volume percent carbon dioxide.

4. A method according to claim 3, wherein the flotation gas is selected from the group consisting of a gas composition consisting essentially of carbon dioxide and nitrogen gas, a gas composition consisting essentially of a mixture of carbon dioxide and air and a gas composition consisting essentially of carbon dioxide.

5. A method according to claim 1, wherein the aqueous liquid medium comprises a combined concentration of dissolved calcium and magnesium of at least 500 milligrams per liter; and not more than 10 percent of acid-consuming carbonate in the mineral material as fed to the flotation is decomposed during the flotation.

6. A method according to claim 5, wherein the mineral material comprises at least 3 weight percent acid-consuming carbonate before and after the conditioning and when the mineral material is fed to the flotation, and the flotation tail and the flotation concentrate together comprise at least 3 weight percent acid-consuming carbonate relative to the combined weight of the flotation tail and the flotation concentrate.

7. A method according to claim 5, wherein: the mineral material as fed to the flotation comprises at least 0.2 parts per million by weight of gold and the flotation concentrate is enriched in the gold relative to the mineral material as fed to the flotation; and the flotation is a bulk sulfide flotation.

8. A method according to claim 1, wherein the method is essentially in the absence of pH adjustment through addition of acid during or prior to the flotation.

9. A method according to claim 1, wherein the conditioning gas comprises at least 10 volume percent carbon dioxide.

10. A method according to claim 1, wherein the conditioning gas comprises at least 25 volume percent carbon dioxide.

11. A method according to claim 1, wherein the conditioning gas comprises no more than 5 volume percent oxygen gas.

12. A method according to claim 1, wherein the conditioning gas is selected from the group consisting of a mixture of gas comprising at least 98 volume percent of a combination of carbon dioxide and nitrogen gas, a gas composition consisting essentially of carbon dioxide and nitrogen gas and a gas composition consisting essentially of carbon dioxide.

13. A method according to claim 1, wherein: the mineral material as fed to the flotation comprises at least 0.5 weight percent sulfide sulfur and at least 3.5 weight percent carbonate minerals selected from the group consisting of dolomite, calcite, magnesite and combinations thereof; and the mineral material as fed to the flotation comprises at least 1 weight percent iron-containing sulfide minerals and the flotation concentrate is enriched in the iron-containing sulfide minerals relative to the mineral material as fed to the flotation.

14. A method according to claim 1, wherein the mineral material as fed to the flotation comprises at least 0.5 weight percent sulfide minerals selected from the group consisting of arsenopyrite, arsenian pyrite, arsenian pyrrhotite, arsenian marcasite and combinations thereof and the flotation concentrate is enriched in the sulfide minerals from the group relative to the mineral material as fed to the flotation; and the mineral material as fed to the flotation comprises at least 500 parts per million by weight of arsenic and the flotation concentrate is enriched in the arsenic relative to the mineral material as fed to the flotation.

15. A method according to claim 1, wherein the flotation processing is a first flotation processing, the flotation is a first flotation, the mineral material is first mineral material, the flotation gas is a first flotation gas, the flotation concentrate is a first flotation concentrate and the flotation tail is a first flotation tail, and wherein the method comprises: size separation of a mineral material feed into at least two fractions, a first said fraction having a smaller weight average particle size and a second said fraction having a larger weight average particle size; wherein the mineral material feed comprises precious metal with one or more sulfide minerals and non-sulfide gangue including acid-consuming carbonate in an amount of at least 1 weight percent relative to the weight of the mineral material feed; and wherein each of the first said fraction and the second said fraction includes a portion of the precious metal from the mineral material feed and a portion of the acid-consuming carbonate from the mineral material feed; wherein, the first mineral material includes at least a portion of the first said fraction; second flotation processing a second mineral material including at least a portion of the second said fraction, the second flotation processing comprising second flotation in aqueous liquid medium at a pH less than pH 7 with second flotation gas to prepare a second flotation concentrate enriched in sulfide minerals and associated precious metal relative to the second mineral material as fed to the second flotation and a second flotation tail enriched in non -sulfide gangue minerals relative to the second mineral material as fed to the second flotation.

16. A method according to claim 15, wherein the conditioning is first conditioning and the second flotation processing comprises second conditioning the second mineral material, the second conditioning comprising treating a slurry including the second mineral material with a second conditioning gas comprising at least 5 volume percent carbon dioxide.

17. A method according to claim 15, wherein the second flotation gas comprises at least 5 volume percent carbon dioxide.

18. A method according to claim 15, comprising post-flotation processing of the first flotation concentrate and the second flotation concentrate, comprising oxidative treatment of the first flotation concentrate and the second flotation concentrate to decompose sulfide minerals and expose precious metal.

19. A method according to claim 18, wherein the post-flotation processing comprises: first oxidative treatment of the first flotation concentrate; and second oxidative treatment of the second flotation concentrate separate from the first oxidative treatment.

20. A method according to claim 19, wherein the post-flotation processing is essentially in the absence of filtration of the first flotation concentrate between the first flotation and the first oxidative treatment.

21. A method according to claim 19, wherein the first oxidative treatment comprises contacting the first flotation concentrate with oxygen gas and calcium-containing base material.

22. A method according to claim 19, wherein the second oxidative treatment is alkaline pressure oxidation.

23. A method according to claim 1, comprising the conditioning and wherein: the flotation tail and the flotation concentrate together comprise at least 2 weight percent of acid consuming carbonate relative to the combined weight of the flotation tail and the flotation concentrate.

24. A method according to claim 23, wherein the mineral material comprises at least 2 weight percent acid-consuming carbonate before and after the conditioning and when the mineral material is fed to the flotation.

25. A method according to claim 1, wherein the conditioning gas comprises at least 15 volume percent carbon dioxide and at least 75 volume percent nitrogen gas.

26. A method according to claim 1, wherein the mineral material as fed to the conditioning comprises at least 0.2 parts per million by weight of gold and the flotation concentrate is enriched in gold relative to the mineral material as fed to the conditioning.

27. A method according to claim 26, wherein: the mineral material as fed to the conditioning comprises at least 1000 parts per million by weight arsenic and the flotation concentrate is enriched in arsenic relative to the mineral material as fed to the conditioning; and the mineral material as fed to the conditioning comprises at least 0.5 weight percent sulfide minerals selected from the group consisting of arsenopyrite, arsenian pyrite, arsenian pyrrhotite, arsenian marcasite and combinations thereof and the flotation concentrate is enriched in the sulfide minerals from the group relative to the mineral material as fed to the conditioning.

28. A method according to claim 1, wherein the conditioning gas comprises no more than 1 volume percent oxygen gas.

29. A method according to claim 1, wherein the flotation gas comprises at least 10 volume percent carbon dioxide.

30. A method according to claim 1, wherein the flotation gas consists essentially of a gas mixture of carbon dioxide and air.

31. A method according to claim 1, wherein the conditioning gas is a mixture of gas comprising at least 98 volume percent of a combination of carbon dioxide and nitrogen gas.

32. A method according to claim 1, wherein the flotation gas is a mixture of gas comprising at least 98 volume percent of a combination of carbon dioxide and nitrogen gas.

33. A method according to claim 1, wherein the conditioning gas and the flotation gas each comprises at least 98 volume percent of a combination of carbon dioxide and nitrogen gas.

34. A method according to claim 1, wherein the flotation gas consists essentially of carbon dioxide and nitrogen gas.

35. A method according to claim 1, wherein the conditioning gas consists essentially of carbon dioxide and nitrogen gas.

36. A method according to claim 1, wherein the conditioning gas and the flotation gas each consists essentially of carbon dioxide and nitrogen gas.

37. A method according to claim 1, wherein the conditioning gas consists essentially of carbon dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a generalized process block diagram illustrating some example processing variations including flotation.

(2) FIG. 2 is a generalized process block diagram illustrating some example processing variations including conditioning and flotation.

(3) FIG. 3 is a generalized process block diagram illustrating some example processing variations including staged flotation.

(4) FIG. 4 is a generalized process block diagram illustrating some example processing variations including staged flotation.

(5) FIG. 5 is a generalized process block diagram illustrating some example processing variations including size separation prior to flotation processing.

(6) FIG. 6 is a generalized process block diagram illustrating some example processing variations including size separation prior to flotation processing and post-flotation processing of flotation concentrates.

(7) FIG. 7 is a generalized process block diagram illustrating some example processing variations including post-flotation processing including combined oxidative treatment of flotation concentrates.

(8) FIG. 8 is a generalized process block diagram illustrating some example processing variations including post-flotation processing including combined oxidative treatment of flotation concentrates.

(9) FIG. 9 is a generalized process block diagram illustrating some example processing variations including post-flotation processing including separate oxidative treatment of flotation concentrates.

