GB2267852A - Improved metals recovery by flotation - Google Patents

Abstract

Froth flotation processes for the beneficiation of platinum, gold and/or silver values from base metal sulfide ores employ an organic solution of diphenyldithiourea as the collector. The use of the organic solutions of diphenyldithiourea provides excellent metallurgical recoveries of platinum, gold and silver values in froth flotation processes conducted over a broad range of pH conditions including acid, neutral and alkaline pH.

Description

IMPROVED METAL RECOVERY BY FLOTATION IMPROVED METAL RECOVERY BY FLOTATION BACRGROUND OF THE INVENTION The present invention relates to froth flotation processes for recovery of platinum, gold and/or silver values from base metal sulfide ores. More particularly, it relates to improved sulfide collectors comprising certain organic solutions of diphenyl dithiourea which exhibit excellent metallurgical performance over a broad range of pH values.

Froth flotation is one of the most-widely used processes for beneficiating ores containing valuable minerals and is described in U.S. Patent No. 4,584,097, hereby incorporated herein by reference.

The success of a sulfide flotation process depends to a great degree on the reagent(s) called collector(s) that impart(s) selective hydrophobicity to the value sulfide mineral that has to be separated from other minerals. Thus, the flotation separation of one mineral species from another depends upon the relative wettability of mineral surfaces by water. Typically, the surface free energy is purportedly lowered by the adsorption of heteropolar collectors. The hydrophobic coating thus provided acts in this explanation as a bridge so that the mineral particles may be attached to an air bubble. The practice of this invention is not, however, limited by this or other theories of flotation.

Xanthates, dithiophosphates, alkyl xanthogen alkyl formates, bis alkyl xanthogen formates, dialkylthiono carbamates, hydrocarboxycarbonyl thionocarbamates, etc.

have been shown to be useful collectors in froth flotation procedures. Most of these known collectors, however, are known to suffer from at least one deficiency which prevents them from being used universally for the recovery of metals from each and every ore requiring refining, such as pH dependency, affinity for some metals versus others etc.

The use of diphenyldithiourea as a collector for the recovery of gold and silver is well known. The collector is known to be capable of forming water-insoluble compounds with metals, however, it suffers from other problems with regard to its use, not the least important of which is that it is a solid.

Being a solid, its use is limited, especially with regard to where in the flotation process that it can be added. Usually, in order to assure complete mixing, the collector is added to the grinding stage of the process.

Addition of the solid collector to the conditioning stage has proven to be less than successful because of its insolubility and a resultant decrease in grade and recovery of values.

When the diphenyldithiourea is utilized as an organic solution, it not only functions to provide increased recoveries and higher grade values but has also been found to be useful for the recovery of metals for which it previously as a dry material, was not effective, i.e., platinum.

Accordingly, it is an object of the present invention to provide an improved sulfide collector and flotation process for the beneficiation of sulfide minerals employing froth flotation methods for the recovery of metals from ore, especially gold, silver and platinum group metals.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a new and improved process for beneficiating an ore containing sulfide minerals with selective rejection of oxides and carbonates, said process comprising: grinding said ore to provide particles of flotation size, slurrying said particles in an aqueous medium, conditioning said slurry with effective amounts of a frothing agent and a metal collector, and frothing the desired sulfide minerals preferentially over gangue minerals by froth flotation procedures; said metal collector comprising an organic solvent solution of diphenyl dithiourea.

In particularly preferred embodiments, a new and improved method for enhancing the recovery of gold, silver and platinum group minerals from an ore containing a variety of sulfide minerals is provided.

The present invention therefore provides a new and improved process for froth flotation of base metal sulfide ores. The diphenyldithiourea organic solution collector and the process of the present invention unexpectedly provide superior metallurgical recovery in froth flotation separations as compared with many conventional sulfide collectors, even at reduced collector dosages, and are effective under conditions of acid, neutral or alkaline pH. In accordance with the present invention, a sulfide ore froth flotation process is provided which provides for superior beneficiation of sulfide mineral values.

