The present invention relates to metal or mineral value separation from base materials and particularly to separation where the desired value is present in low concentrations.

It is known to beneficiate gold ores by treating the ore with coal-oil agglomerates. Thus in US Patent No. 4585548 an aqueous gold ore slurry is contacted with coal-oil agglomerates in a contacting zone. The agglomerates and any adsorbed gold are recycled until the gold concentration has reached a desired level, the gold then being recovered from the agglomerate. It is also known to pre-form coal-oil agglomerates prior to contacting the ore. However, it sometimes occurs that the pre-formed agglomerates do not have the appropriate properties e.g. in size and strength which may lead to operational problems. The present invention relates to an improved separation process in which these problems are alleviated or eliminated.

Thus according to the present invention there is provided a process for separation of a metal or mineral value from a base material comprising the steps of (a) slurrying 30 to 70% of a particulate hydrophobic material under conditions of shear with a hydrophobic liquid, (b) after a pre-determined time period, adding the remainder of the particulate hydrophobic material to the slurry and further slurrying to form agglomerates of the hydrophobic material and the hydrophobic liquid, (c) treating a slurry of the base material with the agglomerates to adsorb the metal or mineral value, and (d) recovering the agglomerates from the slurry.

Preferably the hydrophobic liquid is a hydrocarbon liquid such as a petroleum derived or a synthetic oil. Typical hydrocarbon liquids include kerosene, gas oil, fuel oil and diesel fuel. The particulate hydrophobic material is preferably a carbonaceous material such as carbon, coal, or coke but other suitable materials include polymeric materials such as polystyrene and polyethylene and also particulate mineral sulphides such as chalcopyrite.

Examples of the metal or mineral values are gold, silver, a platinum group metal, metal oxides or sulphides, or diamonds. The minerals or ores to which the present invention is particularly applicable are gold present in its native form, copper present as chalcopyrite and other metallic, metallic sulphide or metallic oxide minerals present in low concentrations. It may be necessary to pretreat the base materials by conditioning them with reagents so that the surfaces of the metal or mineral values present are rendered hydrophobic to enhance separation. Gold may require no pretreatment as its surface tends to be naturally hydrophobic.

The particulate hydrophobic material is slurried with water under conditions of shear, preferably achieved by use of an axial flow stirrer which tends to yield a more desirable agglomerate structure than a turbine-shaped stirrer operating under similar conditions.

The preferred final agglomerate size is in the range 1.5 to 5 mm. The preferred shear as measured by agitator power input is of the order up to 30 W/m^ and is most preferably 1 to 10 kW/rn^. The preferred temperature range is up to 50 ^β C, the higher temperatures being more suitable for heavier oils. The pulp density i.e. the weight percent ratio of solids and solids plus liquid is typically 10 to 60%.

The particulate hydrophobic material may be added either dry or in the form of an aqueous slurry. The shear conditions of stage (b) of the process may be the same as for stage (a) but may also be more or less vigorous. Preferably the shear conditions for pre-agglomeration are similar to those of the separation process.

The particulate hydrophobic material preferably has a particulate size (d80) in the range 10 to 500 microns. In the stage (a) it is preferred that the weight ratio of particulate ** material/hydrophobic liquid is from 10 to 50 weight percent for

5 coal-oil agglomerates. In the stage (b) it is preferred that the weight ratio of particulate material/hydrophobic liquid is from 5 to 25 weight percent. Clearly these weight ratios will be dependent on the sizes and densities of the particulate material and hydrocarbon liquid. 10 The base material containing the metal or mineral values may be treated with the agglomerates under conditions of countercurrent flow.

After recovery of the metal or mineral value containing agglomerates from the slurry, the metal or mineral value is 15 recovered by conventional techniques such as by combustion of the agglomerates.

The invention will now be described by way of example only and with reference to Figures 1 and 2 of the accompanying drawings. Figure 1 is a schematic diagram of a process for the 20 separation of metal values from an ore by use of the present invention. Figure 2 is a schematic diagram of a contacting vessel used in the process.