(10) FIG. 10 is a generalized process block diagram illustrating some example processing variations including post-flotation processing including separate oxidative treatment of flotation concentrates.

(11) FIG. 11 shows plots of relative concentration as a percentage of initial concentration of calcium in solution in test slurries as a function of time for different ore samples during conditioning.

(12) FIG. 12 shows plots of relative concentration as a percentage of initial concentration of magnesium in solution in test slurries as a function of time for different ore samples during conditioning.

(13) FIG. 13 shows plots of relative concentration as a percentage of initial concentration of dissolved iron in solution in test slurries as a function of time for different ore samples during conditioning.

(14) FIG. 14 shows plots of relative concentration as a percentage of initial concentration of sulfur in solution in solution in test slurries as a function of time for different ore samples during conditioning.

DETAILED DESCRIPTION

(15) FIG. 1 shows an illustration of an embodiment for flotation processing 100. As shown in FIG. 1, flotation processing 100 includes subjecting a mineral material 102 to flotation 104 using a flotation gas 110 to prepare a flotation concentrate 106 and a flotation tail 108. The flotation gas 110 may be or include carbon dioxide.

(16) FIG. 2 shows a variation on the embodiment for flotation processing 100 shown in FIG. 1. As shown in FIG. 2, the flotation processing 100 includes the flotation 104 as described with FIG. 1. In the variation of FIG. 2, the mineral material 102 is subjected to conditioning 120 prior to the flotation 104. In the conditioning 120, the mineral material 102 is treated with a conditioning gas 122. One or both of the flotation gas 110 and the conditioning gas 122 is or includes carbon dioxide.

(17) FIGS. 3 and 4 show some examples of variations on the flotation 104 of FIGS. 1 and 2 including multiple flotation stages. As shown in FIG. 103, the flotation 104 may include a rougher flotation 130 stage, cleaner flotation 132 stage and scavenger flotation 134 stage. The mineral material 102 is first subjected to the rougher flotation 130 to prepare a rougher flotation concentrate 136 and a rougher flotation tail 138. The rougher flotation concentrate 136 is subjected to the cleaner flotation 132 to prepare the flotation concentrate 106 and a cleaner flotation tail 140. The rougher flotation tail 138 is subjected to the scavenger flotation 134 to prepare a scavenger flotation concentrate 142 and the flotation tail 108. The cleaner flotation tail 140 and the scavenger flotation concentrate 142 are recycled for processing through the rougher flotation 130 with the mineral material 102. A flotation gas 110a, 110b, 110c is used in each of the rougher flotation 130, cleaner flotation 132 and scavenger flotation 134. The flotation gases 110a, b, c may be the same or may be different compositions, and one or more of the flotation gases 110a, 110b, 110c may be or include carbon dioxide.

(18) FIG. 4 shows a variation for the flotation 104 including a rougher flotation 130 stage, cleaner flotation 132 stage and scavenger flotation 134 stage similar to FIG. 3, except with slightly different processing flow among the flotation stages. As shown in FIG. 4, the scavenger flotation concentrate 142 is subjected to the cleaner flotation 132 together with the rougher flotation concentrate 136, rather than being recycled to the rougher flotation 130 as shown in FIG. 3.

(19) Reference is now made to FIG. 5 to illustrate an example embodiment including size separation of a mineral material feed and separate flotation processing of different separated size fractions of mineral material. As shown in FIG. 5, a first mineral material 102a is subjected to first flotation processing 100a and a second mineral material 102b is subjected to second flotation processing 100b. Either one or both of the first flotation processing 100a and the second flotation processing 100b may for example be according to or including features of the flotation processing 100 as shown and described in relation to any of and FIGS. 1-4. The first mineral material 102a includes a first fraction from size separation 152 of a mineral material feed 150. The second mineral material 102b includes a second fraction from the size separation 152 of the mineral material feed 150. The mineral material feed 150 may be the result of prior comminution operations. The first fraction included in the mineral material 102a has a smaller weight average particle size than the second fraction included in the second mineral material 102b. The processing as shown in FIG. 5 provides significant flexibility to beneficially process the different size fractions for more optimal flotation processing of each fraction. Such processing also permits significant flexibility for post-flotation processing with oxidative treatment to prepare flotation concentrate for precious metal leaching.

(20) FIG. 6 shows the same processing as shown in FIG. 5 including the size separation 152, first flotation processing 100a and second flotation processing 100b. However, in the processing of FIG. 6, a first flotation concentrate 106a from the first flotation processing 100a and a second flotation concentrate 106b from the second flotation processing 100b are subjected to post-flotation processing 160. During the post-flotation processing 160, at least a portion of the first flotation concentrate 106a and the second flotation concentrate 106b may be subjected to oxidative treatment to decompose sulfide minerals and expose precious metal to permit enhanced leach recovery of precious metal.

(21) FIGS. 7 and 8 show some example embodiments for the post-flotation processing 160 of FIG. 6 in which material from the first flotation concentrate 106a and the second flotation concentrate 106b may be processed together for oxidative treatment. As shown in FIG. 7, the post-flotation processing 160 may include filtration 170a of the first flotation concentrate 106a and separate filtration 170b of the second flotation concentrate 106b. Separate filtration of the concentrates permits more optimized filtration techniques to be used for the different particle sizes of the different concentrates. As a processing alternative to that shown in FIG. 7, the first flotation concentrate 106a and the second flotation concentrate 106b could be combined and subjected as a combined feed to a single filtration step. As shown in FIG. 7, the filtered first flotation concentrate 106a from the retentate of the filtration 170a is combined with the filtered second flotation concentrate 106b from retentate of the filtration 170b to form a combined concentrate 172. The combined concentrate 172 is subjected to oxidative treatment 174 to decompose sulfide minerals and expose precious metal to make the precious metal more amenable to recovery by leaching. Residual solids 176 from the oxidative treatment 174 may be further processed for gold recover, such as by leaching precious metal from residual solids 176 resulting from the oxidative treatment 174.

(22) In the alternative processing embodiment shown in FIG. 8, the post-flotation processing 160 may include subjecting the second flotation concentrate 106b to filtration 170 and may include no filtration of the first flotation concentrate 106a before combining the first flotation concentrate 106a with the second flotation concentrate 106b to prepare the combined concentrate 172. The first flotation concentrate 106a, comprised of smaller-size particles than the second flotation concentrate 106b, is more difficult to filter without complications, although the combined concentrate 172 may have greater acidification requirements to an extent the oxidative treatment 174 involves acidic processing (e.g., acidic pressure oxidation, biooxidation).

(23) The post-flotation processing 160 shown in FIG. 6 may also involve separate oxidative treatment of the first flotation concentrate 106a and the second flotation concentrate 106b. FIGS. 9 and 10 show some example embodiments for the post-flotation processing 160 that may include separate oxidative treatments. As shown in FIG. 9, the post-flotation processing 160 includes subjecting the first flotation concentrate 106a to filtration 170a and the second flotation concentrate 106b to the filtration 170b. After the filtration 170a, the first flotation concentrate 106a is subjected to first oxidative treatment 174a to decompose sulfide minerals and prepare a first solid residue 176a that is more amenable to recovery of precious metal, such as by leaching. After the filtration 170b, the second flotation concentrate 106b is subjected to second oxidative treatment 174b to decompose sulfide minerals and prepare second residual solid residue 176b that is more amenable to precious metal recovery, such as by leaching. FIG. 10 shows the same processing as shown in FIG. 9 except that the second flotation concentrate 106b is subjected to filtration 170 and the first flotation concentrate 106a is not subjected to filtration. The first oxidative treatment 174a and the second oxidative treatment 174b may be the same or different oxidative techniques. For example, the first oxidative treatment 174a may be an atmospheric oxidation process due to the small particle size of the first flotation concentrate 106a, whereas the second oxidative treatment 174b may be a pressure oxidation process due to the larger particle size of the second flotation concentrate 106b.

(24) Unless otherwise expressly stated percentages and concentrations are on a weight basis, except that gas composition percentages and concentrations are on a volume basis unless otherwise expressly stated.

(25) The following examples further illustrate and describe various aspects, embodiments and features regarding the invention.

EXAMPLE 1

(26) Three different samples of gold-bearing sulfide ore materials from the Carlin region of Nevada, USA having various carbonate contents are tested. Table 1 summarizes chemical analysis information for the samples. Table 2 provides a summary of mineralogical composition information on the ore samples estimated based on semi-quantitative x-ray diffraction (XRD) analysis. Table 3 summarizes mineralogical composition information on the ore samples estimated based on modal mineralogy analysis.