Other objects and advantages of the present invention will become apparent from the following detailed description and illustrative working examples.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, sulfide metal and mineral values are recovered by froth flotation methods in the presence of a novel sulfide collector, said collector comprising an organic solution of diphenyldithiourea. The organic liquids used to form the diphenyldithiourea solutions include dimethyl formamide, dimethyl sulfoxide, N-methyl pyrrolidone and the like. The preferred organic liquid is dimethylformamide.

The above-described diphenyldithiourea solutions are employed as sulfide collectors in a new and improved froth flotation process which provides a method for enhanced beneficiation of sulfide mineral values from base metal sulfide ores over a wide range of pH values and more particularly under acidic, neutral, and alkaline conditions.

The new and improved, essentially pH-independent process for the beneficiation of mineral values from base metal sulfide ores comprises, firstly, the step of size-reducing the ore to provide ore particles of flotation size. Generally, and without limitation, suitable particle size will vary from between about 50 mesh to about 800 mesh sizes.

Preferably, the ore will be size-reduced to provide flotation sized particles of between about +65 mesh and about -400 mesh. Especially preferably for use in the present method are base metal sulfide ores which have been size-reduced to provide from about 14% to about 30% by weight of particles of +200 mesh and from about 45% to about 75% by weight of particles of -400 mesh sizes.

Size reduction of the ores may be performed in accordance with any method known to those skilled in this art.

Preadjustment of pH is conveniently performed by addition of the modifier to the grind during the size reduction step.

The pH of the pulp slurry may be pre-adjusted to any desired value by the addition of either acid or base, and typically sulfuric acid or lime are used for this purpose, respectively. Thus, for example, good beneficiation has been obtained in accordance with the process of the present invention at pH values ranging between 3.5 and 11.0, and especially good beneficiation has been observed with pH values within the range of from about 4.0 to about 10.0 pH.

The size-reduced ore, e.g., comprising particles of liberation size, is thereafter slurried in aqueous medium to provide a floatable pulp. The aqueous slurry or pulp of flotation sized ore particles, typically in a flotation apparatus, is adjusted to provide a pulp slurry which contains from about 10 to 60% by weight of pulp solids, preferably 25 to 50% by weight and especially preferably from about 30% to about 40% by weight of pulp solids.

In accordance with a preferred embodiment of the process of the present invention, the flotation of platinum values is performed at a pH of over 7.0 whereas the gold and silver value flotation is performed at a pH of less than or equal to 6.0 and preferably less than 4.0. It has been discovered that in conducting the flotation at this pH, the collectors of the present invention exhibit exceptionally good collector strength, together with excellent collector selectivity, even at reduced collector dosages. It is to be understood however, that gold and silver ofttimes may be recovered at basic pH and platinum may be recovered at acidic pH.

After the pulp slurry has been prepared, the slurry is conditioned by adding effective amounts of a frothing agent and the collector. By "effective amount" is meant any amount of the respective components which provides a desired level of beneficiation of the desired metal values. Generally, about 0.005 to about 0.5 lb.

of active collector per ton of ore is sufficient.

Any known frothing agent may be employed in the process of the present invention. By way of illustration, such frothing agents as straight or branched chain low molecular weight hydrocarbon alcohols, such as C6 to C8 alkanols, 2-ethyl hexanol and 4-methyl-2-pentanol, also known as methyl isobutyl carbinol (MIBC) may be employed, as well as pine oils, cresylic acid, polyglycol or monoethers of polyglycols and alcohol ethoxylates, to name but a few of the frothing agents which may be used as frothing agent(s) herein. Generally, and without limitation, the frothing agent(s) will be added in conventional amounts and amounts of from about 0.01 to about 0.2 pound of frothing agent per ton or ore treated are suitable.

Thereafter, the conditioned slurry, containing an effective amount of frothing agent and an effective amount of collector, is subjected to a frothing step in accordance with conventional froth flotation methods to float the desired sulfide mineral values in the froth concentrate and selectively reject or depress other gangue minerals.

The collectors of the present invention may be added to the flotation cell as well as to the grind.

The collectors of the present invention have been described for use in those applications wherein it is desired to selectively concentrate or collect certain metal value sulfides, mainly those containing platinum, gold and silver group metals from gangue materials, e.g., silicates, carbonates, oxides, etc.

