AU569769B2 - Recovery of metal values from mineral ores as seeded hydrocarbon oil aggregates - Google Patents

Description

HYDROCARBON OIL AGGLOMERATES . ..

This invention relates to a method of separating minerals from solid mixtures (e.g. mined ore) particularly where the mineral is present in low concentration. Proposals have been made to separate minerals by utilizing the lyophilic properties of certain minerals. U.S. patent 3,268,071 uses a liquid suspendant to separate two materials one of which is lyophilic to said liquid and the other being lyophobic. This technique, however, is difficult to initiate where the mineral which is sought to be recovered is present in low concentrations.

Australian Patent 476, 432 discloses a process of separating a solid from contaminating material by selective agglomeration of the desired solid with a binding material. This patent is primarily concerned with separating coal from mineral contaminants and uses fuel oil as a binding agent to form agglomerates of coal. This specification also mentions recyling of agglomerates to the grinding and agglom¬ eration zones. There is no indication that the method is applicable for low concentrations of the desired solid. European patent 0072060 discloses a method of agglomerating solids with a binder in which seed pellets hav¬ ing particle sizes of 0.5 to 1.0 mm are used to assist in formation of larger agglomerates in a pelletizing process. There is no suggestion in this patent that this pelletizing technique can be used for minerals present in low concentrat¬ ions or that as in our submission small recycle agglomerates are used to maximize recovery by increasing the number of collisions between particles. It is an object of this invention to provide a means of recovering minerals present in low concentrations.

To this end the present invention provides a method of separating a mineral having a natural or reagent induced lyophilic surface present in low concentration in a solid mixture which comprises grinding the solid mixture, forming a slurry of said solids either before or after said grinding step, adding thereto agglomerates of said mineral having a size below 500 microns with a hydrocarbon liquid, carryingING out an agglomeration treatment with said agglomerates and said solid mixture to increase the mineral content of said agglomerates and separating said agglomerates from said solid mixture, for recycling or subsequent mineral recovery.

The hydrocarbon liquid is preferably selected from kerosine, light gas oil or fuel oils. In most cases it is necessary to pretreat the ores to condition them so that the surfaces of the minerals present are rendered lyophilic.

On addition of the hydrocarbon liquid, the lyophilic particles associate to form agglomerate structures. By keeping a high concentration of the mineral being collected present in the agglomeration zone through recycling, the level of recovery is enhanced and larger agglomerates are formed which are more readily separated by conventional techniques such as screening or cycloning. By withdrawing a small portion of agglomerates and recycling the remainder the extraction of the mineral can proceed continuously. This invention is of particular value when concen¬ trating minerals present initially at low concentrations (below 107o in the feed ore to agglomeration) . It can be applied to all minerals where the surface is lyophilic or can be made lyophilic by pretreatment with a promoter/collect- or. The main classes of compounds of interest are metallic sulphides and oxides. Particular examples are cassiterite ⁽tin oxide), chalcopyrite (copper iron sulphide); sphaler¬ ite (zinc sulphide; galena (lead sulphide).

An important aspect of this invention is that the size of the seed agglomerates is kept low so that the surface area of a given mass of agglomerates is high. This ensures maximum opportunity for the mineral to contact the agglomer¬ ates .

In a batch mode a mineral ore containing 0.5% valuable mineral may need 20 to 60 recycles of fresh ore, with an initial recycle^' valuable mineral content of 20% before reaching a target concentration usually between 30% and 60% valuable mineral. The seed agglomerates can simply be small size agglomerates collected during the step of separating agglomer¬ ates from the gangue. Alternatively agglomerates can be reduced in size by an agglomerate breakdowns and age, e.g. grinding or shear scrubbing before returning to the agglom¬ eration zone.

An embodiment of this invention concerned with cassiterite (tin oxide) and chalocopyrite (copper iron sulphide) concentration will now be described. As a blank run, an attempt was made to agglomerate cassiterite at a 27. concentration, using quartz as diluent. Conditions were:

Cassiterite. Mineral sample with a tin content of 68.57o (equivalent to 86.77, S O«) , ground to a top size of 40 microns. Particles size distribution as measur¬ ed by Coulter Counter given in Figure 1 and Table 1. Diluent crushed to a top size of - 53 microns . Agglomeration carried out at 207o w/w solids concentrat¬ ion in all cases, using specially prepared baffled 600 ml beakers .

Bridging oil used in 50/50 light gas oil/heavy fuel oil mixture, emulsified prior to use. Cyanmid Promoter 830 has been used as a collector at

_ tthhee manufacturers recommended rate of 4.7 x 10 g/g pH adjusted to 3 using hydrochloric acid and held constant at this level during agglomeration, stirrer speed of 2,000 rpm. A relatively turbulent mixing system is required for Sn0₂ agglomeration because of the very high density of the mineral.