(27) TABLE-US-00001 TABLE 1 Ore Sample Chemical Analysis Ore Sample #1 Ore Sample #2 Ore Sample #3 As ppm 1132 1080 2411 Sb ppm 57 41 82 Se ppm <1 <1 <1 Au ppm 2.07 2.55 2.85 C Total % 0.07 0.96 1.15 S Total % 1.59 1.88 2.37 CO.sub.3 % 0.25 4.7 5.5 Sulfide S % 1.08 1.28 1.72 Ag ppm <2 <2 <2 Al ppm 24081 33811 31215 Be ppm <2 <2 <2 Ca ppm 1404 21485 28531 Cd ppm 9 4 5 Co ppm 10 9 7 Cr ppm 51 60 39 Cu ppm 85 74 104 Fe ppm 21662 25115 25354 K ppm 13659 15064 14663 Mg ppm 1889 10470 12390 Mn ppm 61 519 526 Mo ppm 26 17 31 Na ppm 229 194 111 Ni ppm 81 96 118 Pb ppm 17 51 21 Sb ppm 78 65 96 Se ppm <10 <10 <10 Sr ppm 167 72 43 Ti ppm 1472 1553 1332 Tl ppm <20 <20 <20 V ppm 776 374 705 Zn ppm 564 1074 1233

(28) TABLE-US-00002 TABLE 2 Semi-quantitative XRD Ore Sample #1 Ore Sample #2 Ore Sample #3 Barite % 0.6 0.8 0.4 Calcite % 0.9 Dolomite % 8.4 8.7 Jarosite % 0.4 Gypsum % 0.8 1.5 Illite % 12.4 10.5 Kaolinite % 2.0 1.6 0.6 Marcasite % 0.9 0.9 1.8 Muscovite % 14.7 Microcline % 2.2 1.4 Pyrite % 1.8 2.3 2.0 Quartz % 79.2 72.4 70.5

(29) TABLE-US-00003 TABLE 3 Modal Mineralogy Ore Sample #1 Ore Sample #2 Ore Sample #3 Alunite % 0.77 0.19 0.06 Anhydrite % 0.0001 0.003 0.01 Apatite % 0.05 0.20 0.22 Arsenopyrite % 0.07 0.15 0.38 Barite % 0.83 0.71 1.06 Bismuthinite % 0.002 0.002 0.02 Calcite % 0.03 0.24 0.45 Chalcopyrite % 0.01 0.002 0.01 Chlorite % 0.01 0.10 0.05 Crandallite % 0.40 0.13 0.06 Dolomite % 0.10 5.07 5.95 FeOx % 0.49 0.18 0.11 Illite % 3.60 7.62 5.18 Ilmenite % 0.002 0.004 0.0005 Iron % 0.13 0.06 0.23 Jarosite % 0.05 0.04 0.03 Kaolinite % 0.41 0.40 0.49 Monazite % 0.0001 0.001 0.001 Plagioclase % 0.43 0.77 0.54 Phlogopite % 0.001 0.12 0.09 Pyrite % 2.23 3.27 4.01 Pyrite_As % 0.36 0.39 1.02 Quartz % 88.14 78.78 78.98 Rutile % 0.25 0.25 0.22 Scorodite % 0.002 0.001 0.07 Siderite % 1.52 1.19 0.53 Sphalerite % 0.08 0.08 0.15 Sphene % 0.00002 0.02 0.02 Tennantite % 0.01 0.01 0.02

(30) Ore samples #2 and #3 contain significant acid-consuming carbonate content in the form of dolomite or dolomite and calcite, whereas ore sample #1 does not contain a significant amount of carbonate minerals. The ore samples are subjected to laboratory flotation testing under various flotation conditions, with and without prior conditioning with a conditioning gas containing carbon dioxide. Different gas compositions used in flotation and/or conditioning in these and other tests in other examples provided below are summarized in Table 4.

(31) TABLE-US-00004 TABLE 4 Test Gas Composition CO.sub.2 % Air % N.sub.2 % G1 100 G2 100 G3 17 83 G4 23 77 G5 17 83 G6 100 G7 44 56 G8 29 71

(32) Each of ore samples #1 to #3 is comminuted to a targeted P.sub.80 size of 105 microns (80 weight percent of particles smaller than 105 microns). Prior to the flotation, but after any conditioning with a conditioning gas, potassium amyl xanthate equivalent to 100 grams per tonne of ore sample is added as a collector and AERO MX6205 (Cytec) equivalent to 50 grams per tonne of ore sample is added as a promoter. Flotation on each ore sample is conducted at an acidic pH. For tests in which 100 percent air is used as the flotation gas (gas composition G1), the slurry is acidified prior to flotation with the addition of sulfuric acid to try to attain a target pH of 5.5 and additional sulfuric acid is added as needed during flotation to try to maintain slurry pH around the target pH. For tests in which the flotation gas contains carbon dioxide, no acid is added to the slurry prior to or during flotation. Flotation is conducted in a laboratory flotation cell for about 16 minutes at a slurry density of about 25 percent solids. Some tests include conditioning with carbon dioxide gas (G6) prior to flotation. A summary of some tests and test results are presented in Tables 5, 6 and 7 for ore samples #1, #2 and #3, respectively.

(33) TABLE-US-00005 TABLE 5 Ore Sample #1 Recovery In Flotation Test Conditions Concentrate Acid Sulfide pH Weight Au Sulfur Test Flotation Conditioning Adjust Other Recovery % Recovery % Recovery % 1-1 G1 none yes 12.47 51.3 86.8 1-5 G1 none yes tap 11.64 47.1 83.3 water 1-3 G3 none no 13.06 54.0 81.4 1-2 G3 G6 no 12.30 53.6 89.4 10 minutes 1-7 G3 none no N.sub.2 in 10.35 55.3 94.5 grind 1-6 G5 none no 12.99 56.5 79.4 1-4 G5 G7 no N.sub.2 in 13.80 62.1 87.7 10 minutes grind

(34) TABLE-US-00006 TABLE 6 Ore Sample #2 Recovery In Flotation Test Conditions Concentrate Acid Sulfide pH Weight Au Sulfur Test Flotation Conditioning Adjust Other Recovery % Recovery % Recovery % 2-1 G1 none yes 14.01 39.0 82.7 2-5 G1 none yes tap 11.64 38.6 83.5 water 2-9 G1 none no natural 12.95 35.5 74.9 pH 2-14 G2 none yes N.sub.2 in 12.63 46.0 83.8 grind 2-13 G2 G6 no 15.25 44.1 84.7 10 minutes 2-12 G1 G6 no 12.40 40.7 82.0 10 minutes 2-3 G3 none no 13.46 37.8 82.5 2-8 G3 none no N.sub.2 in 12.60 44.0 95.1 grind 2-10 G3 G6 no 11.20 36.1 76.3 2 minutes 2-11 G3 G6 no 13.87 42.8 81.8 5 minutes 2-2 G3 G6 no 14.58 44.9 88.4 10 minutes 2-6 G3 G6 no 13.90 44.8 93.3 10 minutes 2-15 G3 G6 no 13.73 46.8 85.8 20 minutes 2-7 G5 none no 13.50 42.9 89.5 2-4 G5 G7 no N.sub.2 in 13.65 51.7 90.5 10 minutes grind

(35) TABLE-US-00007 TABLE 7 Ore Sample #3 Recovery In Flotation Test Conditions Concentrate Acid Sulfide pH Weight Au Sulfur Test Flotation Conditioning Adjust Other Recovery % Recovery % Recovery % 3-1 G1 none yes 12.50 34.7 85.1 3-5 G1 none yes tap 12.58 36.7 85.3 water 3-3 G3 none no 13.83 36.7 84.0 3-7 G3 none no N.sub.2 in 13.58 41.7 86.3 grind 3-2 G3 G6 no 14.12 40.6 83.2 10 minutes 3-6 G5 none no 13.90 40.0 87.9 3-4 G5 G7 no N.sub.2 in 16.46 53.3 90.0 10 minutes grind

(36) Referring to Table 5 summarizing tests for ore sample #1, Tests 1-1 and 1-5 represent baseline air flotation tests with addition of sulfuric acid for pH control, with test 1-5 using tap water instead of process water that is used in other tests. In tests 1-3 and 1-2 somewhat higher gold recoveries in the concentrate result from using CO.sub.2 in the flotation gas with or without prior conditioning with CO.sub.2 gas. This modest recovery improvement is achieved without eliminating oxygen from the flotation gas. In test 1-7, the ore sample is comminuted in a nitrogen gas environment to help prevent oxidation of newly-exposed sulfide mineral grains. Relative to test 1-3, test 1-7 shows only a small improvement in gold recovery in the concentrate. A further small improvement in gold recovery in the concentrate is seen for test 1-6 when the flotation gas is a mixture of only carbon dioxide and nitrogen gas. A significantly higher gold recovery, however, is exhibited by test 1-4 in which the ore sample is comminuted in a nitrogen gas environment and the slurry is conditioned with a mixture of carbon dioxide and nitrogen gas prior to flotation with a mixture of carbon dioxide and nitrogen gas.