The collectors of the present invention may be used alone, however it is ofttimes preferred to use them in conjunction with such compounds as dithiophosphates, dithiophosphinates, xanthates, mercaptobenzothiazole, and the like, in amounts ranging from about 5-95% to about 95-5%, respectively.

The following examples are set forth for purposes of illustration only and are not to be construed as limiting the instant invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

The dosage of collector is indicated on GPT, grams per ton.

The samples utilized in the following examples may be conditioned by any known procedure. For purposes of exemplification, there are set out below three (3) related procedures which may be followed depending primarily on the pH to be used and the source of the sample to be treated.

PROCEDURE A ALKALINE CIRCUIT PRECIOUS METALS FLOTATION SAMPLE PLATINUM GROUP METALS AND GOLD 1) A 1 kg sample of ore is charged to a laboratory rod mill with 350 ml water and ground to achieve a target size of 66% passing 74 microns.

2) The resultant pulp is transferred to a flotation machine (a Denver D12) and the density is adjusted to 40% solids by mass with water. (500 gram Denver cell used).

3) The flotation machine speed is set at 1000 rpm.

4) Addition of reagents: a) Copper sulphate modifier e.g., (40-60 gpt) 5) The pulp is then conditioned for 7 minutes.

6) Addition of reagents: b) Collector 7) Condition for 5 minutes.

8) Addition of reagents: c) Modifiers 9) Condition for 1 minute.

10) Addition of reagents.

d) Frother (30-50 gpt) 11) Condition for 1 minute.

12) Open the gasflow (air) and set to 6 lpm; allow the froth to stabilize and remove the first flotation concentrate (RC1) for 1 minute. Close the gas valve.

13) Open the gasflow (air) and set to 6 lpm; allow the froth to stabilize froth to stabilize and remove the second flotation concentrate (RC2) for 3 minutes. Close the gas valve.

14) Open the gasflow (air) and set to 6 lpm, allow the froth to stabilize and remove the third flotation concentrate (RC3) for 4 minutes. Close the gas valve.

16) Prepare the fractions (4) for anlaysis by accepted means.

Example 1 Samples are received as mill feeds having a size distribution of about -15mm +0 mm. The samples are subdivided into 1 kg charges and treated as in Procedure A. The reagent collector is a dimethyl formamide solution of diphenyldithiourea (designated LDPDT) and is compared to solid diphenyldithiourea (designated SDPDT) at two (2) different dosages. The results are set forth in Table 1, below.

TABLE I Sample Reagent GPT Recovery (%) Grade (% Conc) real Pt and Au Pt and Au RC1 RC2 RC Total RC1 RC Total A SDPDT* 25 39.0 51.8 54.8 117.9 57.0 B LDPDT* 25 38.9 50.9 53.4 106.8 50.7 C LDPDR1 25 42.3 54.1 56.3 124.3 52.5 D SDPDT* 50 38.0 49.8 52.4 108.6 52.4 E LDPTD* 50 43.3 53.6 56.3 121.7 50.6 F LDPDT1 50 51.6 64.2 66.3 156.8 59.1 * = added to ore grind 1 = added to conditioner The data of Table I demonstrates that the solid diphenyl thiourea, which cannot be added to the conditioning stage as it is insoluble, provides significantly lower grades and recoveries when compared to the organic solution of the diphenyldithiourea which is added directly to the conditioning step. This latter point is equally obviously NOT possible with the solids reagent.This ability to add directly to the process (and not into the grinding stage as is current practice with the solid reagent) enhances significantly the selectivity of the liquid collector producing higher recoveries and grades.

EXAMPLE 2 Procedure A is again followed except that a standard xanthate collector is used alone and in conjunction with a dimethylformamide solution of diphenyldithioure (LDPDT). The results are set forth in Table II, below.