&« TABLE 1 CASSITERITE GROUND IN THE LABORATORY ROD MILL TO - 38 MICRONS

PARTICLE SIZE FRACTION CUMULATIVE DISTRIBUTION (microns ) (%) (%)

2.00 1.5 100.0

2.52 2.0 98.5

3.17 2.7 96.5

4.00 3.6 93.8

5.04 4, 5 90.2

6.35 5, 3 85.7

8.00 6 2 80.4

10.10 7 4 74.2

12.70 9 3 66.8

16.00 10.3 57.5

20.20 13.7 47.2

25.40 16.6 33.5

32.00 12.6 16.9

40.30 4.3 4.3

50.80 0.0 0.0

Even at a relatively high oil addition rate of 12% (on a cassiterite base), no agglomeration that could be screened were formed.

In the second experiment, cassiterite was agglom¬ erated at a concentration of 20%. wt (again using quartz as diluent). A portion of the agglomerates so formed were add¬ ed to an equivalent agglomeration to the blank run (i.e. one at 27> cassiterite concentration). Results from these runs are set out below.

TABLE 2

Run Diluent Cassiterite Oil % Sn0₂ Recov¬ Number % t. Addition Agglom¬ ered Agglom- Fresh % Wt. erates Reject erates

SN05.2 quartz 20 6.5 99.5 0.5 SN05.3 quartz 10 2 8.6 99.0 1.0

A Oil addition in Run SN05.3 is based on fresh cassiterite added.

The results show the high cassiterite collection that can be achieved using agglomeration, even down to the fine particle sizes which are most difficult to recover by flotation. It is also shown that, by recycling agglomer¬ ates, it is possible to satisfactorily concentrate low grade ores which cannot be collected in a single pass agglomera¬ tion. As a second example, a series of recycle agglomer¬ ation experiments have been completed using an initial chalcopyrite concentration of 207, to form the initial agglom¬ erates and then various fresh feed concentrations of chalcopy¬ rite varying from 57. (i.e. 1.87, Cu) down to 0.5%> (i.e. 0.27. Cu).

The constant operating conditions in these runs are shown below.

Chalcopyrite - mineral sample ground to a top size of 53 microns . . Quartz used as diluent crushed to a top size of 53 microns.

Agglomeration carried out at 207. w/w solids concentrat¬ ion in all cases, using specially prepared baffled 1 000 ml beaker. . Potassium Amyl Xanthate was used as collector at a dose- age of 2.0 g/kg chalcopyrite.

Bridging oil used was Wansol oil distilled light oil with a boiling range of 260°C to 290°C. pH was held at the natural pH of 8.3 to 8.5. The initial agglomerates were used in the recycle runs at various chalcopyrite concentrations in the fresh feed. The duration of each recycle agglomeration was 30 minutes and the results are given below.

_f' EXPERIMENT % COPPER IN % CHALCOPYRITE % OIL ADDITION % RECOVER FRESH FEED IN FRESH FEED CHALCOPYRITE OF COPPER

BASIS

7.0 20 6.0 98.3 1.8 5 9.0 98.3 1.8 5 9.0 98.2 1.8 5 9.0 97.3

7.0 20 6.0 ' 97.5 0.7 2 9.0 94.2 0.7 2 9.0 97.4 0.7 2 9.0 97.6

7.0 20 6.0 98.2 0.2 0. 5 9.0 75.4 0.2 0. 5 9.0 90.5 0.2 0. 5 9.0 93.7

*

By increasing the chalcopyrite concentration in agglomeration by recycle, it is possible to concentrate chal¬ copyrite at low grades, and producing recoveries as high as 98%. The product grade of the chalcopyrite agglomerates ranged between 28% and 30% copper whilst the agglomerate size was between 0.5 mm and 0.1 mm which resulted in easy separation from the reject material.

The major advantages seen for the described proced- ure for recycling agglomerates are :

(i) Aglomeration has the ability to give very high recoveries of minerals. The process operates in a way which is independent of feed particle size in the range of interest (-500 microns). In this respect, agglomeration is superior to other methods of collection, such as flotation, where particle size is a significant factor in collection efficiency. The invention allows these benefits of agglomeration to be obtained on low grade mater- ials which, without agglomerate recycle, either do not form agglomerates at all or form relatively small agglomerates which would be difficult to separate from reject material, ⁽ii) By being able to agglomerate low grade minerals, other advantages of agglomeration can be obtained.

These include the low water content of agglomerates and their ease of handling, which would allow concentration at a mine site prior to shipment to a centralised refining plant.

Claims (3)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of separating a mineral having a natural or reagent induced lyophilic surface present in low concent¬ ration in a solid mixture which comprises grinding the solid mixture, forming a slurry of said solids either before or after said grinding step, adding thereto agglomerates of said mineral having a size below 500 microns with a hydrocarbon liquid, carrying out an agglomeration treatment with said agglomerates and said solid mixture to increase the mineral content of said agglomerates and separating said agglomerates from said solid mixtures for recycling or subsequent mineral recovery.

2. A method as claimed in claim 1 wherein the mineral is selected from cassiterite, chalcopyrite sphalerite and galena.

3. A method as claimed in claim 1 or claim 2 wherein the major portion of the agglomerates separated are recycled.

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