(37) Ore samples #2 and #3 are much more difficult ores to process by flotation than ore sample #1. Not only do they contain significant concentrations of acid-consuming carbonate that impedes pH control in a desired acidic pH range by acid addition, but they also contain higher concentrations of arsenian iron sulfides that are difficult to float. Nitrogen gas flotation with pH control by addition of sulfuric acid has been a state-of-the-art technique for enhanced flotation of such ores.

(38) Referring to results summarized in Table 6 for ore sample #2, tests 2-1 and 2-5 represent baseline tests using air flotation and test 2-14 represents a comparison with state -of-the-art nitrogen gas flotation, all of which include the conventional practice of adding sulfuric acid to attempt to achieve a desired acidic slurry pH of 5.5, which is significantly complicated by reaction of acid with of carbonate minerals. As seen in Table 6, nitrogen gas flotation (test 2-14) achieves a significantly higher recovery of gold in the concentrate than baseline air flotation (tests 2-1 and 2-5). For comparison purposes, test 2-9 floats the ore sample with air at a natural pH, with no pH control. As expected, gold recovery is higher with nitrogen gas flotation than with baseline air flotation tests, and air flotation without addition of sulfuric acid is lower than baseline air flotation with addition of sulfuric acid to attain an acidic pH for flotation.

(39) Test 2-13 tests performance using nitrogen gas flotation but without addition of sulfuric acid to decompose acid-consuming carbonates to attain an acidic pH for flotation, but instead subjecting the slurry to conditioning with CO.sub.2 gas prior to flotation. Surprisingly, gold recovery is almost as high as with the state-of-the-art nitrogen gas flotation test with sulfuric acid addition, but without the cost or complexity of high acid additions to decompose acid-consuming carbonates to achieve a desired acidic pH. Test 2-12 uses air flotation without sulfuric acid addition, but with prior CO.sub.2 gas conditioning. Although gold recovery for test 2-12 is not as high as for test 2-13 using nitrogen gas for flotation, gold recovery is slightly higher than gold recovery in baseline air flotation tests with addition of sulfuric acid. This is surprising, since gold recovery is maintained without the expense and complication of large sulfuric acid additions to decompose carbonates to try to control slurry pH at a desired acidic pH level during flotation.

(40) A number of tests are run on different processing combinations without sulfuric acid addition and using flotation gas made up of a mixture of carbon dioxide and air (17:83). In test 2-3, the flotation is performed without prior CO.sub.2 gas conditioning and pH control during flotation is provided only by the CO.sub.2 in the flotation gas. Notably, gold recovery in the concentrate is only slightly lower than for the baseline air flotation tests, but without the expense or complication of large sulfuric acid additions. Test 2-8 uses the same conditions as test 2-3, except that the ore is communicated in a nitrogen gas environment to reduce potential for newly -exposed sulfide mineral grain surfaces to oxidize before flotation. This resulted in a gold recovery almost as high as the baseline nitrogen gas flotation of test 2-14. Surprisingly, this is achieved without requiring large additions of sulfuric acid and without eliminating oxygen from the flotation gas, as the flotation gas in test 2-8 includes 83% air, equating to about 17% oxygen gas in the flotation gas mixture.

(41) Tests 2-10, 2-11, 2-2, 2-6 and 2-15 all include CO.sub.2 gas conditioning for different lengths of time prior to flotation with the mixture of CO.sub.2 and air for the flotation gas. Significant enhancement in gold recovery in the concentrate is observed relative to baseline air flotation tests for 5, 10 and 20 minutes of conditioning, with gold recoveries generally comparable with the baseline nitrogen gas flotation of test 2-14. This is surprising given that test 2-15 does not include the expense or complication of large sulfuric acid additions or elimination of oxygen gas from the flotation gas.

(42) Tests 2-7 and 2-4 use a mixture of carbon dioxide and nitrogen gas (17:83) as a flotation gas, with and without prior conditioning with CO.sub.2 gas, and without sulfuric acid addition. Control of pH is provided only by carbon dioxide in the conditioning and/or flotation gas. As seen in a comparison of test 2-7 with test 2-3, use of this flotation gas mixture has a positive effect on gold recovery relative to use of a mixture of CO.sub.2 and air. Particularly surprising are the results for test 2-4 including conditioning with a mixture of CO.sub.2 and nitrogen gas prior to flotation with a mixture of CO.sub.2 and nitrogen gas, which show significantly higher gold recovery in the concentrate than with the state-of-the-art nitrogen gas flotation conditions of test 2-14.

(43) Referring to results summarized in Table 7 for ore sample #3, flotation with a mixture of CO.sub.2 and air (17:83) without prior conditioning (test 3-3) resulted in comparable or slightly better gold recovery than baseline air flotation conditions with sulfuric acid addition to decompose acid-consuming carbonates and adjust pH (tests 3-1 and 3-5). Combining use of the mixture of CO.sub.2 and air for the flotation gas with either prior comminution in nitrogen gas (test 3-7), prior CO.sub.2 gas conditioning (test 3-2) or use of a mixture of CO.sub.2 and N.sub.2 (17:83) as the flotation gas without prior conditioning (test 3-6) results in significant improvement in gold recovery in the concentrate relative to baseline air flotation tests, and without the cost or complexity of large additions of sulfuric acid. Particularly surprising is the very high level of gold recovery in the concentrate achieved using a mixture of CO.sub.2 and N.sub.2 for the flotation gas with prior conditioning with a mixture of CO.sub.2 and nitrogen gas conditioning (test 3-4), again without the cost or complexity of large additions of sulfuric acid required to decompose acid-consuming carbonates for flotation at a desired acidic pH.

EXAMPLE 2

(44) Samples are of gold-bearing sulfide ore materials obtained from slurry samples taken from a conventional air flotation operation in Nevada, USA. Tables 8-10 summarize chemical analysis information for the ore samples, designated herein as ore samples #4, #5 and #6. Tables 8-10 also show particle size distribution information and chemical analysis information for different particle size ranges. Table 11 summarizes mineralogical composition information for the ore samples estimated by model mineralogy analysis. Ore sample #4 is a higher -quality ore sample having negligible carbonate content that is relatively amenable to processing by conventional air flotation to prepare a sulfide concentrate enriched in gold. Ore samples #5 and #6 are more difficult ores that each contains significant acid-consuming carbonate, mostly present in the form of dolomite, and contain more arsenian iron sulfide content than sample #4.

(45) TABLE-US-00008 TABLE 8 Ore Sample #4 Component Weight Content By Particle Size Distribution By Particle (ppm or %) Size (%) Particle Size Mesh 200+ 200 325 325 500 -500 Total 200+ 200 325 325 500 -500 Weight % 35.8 16.1 10.0 38.1 100.0 Distribution As ppm 727 843 1009 1755 1166 22.3 11.7 8.6 57.4 Sb ppm 32 42 51 96 60 19.1 11.3 8.5 61.1 Se ppm <1 <1 <1 <1 <1 Au ppm 1.60 1.71 1.79 3.73 2.45 23.4 11.3 7.3 58.0 C Total % 0.06 0.1 0.09 0.11 0.09 24.3 18.2 10.1 47.4 S Total % 1.04 1.91 2.43 2.09 1.72 21.7 17.9 14.1 46.3 CO.sub.3 % 0.00 0.2 0.20 0.00 0.1 0.0 61.8 38.2 0.0 Sulfide S % 0.73 1.39 1.73 1.16 1.10 23.8 20.4 15.7 40.2 Ag ppm 2.4 2.4 2.5 3.5 2.8 Al ppm 23024 20943 19002 37641 27859 29.6 12.1 6.8 51.5 Be ppm <2 <2 <2 <2 <2 Ca ppm 968 1110 1221 1690 1291 26.8 13.9 9.4 49.9 Cd ppm 5 6 8 13 9 21.0 11.4 9.4 58.2 Co ppm 5 7 8 12 8 21.6 13.6 9.6 55.2 Cr ppm 15 23 22 42 27 19.7 13.6 8.0 58.7 Cu ppm 50 65 84 119 82 21.8 12.8 10.2 55.2 Fe ppm 14551 25514 29234 33782 25111 20.7 16.4 11.6 51.3 K ppm 10439 8919 7841 20687 13841 27.0 10.4 5.6 57.0 Mg ppm 1424 1260 1202 2181 1664 30.6 12.2 7.2 50.0 Mn ppm 32 64 68 46 46 24.9 22.4 14.7 38.0 Mo ppm 22 23 23 39 29 27.4 12.9 8.0 51.7 Na ppm 200 217 248 1600 741 9.7 4.7 3.3 82.3 Ni ppm 58 76 86 91 76 27.2 16.1 11.2 45.5 Pb ppm 13 18 23 117 54 8.5 5.3 4.2 81.9 Sb ppm 43 55 64 100 69 22.4 12.9 9.3 55.4 Se ppm <10 <10 <10 <10 <10 Sr ppm 108 117 115 268 171 22.6 11.0 6.7 59.7 Ti ppm 1258 1302 1320 1559 1386 32.5 15.1 9.5 42.9 Tl ppm <20 <20 <20 <20 <20 V ppm 692 635 610 1081 823 30.1 12.4 7.4 50.1 Zn ppm 457 483 563 849 621 26.3 12.5 9.0 52.1