TABLE II Sample Reagent GPT Recovery (%) Grade (% Conc) real Pt and Au Pt and Au RC1 RC2 RC Total RC1 RC Total A Xanthate 130 47.4 56.5 56.9 133.6 56.8 B Xanthate 150 51.5 62.1 62.6 127.3 50.1 C Xanthate & 130 54.6 65.5 68.3 167.2 59.7 LDPDT 10 D Xanthate & 130 53.8 64.6 67.4 149.5 56.1 LDPDT 25 E Xanthate & 130 56.5 67.3 70.3 161.2 55.6 LDPDT 50 F Xanthate & 50 54.7 65.9 68.3 161.1 64.5 LDPDT 25 G Xanthate & 50 51.9 60.8 61.2 116.5 50.0 LDPDT 50 The data of Table II clearly indicate the superior performance of the LDPDT - xanthate combination versus the xanthate alone. Increasing xanthate from 130 to 150 gpt increases recovery at the expense of grade.

Partially replacing the 130 gpt xanthate with 25 gpt LDPDT yields significantly increased recoveries and enhanced grades. An additive amount of LDPDT to the standard 130 gpt xanthate increases the recovery and grade of Platinum + Gold when compared to the higher (150 gpt) addition of xanthate.

Procedure B Acid Circuit Precious Metals Flotation Gold and Siver The major feature of the use of the collector of the present invention in this area is that the solid diphenyl thiourea is not dispersible in these systems as there is no grind stage. Attempts to add the solid to the conditioners results in a white powder floating on the surface with no dispersion.

1) Repulp solids to 50% solid by mass with water.

2) Mechanically stir pulp, measure pH and add acid (preferably sulfuric) to achieve a stable pH 3) Condition the pulp as in 2) for 30 minutes.

4) Transfer the pulp to a flotation machine (a Denver D12) and dilute with water to the flotation density of 33% solid by mass. (500 gram Denver cell used).

5) Set flotation machine speed to 1300 rpm.

6) Add reagents (preferably but not necessarily) in the order given: a) Depressant (40-60 gpt).

b) Collector(s) c) Frother (30-50 gpt).

7) Condition for 1 minute.

8) Add reagent.

d) Modifier Copper Sulfate (40-60 gpt).

9) Condition 0.5 minutes.

10) Open gas (air) flow and set to 8 lpm, allow the froth to stabilize and collect the first flotation concentrate (RC1) for 1 minute.

11) Collect the second flotation concentrate (RC2) for 2 minutes.

12) Collect the third flotation concentrate (RC3) for 7 minutes.

13) Close the gasflow and prepare the fractions (4) for analysis by accepted methods.

EXAMPLE 3 These sample ores are received for testing as damp, preground solids or high density pulps from a gold mining company dam reclamation and processed as in Procedure B. The dimethylformamide solution of diphenyldithiourea is again designated LDPDT.

Comparisons are run with standard, commercially available mercaptobenzothiazole (designated MCBT). The results are set forth in Table III.

TABLE III Sample Reagent GPT Recovery (%) Gold Rec.

real Auras @30% SulPhur RC1 RC2 RC Total A MCBT 30 30.7 45.8 85.6 39.1 B LDPDT & 15/ 41.8 56.8 86.9 49.0 MCBT 15 As can be seen, partial replacement of the benzothiazole by the liquid diphenyldithiourea results in a significant increase in rate of and overall silver and gold recovery.

EXAMPLE 4 Again following the procedure of Example 3, further testing of the feed ores is conducted. In this example, another known standard collector, a mixture of diisobutyl dithiophosphate/sodium mercaptobenzothiazole (50/50), designated DDSM, is compared. The results are set forth in Table IV, below.

TABLE IV Sample Reagent GPT Recovery (%) Series I real Au/Ag RC1 RC2 RC3 A MCBT 50 27.6 42.6 57.1 B LDPDT 50 28.7 47.9 58.1 C LDPDT & 15 38.1 53.8 60.2 MCBT 50 Series II RC1 RC2 RC3 D DDSM 50 35.2 54.5 57.1 43.2 68.4 78.5 E DDSM & 35 35.6 53.1 61.8 70.9 83.8 89.4 LDPDT 15 F DDSM & 15 35.2 52.1 60.8 75.7 83.8 90.7 LDPDT 35 G LDPDT 50 46.8 67.3 74.8 66.7 84.6 89.8 The Series I data demonstrates the significant increase in rate of and overall recovery when LDPDR totally replaces the standard and an even more significant increase when LDPDT is used additive to the standard.