The present example relates to the beneficiation of gold ores by treatment with coal oil agglomerates. Crushed gold ore is fed 25 via line 1 and ground by any conventional method, for example, a ball mill, 2 to the required particle size. At this stage, the ore is normally in the form of an aqueous slurry which is pumped via line 3 to a holding vessel 4 fitted with an agitator 5. The ore slurry is stored under agitation conditions to maintain a uniform 30 feed supply to the remainder of the plant. The ore slurry is fed to the smaller conditioning vessel 7 fitted with an agitator 8 via line 6. A chemical collector can be added via line 29 if required to improve the magnitude and/or rate of gold recovery.

The conditioned ore slurry flows by gravity from vessel 7 to a 35 train of three tanks (10, 13, 16) fitted with agitators (11, 14,

17). These tanks are referred to as contactors where the ore comes into contact with the coal oil agglomerates. The tanks (10, 13, 16) have inlets (9, 12, 15).

The agglomerates are separately prepared in tank 22 fitted with agitator 23 in the following manner. Firstly about 50% of the total required particulate hydrophobic material (coal), the hydrophobic liquid (oil) and water are added to vessel 22 via lines 19, ^' 20 and 21 respectively. The shear conditions are maintained by the agitator 23 at a sufficient level to form pasty agglomerates. The remaining 50% of the particulate hydrophobic material (coal) is then added and stirring continued until the agglomerates grow to a size of the order of 1.5 - 5mm. Optimum agitation rates are dependent upon several factors including coal type, pulp density, oil type, mode of oil addition (e.g. whether in the form of an emulsion or as a neat oil) but preferred values are in the range 1 to 10 kW/ir . The two stage coal addition enables the agglomerates to grow much more rapidly and to a larger size under the shear conditions used.

The agglomerates are passed from outlet 24 and are screened on a two-deck screen 25 to remove traces of over or undersize material, and split into three portions passing via line 26 to each of the contacting vessels 10, 13 and 16 where they come into contact with the gold ore slurry. One type of contacting vessel is shown in Figure 2 and comprises a baffled cylinder 31 with a screen 32 fitted to the outlet 33. The mesh size of the screen is above the top size of the ore but below the bottom size of the agglomerates. The ore can therefore flow freely through the screens and thus be fed continuously through the train of contacting vessels. The agglomerates however are constrained by the outlet screen to remain in the contacting vessel and do not flow through the circuit. In Figure 2, the contacting vessel is fitted with a six-bladed turbine impeller 34 to agitate the slurry and enable successful gold particle/coal oil agglomerate collisions to occur whereby the gold and agglomerate adhere. However, other impeller types are also effective. With continuous feeding of ore past the agitated agglomerates

retained in the contacting vessels, the gold loading on the agglomerates gradually increases. When the gold loading reaches a sufficient value, the agglomerates can be removed from the system and replaced with fresh ones. The tailings flow out of the final contacting vessel 16 via line 18 and are combined with the agglomerate screen undersize (line 27) to form a final tailings stream 28.

In a more specific example, coal from the Tahmoor colliery in New South Wales and a commercial grade gas oil were used to prepare the agglomerates. After two stages of coal addition and agitating for a total of about 3 hours the agglomerates were almost totally in the size range 1.5-4 mm. Continuous coal gold agglomeration was performed using contacting vessels as shown in Figure 2. Agitation rate as measured by power input per unit volume was 2kW/m^. The ore was from a tailings deposit in Victoria, Australia. During the contacting of the agglomerates with the ground ore losses of agglomerates into the tailings stream were minimal and there was little tendency for the intervessel screens to block.

The present method of agglomerate preparation is believed to be important for successful continuous operation through the vessel. Agglomerates prepared by single-stage coal addition are too small and rapidly lead to screen blockage and/or loss of coal. Attempts to increase agglomerate size in single stage addition either by increasing oil addition or reducing shear lead respectively to 'pasty' or weak agglomerates which again causes screen blockage and/or coal losses. With the two-stage preparation coal losses are barely detectable and screen blockages are reduced or eliminated giving greater reliability of operation.

The present process produces agglomerates which are sufficiently large to enable the operation of a mineral separation process requiring only single stage contacting of agglomerates with the mineral and this may be advantageous over previous mineral separation processes which need to recycle the agglomerates. The process also enables certain other operational advantages to be achieved such as the use of lower power rated agitators and the dispensing of the need for a separate agglomerate growth stage.