(46) TABLE-US-00009 TABLE 9 Ore Sample #5 Component Weight Content By Particle Size Distribution By Particle (ppm or %) Size (%) Particle Size Mesh 200+ 200 325 325 500 -500 Total 200+ 200 325 325 500 -500 Weight % 31.1 27.1 20.4 21.4 100.0 Distribution As ppm 1531 2007 2899 2618 2172 21.9 25.1 27.2 25.8 Sb ppm 25 34 42 55 37 20.8 24.7 23.0 31.5 Se ppm <1 <1 <1 <1 Au ppm 1.82 2.19 2.48 4.10 2.54 22.2 23.4 19.9 34.5 C Total % 0.7 0.8 0.89 0.96 0.82 26.5 26.4 22.1 25.0 S Total % 1.32 2.45 3.03 2.06 2.13 19.2 31.1 29.0 20.7 CO.sub.3 % 0.00 3.9 4.25 4.40 2.9 0.0 36.6 30.4 33.0 Sulfide S % 0.94 1.76 2.34 1.23 1.51 19.4 31.6 31.6 17.4 Ag ppm <2 <2 <2 2.1 Al ppm 22314 21182 21662 44846 26695 26.0 21.5 16.6 35.9 Be ppm <2 <2 <2 <2 Ca ppm 17196 20238 22135 21639 19979 26.8 27.5 22.6 23.2 Cd ppm 5 5 5 9 6 26.6 23.2 17.4 32.9 Co ppm 5 8 11 11 8 18.7 26.1 27.0 28.3 Cr ppm 26 29 28 46 32 25.7 25.0 18.1 31.2 Cu ppm 53 95 110 127 92 17.9 28.0 24.4 29.6 Fe ppm 18158 27328 33577 32435 26844 21.0 27.6 25.5 25.9 K ppm 10432 9844 10133 21570 12594 25.8 21.2 16.4 36.6 Mg ppm 7096 7848 8803 11322 8552 25.8 24.9 21.0 28.3 Mn ppm 282 352 414 507 376 23.3 25.4 22.5 28.8 Mo ppm 35 32 30 39 34 32.0 25.5 18.0 24.5 Na ppm 266 353 393 368 337 24.5 28.4 23.8 23.3 Ni ppm 99 111 129 162 122 25.3 24.7 21.6 28.4 Pb ppm 15 19 25 64 29 16.3 18.0 17.8 47.9 Sb ppm 32 42 52 63 45 21.9 25.1 23.4 29.7 Se ppm <10 <10 <10 <10 Sr ppm 41 46 50 94 56 23.0 22.5 18.4 36.2 Ti ppm 1069 1227 1404 1784 1333 24.9 25.0 21.5 28.6 Tl ppm <20 <20 <20 <20 V ppm 1006 856 761 1227 963 32.5 24.1 16.1 27.3 Zn ppm 853 875 942 1418 998 26.6 23.8 19.3 30.4

(47) TABLE-US-00010 TABLE 10 Ore Sample #6 Component Weight Content By Particle Size Distribution By Particle (ppm or %) Size (%) Particle Size Mesh 200+ 200 325 325 500 -500 Total 200+ 200 325 325 500 -500 Weight % 41.3 10.8 7.6 40.3 100.0 Distribution As ppm 1317 1741 2455 2404 1887 28.8 10.0 9.9 51.3 Sb ppm 34 50 57 80 56 24.8 9.7 7.8 57.7 Se ppm <1 <1 <1 <1 <1 Au ppm 1.81 2.06 2.20 4.11 2.79 26.7 8.0 6.0 59.3 C Total % 0.88 0.97 1.1 1.22 1.04 34.8 10.1 8.0 47.1 S Total % 1.31 2.41 2.94 2.11 1.88 28.8 13.9 11.9 45.3 CO.sub.3 % 0.0 3.9 5.1 5.65 3.1 0.0 13.7 12.5 73.8 Sulfide S % 0.98 1.71 2.17 1.28 1.27 31.8 14.6 13.0 40.6 Ag ppm <2 <2 <2 <2 <2 Al ppm 22777 20659 19309 48122 32499 28.9 6.9 4.5 59.7 Be ppm <2 0 0 <2 <2 Ca ppm 20236 22199 24861 25903 23083 36.2 10.4 8.2 45.2 Cd ppm 4 5 6 9 6 28.7 8.4 6.6 56.3 Co ppm 5 7 10 10 7 26.0 10.5 9.7 53.8 Cr ppm 20 19 20 38 27 30.1 7.6 5.7 56.6 Cu ppm 45 51 59 106 71 26.2 7.8 6.2 59.8 Fe ppm 18110 29116 34154 30540 25529 29.3 12.3 10.2 48.2 K ppm 10318 9183 8364 21004 14353 29.7 6.9 4.4 59.0 Mg ppm 9146 10215 10994 13636 11212 33.7 9.9 7.4 49.0 Mn ppm 381 463 513 625 498 31.6 10.1 7.8 50.6 Mo ppm 26 24 22 33 28 37.6 9.3 6.0 47.0 Na ppm 145 277 136 245 199 30.1 15.1 5.2 49.7 Ni ppm 91 111 125 151 120 31.2 10.0 7.9 50.8 Pb ppm 13 14 18 32 21 25.2 7.2 6.3 61.3 Sb ppm 50 65 70 90 69 29.8 10.2 7.7 52.3 Se ppm <10 <10 <10 <10 <10 Sr ppm 36 42 44 110 67 22.0 6.8 5.0 66.2 Ti ppm 1110 1193 1284 1557 1312 34.9 9.8 7.4 47.8 Tl ppm <20 <20 <20 <20 <20 V ppm 717 620 550 936 782 37.8 8.6 5.3 48.2 Zn ppm 872 1018 1144 1821 1291 27.9 8.5 6.7 56.9

(48) TABLE-US-00011 TABLE 11 Modal Mineralogy Ore Sample #4 Ore Sample #5 Ore Sample #6 Alunite % 0.76 0.08 0.14 Anhydrite % 0.003 0.003 0.001 Apatite % 0.13 0.19 0.17 Arsenopyrite % 0.04 0.34 0.25 Barite % 0.80 0.97 1.42 Bismuthinite % 0.002 0.01 0.001 Calcite % 0.08 0.30 0.05 Chalcopyrite % 0.01 0.01 0.01 Chlorite % 0.11 0.10 0.02 Crandallite % 0.56 0.14 0.09 Dolomite % 0.01 3.63 5.85 FeOx % 0.62 0.10 0.22 Illite % 3.22 5.31 6.67 Ilmenite % 0.01 0.001 0.001 Iron % 0.03 0.01 0.03 Jarosite % 0.05 0.02 0.01 Kaolinite % 0.48 0.42 0.27 Monazite % 0.001 0.003 Plagioclase % 0.82 0.84 0.69 Phlogopite % 0.05 0.11 0.04 Pyrite % 2.32 2.87 2.98 Pyrite_As % 0.29 0.70 0.62 Quartz % 87.90 82.54 79.13 Rutile % 0.24 0.20 0.29 Scorodite % 0.01 0.005 0.0001 Siderite % 1.35 0.95 0.82 Sphalerite % 0.09 0.09 0.19 Sphene % 0.00004 0.03 0.004 Tennantite % 0.003 0.01 0.01 Zircon % 0.01 0.02 0.03

(49) Each ore sample is subjected to cyclone separation to separate the ore sample into a smaller particle-size fraction (cyclone overflow) and a larger particle-size fraction (cyclone underflow) for separate flotation testing on the different fractions. Flotation tests are also run on the whole ore samples for comparison. Tables 12-14 summarize particle size information for the whole ore sample and the separated overflow and underflow fractions from the cyclone separation. Flotation tests are performed in a laboratory flotation cell in a slurry with a solids density generally of about 30-35 weight percent solids for the underflow flotation tests and about 15-20 weight percent solids for the overflow flotation tests, with some tests including prior conditioning by sparging the slurry with a conditioning gas containing carbon dioxide. Flotation is conducted for about 16 minutes. Test results are summarized in Tables 15-20. In Tables 15-20 cyclone underflow fractions are designated U/F and cyclone overflow fractions are designated 0/F. Testing also includes cyanide leaching of gold from flotation tails to evaluate the total amount of gold that is recoverable either in the flotation concentrate or through cyanide leaching of the flotation tails.