The Series II data demonstrates the effect of LDPDT on the other recognized standard in this area, i.e.

significant increases in recovery are achieved by the partial replacement of DDSM with LDPDR. The effect of total replacement offers both significant rate and overall recovery increases for gold/silver.

PROCEDURE C ALKALINE CIRCUIT PRECIOUS METALS FLOTATION GOLD AND SILVER 1) A 1 kg. sample of ore is charged to a laboratory ball mill with 500 ml water and a quantity of lime (if required) to control the pH and ground to achieve a target size of 60% passing 74 microns.

2) The resultant pulp is transferred to a flotation machine (a Denver D12) and the density adjusted to 40% solids by mass with water. (500 gram Denver cell used).

3) The flotation machine speed is set at 900 rpm.

4) The pulp is then conditioned for 5 minutes.

5) Addition of reagents: a) Collector(s) b) Frother (30-50gpt) 6) Condition for four minutes.

7) Addition of reagents: c) Modifiers - depressant (40-60 gpt) 8) Condition for 0.5 minutes.

9) Addition of reagents: d) Modifiers - Copper Sulfate (40-60 gpt) 10) Condition for 0.5 minutes, increase machine speed to 1100 rpm.

11) Open the gasflow (air) and set to 6 lpm, allow the froth to stabilize and remove the first flotation concentrate (RC1) for 1 minutes. Close the gas valve.

12) Condition for 0.5 minutes.

13) Open the gasflow (air) and set to 6 lpm, allow the froth to stabilize and remove the second flotation concentrate (RC2) for 3 minutes. Close the gas valve.

14) Condition for 0.5 minutes.

15) Open the gasflow (air) and set to 6 lpm, allow the froth to stabilize and remove the third flotation concentrate (RC3) for 6 minutes. Close the gas valve.

16) Prepare the fractions (4) for analysis by accepted means.

EXAMPLE 6 These sample ores are received as mill feeds of size distribution of about -15mm +Omm. The samples (run of mine) are subdivided into 1 kg. charges by accepted means and processed according to Procedure C. The same designations as previously expressed are followed for the reagents tested. The results are set forth in Table V, below.

TABLE V Sample Reagent GPT Recovery (t) real Au and Aq RC1 RC2 RC Total A Xanthate 50 82.7 90.1 91.9 B LDPDT 50 22.9 27.2 28.6 C Xanthate 35 82.9 90.5 92.5 LDPDT 15 D Xanthate 25 82.3 92.2 93.6 LDPDT 25 E Xanthate 15 78.4 84.4 86.1 LDPDT 35 EXAMPLE 6 The procedure of Example 1 is again follows except that the dimethylformamide solvent is replaced by dimethylsulfoxide. Again, excellent results are achieved.

EXAMPLE 7 When the solvent of Example 1 is replaced by N-methypyrrolidone, similar results are achieved.

Claims (8)

WHAT IS CLAIMED IS:

1. In a froth flotation process for beneficiating a sulfide ore containing platinum, gold and/or silver comprising slurrying liberation sized particles of said ore in an aqueous medium, conditioning said slurry with effective amounts of a frothing agent and a collector, respectively, and frothing the desired platinum, gold and/or silver containing sulfide minerals by froth flotation methods, the improvement comprising: employing as the collector, an organic solvent solution of diphenyl dithiourea.

2. A process as recited in Claim 1, wherein said collector is added in an amount of from about 0.005 to about 0.5 lb/ton of ore.

3. A process as recited in Claim 1, wherein said aqueous slurry of liberation-sized ore particles has a pH value of from about 3.5 to about 11.0, inclusive.

4. A process as recited in Claim 1, wherein said solvent is dimethyl formamide.

5. A process as recited in Claim 1, wherein said solvent is N-methylpyrrolidone.

6. A process as recited in Claim 1, wherein said solvent is dimethylsulfoxide.

7. A process as recited in Claim 1, wherein in said collector is used in conjunction with a second collector.

8. A process as recited in Claim 1, wherein in said second collector is a dithiophosphate, a dithiophosphonate, mercaptobenzothiazole, or a xanthate.