(50) TABLE-US-00012 TABLE 12 Ore Sample #4 Cyclone Size Separation Ore Sample Feed Underflow Overflow Weight Distribution % 100.0 62.8 37.2 P.sub.80 Size microns 180 216 21 (calculated) Gold Distribution % 100.0 49.5 50.5

(51) TABLE-US-00013 TABLE 13 Ore Sample #5 Cyclone Size Separation Ore Sample Feed Underflow Overflow Weight Distribution % 100.0 67.9 32.1 P.sub.80 Size microns 119 135 10 (calculated) Gold Distribution % 100.0 54.0 46.0

(52) TABLE-US-00014 TABLE 14 Ore Sample #6 Cyclone Size Separation Ore Sample Feed Underflow Overflow Weight Distribution % 100.0 72.4 27.6 P.sub.80 Size microns 155 187 21 (calculated) Gold Distribution % 100.0 58.2 41.8

(53) TABLE-US-00015 TABLE 15 Ore Sample #4 Recovery From Test Feed Total Au Recovered Flotation Test Conditions Into Concentrate From Test Feed Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 4-13 U/F G1 none yes 11.08 43.1 87.6 21.3 15.0 36.3 pH 5.7 4-6 U/F G1 none yes 11.67 47.3 89.0 23.4 13.8 37.3 pH 5.7 4-7 U/F G3 none no 10.96 45.6 88.3 22.6 14.1 36.7 pH 5.5-6.0 4-8 U/F G4 none no 12.05 48.4 90.5 24.0 13.5 37.5 pH 5.5-6.0 4-14 U/F G3 G8 no 12.01 46.9 90.0 23.2 13.4 36.7 pH 5.7-6.0 10 minutes 4-15 U/F G5 G5 no 11.59 46.2 89.9 22.9 13.4 36.3 pH 5.7-6.0 10 minutes 4-16 O/F G1 none yes 21.18 44.6 73.0 22.5 17.6 40.1 pH 5.7 4-9 O/F G1 none yes 17.37 43.2 68.7 21.8 19.3 41.1 pH 5.7 4-10 O/F G3 none no 17.69 44.1 68.0 22.3 19.1 41.4 pH 5.5-6.0 4-72-2 O/F G3 G6 no 27.3 61.6 87.9 31.1 12.4 43.5 pH 5.7-6.0 20 minutes 4-72-1 O/F G5 G8 no 21.75 57.3 89.3 28.9 14.0 43.0 20 minutes

(54) TABLE-US-00016 TABLE 16 Ore Sample #4 Recovery From Ore Sample Into Total Au Recovered Flotation Test Conditions Concentrate From Ore Sample Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 4-11 Whole G1 none yes 17.69 47.6 83.9 47.6 31.0 78.6 Ore pH 5.5 4-12 Whole G3 G6 no 12.13 48.2 85.5 48.2 29.6 77.8 Ore pH 5.7-6.0 10 minutes 4-13 + Combined G1 none yes 43.8 32.6 76.4 4-16 U/F + O/F 4-6 + Combined G1 none yes 45.2 33.1 78.3 4-9 U/F + O/F 4-7 + Combined G3 none no 44.9 33.2 78.1 4-10 U/F + O/F 4-14 + Combined G3 G6 no 54.3 25.8 80.1 4-72-2 U/F + O/F 4-15 + Combined G5 G8 no 51.8 27.4 79.2 4-72-1 U/F + O/F

(55) TABLE-US-00017 TABLE 17 Ore Sample #5 Recovery From Test Feed Into Total Au Recovered From Flotation Test Conditions Concentrate Test Feed Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 5-13 U/F G1 none yes 11.28 49.2 89.9 26.6 6.5 33.0 pH 5.7 5-6 U/F G1 none yes 10.70 46.8 91.2 25.3 6.8 32.1 pH 5.7 5-7 U/F G3 none no 12.52 53.7 95.7 29.0 6.4 35.4 pH 5.5-6.0 5-8 U/F G4 none no 12.83 52.1 96.3 28.2 6.6 34.8 pH 5.5-6.0 5-14 U/F G3 G6 no 16.14 59.9 94.5 32.4 5.7 38.1 pH 5.7-6.0 10 minutes 5-15 U/F G5 G8 no 13.95 55.8 92.7 30.2 6.3 36.4 pH 5.7-6.0 10 minutes 5-16 O/F G1 none yes 13.41 26.5 31.2 12.2 13.0 25.1 pH 5.7 5-9 O/F G1 none yes 14.51 28.8 43.5 13.2 11.2 24.4 pH 5.7 5-10 O/F G3 none no 15.41 27.2 44.1 12.7 12.2 24.9 pH 5.5-6.0 5-74-1 O/F G3 G6 no 14.69 30.3 43.4 13.9 12.3 26.3 pH 5.7-6.0 20 minutes 5-74-2 O/F G5 G8 no 19.05 40.9 63.7 18.8 11.2 30.0 20 minutes

(56) TABLE-US-00018 TABLE 18 Ore Sample #5 Recovery From Ore Sample Into Total Au Recovered From Flotation Test Conditions Concentrate Ore Sample Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 5-11 Whole G1 none yes 10.09 35.2 70.0 35.2 17.8 53.0 Ore pH 5.5 5-12 Whole G3 G6 no 10.10 35.3 75.4 35.3 19.1 54.4 Ore pH 5.7-6.0 10 minutes 5-13 + Combined G1 none yes 38.8 19.4 58.2 5-16 U/F + O/F 5-6 + Combined G1 none yes 38.5 18.0 56.5 5-9 U/F + O/F 5-7 + Combined G3 none no 41.7 18.6 60.3 5-10 U/F + O/F 5-14 + Combined G3 G6 no 46.3 18.0 64.3 5-74-1 U/F + O/F 4-15 + Combined G5 G8 no 49.0 17.4 66.4 5-74-2 U/F + O/F

(57) TABLE-US-00019 TABLE 19 Ore Sample #6 Recovery From Test Feed Into Total Au Recovered From Flotation Test Conditions Concentrate Test Feed Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 6-10 U/F G1 none yes 17.18 59.8 92.5 34.8 5.9 40.6 pH 5.7 6-3 U/F G1 none yes 19.93 59.9 90.2 34.8 5.5 40.4 pH 5.7 6-4 U/F G3 none no 19.86 61.1 89.6 35.5 5.6 41.1 pH 5.5-6.0 6-5 U/F G4 none no 20.75 63.9 90.3 37.2 5.3 42.5 pH 5.5-6.0 6-11 U/F G3 G6 no 18.81 61.9 92.7 36.0 6.2 42.2 pH 5.7-6.0 10 minutes 6-12 U/F G5 G8 no 17.70 60.1 91.3 34.9 5.9 40.8 pH 5.7-6.0 10 minutes 6-13 O/F G1 none yes 15.03 45.0 61.3 18.8 9.3 28.1 pH 5.7 6-6 O/F G1 none yes 15.68 40.5 53.8 16.9 9.0 26.0 pH 5.7 6-7 O/F G3 none no 17.90 43.1 60.6 18.0 8.7 26.7 pH 5.5-6.0 6-14 O/F G3 G6 no 18.06 51.9 79.7 21.7 8.8 30.5 20 minutes 6-15 O/F G5 G8 no 18.36 53.3 80.9 22.3 8.4 30.7 pH 5.7-6.0 20 minutes

(58) TABLE-US-00020 TABLE 20 Ore Sample #6 Recovery From Ore Sample Into Total Au Recovered From Flotation Test Conditions Concentrate Ore Sample Acid Sulfide Tail Test pH Weight Au Sulfur Concentrate Leach Total Test Feed Flotation Conditioning Adjust Recovery % Recovery % Recovery % Au % Au % Au % 6-8 Whole G1 none yes 12.35 47.9 83.3 47.9 16.1 64.0 Ore pH 5.5 6-9 Whole G3 G6 no 12.82 47.8 85.7 47.8 17.2 65.0 Ore 6-10 + Combined G1 none yes 53.6 15.1 68.7 6-13 U/F + O/F 6-3 + Combined G1 none yes 51.7 14.5 66.3 6-6 U/F + O/F 6-4 + Combined G3 none no 53.5 14.3 67.8 6-7 U/F + O/F 6-11 + Combined G3 G6 no 57.7 14.9 72.7 6-14 U/F + O/F 6-12 + Combined G5 G8 no 57.2 14.3 71.6 6-15 U/F + O/F

(59) Tables 15 and 16 summarize test results for ore sample #4. Table 15 shows results for the separate testing performed on underflow and overflow fractions, designated as U/F and O/F in the tables. Table 16 shows combined results for corresponding overflow and underflow test pairs compared with flotation tests performed on a whole ore sample. As shown in Table 15, for the underflow fractions of ore sample #4, both gold recovery in the concentrate and total gold recovery including tails leaching do not vary greatly between the different test conditions. For overflow fractions, gold recovery in the concentrate is higher in tests using carbon dioxide in the flotation gas preceded by conditioning with a gas containing carbon dioxide (tests 4-72-2 and 4-72-1), however total gold recovery from overflow samples including tails leaching is affected by a much smaller amount. As shown in Table 16, separate flotation of overflow and underflow fractions showed only a small increase in total gold recovery for the best performing tests relative to flotation of whole ore samples (tests 4-11 and 4-12), and whole ore processing with carbon dioxide (test 4-12) shows no total gold recovery increase over conventional air flotation (test 4-11). Again, ore sample #4 is a higher-quality ore that is generally amenable to conventional air flotation and that does not contain significant qualities of acid-consuming carbonate.

(60) Referring to Table 17 in relation to sample #5, total gold recovery is significantly higher for both overflow and underflow fractions using carbon dioxide gas, with best gold recoveries corresponding with tests including both conditioning and flotation with gas compositions including carbon dioxide. Particularly noteworthy is the information summarized in Table 18. For whole ore sample tests (5-11 and 5-12) total gold recovery is improved by only a small amount using carbon dioxide gas (from 53.0% to 54.4%). However, combined gold recoveries from separate flotation of underflow and overflow fractions using gas containing carbon dioxide during flotation and with prior conditioning with a gas containing carbon dioxide resulted in much higher gold recoveries (more than 11 percentage points), with the combined testing using a mixture of CO.sub.2 and N.sub.2 (17:83) providing the largest increase (more than 13 percentage points).

(61) Results for tests on ore sample #6 summarized in Table 19 show improvements in total gold recovery for some underflow tests and some overflow tests relative to baseline air flotation, although not to as great an extent as experienced for ore sample #5. As shown in Table 20, conditioning and flotation using carbon dioxide increased total gold recovery only by a small amount on whole ore sample tests (from 64.0% to 65.0%). However, total gold recoveries for ore sample #6 increase significantly for combined results of separate flotation on overflow and underflow fractions. As with the results for ore sample #5, these improved gold recoveries are obtained without the large sulfuric acid additions and pH control issues resulting from the presence of significant amounts of acid-consuming carbonates.

EXAMPLE 3

(62) Ore sample #2 in an aqueous slurry at about 25 weight % solids density is conditioned for 20 minutes with conditioning gas of composition G6 (100% CO.sub.2) by sparging the conditioning gas into the slurry contained in a laboratory flotation cell. Samples of the slurry are taken at various times and slurry liquid is analyzed for concentrations of various dissolved components. Table 21 summarizes results of the solution analysis over time for a number of components. Calcium concentration increases moderately over time, which may be due at least in part to cleaning calcium-containing surface species from sulfide mineral grains. Particularly noticeable is the large increase over time of dissolved iron, which increased by a factor of about 5, which may be due at least in part to dissolution of iron-containing species, such as iron hydroxides, from sulfide mineral grains. Such cleaning of sulfide mineral grains may be particularly beneficial for effective flotation of sulfide minerals.

(63) TABLE-US-00021 TABLE 21 Ore Sample #2 Concentration in Solution at Different CO.sub.2 Conditioning Times 0 minute 1 minute 2 minutes 3 minutes 5 minutes 10 minutes 20 minutes Ag mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 0.8 Al mg/l 6.0 8.2 15.3 11.7 12.6 12.5 11.8 As mg/l 0.6 0.7 0.9 1.0 0.6 0.9 0.6 Ba mg/l 0.6 0.8 1.8 1.5 1.7 1.6 1.9 Be mg/l <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Ca mg/l 497 531 516 550 558 568 587 Cd mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Co mg/l 0.4 0.6 0.5 0.6 0.6 0.6 0.7 Cr mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Cu mg/l 0.7 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Fe mg/l 9.2 21.4 34.3 35.2 39.5 40.8 49.1 K mg/l 342.1 359.9 326.7 346.9 351.6 354.8 354.4 Mg mg/l 168.5 177.7 168.3 177.4 179.1 181.0 183.7 Mn mg/l 7.4 12.7 10.2 13.7 14.0 13.4 14.2 Mo mg/l 0.7 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Na mg/l 1145 1191 1052 1155 1162 1169 1167 Ni mg/l 1.8 2.2 2.0 2.2 2.3 2.2 2.2 Pb mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 S mg/l 1392 1466 1302 1388 1404 1411 1415 Sb mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Se mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Si mg/l 20.5 28.0 48.6 36.8 42.9 41.7 39.0 Sn mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Sr mg/l 1.0 1.1 1.0 1.0 1.0 1.0 1.1 Ti mg/l <0.25 <0.25 0.3 0.3 0.3 0.3 0.3 Tl mg/l <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 V mg/l <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Zn mg/l <0.25 5.7 6.1 9.3 9.7 8.8 9.6

EXAMPLE 4

(64) One kilogram samples of gold-bearing sulfide ore materials (ore samples #7, #8, #9 and #10) are each comminuted to a P.sub.80 size of approximately 140 microns and wet rotary split into quarter splits that are used as feed for four different conditioning tests. Mineralogical composition information on the sample estimated from XRD analysis is summarized in Table 22. For testing, the sample spits are slurried with either process water or tap water. Analyses on two different process waters and tap water used in tests are shown in Table 23. Conditioning tests use gas compositions G1, G2, G5 and G6 as conditioning gases. Gas sparging rates during conditioning tests with the various gases are summarized in Table 24. For tests using 100% nitrogen gas (G2), prior to gas sparging sulfuric acid is added to decompose carbonates and attempt to achieve a reduction in the slurry pH to a target pH of 5.5, and additional sulfuric acid is added periodically to attempt to maintain approximately that target pH. Following conditioning with the conditioning gas, each ore sample is subjected to flotation using the same gas composition for the flotation gas as was used for the conditioning gas, except that tests using G6 as a conditioning gas are followed by flotation with a flotation gas of composition G3. Slurry samples are taken periodically during conditioning and slurry liquid is analyzed for concentration of selected dissolved components. Following flotation, flotation concentrates are analyzed by XRD for the purpose of estimating mineralogical composition information for the concentrates. After conditioning and prior to flotation, potassium amyl xanthate collector is added to the slurry equivalent to about 100 grams per tonne of ore and AERO MX6205 promoter is added to the slurry equivalent to about 50 grams per tonne of ore. Tests on ore Sample #8 are performed using process water and also using tap water.

(65) TABLE-US-00022 TABLE 22 Ore Ore Ore Ore Component Sample #7 Sample #8 Sample #9 Sample #10 Barite - % 3 4 11.2 Calcite - % 14 22.2 Dolomite - % 16 31 10 10.4 Gypsum - % 3.7 Kaolinite - % 7 Illite - % 17 14 11.1 Marcasite - % 2 3 Muscovite - % 24.3 Pyrite - % 3 3 1.2 2.7 Quartz - % 61 35 43 48.4

(66) TABLE-US-00023 TABLE 23 Process Water #1 Process Water #2 Tap Water (mg/L) (mg/L) (mg/L) Ag <0.050 <0.050 <0.050 Ad 0.13 0.34 <0.050 As 0.68 2.3 <0.050 Ba <0.020 <0.020 <0.020 Be <0.020 <0.020 <0.020 Ca 662 584 21 Cd <0.050 <0.050 <0.050 Co 0.95 0.43 <0.050 Cr <0.050 <0.050 <0.050 Cu <0.050 0.20 <0.050 Fe 0.27 0.29 <0.050 K 435 253 <0.050 Mg 83 42 5.4 Mn 0.09 0.026 <0.010 Mo 2.5 1.8 <0.050 Na <0.050 <0.050 11.2 Ni 0.69 1.4 <0.050 Pb <0.050 <0.050 <0.050 S 1604 1233 12.9 Sb 0.097 0.212 <0.050 Se <0.050 <0.050 <0.050 Si 2.4 1.1 <0.100 Sn <0.050 0.15 Sr 1.8 1.2 0.12 Ti <0.050 <0.050 <0.050 Tl 0.28 0.37 <0.100 V <0.050 <0.050 <0.050 Zn <0.050 <0.050 <0.050

(67) TABLE-US-00024 TABLE 24 Conditioning Gas Conditioning Gas Sparge Rate Composition (L/min) G1 <0.002 (slight aeration) G2 ~1.0 G6 ~0.8 G5 ~1.8 (~0.8 CO.sub.2 + ~1.0 N.sub.2)

(68) Tables 25-29 summarize pH results as a function of time for tests on the different ore samples. FIGS. 11-14 graphically summarize changes in concentrations of calcium, magnesium, iron and sulfur in the slurry liquid as a function of time as a percentage relative to the initial concentration at the beginning of the test. Tests using sulfuric acid and nitrogen gas uniformly show larger increases in concentrations of dissolved calcium and magnesium, which may reflect in part the decomposition of carbonates with addition of sulfuric acid. Dissolved iron concentrations tend to increase significantly for tests using nitrogen, carbon dioxide or a mixture of carbon dioxide and nitrogen, which may indicate that conditions in all those tests may be conducive to removing oxidized iron species, such as iron hydroxides, from sulfide mineral grain surfaces. The air tests uniformly show a reduction over time of dissolved iron concentrations, indicating iron may be precipitating, which is generally a detrimental condition for effective sulfide mineral flotation. With respect to sulfur in solution, only the tests using sulfuric acid and nitrogen gas show significant increases in concentration over time.

(69) TABLE-US-00025 TABLE 25 Ore Sample #7/Process Water pH Conditioning G1 G2* G5 G6 0 min 6.50 4.79 6.58 6.60 2 min 6.32 5.63 5.36 5.04 5 min 6.25 5.45 5.41 5.11 10 min 6.14 5.62 5.46 5.17 20 min 6.14 4.91 5.50 5.23 30 min 6.20 5.20 5.54 5.25 Flotation G1 G2 G5 G3 0 min 6.37 5.14 5.57 5.29 After Collector 6.40 5.21 5.51 5.22 Addition 6 min 6.69 5.78 5.87 5.54 *H.sub.2SO.sub.4 addition equal to 2.120 kg per tonne of ore

(70) TABLE-US-00026 TABLE 26 Ore Sample #8/Process Water pH Conditioning G1 G2* G5 G6 0 min 6.82 5.85 6.86 6.85 2 min 6.73 4.13 5.95 5.62 5 min 6.83 5.54 5.96 5.68 10 min 7.07 5.44 6.00 5.70 20 min 7.39 5.48 6.02 5.72 30 min 7.51 5.42 6.05 5.76 Flotation G1 G2 G5 G3 0 min 7.60 5.10 6.03 5.73 After Collector 7.62 6.00 5.70 Addition 6 min 7.72 5.89 6.29 6.40 *H.sub.2SO.sub.4 addition equal to 21.032 kg per tonne of ore

(71) TABLE-US-00027 TABLE 27 Ore Sample #8/Tap Water pH Conditioning G1 G2* G5 G6 0 min 6.79 6.70 6.67 6.65 2 min 6.63 5.45 5.78 5.53 5 min 6.71 5.53 5.84 5.60 10 min 6.93 5.53 5.90 5.64 20 min 7.27 5.59 5.93 5.67 30 min 7.42 5.38 5.95 5.70 Flotation G1 G2 G5 G3 0 min 7.47 5.20 5.97 5.68 After Collector 7.50 5.10 5.91 5.64 Addition 6 min 7.73 5.02 6.22 5.84 *H.sub.2SO.sub.4 addition equal to 16.516 kg per tonne of ore

(72) TABLE-US-00028 TABLE 28 Ore Sample #9/Process Water pH Conditioning G1 G2* G5 G6 0 min 7.80 5.29 7.66 7.73 2 min 7.82 5.85 6.08 5.80 5 min 7.84 5.57 6.15 5.84 10 min 7.84 5.11 6.19 5.86 20 min 7.84 5.40 6.19 5.88 30 min 7.86 5.08 6.21 5.90 Flotation G1 G2 G5 G3 0 min 7.97 5.11 6.15 5.90 After Collector 7.97 5.50 6.15 5.84 Addition 6 min 8.01 5.49 6.41 6.47 *H.sub.2SO.sub.4 addition equal to 32.168 kg per tonne of ore

(73) TABLE-US-00029 TABLE 29 Ore Sample #10/Process Water pH Conditioning G1 G2* G5 G6 0 min 7.64 4.68 7.48 7.58 2 min 7.68 5.36 5.52 5.23 5 min 7.72 5.18 5.56 5.25 10 min 7.75 5.51 5.62 5.26 20 min 7.75 5.12 5.66 5.32 30 min 7.77 4.57 5.68 5.34 Flotation G1 G2 G5 G3 0 min 7.87 4.39 5.65 5.32 After Collector 7.87 5.21 5.65 5.28 Addition 6 min 8.02 6.07 6.00 *H.sub.2SO.sub.4 addition equal to 8.220 kg per tonne of ore

(74) Table 30 summarizes mineralogical composition information on flotation concentrates estimated from XRD analysis for process water tests. Notably, for tests using sulfuric acid and nitrogen gas on ore samples that contain high concentrations of calcite (ore samples #8 and #9), significant gypsum is identified in the concentrates, which may indicate precipitation of calcium sulfate during testing as a consequence of sulfuric acid addition and corresponding decomposition of a portion of the calcite. Also, Tables 25-29 provide the quantities of sulfuric acid added during the nitrogen gas tests, expressed on a basis of kilograms of sulfuric acid requirement per tonne of ore. As seen in Tables 25-29, ore samples #8 and #9 that contain significant calcite concentrations have much higher sulfuric acid requirements than ore samples #7 and #10 that contain lower levels of carbonate minerals and only in the form of dolomite. The high sulfuric acid requirements for ore samples #8 and #9 together with significant levels of gypsum in the resulting concentrates may indicate that the calcite in those samples is very reactive in consuming sulfuric acid relative to the dolomite content of ore samples #7 and #10. Gypsum precipitation may present a significant processing problem in that the presence of very fine particles of gypsum precipitate may significantly complicate filtration of concentrate in preparation for further processing.

(75) TABLE-US-00030 TABLE 30 Process Water Tests - Concentrate XRD Ore Gangue-silicate Sulfide Carbonate Sulfate Sample Gas quartz % illite % kaolinite % pyrite % marcasite % dolomite % calcite % jarosite % gypsum % barite % #7 G1 30.05 25.7 15.5 10.7 12.4 5.2 G2 39.2 20.7 13.6 10.0 12.1 4.5 G5 35.4 22.6 14.6 11.0 11.7 4.7 G6 38.0 19.5 14.7 11.1 12.3 4.4 #8 G1 23.3 20.7 14.7 14.1 18.7 8.4 G2 28.0 19.2 11.5 12.1 18.7 3.3 7.0 G5 27.9 20.9 12.6 12.1 19.7 6.8 G6 29.5 17.8 13.3 12.8 20.3 6.4 #9 G1 24.9 29.3 5.9 9.5 9.0 8.6 12.8 G2 26.0 20.9 5.1 12.2 12.9 5.4 4.9 13.1 G5 26.6 20.5 4.8 14.8 15.2 8.3 9.7 G6 28.5 19.5 4.4 13.5 14.8 9.1 10.2 #10 G1 27.4 19.1 17.8 20.5 9.4 2.4 3.1 G2 36.0 22.2 10.7 18.8 8.8 2.0 1.4 G5 34.8 17.5 13.1 21.8 9.1 2.2 1.5 G6 36.9 18.4 11.6 19.6 9.7 1.8 1.9

(76) The foregoing discussion of the invention and different aspects thereof has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to only the form or forms specifically disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art. Although the description of the invention has included description of one or more possible embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter. Furthermore, any feature described or claimed with respect to any disclosed variation may be combined in any combination with one or more of any other features of any other variation or variations, to the extent that the features are not necessarily technically compatible, and all such combinations are within the scope of the present invention. The description of a feature or features in a particular combination do not exclude the inclusion of an additional feature or features. Processing steps and sequencing are for illustration only, and such illustrations do not exclude inclusion of other steps or other sequencing of steps. Additional steps may be included between illustrated processing steps or before or after any illustrated processing step.

(77) The terms comprising, containing, including and having, and grammatical variations of those terms, are intended to be inclusive and nonlimiting in that the use of such terms indicates the presence of some condition or feature, but not to the exclusion of the presence also of any other condition or feature. The use of the terms comprising, containing, including and having, and grammatical variations of those terms in referring to the presence of one or more components, subcomponents or materials, also include and is intended to disclose the more specific embodiments in which the term comprising, containing, including or having (or the variation of such term) as the case may be, is replaced by any of the narrower terms consisting essentially of or consisting of or consisting of only (or the appropriate grammatical variation of such narrower terms). For example, the a statement that some thing comprises a stated element or elements is also intended to include and disclose the more specific narrower embodiments of the thing consisting essentially of the stated element or elements, and the thing consisting of the stated element or elements. Examples of various features have been provided for purposes of illustration, and the terms example, for example and the like indicate illustrative examples that are not limiting and are not to be construed or interpreted as limiting a feature or features to any particular example. The term at least followed by a number (e.g., at least one) means that number or more than that number. The term at at least a portion means all or a portion that is less than all. The term at least a part means all or a part that is less than all.